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|---|---|---|---|---|
2022ApJS..261...24L
|
The Active Galactic Nuclei in the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX). I. Sample Selection
|
We present the first active galactic nuclei (AGN) catalog of the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX) observed between 2017 January and 2020 June. HETDEX is an ongoing spectroscopic survey (3500-5500 Å) with no target preselection based on magnitudes, colors or morphologies, enabling us to select AGN based solely on their spectral features. Both luminous quasars and low-luminosity Seyferts are found in our catalog. AGN candidates are selected with at least two significant AGN emission lines, such as the Lyα and C IV λ1549 line pair, or with a single broad emission line with FWHM > 1000 km s<SUP>-1</SUP>. Each source is further confirmed by visual inspections. This catalog contains 5322 AGN, covering an effective sky coverage of 30.61 deg<SUP>2</SUP>. A total of 3733 of these AGN have secure redshifts, and we provide redshift estimates for the remaining 1589 single broad-line AGN with no crossmatched spectral redshifts from the Sloan Digital Sky Survey Data Release 14 of QSOs. The redshift range of the AGN catalog is 0.25 < z < 4.32, with a median of z = 2.1. The bolometric luminosity range is 10<SUP>9</SUP>-10<SUP>14</SUP> L <SUB>⊙</SUB> with a median of 10<SUP>12</SUP> L <SUB>⊙</SUB>. The median r-band magnitude of our AGN catalog is 21.6 mag, with 34% having r > 22.5, and 2.6% reaching the detection limit at r ~ 26 mag of the deepest imaging surveys we searched. We also provide a composite spectrum of the AGN sample covering 700-4400 Å.
|
[
16
] |
[
"active galactic nuclei"
] |
2021ApJ...906...37M
|
The Impact of Kinetic Neutrals on the Heliotail
|
The shape of the heliosphere is thought to resemble a long, comet tail, however, recently it has been suggested that the heliosphere is tailless with a two-lobe structure. The latter study was done with a three-dimensional (3D) magnetohydrodynamic code, which treats the ionized and neutral hydrogen atoms as fluids. Previous studies that described the neutrals kinetically claim that this removes the two-lobe structure of the heliosphere. In this work, we use the newly developed Solar-wind with Hydrogen Ion Exchange and Large-scale Dynamics (SHIELD) model. SHIELD is a self-consistent kinetic-MHD model of the outer heliosphere that couples the MHD solution for a single plasma fluid from the BATS-R-US MHD code to the kinetic solution for neutral hydrogen atoms solved by the Adaptive Mesh Particle Simulator, a 3D, direct simulation Monte Carlo model that solves the Boltzmann equation. We use the same boundary conditions as our previous simulations using multi-fluid neutrals to test whether the two-lobe structure of the heliotail is removed with a kinetic treatment of the neutrals. Our results show that despite the large difference in the neutral hydrogen solutions, the two-lobe structure remains. These results are contrary to previous kinetic-MHD models. One such model maintains a perfectly ideal heliopause and does not allow for communication between the solar wind and interstellar medium. This indicates that magnetic reconnection or instabilities downtail play a role for the formation of the two-lobe structure.
|
[
711,
707,
710,
1690,
1635,
1535,
1966,
1964
] |
[
"heliosphere",
"heliopause",
"heliosheath",
"termination shock",
"stellar wind bubbles",
"solar wind termination",
"magnetohydrodynamical simulations",
"magnetohydrodynamics"
] |
2021ApJ...918...84R
|
The SAMI Galaxy Survey: Detection of Environmental Dependence of Galaxy Spin in Observations and Simulations Using Marked Correlation Functions
|
The existence of a kinematic morphology-density relation remains uncertain, and instead stellar mass appears the more dominant driver of galaxy kinematics. We investigate the dependence of the stellar spin parameter proxy ${\lambda }_{{R}_{e}}$ on environment using a marked cross-correlation method with data from the Sydney Australian Astronomical Observatory Multi-object Integral-field Spectrograph (SAMI) Galaxy Survey. Our sample contains 710 galaxies with spatially resolved stellar velocity and velocity dispersion measurements. By utilizing the highly complete spectroscopic data from the Galaxy and Mass Assembly Survey, we calculate marked cross-correlation functions for SAMI galaxies using a pair count estimator and marks based on stellar mass and ${\lambda }_{{R}_{e}}$ . We detect an anticorrelation of stellar kinematics with environment at the 3.2σ level, such that galaxies with low ${\lambda }_{{R}_{e}}$ values are preferably located in denser galaxy environments. However, a significant correlation between stellar mass and environment is also found (correlation at 2.4σ), as found in previous works. We compare these results to mock observations from the cosmological Evolution and Assembly of Galaxies and their Environments (EAGLE) simulations, where we find a similar significant ${\lambda }_{{R}_{{\rm{e}}}}$ anticorrelation with environment, and a mass and environment correlation. We demonstrate that the environmental correlation of ${\lambda }_{{R}_{{\rm{e}}}}$ is not caused by the mass-environment relation. The significant relationship between ${\lambda }_{{R}_{{\rm{e}}}}$ and environment remains when we exclude slow rotators. The signals in SAMI and EAGLE are strongest on small scales (10-100 kpc) as expected from galaxy interactions and mergers. Our work demonstrates that the technique of marked correlation functions is an effective tool for detecting the relationship between ${\lambda }_{{R}_{{\rm{e}}}}$ and environment.
|
[
1951,
1378,
602,
2029,
584
] |
[
"two-point correlation function",
"redshift surveys",
"galaxy kinematics",
"galaxy environments",
"galaxy clusters"
] |
2024ApJ...960...66G
|
The Observed O VI Is Just the Tip of the Iceberg: Estimating the Hidden Material in Circumgalactic and Intergalactic Clouds
|
This paper proposes a new method for estimating the total quantity of material in moving circumgalactic and intergalactic clouds from O VI measurements. We simulate high-velocity clouds (HVCs) with the FLASH hydrodynamic code and track the ionization and recombination of all ionization levels of oxygen as a function of time. We calculate the O VI/oxygen ratio (f <SUB>O VI </SUB>) in our dynamic nonequilibrium ionization clouds, finding that it differs significantly from that in static gas. We find that O VI exists in cool, medium, and hot gas in the clouds. As such, it traces all of the hydrogen rather than merely the ionized hydrogen. The total quantity of hydrogen along a typical observed line of sight through a cloud can be estimated from the observed O VI column density, metallicity, and our f <SUB>O VI </SUB>. We provide the simulations' f <SUB>O VI </SUB> values, a prescription for finding f <SUB>O VI </SUB> for observed dynamic clouds, and a methodology for calculating the total hydrogen column density from f <SUB>O VI </SUB> and an observed O VI column density. As examples, we use our f <SUB>O VI </SUB> values to estimate the total hydrogen column densities along various observed sight lines through two HVCs, Complex C and the Magellanic Stream, finding that these clouds contain more material than previous lower limits. We also extend this analysis to low-redshift intergalactic O VI clouds, finding that they contain several times more baryonic material than previously thought and therefore may account for a significant fraction of the Universe's baryons.
|
[
735,
991,
834,
809,
767,
752
] |
[
"high-velocity clouds",
"magellanic stream",
"interstellar clouds",
"intergalactic clouds",
"hydrodynamical simulations",
"hot ionized medium"
] |
2020ApJ...893...26S
|
Spinning Bar and a Star-formation Inefficient Repertoire: Turbulence in Hickson Compact Group NGC 7674
|
The physics regulating star formation (SF) in Hickson Compact Groups (HCG) has thus far been difficult to describe, due to their unique kinematic properties. In this study, we expand upon previous works to devise a more physically meaningful SF relation able to better encompass the physics of these unique systems. We combine CO(1-0) data from the Combined Array from Research in Millimeter Astronomy to trace the column density of molecular gas ${{\rm{\Sigma }}}_{\mathrm{gas}}$ and deep Hα imaging taken on the Southern Astrophysical Research Telescope tracing ${{\rm{\Sigma }}}_{\mathrm{SFR}}$ to investigate SF efficiency across face-on HCG, NGC 7674. We find a lack of universality in SF, with two distinct sequences present in the ${{\rm{\Sigma }}}_{\mathrm{gas}}$ - ${{\rm{\Sigma }}}_{\mathrm{SFR}}$ plane; one for inside and one for outside the nucleus. We devise an SF relation based on the multi-freefall nature of gas and the critical density, which itself is dependent on the virial parameter ${\alpha }_{\mathrm{vir}}$ , the ratio of turbulent to gravitational energy. We find that our modified SF relation fits the data and describes the physics of this system well with the introduction of a virial parameter of about 5-10 across the galaxy. This ${\alpha }_{\mathrm{vir}}$ leads to an order-of-magnitude reduction in SFR compared to ${\alpha }_{\mathrm{vir}}\approx 1$ systems.
|
[
1569,
1565,
2017,
573,
729
] |
[
"star formation",
"star forming regions",
"agn host galaxies",
"galaxies",
"hickson compact group"
] |
2024ApJ...964..167L
|
Intensive Swift and LCO Monitoring of PG 1302–102: Active Galactic Nucleus Disk Reverberation Mapping of a Supermassive Black Hole Binary Candidate
|
We present an intensive multiwavelength monitoring campaign of the quasar PG 1302‑102 with Swift and the Las Cumbres Observatory network telescopes. At z ∼ 0.3, it tests the limits of the reverberation mapping (RM) technique in probing the accretion disk around a supermassive black hole (SMBH) and extends the parameter space to high masses and high accretion rates. This is also the first time the RM technique has been applied to test disk structures predicted in the SMBH binary model that has been suggested for this source. PG 1302‑102 was observed at a ∼daily cadence for ∼9 months in 14 bands spanning from X-ray to UV and optical wavelengths, and it shows moderate to significant levels of variability correlated between wavelengths. We measure the interband time lags, which are consistent with a τ ∝ λ <SUP>4/3</SUP> relation as expected from standard disk reprocessing, albeit with large uncertainties. The disk size implied by the lag spectrum is consistent with the expected disk size for its black hole mass within uncertainties. While the source resembles other reverberation-mapped active galactic nuclei in many respects, and we do not find evidence supporting the prevalent hypothesis that it hosts an SMBH binary, we demonstrate the feasibility of studying SMBH binaries from this novel angle and suggest possibilities for the LSST Deep Drilling Fields.
|
[
16,
1663,
2019
] |
[
"active galactic nuclei",
"supermassive black holes",
"reverberation mapping"
] |
2023PSJ.....4..188D
|
The Origin of Jupiter's Obliquity
|
The origin of the 3.°12 obliquity of Jupiter's spin axis to its orbit normal is unknown. Improved estimates of Jupiter's moment of inertia rule out a previously proposed explanation involving a resonance with the precession of the inclined orbit of Uranus. We find that a nonadiabatic crossing of the resonance between Jupiter's spin precession and the -f <SUB>5</SUB> + f <SUB>6</SUB> + g <SUB>6</SUB> mode could have tilted Jupiter to its present-day obliquity starting from a 0° primordial obliquity. This places constraints on the migration rates of the satellites Ganymede and Callisto.
|
[
873,
2296
] |
[
"jupiter",
"spin-orbit resonances"
] |
2021PSJ.....2..223D
|
Taurid Stream #628: A Reservoir of Large Cometary Impactors
|
The Desert Fireball Network observed a significant outburst of fireballs belonging to the Southern Taurid Complex of meteor showers between 2015 October 27 and November 17. At the same time, the Cameras for Allsky Meteor Surveillance project detected a distinct population of smaller meteors belonging to the irregular IAU shower #628, the s-Taurids. While this returning outburst was predicted and observed in previous work, the reason for this stream is not yet understood. 2015 was the first year that the stream was precisely observed, providing an opportunity to better understand its nature. We analyze the orbital elements of stream members and establish a size-frequency distribution from millimeter to meter size range. The stream is highly stratified with a large change of entry speed along Earth's orbit. We confirm that the meteoroids have orbital periods near the 7:2 mean motion resonance with Jupiter. The mass distribution of this population is dominated by larger meteoroids, unlike that for the regular Southern Taurid shower. The distribution index is consistent with a gentle collisional fragmentation of weak material. A population of meter-sized objects is identified from satellite observations at a rate consistent with a continuation of the size-frequency distribution established at centimeter size. The observed change of longitude of perihelion among the s-Taurids points to recent (a few centuries ago) activity from fragmentation involving surviving asteroid 2015 TX24. This supports a model for the Taurid Complex showers that involves an ongoing fragmentation cascade of comet 2P/Encke siblings following a breakup some 20,000 yr ago.
|
[
1035,
538,
1452
] |
[
"meteor streams",
"fireballs",
"short period comets"
] |
2021ApJ...907...21N
|
Fundamental Properties of Sheared/Guide Field MHD Magnetic Reconnection
|
The properties of the sheared/guide field magnetic reconnection (MRX) are investigated with two-dimensional MHD simulation. We simulate the spontaneous evolution from the isothermal current sheet (CS) equilibrium in which distribution of the thermodynamical quantities is symmetric about the CS. The magnetic shear is characterized by two parameters: the shear parameter and the asymmetry parameter. The asymmetry of the Alfvén speed (V<SUB>A0x</SUB>) perpendicular to the X-line along the CS is essential. We focus on the asymptotic self-similarly expanding phase of the evolution. This research is unique for the discussion based on the consistency across the entire MRX system, although the sheared MRX has been studied since the early 1980s. In addition to reconfirmation of the previously reported properties of the sheared MRX, the following new properties are found. (1) The reconnection jet changes to the "core-envelope structure" (a high-density core with a low-density envelope) for the sheared symmetric V<SUB>A0x</SUB> case but the "two-layered structure" (the high-speed, low-density layer and the medium-speed, high-density layer) for the asymmetric V<SUB>A0x</SUB> case. (2) The parameter dependence of the reconnection rate is clarified. The MRX is fastest for the symmetric case and slows as the asymmetry increases for any fixed shear angle. For the symmetric case, the reconnection rate has a monotonically decreasing dependence on the shear angle. (3) In the asymmetric case, the plasmas from both sides of the CS coexist on the same magnetic field lines in the larger V<SUB>A0x</SUB> side plasmoid. This characteristic structure suggests an efficient plasma mixing when the plasmoid breaks.
|
[
1261,
1504
] |
[
"plasma astrophysics",
"solar magnetic reconnection"
] |
2020AJ....159...54Z
|
Atomic Oxygen Escape on Mars Driven by Electron Impact Excitation and Ionization
|
Neutral escape on Mars is well known to be dominated by atomic oxygen (O) escape via the dissociative recombination (DR) of ${{\rm{O}}}_{2}^{+}$ , the most abundant ion species in the Martian upper atmosphere. In this study, we suggest an alternative mechanism due to the impact excitation and ionization of CO<SUB>2</SUB> by photoelectrons on the dayside or precipitating solar wind electrons on the nightside. These electron impact (EI) processes are capable of producing hot O atoms via the predissociation of CO<SUB>2</SUB> and ${\mathrm{CO}}_{2}^{+}$ in electronically excited states. An evaluation with the aid of the combined data set accumulated by several instruments on board the Mars Atmosphere and Volatile Evolution spacecraft reveals that CO<SUB>2</SUB> EI makes a non-negligible contribution to total atomic O escape on Mars, with a median EI-to-DR escape flux ratio of 10% on the dayside and 20% on the nightside. CO<SUB>2</SUB> EI is found to be able to drive stronger O escape than atmospheric sputtering, an alternative escape mechanism well studied on Mars. Our results highlight the importance of a neutral escape mechanism largely ignored in previous studies.
|
[
1244,
1748,
2059
] |
[
"planetary atmospheres",
"upper atmosphere",
"electron impact ionization"
] |
2024AJ....167...88R
|
Systematic KMTNet Planetary Anomaly Search. X. Complete Sample of 2017 Prime-field Planets
|
We complete the analysis of planetary candidates found by the KMT AnomalyFinder for the 2017 prime fields that cover ∼13 deg<SUP>2</SUP>. We report three unambiguous planets: OGLE-2017-BLG-0640, OGLE-2017-BLG-1275, and OGLE-2017-BLG-1237. The first two of these were not previously identified, while the last was not previously published due to technical complications induced by a nearby variable. We further report that a fourth anomalous event, the previously recognized OGLE-2017-BLG-1777, is very likely to be planetary, although its light curve requires unusually complex modeling because the lens and source both have orbiting companions. One of the three unambiguous planets, OGLE-2017-BLG-1275, is the first AnomalyFinder discovery that has a Spitzer microlens parallax measurement, π <SUB>E</SUB> ≃ 0.045 ± 0.015, implying that this planetary system almost certainly lies in the Galactic bulge. In the order listed, the four planetary events have planet-host mass ratios q and normalized projected separations s of $(\mathrm{log}q,s)=(-2.31,0.61)$ , (‑2.06, 0.63/1.09), (‑2.10, 1.04), and (‑2.86, 0.72). Combined with previously published events, the 2017 prime fields contain 11 unambiguous planets with well-measured q and one very likely candidate, of which three are AnomalyFinder discoveries. In addition to these 12, there are three other unambiguous planets with large uncertainties in q.
|
[
672
] |
[
"gravitational microlensing"
] |
2023ApJ...956...97M
|
XMM-Newton and INTEGRAL Observations of the Bright GRB 230307A: Vanishing of the Local Absorption and Limits on the Dust in the Magellanic Bridge
|
GRB 230307A is the second brightest gamma-ray burst detected in more than 50 years of observations and is located in the direction of the Magellanic Bridge. Despite its long duration, it is most likely the result of the merger of a compact binary ejected from a galaxy in the local universe (redshift z = 0.065). Our XMM-Newton observation of its afterglow at 4.5 days shows a power-law spectrum with photon index Γ = 1.73 ± 0.10, unabsorbed flux F <SUB>0.3-10 keV</SUB> = (8.8 ± 0.5) × 10<SUP>-14</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP>, and no absorption in excess of that produced in our Galaxy and in the Magellanic Bridge. We derive a limit of ${N}_{{\rm{H}}}^{{\rm{HOST}}}\lt 5\times {10}^{20}$ cm<SUP>-2</SUP> on the absorption at the GRB redshift, which is a factor ~5 below the value measured during the prompt phase. We searched for the presence of dust scattering rings with negative results and set an upper limit of the order of A <SUB> V </SUB> < 0.05 on the absorption from dust in the Magellanic Bridge.
