diff --git "a/69E0T4oBgHgl3EQffAC0/content/tmp_files/2301.02399v1.pdf.txt" "b/69E0T4oBgHgl3EQffAC0/content/tmp_files/2301.02399v1.pdf.txt" new file mode 100644--- /dev/null +++ "b/69E0T4oBgHgl3EQffAC0/content/tmp_files/2301.02399v1.pdf.txt" @@ -0,0 +1,6045 @@ +Mon. Not. R. Astron. Soc. 000, 1–?? (0000) +Printed 9 January 2023 +(MN LaTEX style file v2.2) +Photometric variable stars in the young open cluster +NGC 6823 +Sneh Lata1⋆, W. P. Chen2,3, J. C. Pandey1, Athul Dileep1, Zhong-Han Ai3, +Alisher S. Hojaev4, Neelam Panwar1, Santosh Joshi1, Soumen Mondal5, +Siddhartha Biswas5, B. C. Bhatt6 +1Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital 263002, Uttarakhand, India +2Graduate Institute of Astronomy, National Central University, 300 Zhongda Road, Zhongli 32001 Taoyuan, Taiwan +3Department of Physics, National Central University, 300 Zhongda Road, Zhongli 32001 Taoyuan, Taiwan +4Ulugh Beg Astronomical Institute, Uzbekistan Academy of Sciences, Tashkent, Republic of Uzbekistan +5S. N. Bose National Centre for Basic Sciences, Kolkata 700106, India +6Indian Institute of Astrophysics, Koramangala, Bangalore-560034, India +Accepted ———. Received ———; +ABSTRACT +We present stellar variability towards the young open cluster NGC 6823. Time series V - +and I-band CCD photometry led to identification and characterization of 88 variable +stars, of which only 14 have been previously recognized. We ascertain the membership +of each variable with optical UBV I and infrared photometry, and with Gaia EDR3 +parallax and proper motion data. Seventy two variable stars are found to be cluster +members, of which 25 are main sequence stars and 48 are pre-main-sequence stars. +The probable cluster members collectively suggest an isochrone age of the cluster to +be about 2 Myrs based on the GAIA photometry. With the color and magnitude, as +well as the shape of the light curve, we have classified the main sequence variables into +β Cep, δ Scuti, slowly pulsating B type, and new class variables. Among the pre-main- +sequence variables, eight are classical T Tauri variables, and four are Herbig Ae/Be +objects, whereas the remaining belong to the weak-lined T Tauri population. The +variable nature of 32 stars is validated with TESS light curves. Our work provides +refined classification of variability of pre-main-sequence and main-sequence cluster +members of the active star-forming complex, Sharpless 86. Despite no strong evidence +of the disk-locking mechanism in the present sample of TTSs, one TTS with larger +∆(I − K) is found to be slow rotator. +Key words: +open clusters and associations: individual NGC 6823, Hertzsprung- +Russell and color-magnitude diagram, stars: pre-main-sequence, stars: variables: T +Tauri, Herbig Ae/Be +1 +INTRODUCTION +Young open clusters serve as useful tools for the studies +of the star formation mechanism and early stellar evolu- +tion. For example, young star clusters are used to trace the +Galactic spiral structure. In particular, variability of young +stellar members provides diagnostics on the sporadic (accre- +tion or occultation) or periodical (rotation) properties of the +stars, and of their relation to the circumstellar environments +(Morales-Calderon et al. 2011). +Pre-main-sequence (PMS) objects are categorized on +⋆ E-mail: sneh@aries.res.in +the basis of the spectral energy distribution in the infrared +wavelengths: Class 0 , Class I, Class II, and Class III (Lada +1987; Andre et al. 1993) with the classification sequence +roughly corresponding to the evolutionary status. Namely, +a Class 0 object signifies a clump of dust and gas heavily en- +shrouded in the molecular envelope, and is detected only in +far-infrared wavelengths or longer. A Class I object is more +evolved, now emerging from the cloud to become visible in +near- and mid-infrared. A Class I object is in the protostellar +stage and derives the luminosity from mass accretion. +A Class