|
[
629,
836,
990
] |
[
"gamma-ray bursts",
"interstellar dust",
"magellanic clouds"
] |
2020PSJ.....1...73M
|
Convex Shape and Rotation Model of Lucy Target (11351) Leucus from Lightcurves and Occultations
|
We report new photometric lightcurve observations of the Lucy Mission target (11351) Leucus acquired during the 2017, 2018, and 2019 apparitions. We use these data in combination with stellar occultations captured during five epochs to determine the sidereal rotation period, the spin axis orientation, a convex shape model, the absolute scale of the object, its geometric albedo, and a model of the photometric properties of the target. We find that Leucus is a prograde rotator with a spin axis located within a sky-projected radius of 3° (1σ) from J2000 Ecliptic coordinates (λ = 208°, β = +77°) or J2000 Equatorial Coordinates (R.A. = 248°, decl. = +58°). The sidereal period is refined to P<SUB>sid</SUB> = 445.683 ± 0.007 h. The convex shape model is irregular, with maximum dimensions of 60.8, 39.1, and 27.8 km. The convex model accounts for global features of the occultation silhouettes, although minor deviations suggest that local and global concavities are present. We determine a geometric albedo of p<SUB>V</SUB> = 0.043 ± 0.002. The derived phase curve supports a D-type classification for Leucus.
|
[
918,
2135,
874,
208
] |
[
"light curves",
"stellar occultation",
"jupiter trojans",
"ccd photometry"
] |
2024AJ....168...52Y
|
In Search of Infall Motion in Molecular Clumps. V. HCO<SUP>+</SUP> (1–0) and HCN (1–0) Observations toward 210 Infall Candidates
|
We have carried out HCO<SUP>+</SUP>(J = 1–0) and HCN (J = 1–0) line observations towards 210 infall candidates selected from the CO blue-profile catalog by Jiang et al., using the Purple Mountain Observatory 13.7 m telescope. Out of the 210 targets, 42 sources are further confirmed to have infall signatures in HCO<SUP>+</SUP> and/or HCN lines, with a confirmation rate of ∼20%. According to the line profiles, we classify them into two categories: double-peaked and peak-shoulder. Some physical properties are estimated through profile fitting using the RATRAN model. We find that the two types are separated in parameter space, indicating they may be of different properties. The median values of kinetic temperature, infall velocity, and mass infall rate for the two types are 10.5 K and 40.8 K, 0.40 km s<SUP>‑1</SUP> and 1.00 km s<SUP>‑1</SUP>, and 4.6 × 10<SUP>‑5</SUP> M <SUB>⊙</SUB> yr<SUP>‑1</SUP> and 3.5 × 10<SUP>‑4</SUP> M <SUB>⊙</SUB> yr<SUP>‑1</SUP>, respectively. The infall velocities and mass-infall rates of peak-shoulder sources are slightly larger than those of double-peaked ones, suggesting they tend to form more massive stars. We also discuss the association of the 42 confirmed sources with other star formation activities such as maser and outflow, which supports this result.
|
[
1569,
847,
1072,
267
] |
[
"star formation",
"interstellar medium",
"molecular clouds",
"collapsing clouds"
] |
2023ApJ...956..105Y
|
Phase-space Analysis of Ordered and Disordered Nonthermal Ion Energization during Magnetic Reconnection
|
Anomalous ion heating is frequently observed to accompany magnetic reconnection, yet there is little consensus on its origin. Instead of the usual velocity-space analysis, we use phase-space analysis to exhaustively explain how ions are nonthermally energized during collisionless, antiparallel magnetic reconnection. There are both ordered and disordered aspects in the process; the former is explained in terms of conservative quantities, and the latter is explained by demonstrating chaos through a direct calculation of Lyapunov exponents. The former induces "multibeam-like heating" in all three directions, whereas the latter induces stochastic bulk heating. Profiles of the ion temperature tensor components during reconnection can be easily understood by the phase-space distributions of ions in different motional stages.
|
[
1504,
1989
] |
[
"solar magnetic reconnection",
"solar coronal heating"
] |
2022ApJ...933...49P
|
Observation of S4716-a Star with a 4 yr Orbit around Sgr A*
|
The ongoing monitoring of the Galactic center and Sgr A*, the central supermassive black hole, produces surprising and unexpected findings. This goes hand in hand with the technical evolution of ground- and space-based telescopes and instruments, but also with the progression of image filter techniques such as the Lucy-Richardson algorithm. As we continue to trace the members of the S cluster close to Sgr A* on their expected trajectory around the supermassive black hole, we present the finding of a new stellar source, which we call S4716. The newly found star orbits Sgr A* in about 4.0 yr and can be detected with NIRC2 (Keck), OSIRIS (Keck), SINFONI (VLT), NACO (VLT), and GRAVITY (VLTI). With a periapse distance of about 100 au, S4716 shows an equivalent distance toward Sgr A* as S4711. These fast-moving stars undergo a similar dynamical evolution, since S4711-S4716 share comparable orbital properties. We will furthermore draw a connection between the recent finding of a new faint star called S300 and the data presented here. Additionally, we observed a blend-star event with S4716 and another newly identified S star S148 in 2017.
|
[
565,
1567,
1596,
1663
] |
[
"galactic center",
"star clusters",
"stellar dynamics",
"supermassive black holes"
] |
2020RNAAS...4..242T
|
Appearance of a New Nebula in the Constellation Puppis after an Outburst in 2015 around WISEA J075915.26-310844.6
|
Here I report the appearance of a new nebula in the constellation Puppis. The nebula was discovered in archived DECam images from 2017 January. Additionally the central source shows an outburst between 2015 February and 2015 April in archived unWISE images. The outburst reached the current brightness in 2016 November (W1 ∼ 3.6 mag, W2 ∼ 1.5 mag). The pre-outburst images from the VST (2012 March) and PanSTARRS (2015 February) do not show any nebulosity around this source. The appearance of reflection nebulae overlapping with the outburst of the central source is known for pre-main sequence stars, such as FU Orionis variables. Follow-up spectroscopy is desired for the central source.
|
[
553,
1381,
786,
1569,
1290
] |
[
"fu orionis stars",
"reflection nebulae",
"infrared astronomy",
"star formation",
"pre-main sequence stars"
] |
2024ApJ...970L...1G
|
Breaking Boundaries: A Universal Wavefront Reconstruction Approach for High-resolution Solar Imaging
|
This Letter proposes a universal wavefront reconstruction approach based on a coupled data set and neural network, aiming to overcome the limitations of current algorithms in terms of universality and wavefront sensing accuracy for variable imaging objects. First, a novel data set, Multi-Object Wavefront Coupling Dataset (MOCD-Dataset), is developed to provide diverse data and enable the network to learn universal wavefront features. Next, a new universal wavefront reconstruction network called Object-Independent Wavefront Decoupling Network (OIWD-Net) is introduced, aiming to separate imaging object information from multiple variable images. Our algorithm eliminates the need for specialized wavefront sensors, has a simple system, high light energy utilization, and does not require customized models for each different type of imaging objects, making it highly practical. By combining the MOCD-Dataset and the OIWD-Net, excellent accuracy in wavefront reconstruction of different imaging objects has been achieved. This research provides a new solution for high-resolution image restoration in fields such as solar structure observation and astronomical high-resolution imaging.
|
[
1475
] |
[
"solar activity"
] |
2022ApJ...932..130P
|
Determining the Spectral Content of MOSES Images
|
The Multi-Order Solar Extreme Ultraviolet Spectrograph (MOSES) sounding rocket was launched from White Sands Missile Range on 2006 February 8th, to capture images of the Sun in the He II 303.8 Å emission line. MOSES is a slitless spectrograph that forms images in multiple spectral orders simultaneously using a concave diffraction grating in an effort to measure line profiles over a wide field of view from a single exposure. Early work on MOSES data showed evidence of solar features composed of neither He II 303.8 Å nor the nearby Si XI 303.3 Å spectral lines. We have built a forward model that uses cotemporal EIT images and the Chianti atomic database to fit synthetic images with known spectra to the MOSES data in order to quantify this additional spectral content. Our fit reveals a host of dim lines that alone are insignificant but combined contribute a comparable intensity to MOSES images as Si XI 303.3 Å. In total, lines other than He II 303.8 Å and Si XI 303.3 Å contribute approximately 10% of the total intensity in the MOSES zero order image. This additional content, if not properly accounted for, could significantly impact the analysis of MOSES and similar slitless spectrograph data, especially those using a zero-order (undispersed) image. More broadly, this serves as a reminder that multilayer EUV imagers are sensitive to a host of weak contaminant lines.
|
[
1532,
1499
] |
[
"solar transition region",
"solar instruments"
] |
2020ApJ...893...55Z
|
Response of the High-latitude Upper Mesosphere to Energetic Electron Precipitation
|
We carried out a statistical study on the effects of strong geomagnetic activity on the mesopause over the auroral region from 2002 to 2018. When the auroral electrojet index increased significantly, the energetic electron precipitation from the Medium Energy Proton and Electron Detector was enhanced by several multiples of 10 for the 55°-70° geomagnetic latitude band. The temperatures measured by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument increased immediately in the mesopause region, together with a descent of the mesopause of about 0.5-2 km. Due to the depth that the precipitation can affect, we conclude that the mesopause is mainly influenced by electrons in the energy range 30-100 keV. The maximum temperature increment at 95 km can reach 4 K and the delay of the response can be up to 1 day. In general, we find that the temperatures significantly respond to the electron precipitation at as low as 93 km, within the mesopause region in most of a year.
|
[
437,
1029,
1030,
22
] |
[
"earth atmosphere",
"mesopause",
"mesosphere",
"aeronomy"
] |
2022PSJ.....3..241B
|
Detecting Lipids on Planetary Surfaces with Laser Desorption Ionization Mass Spectrometry
|
In the search for extraterrestrial life, biosignatures (e.g., organic molecules) play an important role, of which lipids are one considerable class. If detected, these molecules can be strong indicators of the presence of life, past or present, as they are ubiquitous in life on Earth. However, their detection is challenging, depending on, e.g., instrument performance, as well as the selected site. In this contribution, we demonstrate that, using laser desorption ionization mass spectrometry, detection of lipids is feasible. Using our space prototype instrument designed and built in-house, six representative lipids were successfully detected: cholecalciferol, phylloquinone, menadione, 17α-ethynylestradiol, α-tocopherol, and retinol, both as pure substances and as mixtures additionally containing amino acids or polycyclic aromatic hydrocarbons. Observed limits of detection for lipids already meet the requirements stated in the Enceladus Orbilander mission concept. The current performance of our LDI-MS system allows for the simultaneous identification of lipids, amino acids, and polycyclic aromatic hydrocarbons, using a single instrument. We therefore believe that the LDI-MS system is a promising candidate for future space exploration missions devoted to life detection.
|
[
2094,
2222,
74,
2018,
1548
] |
[
"mass spectrometry",
"time-of-flight mass spectrometry",
"astrobiology",
"biosignatures",
"space vehicle instruments"
] |
2022ApJ...932....2I
|
Effects of Total Solar Eclipse on Ionospheric Total Electron Content over Antarctica on 2021 December 4
|
The effects of a total solar eclipse that occurred on 2021 December 4 on ionospheric total electron content (TEC) over Antarctic stations were studied. The study was based on GPS data obtained over Antarctica on the day of the eclipse and the days before and after the eclipse over six GPS stations. The findings of this study show that a total solar eclipse lowers the amount of ionization reaching the Earth's surface with TEC values dropping across the stations. Finally, the enhancement of ΔTEC is quite different from one station to another station. This may also be due to the effect of solar heating conditions and the density of the Sun as exerted over the stations with the Sun side over one station and the clouded part over the others.
|
[
1489
] |
[
"solar eclipses"
] |
2022ApJ...938...70Z
|
Response of Electric Field in Terrestrial Magnetosphere to Interplanetary Shock
|
Electric field impulses generated by interplanetary shocks can cause a series of dynamic processes in the Earth's magnetosphere and were previously explained by either fast-mode wave propagation or flow related to compression of the magnetopause. Based on a Space Weather Modeling Framework simulation, we suggest a new scenario in which the evolution of the impulse is due to both the propagation of the fast-mode wave and the compression of the magnetopause, which can explain the simulation and observations in previous related studies. The onset of the electric field impulse is determined by the propagation of the fast-mode wave in the magnetosphere while the peak of the impulse is determined by the propagation of the compression of the magnetopause. The new understanding of the impulse is important for the generation of subsequent ultralow frequency waves through the coupling of the fast-mode to Alfvén waves and field line resonances and related radiation-belt electron acceleration.
|
[
1544,
2037,
1758,
997,
1966,
1964,
1473,
1472,
829
] |
[
"space plasmas",
"space weather",
"van allen radiation belts",
"planetary magnetospheres",
"magnetohydrodynamical simulations",
"magnetohydrodynamics",
"solar-terrestrial interactions",
"solar-planetary interactions",
"interplanetary shocks"
] |
2024ApJ...962...88V
|
The EDGE-CALIFA Survey: Molecular Gas and Star Formation Activity across the Green Valley
|
We present a <SUP>12</SUP>CO(J = 2‑1) survey of 60 local galaxies using data from the Atacama Compact Array as part of the Extragalactic Database for Galaxy Evolution: the ACA EDGE survey. These galaxies all have integral field spectroscopy from the CALIFA survey. Compared to other local galaxy surveys, ACA EDGE is designed to mitigate selection effects based on CO brightness and morphological type. Of the 60 galaxies in ACA EDGE, 36 are on the star formation main sequence, 13 are on the red sequence, and 11 lie in the "green valley" transition between these sequences. We test how star formation quenching processes affect the star formation rate (SFR) per unit molecular gas mass, SFE<SUB>mol</SUB> = SFR/M <SUB>mol</SUB>, and related quantities in galaxies with stellar masses 10 ≤ log[M <SUB>⋆</SUB>/M <SUB>⊙</SUB>] ≤ 11.5 covering the full range of morphological types. We observe a systematic decrease of the molecular-to-stellar mass fraction ( ${R}_{\star }^{\mathrm{mol}}$ ) with a decreasing level of star formation activity, with green valley galaxies also having lower SFE<SUB>mol</SUB> than galaxies on the main sequence. On average, we find that the spatially resolved SFE<SUB>mol</SUB> within the bulge region of green valley galaxies is lower than in the bulges of main-sequence galaxies if we adopt a constant CO-to-H<SUB>2</SUB> conversion factor, α <SUB>CO</SUB>. While efficiencies in main-sequence galaxies remain almost constant with galactocentric radius, in green valley galaxies, we note a systematic increase of SFE<SUB>mol</SUB>, ${R}_{\star }^{\mathrm{mol}}$ , and specific SFR with increasing radius. As shown in previous studies, our results suggest that although gas depletion (or removal) seems to be the most important driver of the star formation quenching in galaxies transiting through the green valley, a reduction in star formation efficiency is also required during this stage.
|
[
506
] |
[
"extragalactic astronomy"
] |
2021PSJ.....2...77M
|
The Enceladus Orbilander Mission Concept: Balancing Return and Resources in the Search for Life
|
Enceladus's long-lived plume of ice grains and water vapor makes accessing oceanic material readily achievable from orbit (around Saturn or Enceladus) and from the moon's surface. In preparation for the National Academies of Sciences, Engineering and Medicine 2023-2032 Planetary Science and Astrobiology Decadal Survey, we investigated four architectures capable of collecting and analyzing plume material from orbit and/or on the surface to address the most pressing questions at Enceladus: Is the subsurface ocean inhabited? Why, or why not? Trades specific to these four architectures were studied to allow an evaluation of the science return with respect to investment. The team found that Orbilander, a mission concept that would first orbit and then land on Enceladus, represented the best balance. Orbilander was thus studied at a higher fidelity, including a more detailed science operations plan during both orbital and landed phases, landing site characterization and selection analyses, and landing procedures. The Orbilander mission concept demonstrates that scientifically compelling but resource-conscious Flagship-class missions can be executed in the next decade to search for life at Enceladus.
|
[
1427,
1255,
2191,
74,
2018,
2208
] |
[
"saturnian satellites",
"planetary science",
"remote sensing",
"astrobiology",
"biosignatures",
"natural satellite surfaces"
] |
2021ApJ...921...34M
|
The Crab Nebula as a Calibrator for Wide-beam Cosmic Microwave Background Polarization Surveys
|
We analyze the effect of polarized diffuse emission in the calibration of wide-beam millimeter-wave polarimeters, when using the Crab Nebula as a reference source for both polarized brightness and polarization angle. We show that, for CMB polarization experiments aiming at detecting B-mode in a scenario with a tensor to scalar ratio r ~ 0.001, wide (a few degrees in diameter), precise ( ${\sigma }_{Q},{\sigma }_{U}\sim 20\,\mu {{\rm{K}}}_{\mathrm{CMB}}\mathrm{arcmin}$ ), high angular resolution (<FWHM) reference maps are needed to properly take into account the effects of diffuse polarized emission and avoid significant bias in the calibration.
|
[
1146,
412,
259,
322,
1278
] |
[
"observational cosmology",
"dust continuum emission",
"cmbr detectors",
"cosmic microwave background radiation",
"polarimetry"
] |
2024ApJ...967..109L
|
Challenges to Inflation in the Post-Planck Era
|
Space-based missions studying the cosmic microwave background (CMB) have progressively refined the parameter space in conventional models of inflation shortly (∼10<SUP>‑37</SUP> s) after the Big Bang. While most inflationary scenarios proposed thus far in the context of general relativity have since been ruled out, the basic idea of inflation may still be tenable, albeit with several unresolved conundrums, such as conflicting initial conditions and inconsistencies with the measured CMB power spectrum. In the new slow-roll inflationary picture, inflation arising in plateau-like potentials requires an initiation beyond the Planck time. This delay may be consistent with the cutoff, ${k}_{\min }$ , measured recently in the primordial power spectrum. However, the actual value of ${k}_{\min }$ would imply an initiation time too far beyond the Big Bang for inflation to solve the horizon problem. In this paper, we also describe several other undesirable consequences of this delay, including an absence of well-motivated initial conditions and a significant difficulty in providing a viable mechanism for properly quantizing the primordial fluctuations. Nevertheless, many of these inconsistencies may still be avoided if one introduces nonconventional modifications to inflation, such as a brief departure from slow-roll dynamics, possibly due to a dramatic change in the inflationary potential, inflation driven by multiple fields, or a nonminimal coupling to gravity. In addition, some of these difficulties could be mitigated via the use of alternative cosmologies based, e.g., on loop quantum gravity, which replaces the initial Big Bang singularity with finite conditions at a bounce-like beginning.
|
[
319,
337,
1146,
1313
] |
[
"cosmic inflation",
"cosmological models",
"observational cosmology",
"quantum cosmology"
] |
2022ApJ...937....5S
|
Radio Nebulae from Hyperaccreting X-Ray Binaries as Common-envelope Precursors and Persistent Counterparts of Fast Radio Bursts
|
Roche lobe overflow from a donor star onto a black hole or neutron star binary companion can evolve to a phase of unstable runaway mass transfer, lasting as short as hundreds of orbits (≲10<SUP>2</SUP> yr for a giant donor) and eventually culminating in a common-envelope event. The highly super-Eddington accretion rates achieved during this brief phase ( $\dot{M}\gtrsim {10}^{5}{\dot{M}}_{\mathrm{Edd}})$ are accompanied by intense mass loss in disk winds, analogous to but even more extreme than ultraluminous X-ray (ULX) sources in the nearby universe. Also in analogy with the observed ULX, this expanding outflow will inflate an energetic "bubble" of plasma into the circumbinary medium. Embedded within this bubble is a nebula of relativistic electrons heated at the termination shock of the faster v ≳ 0.1c wind/jet from the inner accretion flow. We present a time-dependent, one-zone model for the synchrotron radio emission and other observable properties of such ULX "hypernebulae." If ULX jets are sources of repeating fast radio bursts (FRB), as recently proposed, such hypernebulae could generate persistent radio emission and contribute large and time-variable rotation measure to the bursts, consistent with those seen from FRB 20121102 and FRB 20190520B. ULX hypernebulae can be discovered independently of an FRB association in radio surveys, such as VLASS, as off-nuclear point sources whose fluxes can evolve significantly on timescales as short as years, possibly presaging energetic transients from common-envelope mergers.
|
[
2008,
2164,
733,
2086,
829,
1261,
739,
187
] |
[
"radio transient sources",
"ultraluminous x-ray sources",
"high mass x-ray binary stars",
"shocks",
"interplanetary shocks",
"plasma astrophysics",
"high energy astrophysics",
"burst astrophysics"
] |
2020ApJ...900...18K
|
Solar Flare Arcade Modeling: Bridging the Gap from 1D to 3D Simulations of Optically Thin Radiation
|
Solar flares are 3D phenomena, but modeling a flare in 3D, including many of the important processes in the chromosphere, is a computational challenge. Accurately modeling the chromosphere is important, even if the transition region and corona are the areas of interest, due to the flow of energy, mass, and radiation through the interconnected layers. We present a solar flare arcade model that aims to bridge the gap between 1D and 3D modeling. Our approach is limited to the synthesis of optically thin emission. Using observed active region loop structures in a 3D domain, we graft simulated 1D flare atmospheres onto each loop, synthesize the emission, and then project that emission onto the 2D observational plane. Emission from SDO/AIA, GOES/XRS, and IRIS/SG Fe XXI λ1354.1 was forward modeled. We analyze the temperatures, durations, mass flows, and line widths associated with the flare, finding qualitative agreement but certain quantitative differences. Compared to observations, the Doppler shifts are of similar magnitude but decay too quickly. They are not as ordered, containing a larger amount of scatter compared to observations. The duration of gradual phase emission from GOES and AIA emission is also too short. Fe XXI lines are broadened, but not sufficiently. These findings suggest that additional physics is required in our model. The arcade model that we show here as a proof of concept can be extended to investigate other lines and global aspects of solar flares, providing a means to better test the coronal response to models of flare energy injection.
|
[
1496,
1982,
1988,
1816,
767,
1521,
1533,
1967
] |
[
"solar flares",
"solar flare spectra",
"active solar corona",
"solar x-ray flares",
"hydrodynamical simulations",
"solar radiation",
"solar ultraviolet emission",
"radiative transfer simulations"
] |
2023RNAAS...7..147P
|
New Dimming Events in Southern R Coronae Borealis Stars
|
This paper reports on photometry of dimming events for three Southern R Coronae Borealis (RCB) stars. Two of these stars have recently entered a dimming phase (IO Nor and V653 Sco), while the other (GU Sgr) is emerging from a dimming event. Low resolution spectra of one of the targets indicates blueshifted Na I D lines, and hydrogen alpha emission. As the number of known RCBs grows, the need to monitor them and detect dimming events at an early stage increases.
|
[
1327,
871,
1558
] |
[
"r coronae borealis variable stars",
"johnson photometry",
"spectroscopy"
] |
2022ApJ...933...34H
|
RXTE Observation of the Nonthermal Emission from the Early Stage Merger in A1750
|
We make the first observation-based calculation of the energy that goes into cosmic ray protons versus cosmic ray electrons in shock acceleration during structure formation. We find a ratio of energy in cosmic ray protons to energy in cosmic ray electrons of 0.86. This value, calculated from the nonthermal X-ray component reported here from RTXE and the Fermi LAT upper limit for gamma-ray emission, is significantly lower than theoretical estimates that place most of the nonthermal energy in protons. Our estimate is based on the detection of nonthermal X-ray emission using the 3-20 keV RXTE spectrum, which shows residual emission not well modeled by a single thermal component. The statistical significance of adding a nonthermal, power-law component is 96%. The significance of adding a second thermal component is 90%. The addition of a component consisting of full cosmic X-ray background fluctuation to an isothermal model is significant with 92% confidence. The cumulative probability for the two-thermal-component model is 81% and 90% for the thermal plus power law. Thus the model with nonthermal emission is the preferred description of the data. Evidence of shock heating between the clusters in the spectro-imaging data of XMM, Chandra, and Suzaku indicates that a cosmic ray component should also be present and supports a nonthermal interpretation for the additional component. The bolometric nonthermal X-ray luminosity is 1.6 × 10<SUP>44</SUP> ergs s<SUP>-1</SUP>, 36% of the total X-ray emission in the 0.1-100 keV band.
|
[
1119,
584
] |
[
"non-thermal radiation sources",
"galaxy clusters"
] |
2020ApJ...888..121S
|
An Observationally Constrained Analytical Model for Predicting the Magnetic Field Vectors of Interplanetary Coronal Mass Ejections at 1 au
|
We report on an observationally constrained analytical model, the INterplanetary Flux ROpe Simulator (INFROS), for predicting the magnetic field vectors of coronal mass ejections (CMEs) in the interplanetary medium. The main architecture of INFROS involves using the near-Sun flux rope properties obtained from the observational parameters that are evolved through the model in order to estimate the magnetic field vectors of interplanetary CMEs (ICMEs) at any heliocentric distance. We have formulated a new approach in INFROS to incorporate the expanding nature and the time-varying axial magnetic field strength of the flux rope during its passage over the spacecraft. As a proof of concept, we present the case study of an Earth-impacting CME which occurred on 2013 April 11. Using the near-Sun properties of the CME flux rope, we have estimated the magnetic vectors of the ICME as intersected by the spacecraft at 1 au. The predicted magnetic field profiles of the ICME show good agreement with those observed by the in situ spacecraft. Importantly, the maximum strength (10.5 ± 2.5 nT) of the southward component of the magnetic field (Bz) obtained from the model prediction is in agreement with the observed value (11 nT). Although our model does not include the prediction of the ICME plasma parameters, as a first-order approximation, it shows promising results in forecasting of Bz in near real time, which is critical for predicting the severity of the associated geomagnetic storms. This could prove to be a simple space-weather forecasting tool compared to the time-consuming and computationally expensive MHD models.
|
[
310,
1496,
2037
] |
[
"solar coronal mass ejections",
"solar flares",
"space weather"
] |
2021ApJ...919..142B
|
A Bright Ultraviolet Excess in the Transitional 02es-like Type Ia Supernova 2019yvq
|
We present photometric and spectroscopic observations of the nearby Type Ia SN 2019yvq, from its discovery ~1 day after explosion to ~100 days after its peak brightness. This SN exhibits several unusual features, most notably an extremely bright UV excess seen within ~5 days of its explosion. As seen in Swift UV data, this early excess outshines its "peak" brightness, making this object more extreme than other supernovae (SNe) with early UV/blue excesses (e.g., iPTF14atg and SN 2017cbv). In addition, it was underluminous M<SUB>B</SUB> = -18.4, relatively quickly declining (Δm<SUB>15</SUB>(B) = 1.37), and shows red colors past its early blue bump. Unusual (although not unprecedented) spectral features include extremely broad-lined and high-velocity Si absorption. Despite obvious differences in peak spectra, we classify SN 2019yvq as a transitional member of the 02es-like subclass due to its similarities in several respects (e.g., color, peak luminosity, peak Ti, and nebular [Ca II]). We model this data set with a variety of published models, including SN ejecta-companion shock interaction and sub-Chandrasekhar-mass white dwarf (WD) double-detonation models. Radio constraints from the VLA place an upper limit of (4.5-20) × 10<SUP>-8</SUP> M<SUB>⊙</SUB> yr<SUP>-1</SUP> on the mass-loss rate from a symbiotic progenitor, which does not exclude a red giant or main-sequence companion. Ultimately, we find that no one model can accurately replicate all aspects of the data set, and further we find that the ubiquity of early excesses in 02es-like SNe Ia requires a progenitor system that is capable of producing isotropic UV flux, ruling out some models for this class of objects.
|
[
1728
] |
[
"type ia supernovae"
] |
2021ApJ...922...34C
|
A Comprehensive Study of Multiflare GRB Spectral Lag
|
We select 48 multiflare gamma-ray bursts (GRBs) (including 137 flares) from the Swift/XRT database and estimate the spectral lag with the discrete correlation function. It is found that 89.8% of the flares have positive lags and only 9.5% of the flares show negative lags when fluctuations are taken into account. The median lag of the multiflares (2.75 s) is much greater than that of GRB pulses (0.18 s), which can be explained by the fact that we confirm that multiflare GRBs and multipulse GRBs have similar positive lag-duration correlations. We investigate the origin of the lags by checking the E<SUB>peak</SUB> evolution with the two brightest bursts and find the leading models cannot explain all of the multiflare lags and there may be other physical mechanisms. All of the results above reveal that X-ray flares have the same properties as GRB pulses, which further supports the observation that X-ray flares and GRB prompt-emission pulses have the same physical origin.
|
[
629
] |
[
"gamma-ray bursts"
] |
2020AJ....159..105L
|
Discovery of Two Nearby Post-T Tauri Stellar Associations
|
In this work we report the discovery of two new stellar associations in close vicinity of the Sun at roughly 180 and 150 pc. These two associations, u Tau assoc and e Tau assoc, were detected based on their clustering in a multi-dimensional parameter space including α, δ, μ<SUB>α</SUB>, μ<SUB>δ</SUB>, and ϖ of Gaia. The fitting of pre-main-sequence model isochrones in their color-magnitude diagrams suggests that the two associations are of about 50 Myr old and the group members lower than ∼0.8 M<SUB>⊙</SUB> are at the stage of post-T Tauri.
|
[
1289,
1290,
1833
] |
[
"pre-main sequence",
"pre-main sequence stars",
"young star clusters"
] |
2021ApJ...916L...2B
|
A Circumplanetary Disk around PDS70c
|
PDS 70 is a unique system in which two protoplanets, PDS 70 b and c, have been discovered within the dust-depleted cavity of their disk, at ~22 and 34 au, respectively, by direct imaging at infrared wavelengths. Subsequent detection of the planets in the Hα line indicates that they are still accreting material through circumplanetary disks. In this Letter, we present new Atacama Large Millimeter/submillimeter Array (ALMA) observations of the dust continuum emission at 855 μm at high angular resolution (~20 mas, 2.3 au) that aim to resolve the circumplanetary disks and constrain their dust masses. Our observations confirm the presence of a compact source of emission co-located with PDS 70 c, spatially separated from the circumstellar disk and less extended than ~1.2 au in radius, a value close to the expected truncation radius of the circumplanetary disk at a third of the Hill radius. The emission around PDS 70 c has a peak intensity of ~86 ± 16 μJy beam<SUP>-1</SUP>, which corresponds to a dust mass of ~0.031 M<SUB>⊕</SUB> or ~0.007 M<SUB>⊕</SUB>, assuming that it is only constituted of 1 μm or 1 mm sized grains, respectively. We also detect extended, low surface brightness continuum emission within the cavity near PDS 70 b. We observe an optically thin inner disk within 18 au of the star with an emission that could result from small micron-sized grains transported from the outer disk through the orbits of b and c. In addition, we find that the outer disk resolves into a narrow and bright ring with a faint inner shoulder.
|
[
1300
] |
[
"protoplanetary disks"
] |
2024ApJ...965..126T
|
Efficiency of Nonthermal Pulsed Emission from Eight MeV Pulsars
|
We report on the properties of pulsed X-ray emission from eight MeV pulsars using XMM-Newton, NICER, NuSTAR, and HXMT data. For five of the eight MeV pulsars, the X-ray spectra can be fit by a broken power-law model with a break energy of ∼5–10 keV. The photon indices below and above the break energy are ∼1 and ∼1.5, respectively. In comparison with the X-ray emission of the Fermi-LAT pulsars, the MeV pulsars have a harder spectrum and a higher radiation efficiency in the 0.3–10 keV energy bands. When isotropic emission is assumed, the emission efficiency in the keV–MeV bands is estimated to be η <SUB>MeV</SUB> ∼ 0.01–0.1, and this is similar to the efficiency of the GeV emission of the Fermi-LAT pulsars with a similar spin-down power. To explain the observed efficiency of the MeV pulsars, we estimate the required pair multiplicity as 10<SUP>4–7</SUP>, which depends on the emission process (curvature radiation or synchrotron radiation) and on the location in the magnetosphere. The high multiplicity indicates that the secondary pairs that are created by a pair-creation process of the GeV photons produce the X-ray/soft gamma-ray emission of the MeV pulsars. We speculate that the difference between MeV pulsars and Fermi-LAT pulsars can be attributed to the difference in viewing angle measured from the spin axis if the emission originates from a region inside the light cylinder (canonical gap model) or to the difference in the inclination angle of the magnetic axis if the emission is produced in the equatorial current sheet outside the light cylinder.
|
[
1108
] |
[
"neutron stars"
] |
2023ApJ...959...88D
|
Variation of the High-mass Slope of the Stellar Initial Mass Function: Theory Meets Observations
|
We present observational evidence of a correlation between the high-mass slope of the stellar initial mass function (IMF) in young star clusters and their stellar surface density, σ <SUB>*</SUB>. When the high-mass end of the IMF is described by a power law of the form ${dN}/d\mathrm{log}{M}_{* }\propto {M}_{* }^{-{\rm{\Gamma }}}$ , the value of Γ is seen to decrease weakly with increasing σ <SUB>*</SUB>, following a ${\rm{\Gamma }}=1.31\,{\sigma }_{* }^{-0.095}$ relation. We also present a model that can explain these observations. The model is based on the idea that the coalescence of protostellar cores in a protocluster-forming clump is more efficient in high-density environments where cores are more closely packed. The efficiency of the coalescence process is calculated as a function of the parental clump properties, in particular the relation between its mass and radius as well as its core formation efficiency. The main result of this model is that the increased efficiency of the coalescence process leads to shallower slopes of the IMF, in agreement with the observations of young clusters, and the observations are best reproduced with compact protocluster-forming clumps. These results have significant implications for the shape of the IMF in different Galactic and extragalactic environments and have very important consequences for galactic evolution.
|
[
1612,
1614,
1297,
2049,
1072,
2286
] |
[
"stellar mass functions",
"stellar masses",
"protoclusters",
"young massive clusters",
"molecular clouds",
"collisional processes"
] |
2023ApJ...951..123H
|
A Hydrodynamic Study of the Escape of Metal Species and Excited Hydrogen from the Atmosphere of the Hot Jupiter WASP-121b
|
In the near-UV and optical transmission spectrum of the hot Jupiter WASP-121b, recent observations have detected strong absorption features of Mg, Fe, Ca, and Hα, extending outside of the planet's Roche lobe. Studying these atomic signatures can directly trace the escaping atmosphere and constrain the energy balance of the upper atmosphere. To understand these features, we introduce a detailed forward model by expanding the capability of a one-dimensional model of the upper atmosphere and hydrodynamic escape to include important processes of atomic metal species. The hydrodynamic model is coupled to a Lyα Monte Carlo radiative transfer calculation to simulate the excited hydrogen population and associated heating/ionization effects. Using this model, we interpret the detected atomic features in the transmission spectrum of WASP-121b and explore the impact of metals and excited hydrogen on its upper atmosphere. We demonstrate the use of multiple absorption lines to impose stronger constraints on the properties of the upper atmosphere than the analysis of a single transmission feature can provide. In addition, the model shows that line broadening due to atmospheric outflow driven by Roche lobe overflow is necessary to explain the observed line widths and highlights the importance of the high mass-loss rate caused by Roche lobe overflow, which requires careful consideration of the structure of the lower and middle atmosphere. We also show that metal species and excited-state hydrogen can play an important role in the thermal and ionization balance of ultrahot Jupiter thermospheres.