II object, corresponding to a classical T Tauri +star (TTS), has dispersed much of the envelope of gas and +dust but retains a circumstellar disk within which plan- +© 0000 RAS +arXiv:2301.02399v1 [astro-ph.SR] 6 Jan 2023 + +2 +Sneh Lata et al. +ets may condense or are being formed. Inside the optically +thick but geometrically thin disk, the dust grains absorb the +starlight and re-emit in the infrared, manifest as infrared +excess seen typically in a classical TTS. Accretion from the +disk onto the star, while matter is partly lost as bipolar +jets/outflows, leads to strong emission lines in the spectrum. +As the inner disk is dissipated (or going into planet forma- +tion), the PMS object then evolves to Class III, now with +negligible infrared excess and with weak emission lines, if +any, due to surface chromospheric activity. A Class III object +hence is called a weak-lined TTS (Joy 1945, Appenzeller & +Mundt 1989). Variability of PMS objects hence serves as an +important diagnosis to understand the earliest PMS stellar +evolution, e.g., the accretion (Johnstone et al. 2018), rota- +tion (Herbst et al. 1994), or dust properties (Huang et al. +2019). +Here we report the variability study of the Galactic +young open cluster NGC 6823. At a distance of about 2 kpc, +the cluster is associated with the prominent H II region, +Sharpless 86. This cluster has been investigated by several +authors (Turner 1979, Stone 1988, Bica et al. 2008, Sagar +and Joshi 1981; Guetter 1992; Massey et al. 1995; Pigulski et +al. 2000; Hojaev et al. 2003, Zahajkiewicz 2012). Using op- +tical and JHK photometric observations Riaz et al. (2012) +found a large population of young stellar sources in the re- +gion, including two δ Scuti variables of PMS nature, and 13 +other variables such as eclipsing binaries, slowly pulsating B +candidates and UX Ori type variables. In the line of sight to +the cluster the reddening has been found to be from 0.7 to +1.1 mag following a normal reddening law (Rangwal et al. +2017). The aim of the present work is to identify variables +in a relatively large field of ∼ 14′ ×14′ of the member versus +nonmember variable stellar populations in the region. Par- +ticularly, photometric rotation periods of PMS members are +derived to add to the data inventory for the study of the +angular momentum evolution of low-mass stars. +We describe in Section 2 observations, data reduction +procedure, detection of variables, and period determina- +tions. In Section 3, membership of the identified variable +candidates is discussed using Gaia proper motion data, pho- +tometric two-color diagrams (TCDs) and color-magnitude +diagrams (CMDs). Section 4 then presents the nature of +known and newly identified variable stars, while Section 5 +deals with TESS light curves. We discuss correlation be- +tween amplitude and rotation periods of TTSs along with +their color excess in Section 6. The results are summarized +in Section 7. +2 +OBSERVATIONS AND DATA REDUCTION +We have observed NGC 6823 with the 0.81-m f/7 Ritchey- +Chretien Tenagra automated telescope in southern Arizona, +equipped with a 1024 × 1024 pixel SITe camera. Each pixel +corresponds to 0.87′′, which yields a field of view of ∼ 14.8′× +14.8′. The observations were carried out from 2012 early +October to 2012 December. In total, data were acquired on +54 nights in two passbands, with 232 frames in V band and +243 frames in I band, with typical seeing of 2–3′′. Bias and +twilight flats were taken every observing night. The observed +region of the cluster in I band is shown in Fig. 1. The log of +the observations is given in Table 1. +Figure 1. The observed region of open cluster NGC 6823. Each +variable star identified in this work is encircled. +Figure 2. Photometric errors as a function of instrumental mag- +nitude in I band. Open circles represent the variables stars iden- +tified in the present work. +The observed images