|
[
2310,
1335,
753,
1748,
2133,
767
] |
[
"exoplanet atmospheric structure",
"radiative transfer",
"hot jupiters",
"upper atmosphere",
"transmission spectroscopy",
"hydrodynamical simulations"
] |
2023ApJ...950L...2S
|
Ponderings on the Possible Preponderance of Perpendicular Planets
|
Misalignments between planetary orbits and the equatorial planes of their host stars are clues about the formation and evolution of planetary systems. Earlier work found evidence for a peak near 90° in the distribution of stellar obliquities, based on frequentist tests. We performed hierarchical Bayesian inference on a sample of 174 planets for which either the full three-dimensional stellar obliquity has been measured (72 planets) or for which only the sky-projected stellar obliquity has been measured (102 planets). We investigated whether the obliquities are best described by a Rayleigh distribution or by a mixture of a Rayleigh distribution representing well-aligned systems and a different distribution representing misaligned systems. The mixture models are strongly favored over the single-component distribution. For the misaligned component, we tried an isotropic distribution and a distribution peaked at 90° and found the evidence to be essentially the same for both models. Thus, our Bayesian inference engine did not find strong evidence favoring a "perpendicular peak," unlike the frequentist tests. We also investigated selection biases that affect the inferred obliquity distribution, such as the bias of the gravity-darkening method against obliquities near 0° or 180°. Further progress in characterizing the obliquity distribution will probably require the construction of a more homogeneous and complete sample of measurements.
|
[
486,
1882
] |
[
"exoplanet astronomy",
"astrostatistics"
] |
2020AJ....160..215V
|
The Solar Neighborhood. XLVI. Revealing New M Dwarf Binaries and Their Orbital Architectures
|
We use 20 yr of astrometric data from the REsearch Consortium On Nearby Stars (RECONS) program on the Cerro Tololo Inter-American Observatory/SMARTS 0.9 m telescope to provide new insight into multiple star systems in the solar neighborhood. We provide new and updated parallaxes for 210 systems and derive nine high-quality astrometric orbits with periods of 2.49-16.63 yr. Using a total of 542 systems' parallaxes from RECONS, we compare systems within 25 pc to Gaia DR2 to define criteria for selecting unresolved astrometric multiples from the DR2 results. We find that three out of four unresolved multistar red dwarf systems within 25 pc in DR2 have parallax_error ≥ 0.32 mas, astrometric_gof_al ≥ 56, astrometric_excess_noise_sig ≥ 108.0, ruwe ≥ 2.0, and parallaxes more than ∼10% different from the long-term RECONS results. These criteria have broad applications to any work targeting nearby stars, from studies seeking binary systems to efforts targeting single stars for planet searches.
|
[
79,
80,
985,
1713,
2050,
154
] |
[
"astrometric binary stars",
"astrometry",
"m stars",
"trigonometric parallax",
"low mass stars",
"binary stars"
] |
2021ApJ...908..139J
|
Reconciling EHT and Gas-dynamics Measurements in M87: Is the Jet Misaligned at Parsec Scales?
|
The Event Horizon Telescope mass estimate for M87* is consistent with the stellar dynamics mass estimate and inconsistent with the gas-dynamics mass estimates by up to 2σ. We have previously explored a new gas-dynamics model that incorporated sub-Keplerian gas velocities and could, in principle, explain the discrepancy in the stellar and gas-dynamics mass estimate. In this paper, we extend this gas-dynamical model to also include non-trivial disk heights, which may also resolve the mass discrepancy independent of sub-Keplerian velocity components. By combining the existing velocity measurements and the Event Horizon Telescope mass estimate, we place constraints on the gas disk inclination and sub-Keplerian fraction. These constraints require the parsec-scale ionized gas disk to be misaligned with the milliarcsecond radio jet by at least 11°, and more typically 27°. Modifications to the gas-dynamics model either by introducing sub-Keplerian velocities or thick disks produce further misalignment with the radio jet. If the jet is produced in a Blandford-Znajek-type process, the angular momentum of the black hole is decoupled with the angular momentum of the large-scale gas feeding M87*.
|
[
17,
609,
591,
602,
601
] |
[
"active galaxies",
"galaxy nuclei",
"galaxy dynamics",
"galaxy kinematics",
"galaxy jets"
] |
2023ApJ...949...96E
|
Modeling the 2022 τ-Herculid Outburst
|
The τ-Herculids (IAU shower number 61 TAH) is a minor meteor shower associated with comet 73P/Schwassmann-Wachmann 3, a Jupiter-family comet that disintegrated into several fragments in 1995. As a consequence of the nucleus breakup, possible increased meteor rates were predicted for 2022. On May 30-31, observation networks around the world reported two distinct peaks of TAH activity, around solar longitudes 69.°02 and 69.°42. This work examines the encounter conditions of the Earth with meteoroids ejected from 73P during the splitting event and on previous perihelion passages. Numerical simulations suggest that the main peak observed in 2022 was caused by meteoroids ejected from the splitting nucleus with four times the typical cometary gas expansion speed. High-resolution measurements performed with the Canadian Automated Meteor Observatory indicate that these meteoroids are fragile, with estimated bulk densities of 250 kg m<SUP>-3</SUP>. In contrast with the main peak, the first TAH activity peak in 2022 is best modeled with trails ejected prior to 1960. We find that ordinary cometary activity could have produced other TAH apparitions observed in the past, including in 1930 and 2017. The extension of our model to future years predicts significant returns of the shower in 2033 and 2049.
|
[
1035,
1040,
280
] |
[
"meteor streams",
"meteoroids",
"comets"
] |
2023AJ....166..238M
|
Compositional Constraints of Ice Lobes at the Edge of Martian South Polar Cap and the Possibility for CO<SUB>2</SUB> Ice
|
As one of the major ice reservoirs on Mars, the south polar layered deposits (SPLD) are mainly composed of water ice and dust except for the perennial CO<SUB>2</SUB> ice deposits on the surface and within buried layers. At the edge of Planum Australe, the Shallow Radar detected the base of two ice lobes, which can be used to estimate their dielectric properties and analyze the components. These measurements, combined with topographic data, allow for the relative permittivity of the lobe materials to be estimated at 2.73 ± 0.67. Under the constraint of the SPLD density, the permittivity value translates to the existence of CO<SUB>2</SUB> ice depending on the dust content. If the dust content is larger than 24%, the lobes are CO<SUB>2</SUB> free and composed of water ice, dust, and pore space. Whereas, for the dust content of <12%, our results suggest that the lobes must contain a certain amount of CO<SUB>2</SUB> ice, which could be an average volume of 30%. When the dust content is between 12% and 24%, the existence of CO<SUB>2</SUB> ice is undetermined. This study improves the understanding of ice deposits at the Martian south polar.
|
[
1007,
1009,
1329,
1965
] |
[
"mars",
"martian satellites",
"radar astronomy",
"computational methods"
] |
2023ApJ...954...86L
|
MFPIM: A Deep Learning Model Based on Multimodal Fusion Technology for Pulsar Identification
|
With the development of radio telescope technology, the quantity and types of acquired pulsar candidate data have increased dramatically. However, it is difficult to accurately identify pulsar candidates. Therefore, we propose to use multimodal fusion technology, called the multimodal fusion-based pulsar identification model (MFPIM), to build a deep learning model to improve the efficiency and accuracy of pulsar candidate identification. MFPIM treats each diagnostic plot of pulsar candidates as a modality and uses multiple convolutional neural networks to extract effective features from the diagnostic plots. After fusing the features, the commonality of different modalities in high-dimensional space is obtained to ensure that the model can take full advantage of the complementarity between diagnostic plots and thus identify pulsar candidates, achieved better classification performance than other current supervised learning algorithms. In addition, a channel attention mechanism is used in the model to enable it to learn the importance of different channel features so that the model focuses more on the channel information in the input data that is more meaningful for classification, reducing the model size while extracting pulsar diagnostic map features more accurately. We conducted experiments on the Five-hundred-meter Aperture Spherical radio Telescope (FAST) data set, and the results show that MFPIM can effectively identify the pulsars in the FAST data set with an identification accuracy of over 98%. To further verify the robustness of the model, we applied the MFPIM to the High Time Resolution Universe data set using transfer learning, with the test accuracy and F1 score reaching over 99%.
|
[
1306,
1353,
1938
] |
[
"pulsars",
"radio pulsars",
"convolutional neural networks"
] |
2024ApJ...961...63Z
|
MAMMOTH-Subaru. III. Lyα Halo Identified by Stacking ∼3300 Lyα Emitters at z = 2.2–2.3
|
In this paper, we present a Lyα halo (LAH) identified by stacking ∼3300 Lyα emitters (LAEs) at z = 2.2–2.3. We carry out imaging observations and data reduction with Subaru/Hyper Suprime-Cam. Our total survey area is ∼12 deg<SUP>2</SUP> and the imaging depths are 25.5–27.0 mag. Using the imaging data, we select 1240 and 2101 LAE candidates at z = 2.2 and 2.3, respectively. We carry out spectroscopic observations of our LAE candidates and data reduction with Magellan/IMACS to estimate the contamination rate of our LAE candidates. We find that the contamination rate of our sample is low (8%). We stack our LAE candidates with a median stacking method to identify the LAH at z = 2. We show that our LAH is detected until ∼100 kpc at the 2σ significance level and likely extended to ∼200 kpc at a surface brightness level of ∼10<SUP>‑20</SUP> erg s<SUP>‑1</SUP> cm<SUP>‑2</SUP> arcsec<SUP>‑2</SUP>. Compared to those of previous studies, our LAH is brighter at radii of ∼25–100 kpc, which is not likely caused by the contamination in our sample but by the different redshifts, fields, and selection methods instead. To investigate how central galaxies affect surrounding LAHs, we divide our LAEs into subsamples based on the Lyα luminosity (L <SUB>Lyα </SUB>), rest-frame Lyα equivalent width (EW<SUB>0</SUB>), and UV magnitude (M <SUB>uv</SUB>). We stack the subsamples and find that higher L <SUB>Lyα </SUB>, smaller EW<SUB>0</SUB>, and brighter M <SUB>uv</SUB> cause more extended halos. Our results suggest that more massive LAEs generally have more extended LAHs.
|
[
978,
734
] |
[
"lyman-alpha galaxies",
"high-redshift galaxies"
] |
2021ApJ...916...35I
|
Interrelation of the Environment of Lyα Emitters and Massive Galaxies at 2 < z < 4.5
|
We present a comparison of the spatial distributions of Lyα emitters (LAEs) and massive star-forming and quiescent galaxies (SFGs and QGs) at 2 < z < 4.5. We use the photometric redshift catalog to select SFGs and QGs and an LAE catalog from intermediate/narrow bands obtained from the Subaru Telescope and Isaac Newton Telescope in the Cosmic Evolution Survey (COSMOS). We derive the auto-/cross-correlation signals of SFGs, QGs, and LAEs and the galaxy overdensity distributions at the position of them. Whereas the cross-correlation signals of SFGs and QGs are explained solely by their halo mass differences, those of SFGs and LAEs are significantly lower than those expected from their autocorrelation signals, suggesting that some additional physical processes are segregating these two populations. Such segregation of SFGs and LAEs becomes stronger for rest-frame ultraviolet faint LAEs (M<SUB>UV</SUB> > -20). From the overdensity distributions, LAEs are located in less dense regions than SFGs and QGs, whereas SFGs and QGs tend to be in the same overdensity distributions. The different spatial distributions of LAEs compared to those of massive galaxies may be attributed to assembly bias or large amounts of neutral hydrogen gas associated with massive halos. These results reinforce the importance of exploring multiple galaxy populations in quantifying the intrinsic galaxy environment of the high-z universe.
|
[
2029,
734,
594
] |
[
"galaxy environments",
"high-redshift galaxies",
"galaxy evolution"
] |
2020ApJ...895L..44L
|
Highly Structured Quasar Outflow in SDSS J010612.22+001920.1
|
Evidence for quasar outflows can be detected via blueshifted broad absorption lines (BALs) in rest-frame ultraviolet spectra of quasars. We have identified 18 narrow absorption line (NAL) systems in the BAL system of SDSS J010612.22+001920.1, indicating that this BAL outflow has achieved a high degree of clumpiness. Moreover, these NAL systems are highly structured in velocity space and separated from each other by the doublet spacings of multiple ionic species, including a sequence of 10 C IV doublets that form arithmetic progression with a common difference of ≈498 $\,\mathrm{km}\,{{\rm{s}}}^{-1}$ . Cases like J010612.22+001920.1 offer strong evidence for the dynamical process of radiative acceleration in quasar outflow, and open up a new way for the research of quasar outflow under the framework of the NAL complex.
|
[
1319,
183,
1317
] |
[
"quasars",
"broad-absorption line quasar",
"quasar absorption line spectroscopy"
] |
2021ApJ...908L..50G
|
Evolution of Subsurface Zonal and Meridional Flows in Solar Cycle 24 from Helioseismological Data
|
The results of determinations of the azimuthal and meridional velocities by time-distance helioseismology from Helioseismic and Magnetic Imager on board Solar Dynamics Observatory from 2010 May to 2020 September at latitudes and Stonyhurst longitudes from - 60° to + 60° and depths to about 19 Mm below the photosphere are used to analyze spatiotemporal variations of the solar differential rotation and meridional circulation. The pattern of torsional oscillations, or latitudinal belts of alternating "fast" and "slow" zonal flows migrating from high latitudes toward the equator, is found to extend in the time-latitude diagrams over the whole time interval. The oscillation period is comparable with a doubled solar-activity-cycle and can be described as an extended solar cycle. The zonal-velocity variations are related to the solar-activity level, the local-velocity increases corresponding to the sunspot-number increases and being localized at latitudes where the strongest magnetic fields are recorded. The dramatic growth of the zonal velocities in 2018 appears to be a precursor of the beginning of Solar Cycle 25. The strong symmetrization of the zonal-velocity field by 2020 can be considered another precursor. The general pattern of poleward meridional flows is modulated by latitudinal variations similar to the extended-solar-cycle behavior of the zonal flows. During the activity maximum, these variations are superposed with a higher harmonic corresponding to meridional flows converging to the spot-formation latitudes. Our results indicate that variations of both the zonal and meridional flows exhibit the extended-solar-cycle behavior, which is an intrinsic feature of the solar dynamo.
|
[
1996,
1874,
709,
1487
] |
[
"solar differential rotation",
"solar meridional circulation",
"helioseismology",
"solar cycle"
] |
2021RNAAS...5..206K
|
Investigating the Accuracy of Virial Cluster Masses: King Model Simulations
|
Stars form in clusters within giant molecular clouds. Spectroscopic observations can reveal radial velocities from which virial masses can be estimated. The question we are investigating is how accurate these estimates are with respect to the number of stars observed. We simulated virialized clusters with King model distributions and from these clusters we simulated mock observations. From these observations cluster sizes and virial masses are estimated, and empirical distribution functions are constructed. A confidence interval table is produced considering the number of objects observed and the ratio of velocity dispersion to observational uncertainty.
|
[
1833,
1569,
1961,
1332
] |
[
"young star clusters",
"star formation",
"confidence interval",
"radial velocity"
] |
2023ApJ...942...66G
|
Salt-bearing Disk Candidates around High-mass Young Stellar Objects
|
Molecular lines tracing the orbital motion of gas in a well-defined disk are valuable tools for inferring both the properties of the disk and the star it surrounds. Lines that arise only from a disk, and not also from the surrounding molecular cloud core that birthed the star or from the outflow it drives, are rare. Several such emission lines have recently been discovered in one example case, those from NaCl and KCl salt molecules. We studied a sample of 23 candidate high-mass young stellar objects (HMYSOs) in 17 high-mass star-forming regions to determine how frequently emission from these species is detected. We present five new detections of water, NaCl, KCl, PN, and SiS from the innermost regions around the objects, bringing the total number of known briny disk candidates to nine. Their kinematic structure is generally disk-like, though we are unable to determine whether they arise from a disk or outflow in the sources with new detections. We demonstrate that these species are spatially coincident in a few resolved cases and show that they are generally detected together, suggesting a common origin or excitation mechanism. We also show that several disks around HMYSOs clearly do not exhibit emission in these species. Salty disks are therefore neither particularly rare in high-mass disks, nor are they ubiquitous.
|
[
235,
1569,
732,
1579
] |
[
"circumstellar disks",
"star formation",
"massive stars",
"stellar accretion disks"
] |
2022ApJ...934...78C
|
The Curious Case of the "Heartworm" Nebula
|
The curious Galactic features near G357.2-0.2 were observed with the MeerKAT radio interferometer array in the UHF and L bands (0.56-1.68 GHz). There are two possibly related features: a newly identified faint heart-shaped partial shell (the "heart"), and a series of previously known but now much better imaged narrow, curved features (the "worm") interior to the heart. Polarized emission suggests that much of the emission is nonthermal and is embedded in a dense plasma. The filaments of the worm appear to be magnetic structures powered by embedded knots that are sites of particle acceleration. The morphology of the worm broadly resembles some known pulsar wind nebulae (PWNe) but there is no known pulsar or PWN which could be powering this structure. We also present eROSITA observations of the field; no part of the nebula is detected in X-rays, but the current limits do not preclude the existence of a pulsar/PWN of intermediate spin-down luminosity.
|
[
571,
504,
1408,
1108,
1667
] |
[
"galactic radio sources",
"extended radiation sources",
"rotation powered pulsars",
"neutron stars",
"supernova remnants"
] |
2021ApJ...907L...1W
|
A Luminous Quasar at Redshift 7.642
|
Distant quasars are unique tracers to study the formation of the earliest supermassive black holes (SMBHs) and the history of cosmic reionization. Despite extensive efforts, only two quasars have been found at z ≥ 7.5, due to a combination of their low spatial density and the high contamination rate in quasar selection. We report the discovery of a luminous quasar at z = 7.642, J0313-1806, the most distant quasar yet known. This quasar has a bolometric luminosity of 3.6 × 10<SUP>13</SUP>L<SUB>⊙</SUB>. Deep spectroscopic observations reveal a SMBH with a mass of (1.6 ± 0.4) × 10<SUP>9</SUP> M<SUB>⊙</SUB> in this quasar. The existence of such a massive SMBH just ∼670 million years after the big bang challenges significantly theoretical models of SMBH growth. In addition, the quasar spectrum exhibits strong broad absorption line (BAL) features in C IV and Si IV, with a maximum velocity close to 20% of the speed of light. The relativistic BAL features, combined with a strongly blueshifted C IV emission line, indicate that there is a strong active galactic nucleus (AGN)-driven outflow in this system. Atacama Large Millimeter/submillimeter Array observations detect the dust continuum and [C II] emission from the quasar host galaxy, yielding an accurate redshift of 7.6423 ± 0.0013 and suggesting that the quasar is hosted by an intensely star-forming galaxy, with a star formation rate of ∼200 M<SUB>⊙</SUB> yr<SUP>-1</SUP> and a dust mass of ∼7 × 10<SUP>7</SUP> M<SUB>⊙</SUB>. Follow-up observations of this reionization-era BAL quasar will provide a powerful probe of the effects of AGN feedback on the growth of the earliest massive galaxies.
|
[
1663,
1319,
183,
435
] |
[
"supermassive black holes",
"quasars",
"broad-absorption line quasar",
"early universe"
] |
2023ApJ...947L...9H
|
Global Dynamic Scaling Relations of H I-rich Ultra-diffuse Galaxies
|
The baryonic Tully-Fisher relation (BTFR), which connects the baryonic mass of galaxies with their circular velocities, has been validated across a wide range of galaxies, from dwarf galaxies to massive galaxies. Recent studies have found that several ultra-diffuse galaxies (UDGs) deviate significantly from the BTFR, indicating a galaxy population with abnormal dynamical properties. However, such studies were still confined within a small sample size. In this study, we used the 100% complete Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) to investigate the BTFR of 88 H I-rich UDGs (HUDGs), which is the largest UDG sample with dynamical information. We found that the HUDGs form a continuous distribution in the BTFR diagram, with high-velocity galaxies consistent with normal dwarf galaxies at a 1σ level, and low-velocity galaxies deviating from the BTFR, in line with that reported in the literature. We point out that the observed deviation may be subject to various selection effects or systemic biases. Nevertheless, we found that the significance of the deviation of HUDGs from the BTFR and TFR are different, i.e., they either deviate from the BTFR or from the TFR. Our result indicates that a high gas fraction may play an important role in explaining the deviation of HUDGs from BTFR.
|
[
416,
940,
591,
595,
594
] |
[
"dwarf galaxies",
"low surface brightness galaxies",
"galaxy dynamics",
"galaxy formation",
"galaxy evolution"
] |
2022ApJ...935..140H
|
Supercritical Growth Pathway to Overmassive Black Holes at Cosmic Dawn: Coevolution with Massive Quasar Hosts
|
Observations of the most luminous quasars at high redshifts (z > 6) have revealed that the largest supermassive black holes (SMBHs) at those epochs tend to be substantially overmassive relative to their host galaxies compared to the local relations, suggesting they experienced rapid early growth phases. We propose an assembly model for the SMBHs that end up in rare massive ~10<SUP>12</SUP> M <SUB>⊙</SUB> host halos at z ~ 6-7, applying a kinetic feedback prescription for BHs accreting above the Eddington rate, provided by radiation hydrodynamic simulations for the long-term evolution of the accretion-flow structure. The large inflow rates into these halos during their assembly enable the formation of >10<SUP>9</SUP> M <SUB>⊙</SUB> SMBHs by z ~ 6, even starting from stellar-mass seeds at z ~ 30, and even in the presence of outflows that reduce the BH feeding rate, especially at early times. This mechanism also naturally yields a high BH-to-galaxy mass ratio of >0.01 before the SMBH mass reaches M <SUB>BH</SUB> > 10<SUP>9</SUP> M <SUB>⊙</SUB> by z ~ 6. These fast-growing SMBH progenitors are bright enough to be detected by upcoming observations with the James Webb Space Telescope over a wide range of redshift (7 < z < 15), regardless of how they were seeded.
|
[
1663,
1319,
734
] |
[
"supermassive black holes",
"quasars",
"high-redshift galaxies"
] |
2023RNAAS...7....2S
|
20 s Cadence TESS Photometry of HR 8799
|
We analyzed 20 s cadence Transiting Exoplanet Survey Satellite time-series photometry of the exoplanet host star HR 8799 collected in Sector 56. The amplitude spectrum shows Gamma Doradus (γ Dor) pulsations consistent with previous space-based photometry from MOST. Assuming that HR 8799 is a representative of γ Dor stars in the Kepler sample, the dominant dipole mode at 1.98 cycles day<SUP>-1</SUP> implies a core rotation period of ~0.7 day, which combined with $v\sin i$ and stellar radius measurements would result in a preliminary stellar inclination of ~28° assuming rigid rotation. We find no significant residual photometric variation after removing the pulsation signal aside from a ~9 days trend that is likely a systematic effect or an artifact from performing aggressive frequency subtraction in the presence of red noise.
|
[
484,
2101,
1242,
1625,
1761
] |
[
"exoplanet systems",
"gamma doradus variable stars",
"planet hosting stars",
"stellar pulsations",
"variable stars"
] |
2021AJ....162..194Z
|
Preview of Comet C/2021 A1 (Leonard) and Its Encounter with Venus
|
Long-period comet C/2021 A1 (Leonard) will approach Venus to within 0.029 au on 2021 December 18 and may subsequently graze the planet with its dust trail less than 2 days later. We observed C/2021 A1 with the Lowell Discovery Telescope on 2021 January 13 and March 3, as well as with the Palomar Hale Telescope on 2021 March 20, while the comet was inbound at heliocentric distances of r = 4.97, 4.46, and 4.28 au, respectively. Tail morphology suggests that the dust is optically dominated by ~0.1-1 mm radius grains produced in the prior year. Neither narrowband imaging photometry nor spectrophotometry reveal any definitive gas emission, placing 3σ upper bounds on CN production of ≲10<SUP>23</SUP> molec<SUP>-1</SUP> at both of the latter two epochs. Trajectory analysis indicates that large (≳1 mm) grains ejected at extremely large heliocentric distances (r ≳ 30 au) are most strongly favored to reach Venus. The flux of such meteors on Venus, and thus their potential direct or indirect observability, is highly uncertain, as the comet's dust production history is poorly constrained at these distances but will likely fall well below the meteor flux from comet C/2013 A1 (Siding Spring)'s closer encounter to Mars in 2014 and thus poses a negligible risk to any spacecraft in orbit around Venus. Dust produced in previous apparitions will not likely contribute substantially to the meteor flux, nor will dust from any future activity apart from an unlikely high-speed (≳0.5 km s<SUP>-1</SUP>) dust outburst prior to the comet reaching r ≈ 2 au in 2021 September.
|
[
274,
933,
1036,
1763
] |
[
"comet tails",
"long period comets",
"meteor trails",
"venus"
] |
2021ApJ...920..100W
|
A New Reconstruction of the Sun's Magnetic Field and Total Irradiance since 1700
|
We model the Sun's large-scale magnetic field and total solar irradiance (TSI) since 1700 by combining flux transport simulations with empirical relationships between facular brightening, sunspot darkening, and the total photospheric flux. The photospheric field is evolved subject to the constraints that (1) the flux emergence rate scales as the yearly sunspot numbers, and (2) the polar field strength at solar minimum is proportional to the amplitude of the following cycle. Simulations are performed using both the recently revised sunspot numbers and an average of these numbers and the Hoyt-Schatten group numbers. A decrease (increase) in the polar field strength from one cycle to the next is simulated either by increasing (decreasing) the poleward flow speed, or by decreasing (increasing) the average axial tilts of active regions; the resulting photospheric field evolution is very similar whichever parameter is varied. Comparisons between irradiance data and both the simulated and observed photospheric field suggest that TSI and facular brightness increase less steeply with the field strength at solar minimum than at other phases of the cycle, presumably because of the dominance of small-scale ephemeral regions when activity is very low. This relative insensitivity of the irradiance to changes in the large-scale field during cycle minima results in a minimum-to-minimum increase of annual TSI from 1700 to 1964 (2008) of 0.2 (0.06) W m<SUP>-2</SUP>, a factor of 2-3 smaller than predicted in earlier reconstructions where the relation between facular brightness and field strength was assumed to be independent of cycle phase.
|
[
824,
1473,
1487,
2001,
1503,
1494,
463,
1521,
1653,
1974,
567
] |
[
"interplanetary magnetic fields",
"solar-terrestrial interactions",
"solar cycle",
"solar dynamo",
"solar magnetic fields",
"solar faculae",
"ephemeral active regions",
"solar radiation",
"sunspots",
"solar active regions",
"galactic cosmic rays"
] |
2021ApJ...915..125S
|
The Effect of the Angular Momentum in the Formation and Evolution of Low Surface Brightness Galaxies
|
Using observed data from the literature, we compare in one single publication the angular momentum (AM) of low surface brightness galaxies (LSBGs), with that of high surface brightness galaxies (HSBGs), a comparison that either is currently spread across many unconnected references, or simply does not exist. Partly because of the subject, this has received little attention outside the realm of simulations. We use previous results of the stellar specific AM j<SUB>*</SUB> from the SPARC database containing Spitzer 3.6 μm photometry and accurate H I rotation curves from Lelli et al. using a sample of 38 LSBGs and 82 HSBGs. We do this with the objective of comparing both galaxy populations, finding that LSBGs are higher in the Fall relation by about 0.174 dex. Additionally, we apply and test different masses and formation models to estimate the spin parameter λ, which quantifies the rotation obtained from the tidal torque theory, finding no clear evidence of a difference in the spin of LSBGs and HSBGs under a classic disk formation model that assumes the ratio (f<SUB>j</SUB>) between j<SUB>*</SUB> and the specific AM of the halo is ~1. In another respect, by using the biased collapse model, where f<SUB>j</SUB> depends on the star formation efficiency, it was found that LSBGs clearly show higher spin values, having an average spin of ~2 times the average spin of HSBGs. This latter result is consistent with those obtained from simulations by Dalcanton et al.
|
[
594,
595,
1880,
602,
591,
940,
618,
619
] |
[
"galaxy evolution",
"galaxy formation",
"galaxy dark matter halos",
"galaxy kinematics",
"galaxy dynamics",
"low surface brightness galaxies",
"galaxy rotation",
"galaxy rotation curves"
] |
2023ApJ...956..113D
|
Transition Probabilities of Near-infrared Ce III Lines from Stellar Spectra: Applications to Kilonovae
|
Kilonova spectra provide us with information of r-process nucleosynthesis in neutron star mergers. However, it is still challenging to identify individual elements in the spectra mainly due to the lack of experimentally accurate atomic data for heavy elements at near-infrared wavelengths. Recently, Domoto et al. proposed that the absorption features around 14500 Å in the observed spectra of GW170817/AT2017gfo are Ce III lines. But they used theoretical transition probabilities (gf-values) whose accuracy is uncertain. In this paper, we derive the astrophysical gf-values of three Ce III lines, aiming at verifying this identification. We model high-resolution H-band spectra of four F-type supergiants showing clear Ce III absorption features by assuming stellar parameters derived from optical spectra in the literature. We also test the validity of the derived astrophysical gf-values by estimating the Ce III abundances of Ap stars. We find that the derived astrophysical gf-values of the Ce III lines are systematically lower by about 0.25 dex than those used in previous work of kilonovae, while they are still compatible within the uncertainty ranges. By performing radiative transfer simulations of kilonovae with the derived gf-values, we find that the identification of Ce III as a source of absorption features in the observed kilonova spectra still stands, even considering the uncertainties in the astrophysical gf-values. This supports the identification of Ce in the spectra of GW170817/AT2017gfo.
|
[
1324,
1967,
2074
] |
[
"r-process",
"radiative transfer simulations",
"transition probabilities"
] |
2023ApJ...950...42L
|
The Spin-down Accretion Regime of Galactic Ultraluminous X-Ray Pulsar Swift J0243.6+6124
|
The relatively high fluxes of the Galactic ultraluminous X-ray pulsar Swift J0243 allow a detailed study of its spin-down regime in the quiescent state for the first time. After the 2017 giant outburst, its spin frequency shows a linearly decreasing trend with some variations due to minor outbursts. The linear spin-down rate is ~ -1.9 × 10<SUP>-12</SUP> Hz s<SUP>-1</SUP> during the period of lowest luminosity, from which one can infer a dipole field of ~1.75 × 10<SUP>13</SUP> G. The $\dot{\nu }\mbox{--}L$ relation during the spin-down regime is complex, and $\dot{\nu }$ is close to zero when the luminosity reaches both the high end (L <SUB>38</SUB> ~ 0.3) and the lowest value (L <SUB>38</SUB> ~ 0.03). The luminosity of zero torque is different for the giant outburst and other minor outbursts. This is likely due to different accretion flows for different types of outburst, as evidenced by the differences in the spectra and pulse profiles at a similar luminosity for different types of outburst (giant or not). The pulse profile changes from double peaks in the spin-up state to a single broad peak in the low spin-down regime, indicating the emission beam/region is larger in the low spin-down regime. These results show that accretion is still ongoing in the low spin-down regime, for which the neutron star is supposed to be in a propeller state.
|
[
733
] |
[
"high mass x-ray binary stars"
] |
2020ApJ...890..166P
|
The Ultraluminous X-Ray Sources Population of the Galaxy NGC 7456
|
Ultraluminous X-ray sources (ULXs) are a class of accreting compact objects with X-ray luminosities above 10<SUP>39</SUP> erg s<SUP>-1</SUP>. The ULX population counts several hundred objects but only a fraction are well studied. Here we present a detailed analysis of all ULXs hosted in the galaxy NGC 7456. It was observed in X-rays only once in the past (in 2005) by XMM-Newton. but the observation was short and strongly affected by high background. In 2018, we obtained a new, deeper (∼90 ks) XMM-Newton observation that allowed us to perform a detailed characterization of the ULXs hosted in the galaxy. ULX-1 and ULX-2, the two brightest objects (L<SUB>X</SUB> ∼ 6-10 × 10<SUP>39</SUP> erg s<SUP>-1</SUP>), have spectra that can be described by a model with two thermal components, as often found in ULXs. ULX-1 also shows one order of magnitude in flux variability on short-term timescales (hundreds to thousands of kiloseconds). The other sources (ULX-3 and ULX-4) show flux changes of at least an order of magnitude, and these objects may be candidate transient ULXs, although longer X-ray monitoring or further studies are required to ascribe them to the ULX population. In addition, we found a previously undetected source that might be a new candidate ULX (labeled as ULX-5), with a luminosity of ∼10<SUP>39</SUP> erg s<SUP>-1</SUP> and hard power-law spectral shape, whose nature is still unclear and for which a background active galactic nucleus cannot be excluded. We discuss the properties of all the ULXs in NGC 7456 within the framework of super-Eddington accretion onto stellar-mass compact objects. Although no pulsations were detected, we cannot exclude that the sources host neutron stars.
|
[
1810,
1811,
1822,
1108,
1306
] |
[
"x-ray astronomy",
"x-ray binary stars",
"x-ray sources",
"neutron stars",
"pulsars"
] |
2023ApJ...952...89M
|
The Planetary Accretion Shock. III. Smoothing-free 2.5D Simulations and Calculation of Hα Emission
|
Surveys have looked for Hα emission from accreting gas giants but found very few objects. Analyses of the detections and nondetections have assumed that the entire gas flow feeding the planet is in radial freefall. However, hydrodynamical simulations suggest that this is far from reality. We calculate the Hα emission from multidimensional accretion onto a gas giant, following the gas flow from Hill sphere scales down to the circumplanetary disk (CPD) and the planetary surface. We perform azimuthally symmetric radiation hydrodynamics simulations around the planet and use modern tabulated gas and dust opacities. Crucially, contrasting with most previous simulations, we do not smooth the gravitational potential but do follow the flow down to the planetary surface, where grid cells are 0.01 Jupiter radii small. We find that roughly only 1% of the net gas inflow into the Hill sphere directly reaches the planet. As expected for ballistic infall trajectories, most of the gas falls at too large a distance on the CPD to generate Hα. Including radiation transport removes the high-velocity subsurface flow previously seen in hydrodynamics-only simulations, so that only the free planet surface and the inner regions of the CPD emit substantial Hα. Unless magnetospheric accretion, which we neglect here, additionally produces Hα, the corresponding Hα production efficiency is much smaller than usually assumed, which needs to be taken into account when analyzing (non)detection statistics.
|
[
14,
1335,
767,
2086,
1241,
691
] |
[
"accretion",
"radiative transfer",
"hydrodynamical simulations",
"shocks",
"planet formation",
"h alpha photometry"
] |
2024RNAAS...8...43K
|
Comparison of Convolutional Neural Networks and Random Forest Classifiers for Strong Gravitational Lens Identification
|
Strong gravitational lenses have been instrumental in providing insight into various astronomical problems, including analyzing the dark matter distribution of the universe. Effective identification of these events is made possible through machine learning algorithms, with many recent studies focusing on neural networks. However, very few have investigated the tradeoffs between different algorithms besides neural networks for lens identification. Our paper compares a convolutional neural network (CNN) and a random forest classifier (RFC) to determine the benefits of each for this task. We find that while CNNs do achieve higher accuracy, using RFCs to supplement them could increase the effectiveness of such algorithms. As a result, models that utilize both side-by-side to make predictions may increase in accuracy. This should be explored by future research.
|
[
1643,
1167
] |
[
"strong gravitational lensing",
"optical identification"
] |
2020ApJ...899..133H
|
Nuclear Structures of <SUP>17</SUP>O and Time-dependent Sensitivity of the Weak s-process to the <SUP>16</SUP>O(n,γ)<SUP>17</SUP>O Rate
|
We revisit the radiative neutron capture reaction <SUP>16</SUP>O(n,γ)<SUP>17</SUP>O of astrophysical interest, based on the new reevaluated cross-section data. Several potentials are proposed to predict direct capture cross sections. The contributions from single-particle resonances to total capture cross section are quantitatively considered in Breit-Wigner formalism, taking into account the interference term between direct capture and resonant cross sections, which is crucial for the description of the behavior around the resonance energies. A new cross section is achieved based upon χ<SUP>2</SUP>-fittings for optimized resonance parameters using Minuit code, and it has a largely improved agreement with updated experimental data. Statistical errors are also evaluated for the total and Maxwellian-averaged cross sections. It is confirmed that the direct captures dominate the total cross sections; however, resonant contribution also becomes progressively more important as the energy increases to 100 keV. Resonance contribution can increase the reaction rates for energy region 50 keV < E < 100 keV by 5% ± 5%-25% ± 5%, and around 8% ± 5% in comparison with KADoNiS v0.3 rate and the latest data evaluations, respectively. We show a detailed propagation of the uncertainty in the <SUP>16</SUP>O(n,γ) reaction rate to abundances of nuclei, including s-nuclei during the weak s-process with a multi-zone nuclear network calculation. Although an enhanced rate of <SUP>16</SUP>O(n,γ) diminishes the s-process efficiency in the 25 M<SUB>⊙</SUB> stellar model adopted from the Modules for Experiments in Stellar Astrophysics, it can lead to larger abundances of neutrons as well as <SUP>22</SUP>Ne in the late epoch of C burning.
|
[
716,
2081,
1419,
732
] |
[
"helium burning",
"reaction rates",
"s-process",
"massive stars"
] |
2023ApJ...953...64S
|
On the Effects of Local Environment on Active Galactic Nucleus (AGN) in the Horizon Run 5 Simulation
|
We use the Horizon Run 5 cosmological simulation to study the effect of galaxy intrinsic properties and the local environment on active galactic nuclei (AGNs) characterized by their threshold of the accretion rate. We select galaxies in the stellar mass range ${10}^{9.5}\leqslant {M}_{* }^{}/{M}_{\odot }^{}\leqslant {10}^{10.5}$ in the snapshot at redshift z = 0.625. Among various intrinsic properties, we find that the star formation rate of the host galaxy is most correlated to the AGN activity. To quantify the environment, we use background galaxy number density (large-scale environment) and distance and morphological type of the nearest neighbors (small-scale environment), and study their relative effects on the AGN properties. We find that, compared to the background density, the nearest neighbor environment is the dominant quantity determining the bolometric luminosity, star formation rate, and kinematic properties of AGNs and better dictates the gas mass of the host galaxy. We show that the cold gas content in the host galaxies is crucial in triggering AGN activity. However, when the nearest neighbor environment effects start to act at the neighbor distance of less than about half the virial radius of the neighbor, the neighbor environmental effects are the most dominant factor for quasar activity.
|
[
2029,
2017,
592,
600
] |
[
"galaxy environments",
"agn host galaxies",
"galaxy encounters",
"galaxy interactions"
] |
2023ApJ...944..128C
|
Wide-band Timing of the Parkes Pulsar Timing Array UWL Data
|
In 2018 an ultra-wide-bandwidth low-frequency (UWL) receiver was installed on the 64 m Parkes Radio Telescope, enabling observations with an instantaneous frequency coverage from 704 to 4032 MHz. Here we present the analysis of a 3 yr data set of 35 ms pulsars observed with the UWL by the Parkes Pulsar Timing Array, using wide-band timing methods. The two key differences compared to typical narrowband methods are (1) generation of two-dimensional templates accounting for pulse shape evolution with frequency and (2) simultaneous measurements of the pulse time of arrival (TOA) and dispersion measure (DM). This is the first time that wide-band timing has been applied to a uniform data set collected with a single large fractional bandwidth receiver, for which such techniques were originally developed. As a result of our study, we present a set of profile evolution models and new timing solutions, including initial noise analysis. Precision of our TOA and DM measurements is in the range of 0.005-2.08 μs and (0.043-14.24) × 10<SUP>-4</SUP> cm<SUP>-3</SUP> pc, respectively, with 94% of the pulsars achieving a median TOA uncertainty of less than 1 μs.
|
[
1305,
1062
] |
[
"pulsar timing method",
"millisecond pulsars"
] |
2022ApJ...935....2C
|
Gamma-Ray Eclipses and Orbital Modulation Transitions in the Candidate Redback 4FGL J1702.7-5655
|
Observations with the Fermi Large Area Telescope (LAT) of the gamma-ray source 4FGL J1702.7-5655, previously classified as a candidate millisecond pulsar, show highly significant modulation at a period of 0.2438033 days (~5.85 hr). Further examination of the folded light curve indicates the presence of narrow eclipses, suggesting that this is a redback binary system. An examination of the long-term properties of the modulation over 13 years of LAT observations indicates that the orbital modulation of the gamma rays changed from a simple eclipse before early 2013 to a broader, more easily detected quasi-sinusoidal modulation. In addition, the time of the eclipse shifts to ~0.05 later in phase. This change in the orbital modulation properties, however, is not accompanied by a significant overall change in gamma-ray flux or spectrum. The quasi-sinusoidal component peaks ~0.5 out of phase with the eclipse, which would indicate inferior conjunction of the compact object in the system. Swift X-ray Telescope observations reveal a possible X-ray counterpart within the LAT error ellipse. However, radio observations obtained with the Australia Telescope Compact Array do not detect a source in the region. 4FGL J1702.7-5655 appears to have changed its state in 2013, perhaps related to changes in the intrabinary shock in the system. We compare the properties of 4FGL J1702.7-5655 to those of other binary millisecond pulsars that have exhibited orbital modulation in gamma-rays.
|
[
633,
939,
1062,
1108,
444
] |
[
"gamma-ray sources",
"low-mass x-ray binary stars",
"millisecond pulsars",
"neutron stars",
"eclipsing binary stars"
] |
2020ApJ...894...74B
|
Protoplanetary Disks in the Orion Nebula Cluster: Gas-disk Morphologies and Kinematics as Seen with ALMA
|
We present Atacama Large Millimeter Array CO(3 - 2) and HCO<SUP>+</SUP>(4 - 3) observations covering the central 1'5 × 1'5 region of the Orion Nebula Cluster (ONC). The unprecedented level of sensitivity (∼0.1 mJy beam<SUP>-1</SUP>) and angular resolution (∼0"09 ≈ 40 au) of these line observations enable us to search for gas-disk detections toward the known positions of submillimeter-detected dust disks in this region. We detect 23 disks in gas: 17 in CO(3 - 2), 17 in HCO<SUP>+</SUP>(4 - 3), and 11 in both lines. Depending on where the sources are located in the ONC, we see the line detections in emission, in absorption against the warm background, or in both emission and absorption. We spectrally resolve the gas with 0.5 km s<SUP>-1</SUP> channels and find that the kinematics of most sources are consistent with Keplerian rotation. We measure the distribution of gas-disk sizes and find typical radii of ∼50-200 au. As such, gas disks in the ONC are compact in comparison with the gas disks seen in low-density star-forming regions. Gas sizes are universally larger than the dust sizes. However, the gas and dust sizes are not strongly correlated. We find a positive correlation between gas size and distance from the massive star θ<SUP>1</SUP> Ori C, indicating that disks in the ONC are influenced by photoionization. Finally, we use the observed kinematics of the detected gas lines to model Keplerian rotation and infer the masses of the central pre-main-sequence stars. Our dynamically derived stellar masses are not consistent with the spectroscopically derived masses, and we discuss possible reasons for this discrepancy.
|
[
1300,
235,
1296,
238,
1833,
1834,
1290,
1241,
1338,
1061
] |
[
"protoplanetary disks",
"circumstellar disks",
"proplyds",
"circumstellar gas",
"young star clusters",
"young stellar objects",
"pre-main sequence stars",
"planet formation",
"radio astronomy",
"millimeter astronomy"
] |
2023ApJ...958...98F
|
Early Planet Formation in Embedded Disks (eDisk). XII. Accretion Streamers, Protoplanetary Disk, and Outflow in the Class I Source Oph IRS 63
|
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the Class I source Oph IRS 63 in the context of the Early Planet Formation in Embedded Disks large program. Our ALMA observations of Oph IRS 63 show a myriad of protostellar features, such as a shell-like bipolar outflow (in <SUP>12</SUP>CO), an extended rotating envelope structure (in <SUP>13</SUP>CO), a streamer connecting the envelope to the disk (in C<SUP>18</SUP>O), and several small-scale spiral structures seen toward the edge of the dust continuum (in SO). By analyzing the velocity pattern of <SUP>13</SUP>CO and C<SUP>18</SUP>O, we measure a protostellar mass of M <SUB>⋆</SUB> = 0.5 ± 0.2 M <SUB>⊙</SUB> and confirm the presence of a disk rotating at almost Keplerian velocity that extends up to ~260 au. These calculations also show that the gaseous disk is about four times larger than the dust disk, which could indicate dust evolution and radial drift. Furthermore, we model the C<SUP>18</SUP>O streamer and SO spiral structures as features originating from an infalling rotating structure that continuously feeds the young protostellar disk. We compute an envelope-to-disk mass infall rate of ~10<SUP>-6</SUP> M <SUB>⊙</SUB> yr<SUP>-1</SUP> and compare it to the disk-to-star mass accretion rate of ~10<SUP>-8</SUP> M <SUB>⊙</SUB> yr<SUP>-1</SUP>, from which we infer that the protostellar disk is in a mass buildup phase. At the current mass infall rate, we speculate that soon the disk will become too massive to be gravitationally stable.
|
[
1300,
1302,
1578,
2050,
1569,
1241
] |
[
"protoplanetary disks",
"protostars",
"stellar accretion",
"low mass stars",
"star formation",
"planet formation"
] |
2023ApJ...956...32L
|
Standardized Luminosity of the Tip of the Red Giant Branch Utilizing Multiple Fields in NGC 4258 and the CATs Algorithm
|
The tip of the red giant branch provides a luminous standard candle for calibrating distance ladders that reach Type Ia supernova (SN Ia) hosts. However, recent work reveals that tip measurements vary at the ~0.1 mag level for different stellar populations and locations within a host, which may lead to inconsistencies along the distance ladder. We pursue a calibration of the tip using 11 Hubble Space Telescope fields around the maser host, NGC 4258, that is consistent with SN Ia hosts by standardizing tip measurements via their contrast ratios. We find F814W-band tips that exhibit a full 0.3 mag range and 0.1 mag dispersion. We do not find any correlation between H I column density and the apparent tip to 0.04 ± 0.03 mag/cm<SUP>-2</SUP>. We search for a tip-contrast relation (TCR) and measure the TCR within the fields of NGC 4258 of -0.015 ± 0.008 mag/R, where R is the contrast ratio. This value is consistent with the TCR originally discovered in the GHOSTS sample of -0.023 ± 0.005 mag/R. Combining these measurements, we find a global TCR of -0.021 ± 0.004 mag/R and a calibration of ${M}_{I}^{\mathrm{TRGB}}=-4.025\pm 0.035-(R-4)\times 0.021$ mag. We also use stellar models to simulate single age and metallicity stellar populations with [Fe/H] from -2.0 to -0.7 and ages from 3 to 12 Gyr and reconstruct the global TCR found here to a factor of ~2. This work is combined in a companion analysis with tip measurements of nearby SN Ia hosts to measure H <SUB>0</SUB>.
|
[
1372,
1563,
1595,
758,
1146,
2179,
10,
942,
1371,
394
] |
[
"red giant stars",
"standard candles",
"stellar distance",
"hubble constant",
"observational cosmology",
"calibration",
"absolute magnitude",
"luminosity function",
"red giant tip",
"distance indicators"
] |
2020ApJ...903...39K
|
Heated Poles on the Companion of Redback PSR J2339-0533
|
We analyze the photometry and spectra of the "redback" millisecond pulsar binary J2339-0533. These observations include new measurements from Keck and the Gamma-Ray Burst Optical/Near-infrared Detector (GROND), as well as archival measurements from the Optical and Infrared Synergetic Telescopes for Education and Research (OISTER), WIYN, Southern Astrophysical Research (SOAR), and Hobby-Eberly Telescope (HET) telescopes. The parameters derived from GROND, our primary photometric data, describe well the rest of the data sets, raising our confidence in our fitted binary properties. Our fit requires hot spots (likely magnetic poles) on the surface of the companion star, and we see evidence that these spots move over the 8 yr span of our photometry. The derived binary inclination i = 69°3 ± 2°3, together with the center-of-mass velocity (from the radial-velocity fits) K<SUB>C</SUB> = 347.0 ± 3.7 $\mathrm{km}\,{{\rm{s}}}^{-1}$ , give a fairly typical neutron star mass of 1.47 ± 0.09 M<SUB>⊙</SUB>.
|
[
1306
] |
[
"pulsars"
] |
2021PSJ.....2...59N
|
No Evidence for Orbital Clustering in the Extreme Trans-Neptunian Objects
|
The apparent clustering in longitude of perihelion ϖ and ascending node Ω of extreme trans-Neptunian objects (ETNOs) has been attributed to the gravitational effects of an unseen 5-10 Earth-mass planet in the outer solar system. To investigate how selection bias may contribute to this clustering, we consider 14 ETNOs discovered by the Dark Energy Survey, the Outer Solar System Origins Survey, and the survey of Sheppard and Trujillo. Using each survey's published pointing history, depth, and TNO tracking selections, we calculate the joint probability that these objects are consistent with an underlying parent population with uniform distributions in ϖ and Ω. We find that the mean scaled longitude of perihelion and orbital poles of the detected ETNOs are consistent with a uniform population at a level between 17% and 94% and thus conclude that this sample provides no evidence for angular clustering.
|
[
1528,
1255,
1705,
893,
376
] |
[
"solar system",
"planetary science",
"trans-neptunian objects",
"kuiper belt",
"detached objects"
] |
2023ApJ...959...65K
|
Particle-in-Cell Simulations of Sunward and Anti-sunward Whistler Waves in the Solar Wind
|
We present particle-in-cell simulations of a combined whistler heat flux and temperature anisotropy instability that is potentially operating in the solar wind. The simulations are performed in a uniform plasma and initialized with core and halo electron populations typical of the solar wind beyond about 0.3 au. We demonstrate that the instability produces whistler-mode waves propagating both along (anti-sunward) and opposite (sunward) to the electron heat flux. The saturated amplitudes of both sunward and anti-sunward whistler waves are strongly correlated with their initial linear growth rates, ${B}_{w}/{B}_{0}\sim {(\gamma /{\omega }_{{ce}})}^{\nu }$ , where for typical electron betas we have 0.6 ≲ ν ≲ 0.9. We show that because of the relatively large spectral width of the whistler waves, the instability saturates through the formation of quasi-linear plateaus around the resonant velocities. The revealed correlations of whistler wave amplitudes and spectral widths with electron beta and temperature anisotropy are consistent with solar wind observations. We show that anti-sunward whistler waves result in an electron heat flux decrease, while sunward whistler waves actually lead to an electron heat flux increase. The net effect is the electron heat flux suppression, whose efficiency is larger for larger electron betas and temperature anisotropies. The electron heat flux suppression can be up to 10%-60% provided that the saturated whistler wave amplitudes exceed about 1% of the background magnetic field. The experimental applications of the presented results are discussed.
|
[
1544,
1534
] |
[
"space plasmas",
"solar wind"
] |
2023ApJ...943L..17M
|
A JWST NIRSpec Phase Curve for WASP-121b: Dayside Emission Strongest Eastward of the Substellar Point and Nightside Conditions Conducive to Cloud Formation
|
We present the first exoplanet phase-curve measurement made with the JWST NIRSpec instrument, highlighting the exceptional stability of this newly commissioned observatory for exoplanet climate studies. The target, WASP-121b, is an ultrahot Jupiter with an orbital period of 30.6 hr. We analyze two broadband light curves generated for the NRS1 and NRS2 detectors, covering wavelength ranges of 2.70-3.72 μm and 3.82-5.15 μm, respectively. Both light curves exhibit minimal systematics, with approximately linear drifts in the baseline flux level of 30 ppm hr<SUP>-1</SUP> (NRS1) and 10 ppm hr<SUP>-1</SUP> (NRS2). Assuming a simple brightness map for the planet described by a low-order spherical harmonic dipole, our light-curve fits suggest that the phase curve peaks coincide with orbital phases 3.°36 ± 0.°11 (NRS1) and 2.°66 ± 0.°12 (NRS2) prior to mideclipse. This is consistent with the strongest dayside emission emanating from eastward of the substellar point. We measure planet-to-star emission ratios of 3924 ± 7 ppm (NRS1) and 4924 ± 9 ppm (NRS2) for the dayside hemisphere and 136 ± 8 ppm (NRS1) and 630 ± 10 ppm (NRS2) for the nightside hemisphere. The latter nightside emission ratios translate to planetary brightness temperatures of 926 ± 12 K (NRS1) and 1122 ± 10 K (NRS2), which are low enough for a wide range of refractory condensates to form, including enstatite and forsterite. A nightside cloud deck may be blocking emission from deeper, hotter layers of the atmosphere, potentially helping to explain why cloud-free 3D general circulation model simulations systematically overpredict the nightside emission for WASP-121b.
|
[
486,
487
] |
[
"exoplanet astronomy",
"exoplanet atmospheres"
] |
2024AJ....167...86C
|
Using AI for Wave-front Estimation with the Rubin Observatory Active Optics System
|
The Vera C. Rubin Observatory will, over a period of 10 yr, repeatedly survey the southern sky. To ensure that images generated by Rubin meet the quality requirements for precision science, the observatory will use an active-optics system (AOS) to correct for alignment and mirror surface perturbations introduced by gravity and temperature gradients in the optical system. To accomplish this, Rubin will use out-of-focus images from sensors located at the edge of the focal plane to learn and correct for perturbations to the wave front. We have designed and integrated a deep-learning (DL) model for wave-front estimation into the AOS pipeline. In this paper, we compare the performance of this DL approach to Rubin's baseline algorithm when applied to images from two different simulations of the Rubin optical system. We show the DL approach is faster and more accurate, achieving the atmospheric error floor both for high-quality images and low-quality images with heavy blending and vignetting. Compared to the baseline algorithm, the DL model is 40× faster, the median error 2× better under ideal conditions, 5× better in the presence of vignetting by the Rubin camera, and 14× better in the presence of blending in crowded fields. In addition, the DL model surpasses the required optical quality in simulations of the AOS closed loop. This system promises to increase the survey area useful for precision science by up to 8%. We discuss how this system might be deployed when commissioning and operating Rubin.
|
[
1933,
1080,
1174,
88,
799
] |
[
"neural networks",
"multiple mirror telescopes",
"optical telescopes",
"astronomical optics",
"astronomical instrumentation"
] |
2023ApJS..266...25P
|
Revised and Extended Analysis of Ar VI
|
This paper analyzes the emission spectrum of Ar VI and adds new information about this ion. We use a capillary light source to study the Ar VI spectrum, presenting 39 line classifications for the first time, including one line in the ultraviolet region. A total of nine possible Ar VI lines in the ultraviolet between 3288 and 3440 Å are analyzed. We revised the wavelengths of the lines at 1284.01 and 1307.42 Å previously used to identify Ar VI in astronomical objects. The lifetimes, weighted transition rates (gA) and their estimated uncertainties, and cancellation factors are obtained using a Hartree-Fock calculation with energy parameters adjusted to fit the values of the experimental levels and modified to include core polarization effects. We analyze all the experimentally known transitions of the Ar VI spectrum, with particular attention to conflicting information. Isoelectronic sequences of energy levels and transitions, for which the trend is not a smooth curve, are analyzed. We revise previous studies where the information needed to support line classifications and level designations is incomplete.
|
[
2099,
1261,
2084,
2074,
752
] |
[
"atomic spectroscopy",
"plasma astrophysics",
"line intensities",
"transition probabilities",
"hot ionized medium"
] |
2021ApJ...915..120M
|
New Candidate Extreme T Subdwarfs from the Backyard Worlds: Planet 9 Citizen Science Project
|
Schneider et al. presented the discovery of WISEA J041451.67-585456.7 and WISEA J181006.18-101000.5, which appear to be the first examples of extreme T-type subdwarfs (esdTs; metallicity ≤-1 dex, T<SUB>eff</SUB> ≲ 1400 K). Here, we present new discoveries and follow-up of three T-type subdwarf candidates, with an eye toward expanding the sample of such objects with very low metallicity and extraordinarily high kinematics, properties that suggest membership in the Galactic halo. Keck/NIRES near-infrared spectroscopy of WISEA J155349.96+693355.2, a fast-moving object discovered by the Backyard Worlds: Planet 9 citizen science project, confirms that it is a mid-T subdwarf. With H<SUB>W2</SUB> = 22.3 mag, WISEA J155349.96+693355.2 has the largest W2 reduced proper motion among all spectroscopically confirmed L and T subdwarfs, suggesting that it may be kinematically extreme. Nevertheless, our modeling of the WISEA J155349.96+693355.2 near-infrared spectrum indicates that its metallicity is only mildly subsolar. In analyzing the J155349.96+693355.2 spectrum, we present a new grid of low-temperature, low-metallicity model atmosphere spectra. We also present the discoveries of two new esdT candidates, CWISE J073844.52-664334.6 and CWISE J221706.28-145437.6, based on their large motions and colors similar to those of the two known esdT objects. Finding more esdT examples is a critical step toward mapping out the spectral sequence and observational properties of this newly identified population.
|
[
185,
1679,
1680
] |
[
"brown dwarfs",
"t dwarfs",
"t subdwarfs"
] |
2023ApJ...942...26G
|
Deep Potential: Recovering the Gravitational Potential from a Snapshot of Phase Space
|
One of the major goals of the field of Milky Way dynamics is to recover the gravitational potential field. Mapping the potential would allow us to determine the spatial distribution of matter-both baryonic and dark-throughout the galaxy. We present a novel method for determining the gravitational field from a snapshot of the phase-space positions of stars, based only on minimal physical assumptions, which makes use of recently developed tools from the field of deep learning. We first train a normalizing flow on a sample of observed six-dimensional phase-space coordinates of stars, obtaining a smooth, differentiable approximation of the distribution function. Using the collisionless Boltzmann equation, we then find the gravitational potential-represented by a feed-forward neural network-that renders this distribution function stationary. This method, which we term "Deep Potential," is more flexible than previous parametric methods, which fit restricted classes of analytic models of the distribution function and potential to the data. We demonstrate Deep Potential on mock data sets and demonstrate its robustness under various nonideal conditions. Deep Potential is a promising approach to mapping the density of the Milky Way and other stellar systems, using rich data sets of stellar positions and kinematics now being provided by Gaia and ground-based spectroscopic surveys.
|
[
1051,
1596,
1933,
667,
1882
] |
[
"milky way dynamics",
"stellar dynamics",
"neural networks",
"gravitational fields",
"astrostatistics"
] |
2021ApJS..256....1T
|
MG1-688432: A Peculiar Variable System
|
The short-period variable star MG1-688432 has been discovered to exhibit occasional extremely high energy optical outbursts as high as 10<SUP>38</SUP> erg. Outbursts are typically several hours in duration. These events are often highly structured, resembling sequential associated releases of energy. Twenty years of time sequence photometry are presented, indicating a basic sinusoidal light curve of mean period 6.65 days, with some phase shifting and long-term temporal trends in amplitude and mean brightness. Spectroscopy reveals a peculiar star, best resembling a K3 subgiant that has evolved off the main sequence moderately redward of the giant branch. Spectroscopic and radial velocity analyses indicate a binary system orbiting its barycenter with an unseen companion to the K3 IV primary. This is not an eclipsing system, with the inclination of the orbit precluding eclipse by the secondary. The system is at a distance of 1.5 kpc, and analysis of Gaia observations leads to the conclusion that the H-R diagram position of MG1-688432 is established by an intrinsic feature of the system, most likely either the stellar evolutionary state of the observed star or the presence of small (nongray) dust within the system. Two mechanisms (or combinations thereof) that might give rise to characteristics of the system are (1) magnetically induced chromospheric activity and (2) impacts with tidally disrupted planetary debris.
|
[
476,
230
] |
[
"eruptive variable stars",
"stellar chromospheres"
] |
2023ApJ...950..133H
|
New <SUP>26</SUP>P(p, γ)<SUP>27</SUP>S Thermonuclear Reaction Rate and Its Astrophysical Implications in the rp-process
|
Accurate nuclear reaction rates for <SUP>26</SUP>P(p, γ)<SUP>27</SUP>S are pivotal for a comprehensive understanding of the rp-process nucleosynthesis path in the region of proton-rich sulfur and phosphorus isotopes. However, large uncertainties still exist in the current rate of <SUP>26</SUP>P(p, γ)<SUP>27</SUP>S because of the lack of nuclear mass and energy level structure information for <SUP>27</SUP>S. We reevaluate this reaction rate using the experimentally constrained <SUP>27</SUP>S mass, together with the shell model predicted level structure. It is found that the <SUP>26</SUP>P(p, γ)<SUP>27</SUP>S reaction rate is dominated by a direct capture reaction mechanism despite the presence of three resonances at E = 1.104, 1.597, and 1.777 MeV above the proton threshold in <SUP>27</SUP>S. The new rate is overall smaller than the other previous rates from the Hauser-Feshbach statistical model by at least 1 order of magnitude in the temperature range of X-ray burst interest. In addition, we consistently update the photodisintegration rate using the new <SUP>27</SUP>S mass. The influence of new rates of forward and reverse reaction in the abundances of isotopes produced in the rp-process is explored by postprocessing nucleosynthesis calculations. The final abundance ratio of <SUP>27</SUP>S/<SUP>26</SUP>P obtained using the new rates is only 10% of that from the old rate. The abundance flow calculations show that the reaction path <SUP>26</SUP>P(p, γ)<SUP>27</SUP>S(β <SUP>+</SUP>,ν)<SUP>27</SUP>P is not as important as previously thought for producing <SUP>27</SUP>P. The adoption of the new reaction rates for <SUP>26</SUP>P(p, γ)<SUP>27</SUP>S only reduces the final production of aluminum by 7.1% and has no discernible impact on the yield of other elements.
|
[
2081,
1814,
2077,
1128,
503
] |
[
"reaction rates",
"x-ray bursts",
"nuclear physics",
"nuclear abundances",
"explosive nucleosynthesis"
] |
2021RNAAS...5..120R
|
Dust Formation in the Nova V1533 Scorpii
|
We present infrared spectroscopy from two epochs of V1533 Scorpii (=Nova Scorpii 2013); one from immediately before dust formation and a second, from one month later when dust formation was complete. The pre-dust spectrum shows strong lines of C I, features that weakened considerably but were still present after dust formation. Also present in the post-formation spectrum was O I emission from the neutral region, indicating that dust formation did not full deplete either carbon or oxygen. While thermal emission from the dust, of a temperature very close to 870 K, dominated the later spectrum, the extinction did not change measurably between epochs, indicating that little or no dust blocked the line-of-sight. Although carbon monoxide was not detected in the first epoch spectrum, weak emission from molecular hydrogen may have been present.
|
[
1127,
530
] |
[
"novae",
"fast novae"
] |
2022ApJ...928..125T
|
Density Turbulence and the Angular Broadening of Outer Heliospheric Radio Sources at High Latitudes and in the Ecliptic Plane
|
Density irregularities are responsible for the scattering of radio waves in the solar wind and astrophysical plasmas. These irregularities significantly affect the inferred physical properties of radio sources, such as size, direction, and intensity. We present here a theory of angular broadening due to the scattering of radio waves by density irregularities that improves the existing formalism used to investigate radio wave scattering in the outer heliosphere and the very local interstellar medium. The model includes an inner scale and both latitudinal and radial dependencies for the density fluctuation spectra and propagation paths for the radiation both near and out of the ecliptic plane. Based on the pickup-ion-mediated solar wind model (PUI model) of Zank et al., we estimate the turbulence and solar wind quantities for the high-latitude fast solar wind. The predictions include the density variance, inner/dissipation scale, velocity correlation length, mean magnetic field, and proton temperature. The density turbulence amplitude is estimated in two ways. First, a simple scaling technique is used to extend the theoretical predictions of the PUI model for the high-latitude wind beyond the heliospheric termination shock. Second, the solar wind and turbulence quantities are calculated near the ecliptic plane using plasma and magnetometer data from the Voyager 2 spacecraft over the period 1977-2018. Based on the turbulence models and observations, we calculate the scattering angle of the radio sources in the high-latitude and near-ecliptic wind. Finally, we compare the numerical results with the analytic predictions from Cairns and Armstrong et al. and the observed source sizes.
|
[
1522,
1534,
711,
830,
1544
] |
[
"solar radio emission",
"solar wind",
"heliosphere",
"interplanetary turbulence",
"space plasmas"
] |
2023RNAAS...7...35M
|
Mass and Color Dependence of the Hubble Spiral Sequence
|
In the classic Hubble spiral sequence, arm windiness correlates with bulge size; Sa type spiral galaxies with larger bulges also have the most tightly wound spirals. Exceptions to this have long been known, and in recent work using Galaxy Zoo morphologies no strong correlation was seen in a volume limited sample. In this Research Note, we explore the impact of galaxy mass and integrated color upon this correlation in the Galaxy Zoo sample, finding that bluer and lower mass spirals show the "expected" correlation; however, it becomes slightly negative for redder and/or more massive spiral galaxies.
|
[
1559,
1560,
1561,
757,
582
] |
[
"spiral arms",
"spiral galaxies",
"spiral pitch angle",
"hubble classification scheme",
"galaxy classification systems"
] |
2020ApJ...892...36T
|
Making a Supermassive Star by Stellar Bombardment
|
Approximately 200 supermassive black holes (SMBHs) have been discovered within the first ∼gigayear after the Big Bang. One pathway for the formation of SMBHs is through the collapse of supermassive stars (SMSs). A possible obstacle to this scenario is that the collapsing gas fragments and forms a cluster of main-sequence stars. Here, we raise the possibility that stellar collisions may be sufficiently frequent and energetic to inhibit the contraction of the massive protostar, avoiding strong UV radiation driven outflows, and allowing it to continue growing into an SMS. We investigate this scenario with semianalytic models incorporating star formation; gas accretion; dynamical friction from stars and gas; stellar collisions; and gas ejection. We find that when the collapsing gas fragments at a density of ≲3 × 10<SUP>10</SUP> cm<SUP>-3</SUP>, the central protostar contracts due to infrequent stellar mergers, and in turn photoevaporates the remaining collapsing gas, resulting in the formation of a ≲10<SUP>4</SUP> M<SUB>⊙</SUB> object. On the other hand, when the collapsing gas fragments at higher densities (expected for a metal-poor cloud with Z ≲ 10<SUP>-5</SUP> Z<SUB>⊙</SUB> with suppressed H<SUB>2</SUB> abundance) the central protostar avoids contraction and keeps growing via frequent stellar mergers, reaching masses as high as ∼10<SUP>5</SUP>-10<SUP>6</SUP> M<SUB>⊙</SUB>. We conclude that frequent stellar mergers represent a possible pathway to form massive BHs in the early universe.
|
[
1284,
1289,
1663,
1319,
435,
1293
] |
[
"population ii stars",
"pre-main sequence",
"supermassive black holes",
"quasars",
"early universe",
"primordial galaxies"
] |
2021RNAAS...5...79N
|
Transit Analysis of HATS-4 b by Citizen Scientists
|
Exoplanets are planets that orbit stars other than our Sun, and the most common way of detecting them is by the transit method. This method consists of plotting the relative brightness of the exoplanets host star against a comparison star to make what is known as a light curve. Periodic dips in the light curve could correspond to the exoplanet coming in front of its host star, and blocking some of its light. One time of great importance to constantly keep up to date is the exoplanets mid-transit time. The mid-transit time is the time in which the exoplanet is in the middle of its transit; however, the problem with this value is that it changes over many periods due to the uncertainty in the period of the planet. Thus, it is important to update transit timings as incorrect timings can hinder observations from expensive telescopes. Crowdsourcing exoplanet transit analysis is a great opportunity to help these large telescopes and get the community involved in exoplanet research. In this study, six citizen scientists from the East Bay Astronomical Society (EAS) performed a transit analysis of HATS-4 b using the Exoplanet Transit Interpretation Code (EXOTIC). Using newly calculated mid-transit times, we were able to see how off the expected mid-transit time based on the existing mid-transit time on the NASA Exoplanet Archive was by calculating the phase difference.
|
[
486
] |
[
"exoplanet astronomy"
] |
2020ApJ...894...19R
|
An Isolated White Dwarf with 317 s Rotation and Magnetic Emission
|
We report the discovery of short-period photometric variability and modulated Zeeman-split hydrogen emission in SDSSJ125230.93-023417.72 (EPIC 228939929), a variable white dwarf star observed at long cadence in K2 Campaign 10. The behavior is associated with a magnetic (B = 5.0 MG) spot on the stellar surface, making the 317.278 s period a direct measurement of the stellar rotation rate. This object is therefore the fastest-rotating, apparently isolated (without a stellar companion) white dwarf yet discovered and the second found to exhibit chromospheric Balmer emission after GD 356, in which the emission has been attributed to a unipolar inductor mechanism driven by a possible rocky planet. We explore the properties and behavior of this object, and consider whether its evolution may hold implications for white dwarf mergers and their remnants.
|
[
1799,
996,
511,
2157,
1629
] |
[
"white dwarf stars",
"magnetic variable stars",
"extrasolar rocky planets",
"stellar mergers",
"stellar rotation"
] |
2020ApJ...894..149W
|
A Systematic Study of Galactic Outflows via Fluorescence Emission: Implications for Their Size and Structure
|
Galactic outflows play a major role in the evolution of galaxies, but the underlying physical processes are poorly understood. This is mainly because we have little information about the outflow structure, especially on large scales. In this paper, we probe the structure of galactic outflows in low-z starbursts using a combination of ultraviolet spectroscopy and imaging of the fluorescence emission lines (associated with transitions to excited fine-structure levels) and spectroscopy of the corresponding strongly blueshifted resonance absorption lines. We find that, in the majority of cases, the observed fluorescence emission lines are much weaker and narrower than the absorption lines, originating in the star-forming interstellar medium and/or the slowest-moving part of the inner outflow. In a minority of cases, the outflowing absorbing material does make a significant contribution to the fluorescence emission. These latter systems are characterized by both strong Lyα emission lines and weak low-ionization absorption lines (both known to be empirical signs of Lyman-continuum leakage). We argue that the observed weakness of emission from the outflow seen in the majority of cases is due to the missing emission arising on scales larger than those encompassed by the aperture of the Cosmic Origins Spectrograph on board the Hubble Space Telescope. This implies shallow radial density profiles in these outflows, and suggests that most of the observed absorbing material must be created/injected at radii much larger than that of the starburst. This has important implications both for our understanding of the physics of galactic outflows and for our estimation of their principal properties.
|
[
1879,
506,
595,
626,
1570,
847
] |
[
"circumgalactic medium",
"extragalactic astronomy",
"galaxy formation",
"galaxy winds",
"starburst galaxies",
"interstellar medium"
] |
2021ApJ...914..120S
|
Extreme HBL-like Behavior of Markarian 421 and Its Two-zone Photohadronic Interpretation
|
Markarian 421 is the nearest high-energy peaked blazar and is also the first extragalactic source to be detected in multi-TeV γ-rays. It has been observed in multiwavelength for an exceptionally long period of time with dense monitoring and several major outbursts have been detected from this source. In 2010 March, the source was in a high state of activity and was observed in multiwavelength by various telescopes for 13 consecutive days. During this period the position of the synchrotron peak was found to be above 10<SUP>17</SUP> Hz and also the position of the second peak was shifted toward higher energy, a signature of extreme HBL-like behavior. We observed that the standard photohadronic model is inadequate to explain the observed spectra. However, a recently proposed two-zone photohadronic model explains very well the GeV-TeV flaring events observed by both MAGIC and VERITAS telescopes. From the observation of the highest energy γ-ray event on MJD 55266 we also estimated the minimum bulk Lorentz factor.
|
[
739,
164,
1390,
158,
637
] |
[
"high energy astrophysics",
"blazars",
"relativistic jets",
"bl lacertae objects",
"gamma-rays"
] |
2020ApJ...895..127B
|
Swift Monitoring of M51: A 38 day Superorbital Period for the Pulsar ULX7 and a New Transient Ultraluminous X-Ray Source
|
We present the results from a monitoring campaign made with the Neil Gehrels Swift Observatory of the M51 galaxies, which contain several variable ultraluminous X-ray sources (ULXs). The ongoing campaign started in 2018 May, and we report here on ∼1.5 yr of observations. The campaign, which consists of 106 observations, has a typical cadence of 3-6 days, and has the goal of determining the long-term X-ray variability of the ULXs. Two of the most variable sources were ULX7 and ULX8, both of which are known to be powered by neutron stars that are exceeding their isotropic Eddington luminosities by factors of up to 100. This is further evidence that neutron-star-powered ULXs are the most variable. Our two main results are, first, that ULX7 exhibits a periodic flux modulation with a period of 38 days varying over a magnitude and a half in flux from peak to trough. Since the orbital period of the system is known to be 2 days, the modulation is superorbital, which is a near-ubiquitous property of ULX pulsars. Second, we identify a new transient ULX, M51 XT-1, the onset of which occurred during our campaign, reaching a peak luminosity of ∼10<SUP>40</SUP> erg s<SUP>-1</SUP>, before gradually fading over the next ∼200 days until it slipped below the detection limit of our observations. Combined with the high-quality Swift/X-ray Telescope lightcurve of the transient, serendipitous observations made with Chandra and XMM-Newton provide insights into the onset and evolution of a likely super-Eddington event.
|
[
1270,
1852,
1820,
1812,
2035,
1851,
918,
609,
16
] |
[
"x-ray point sources",
"x-ray transient sources",
"x-ray photometry",
"x-ray bright point",
"x-ray active galactic nuclei",
"transient sources",
"light curves",
"galaxy nuclei",
"active galactic nuclei"
] |
2024ApJS..271...49F
|
Modeling the Morphology of Fast Radio Bursts and Radio Pulsars with fitburst
|
We present a framework for modeling astrophysical pulses from radio pulsars and fast radio bursts (FRBs). This framework, called fitburst, generates synthetic representations of dynamic spectra that are functions of several physical and heuristic parameters; the heuristic parameters can nonetheless accommodate a vast range of distributions in spectral energy. fitburst is designed to optimize the modeling of features induced by effects that are intrinsic and extrinsic to the emission mechanism, including the magnitude and frequency dependence of pulse dispersion and scatter broadening. fitburst removes intrachannel smearing through two-dimensional upsampling, and can account for phase-wrapping of "folded" signals that are typically acquired during pulsar-timing observations. We demonstrate the effectiveness of fitburst in modeling data containing pulsars and FRBs observed with the Canadian Hydrogen Intensity Mapping Experiment telescope.
|
[
1306,
2008,
847,
855,
1855
] |
[
"pulsars",
"radio transient sources",
"interstellar medium",
"interstellar scintillation",
"astronomy software"
] |
2023ApJ...955...47S
|
Global Electron Thermodynamics in Radiatively Inefficient Accretion Flows
|
In the collisionless plasmas of radiatively inefficient accretion flows, heating and acceleration of ions and electrons are not well understood. Recent studies in the gyrokinetic limit revealed the importance of incorporating both the compressive and Alfvénic cascades when calculating the partition of dissipated energy between the plasma species. In this paper, we use a covariant analytic model of the accretion flow to explore the impact of compressive and Alfvénic heating, Coulomb collisions, compressional heating, and radiative cooling on the radial temperature profiles of ions and electrons. We show that, independent of the partition of heat between the plasma species, even a small fraction of turbulent energy dissipated to the electrons makes their temperature scale with a virial profile and the ion-to-electron temperature ratio smaller than in the case of pure Coulomb heating. In contrast, the presence of compressive cascades makes this ratio larger because compressive turbulent energy is channeled primarily into the ions. We calculate the ion-to-electron temperature in the inner accretion flow for a broad range of plasma properties, mass accretion rates, and black hole spins and show that it ranges between 5 ≲ T <SUB> i </SUB>/T <SUB> e </SUB> ≲ 40. We provide a physically motivated expression for this ratio that can be used to calculate observables from simulations of black hole accretion flows for a wide range of conditions.
|
[
159,
98,
1261,
2089
] |
[
"black hole physics",
"astrophysical black holes",
"plasma astrophysics",
"plasma physics"
] |
2022ApJ...931...25T
|
Investigating the Disk-Jet Structure in M87 through Flux Separation in the Linear and Circular Polarization Images
|
For testing different electron temperature (T <SUB>e</SUB>) prescriptions in general relativistic magnetohydrodynamics (GRMHD) simulations through observations, we propose to utilize linear polarization (LP) and circular polarization (CP) images. We calculate the polarization images based on a semi-magnetically arrested disk GRMHD model for various T <SUB>e</SUB> parameters, bearing M87 in mind. We find an LP-CP separation in the images of the low-T <SUB>e</SUB> disk cases at 230GHz; namely, the LP flux mainly originates from downstream of the jet, and the CP flux comes from the counter-side jet, while the total intensity is maximum at the jet base. This can be understood as follows: although the LP flux is generated through synchrotron emission widely around the black hole, most of the LP flux from the jet base does not reach the observer, since it undergoes Faraday rotation ( $\propto {T}_{{\rm{e}}}^{-2}$ ) when passing through the outer cold disk and is thus depolarized. Hence, only the LP flux from the downstream (not passing the cold dense plasmas) can survive. Meanwhile, the CP flux is generated from the LP flux by Faraday conversion ( ∝ T <SUB>e</SUB>) in the inner hot region. Stronger CP flux is thus observed from the counter-side jet. Moreover, the LP-CP separation is more enhanced at a lower frequency, such as 86 GHz, but is rather weak at 43 GHz, since the media in the latter case is optically thick for synchrotron self-absorption so that all of the fluxes should come from the photosphere. The same is true for cases with higher mass accretion rates and/or larger inclination angles.
|
[
159,
16,
1347,
1335,
1278
] |
[
"black hole physics",
"active galactic nuclei",
"radio jets",
"radiative transfer",
"polarimetry"
] |
2022ApJ...938..103H
|
The Mouse That Squeaked: A Small Flare from Proxima Cen Observed in the Millimeter, Optical, and Soft X-Ray with Chandra and ALMA
|
We present millimeter, optical, and soft X-ray observations of a stellar flare with an energy squarely in the regime of typical X1 solar flares. The flare was observed from Proxima Cen on 2019 May 6 as part of a larger multi-wavelength flare monitoring campaign and was captured by Chandra, the Las Cumbres Observatory Global Telescope, the Iréné du Pont Telescope at Las Campanas Observatory, and the Atacama Large Millimeter Array. Millimeter emission appears to be a common occurrence in small stellar flares that had gone undetected until recently, making it difficult to interpret these events within the current multi-wavelength picture of the flaring process. The May 6 event is the smallest stellar millimeter flare detected to date. We compare the relationship between the soft X-ray and millimeter emission to that observed in solar flares. The X-ray and optical flare energies of 10<SUP>30.3 ± 0.2</SUP> and 10<SUP>28.9 ± 0.1</SUP> erg, respectively, the coronal temperature of T = 11.0 ± 2.1 MK, and the emission measure of 9.5 ± 2.2 × 10<SUP>49</SUP> cm<SUP>-3</SUP> are consistent with M-X class solar flares. We find the soft X-ray and millimeter emission during quiescence are consistent with the Güdel-Benz relation, but not during the flare. The millimeter luminosity is >100× higher than that of an equivalent X1 solar flare and lasts only seconds instead of minutes as seen for solar flares.
|
[
1637,
1166,
1367,
1816,
1342,
1983,
1061
] |
[
"stellar x-ray flares",
"optical flares",
"red dwarf flare stars",
"solar x-ray flares",
"solar radio flares",
"solar white-light flares",
"millimeter astronomy"
] |
2023ApJ...950...51J
|
Anterograde Collisional Analysis of Solar Wind Ions
|
Owing to its low density and high temperature, the solar wind frequently exhibits strong departures from local thermodynamic equilibrium, which include distinct temperatures for its constituent ions. Prior studies have found that the ratio of the temperatures of the two most abundant ions-protons (ionized hydrogen) and α-particles (ionized helium)-is strongly correlated with the Coulomb collisional age. These previous studies, though, have been largely limited to using observations from single missions. In contrast, this present study utilizes contemporaneous, in situ observations from two different spacecraft at two different distances from the Sun: the Parker Solar Probe (PSP; r = 0.1-0.3 au) and Wind (r = 1.0 au). Collisional analysis, which incorporates the equations of collisional relaxation and large-scale expansion, was applied to each PSP datum to predict the state of the plasma farther from the Sun at r = 1.0 au. The distribution of these predicted α-proton relative temperatures agrees well with that of values observed by Wind. These results strongly suggest that, outside of the corona, relative ion temperatures are principally affected by Coulomb collisions and that the preferential heating of α-particles is largely limited to the corona.
|
[
1534,
2065,
2089
] |
[
"solar wind",
"collision physics",
"plasma physics"
] |
2023ApJ...945...69R
|
Updated Measurements of [O III] 88 μm, [C II] 158 μm, and Dust Continuum Emission from a z = 7.2 Galaxy
|
We present updated measurements of the [O III] 88 μm, [C II] 158 μm, and dust continuum emission from a star-forming galaxy at z = 7.212, SXDF-NB1006-2, by utilizing Atacama Large Millimeter/submillimeter Array (ALMA) archival data sets analysed in previous studies and data sets that have not been analysed before. The follow-up ALMA observations with higher angular resolution and sensitivity reveal a clumpy structure of the [O III] emission on a scale of 0.32-0.85 kpc. We also combined all the ALMA [O III] ([C II]) data sets and updated the [O III] ([C II]) detection to 5.9σ (3.6σ-4.5σ). The non-detection of [C II] with data from the REBELS large program implies the incompleteness of spectral-scan surveys using [C II] to detect galaxies with high star formation rates (SFRs) but marginal [C II] emission at high-z. The dust continuum at 90 and 160 μm remains undetected, indicating little dust content of <3.9 × 10<SUP>6</SUP> M <SUB>⊙</SUB> (3σ), and we obtained a more stringent constraint on the total infrared luminosity. We updated the [O III]/[C II] luminosity ratios to 10.2 ± 4.7 (6.1 ± 3.5) and 20 ± 12 (9.6 ± 6.1) for the 4.5σ and 3.6σ [C II] detections, respectively, where the ratios in the parentheses are corrected for the surface brightness dimming effect on the extended [C II] emission. We also found a strong [C II] deficit (0.6-1.3 dex) between SXDF-NB1006-2 and the mean L <SUB>[C II]</SUB>-SFR relation of galaxies at 0 < z < 9.
|
[
595,
594,
847,
734
] |
[
"galaxy formation",
"galaxy evolution",
"interstellar medium",
"high-redshift galaxies"
] |
2022ApJ...936..127F
|
Nature and Scalings of Density Fluctuations of Compressible Magnetohydrodynamic Turbulence with Applications to the Solar Wind
|
The solar wind is a magnetized and turbulent plasma. Its turbulence is often dominated by Alfvénic fluctuations and often deemed as nearly incompressible far away from the Sun, as shown by in situ measurements near 1 au. However, for solar wind closer to the Sun, the plasma β decreases (often lower than unity) while the turbulent Mach number M <SUB> t </SUB> increases (can approach unity, e.g., transonic fluctuations). These conditions could produce significantly more compressible effects, characterized by enhanced density fluctuations, as seen by several space missions. In this paper, a series of 3D MHD simulations of turbulence are carried out to understand the properties of compressible turbulence, particularly the generation of density fluctuations. We find that, over a broad range of parameter space in plasma β, cross helicity, and polytropic index, the turbulent density fluctuations scale linearly as a function of M <SUB> t </SUB>, with the scaling coefficients showing weak dependence on parameters. Furthermore, through detailed spatiotemporal analysis, we show that the density fluctuations are dominated by low-frequency nonlinear structures, rather than compressible MHD eigenwaves. These results could be important for understanding how compressible turbulence contributes to solar wind heating near the Sun.
|
[
1534,
1966
] |
[
"solar wind",
"magnetohydrodynamical simulations"
] |
2022ApJ...933L..42K
|
Jansky Very Large Array Detections of CO(1-0) Emission in H I-absorption-selected Galaxies at z ≳ 2
|
We report a Karl G. Jansky Very Large Array search for redshifted CO(1-0) emission from three H I-absorption-selected galaxies at z ≈ 2, identified earlier in their CO(3-2) or CO(4-3) emission. We detect CO(1-0) emission from DLA B1228-113 at z ≈ 2.1933 and DLA J0918+1636 at z ≈ 2.5848; these are the first detections of CO(1-0) emission in high-z H I-selected galaxies. We obtain high molecular gas masses, M <SUB>mol</SUB> ≈ 10<SUP>11</SUP> × (α <SUB>CO</SUB>/4.36) M <SUB>⊙</SUB>, for the two objects with CO(1-0) detections, which are a factor of ≈1.5-2 lower than earlier estimates. We determine the excitation of the mid-J CO rotational levels relative to the J = 1 level, r <SUB> J1</SUB>, in H I-selected galaxies for the first time, obtaining r <SUB>31</SUB> = 1.00 ± 0.20 and r <SUB>41</SUB> = 1.03 ± 0.23 for DLA J0918+1636, and r <SUB>31</SUB> = 0.86 ± 0.21 for DLA B1228-113. These values are consistent with thermal excitation of the J = 3 and J = 4 levels. The excitation of the J = 3 level in the H I-selected galaxies is similar to that seen in massive main-sequence and submillimeter galaxies at z≳2, but higher than that in main-sequence galaxies at z ≈ 1.5; the higher excitation of the galaxies at z ≳ 2 is likely to be due to their higher star formation rate (SFR) surface density. We use Hubble Space Telescope Wide Field Camera 3 imaging to detect the rest-frame near-ultraviolet (NUV) emission of DLA B1228-113, obtaining an NUV SFR of 4.44 ± 0.47 M <SUB>⊙</SUB> yr<SUP>-1</SUP>, significantly lower than that obtained from the total infrared luminosity, indicating significant dust extinction in the z ≈ 2.1933 galaxy.
|
[
734,
262,
349
] |
[
"high-redshift galaxies",
"co line emission",
"damped lyman-alpha systems"
] |
2020ApJ...892..150R
|
A NICER View of Spectral and Profile Evolution for Three X-Ray-emitting Millisecond Pulsars
|
We present two years of Neutron star Interior Composition Explorer (NICER) X-ray observations of three energetic rotation-powered millisecond pulsars (MSPs): PSRs B1937+21, B1821-24, and J0218+4232. We fit Gaussians and Lorentzians to the pulse profiles for different energy sub-bands of the soft X-ray regime to measure the energy dependence of pulse separation and width. We find that the separation between pulse components of PSR J0218+4232 decreases with increasing energy at >3σ confidence. The 95% upper limit on pulse separation evolution for PSRs B1937+21 and B1821-24 is less than 2 milliperiods per keV. Our phase-resolved spectral results provide updated constraints on the non-thermal X-ray emission of these three pulsars. The photon indices of the modeled X-ray emission spectra for each pulse component of PSR B1937+21 are inconsistent with each other at the 90% confidence level, suggesting different emission origins for each pulse. We find that the PSR B1821-24 and PSR J0218+4232 emission spectra are invariant with phase at the 90% confidence level. We describe the implications of our profile and spectral results in the context of equatorial current sheet emission models for these three MSPs with non-thermal, magnetospheric X-ray emission.
|
[
1062,
1108,
1810
] |
[
"millisecond pulsars",
"neutron stars",
"x-ray astronomy"
] |
2024ApJ...964..187B
|
Merger-driven Growth of Intermediate-mass Black Holes: Constraints from Hubble Space Telescope Imaging of Hyper-luminous X-Ray Sources
|
Hyper-luminous X-ray sources (HLXs) are extragalactic off-nuclear X-ray sources with luminosities exceeding the theoretical limit for accretion onto stellar-mass compact objects. Many HLXs may represent intermediate-mass black holes (IMBHs) deposited in galaxy halos through mergers, and the properties of the stellar cores surrounding HLXs provide powerful constraints on this scenario. Therefore, we have systematically built the largest sample of HLX candidates with archival Hubble Space Telescope (HST) imaging (24) for the first uniform population study of HLX stellar cores down to low masses. Based on their host galaxy redshifts, at least 21 (88%) have stellar core masses ≥ 10<SUP>7</SUP> M <SUB>⊙</SUB> and hence are consistent with accretion onto massive black holes from external galaxies. In 50% of the sample, the HST imaging reveals features connecting the HLXs with their host galaxies, strongly suggesting against the background/foreground contaminant possibility in these cases. Assuming a mass scaling relation for active galactic nuclei and accounting for an estimated contamination fraction of 29%, up to ∼60% of our sample may be associated with IMBHs. Similar to previously known HLXs, the X-ray luminosities are systematically elevated relative to their stellar core masses, possibly from merger-driven accretion rate enhancements. The least massive stellar cores are preferentially found at larger nuclear offsets and are more likely to remain wandering in their host galaxy halos. The HLX galaxy occupation fraction is ∼ 10<SUP>‑2</SUP> and has a strong inverse mass dependence. Up to three of the HLX candidates (12%) are potentially consistent with formation within globular clusters or with exceptionally luminous X-ray binaries.
|
[
416,
608,
816,
1663,
2035
] |
[
"dwarf galaxies",
"galaxy mergers",
"intermediate-mass black holes",
"supermassive black holes",
"x-ray active galactic nuclei"
] |
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