were processed using standard +IRAF tasks: zerocombine, flatcombine and CCDPROC. We +have performed aperture as well as point spread function +(PSF) photometry to derive the magnitude of stars. The +PSF photometry was obtained using program ALLSTAR +(Stetson 1987). To match the stars between different pho- +tometric files we used the daomatch routine of DAOPHOT +(Stetson 1992) whereas daomaster was used to match the +point sources, and to obtain a file having corrected mag- +nitude of stars from all the files. The daomaster program +also removes the flux variation of stars in different frames +© 0000 RAS, MNRAS 000, 1–?? + +23.400 +42 +213 +240 +264 +298 +4498. +0SE'E2 +402 +6FF +478 +546 +521 +I +.614 +6.3 +DEC +23.300 +7月 +826 +831 +965 +950 +10002 +1025 +1122 +23.250 +1151 +1156 +1226 +1235 +1268 +1298 +1317 +1352 +682 +1406 +1405 +23.200 +1459 +1500 +1155 +15506 +295.91010 +295.850 +295.800 +295.750 +295.700 +RA0.04 +0.02 +10 +12 +8 +14 +16 +18 +instVariable stars in NGC 6823 +3 +Figure 3. The V and I band sample light curves of a few variables +identified in the present work where ∆m represents the differential +magnitude. +due to exposure time and airmass. This program makes the +magnitudes of stars in each photometry file equal to that of +reference file by applying a constant value. +We have used the V and I observations of Massey et +al. (1995) for conversion of the present instrumental magni- +tudes to the standard ones. For this, the mean instrumental +magnitudes in V and I bands given by DAOMASTER (Stet- +son 1992) have been converted into standard ones with the +following transformation equations. +V = v + (−0.042 ± 0.001) × (V − I) + 0.818 ± 0.014 +V − I = (0.982 ± 0.004) × (v − i) + 1.185 ± 0.002, +where v and i are the instrumental magnitudes, and V and I +refer to the standard magnitudes of stars in V and I filters. +The estimated photometric error as a function of the mean +instrumental magnitude is shown in Fig. 2. +2.1 +Variables identification +To identify variable stars, we first produced the light curves +of all the stars cross-matched in different CCD frames. The +light curves were obtained by plotting the differential mag- +nitudes (∆m) of stars (variable minus the comparison star) +against the given Julian date (JD). We used the Lomb- +Scargle periodogram (Lomb 1976; Scargle 1982) to derive +the periods and produced phased light curves accordingly to +Table 1. Log of the observations of NGC 6823. N and Exp. rep- +resent number of frames obtained and exposure time in seconds, +respectively. +S. No. +Date of +I +V +Observations +(N×Exp.) +(N×Exp.) +1 +13 oct 2012 +6× 30 +6 × 50 +2 +15 oct 2012 +3× 30 +3 × 50 +3 +16 oct 2012 +6× 30 +5 × 50 +4 +17 oct 2012 +6× 30 +6 × 50 +5 +19 oct 2012 +3× 30 +5 × 50 +6 +20 oct 2012 +6× 30 +6 × 50 +7 +21 oct 2012 +6× 30 +4 × 50 +8 +22 oct 2012 +6× 30 +6 × 50 +9 +23 oct 2012 +3× 30 +2 × 50 +10 +24 oct 2012 +6× 30 +6 × 50 +11 +25 oct 2012 +6× 30 +5 × 50 +12 +26 oct 2012 +5× 30 +5 × 50 +13 +27 oct 2012 +6× 30 +6 × 50 +14 +28 oct 2012 +6× 30 +6 × 50 +15 +29 oct 2012 +6× 30 +6 × 50 +16 +30 oct 2012 +6× 30 +6 × 50 +17 +31 oct 2012 +6× 30 +6 × 50 +18 +01 nov 2012 +6× 30 +4 × 50 +19 +02 nov 2012 +- +2 × 50 +20 +03 nov 2012 +6× 30 +5 × 50 +21 +04 nov 2012 +6× 30 +5 × 50 +22 +05 nov 2012 +5× 30 +5 × 50 +23 +06 nov 2012 +6× 30 +6 × 50 +24 +08 nov 2012 +6× 30 +6 × 50 +25 +11 nov 2012 +5× 30 +5 × 50 +26 +12 nov 2012 +2× 30 +3 × 50 +27 +14 nov 2012 +6× 30 +6 × 50 +28 +17 nov 2012 +3× 30 +3 × 50 +29 +19 nov 2012 +3× 30 +3 × 50 +30 +20 nov 2012 +6× 30 +6 × 50 +31 +22 nov 2012 +6× 30 +6 × 50 +32 +25 nov 2012 +6× 30 +6 × 50 +33 +27 nov 2012 +6× 30 +6 × 50 +34 +28 nov 2012 +6× 30 +6 × 50 +35 +29 nov 2012 +5× 30 +3 × 50 +36 +30 nov 2012 +6× 30 +6 × 50 +37 +01 dec 2012 +3× 30 +3 × 50 +38 +02 dec 2012 +3× 30 +3 × 50 +39 +03 dec 2012 +3× 30 +3 × 50 +40 +04 dec 2012 +3× 30 +3 × 50 +41 +05 dec 2012 +3× 30 +3 × 50 +42 +06 dec 2012 +3× 30 +3 × 50 +43 +07 dec 2012 +3× 30 +3 × 50 +44 +08 dec 2012 +3× 30 +3 × 50 +45 +09 dec 2012 +3× 30 +3 × 50 +46 +10 dec 2012 +3× 30 +1 × 50 +47 +11 dec 2012 +2× 30 +2 × 50 +48 +12 dec 2012 +3× 30 +3 × 50 +49 +13 dec 2012 +3× 30 +3 × 50 +50 +17 dec 2012 +3× 30 +3 × 50 +51 +18 dec 2012 +3× 30 +3 × 50 +52 +20 dec 2012 +3× 30 +3 × 50 +53 +21 dec 2012 +3× 30 +3 × 50 +54 +26 dec 2012 +6× 30 +- +ascertain their most probable periods. A few variables seem +to show periodic variability but their periodic nature was +not obvious in their observed light curves. The phased light +curves of all stars were inspected, and we adopted the pe- +riod value which produces the most consistent phased light +curve. The light curves of a few variables are shown in Fig. 3 +as examples. The phased light curves of variables identified +in both V and I bands are presented in Fig. 4 and Fig. 5, +whereas Fig. 6 shows variables identified in the I band only. +By eye inspection and periodogram analysis, we have +detected 88 variables. We have listed optical and near- +infrared (NIR) data of the variable stars in Table 2, including +an identification number, coordinates, and optical as well as +NIR photometric data. These are the star ID numbers la- +belled in Fig. 1. These 88 variable stars include 14 known +variables, with periods varying from ∼0.03 days to more +than 60 days. We have plotted in Fig. 7 the root mean square +(RMS) scatter of each star to confirm their variability. The +observed RMS scatter includes both the intrinsic variability +and the mean photometric error. The larger circles in Fig. 7 +show the variables identified in the present work, indicat- +ing large RMS values for variables. Some stars have large +RMS values but do not show noticeable brightness varia- +tion. Some of these objects are found to be close to the edge +© 0000 RAS, MNRAS 000, 1–?? + +154v +154i +385v +385i +-0.6 +-0.4 +-1.0 +-0.6 +-0.5 +-0.4 +-0.4 +-0.2 +-0.2 +0.0 +-0.2 +0.0 +m +m +m +m +0.0 +0.5 +0.0 +0.2 +0.2 +1.0 +0.2 +1 +0.4 +0.4 +1.5 +0.4 +0.6 +0.6 +2.0 +0.6 +0 20 40 60 80 +0 20 40 60 80 +0 20 40 60 80 +0 20 40 60 80 +JD-JDmin +JD-JDmin +JD-JDmin +JD-JDmin +531v +531i +561v +561i +-0.6 +-0.4 +-0.6 +-0.4 +-0.4 +-0.4 +-0.2 +-0.2 +-0.2 +-0.2 +7 +m +m +m +m +0.0 +0.0 +0.0 +0.0 +0.2 +0.2 +0.2 +0.2 +0.4 +0.4 +0.6 +0.4 +0.6 +0.4 +0 20 40 60 80 +0 20 40 60 80 +0 20 40 60 80 +0 20 40 60 80 +JD-JDmin +JD-JDmin +JD-JDmin +JD-JDmin +655v +655i +752v +752i +-0.4 +-0.4 +-0.4 +-0.4 +-0.2 +-0.2 +-0.2 +-0.2 +0.0 +0.0 +m +0.2 +m +m +m +0.2 +0.0 +0.0 +0.4 +0.4 +0.6 +0.2 +0.2 +0.8 +0.6 +1.0 +0.8 +0.4 +0.4 +0 20 40 60 80 +0 20 40 60 80 +0 20 40 60 80 +0 20 40 60 80 +JD-JDmin +JD-JDmin +JD-JDmin +JD-JDmin +757v +1235v +757i +1235i +-0.4 +-0.3 +-0.4 +-0.4 +-0.2 +-0.2 +-0.2 +0.2 +0.1 +0.0 +0.0 +m +m +m +m +0.0 +0.0 +0.2 +0.2 +0.1 +0.4 +0.4 +0.2 +0.2 +0.6 +0.6± +0.4 +0.3 +0.8 +0.8 +0 20 40 60 80 +0 20 40 60 80 +0 20 40 60 80 +0 20 40 60 80 +JD-JDmin +JD-JDmin +JD-JDmin +JD-JDmin1548v +1548i +1268i +-1.0 +-0.3 +-0.4 +-0.2 +-0.5 +-0.2 +-0.1 +F +0.0 +m +m +0.0 +0.0 +0.5 +0.1 +0.2 +1.0 +0.2 +1.5 +0.3 +0.4 +0 +20 40 60 80 +0 20 40 60 80 +0 +20 40 60 80 +JD-JDmin +JD-JDmin +JD-JDmin4 +Sneh Lata et al. +Table 2. The V I and JHK 2mass data, amplitude and period of variables identified towards NGC 6823. The 2MASS data were obtained +from the 2mass catalog (Cutri et al. 2003). The first column with an asterisk symbol represents a known variable. +ID +RA +Dec +V +V − I +J +H +K +(mag) +(mag) +(mag) +(mag) +(mag) +103 +295.668444 +23.412417 +18.115±0.101 +2.190±0.048 +14.231±0.041 +13.140±0.036 +12.508±0.034 +135 +295.730111 +23.406833 +18.454±0.124 +2.428±0.054 +14.324±0.056 +12.758±0.081 +11.586±0.044 +142 +295.921528 +23.403194 +- +- +9.997±0.022 +8.072±0.034 +7.137±0.020 +147 +295.717833 +23.404972 +18.251±0.102 +2.442±0.043 +13.925±0.029 +12.915±0.037 +12.452±0.031 +154 +295.729444 +23.404194 +15.305±0.021 +2.514±0.015 +10.509±0.021 +9.561±0.030 +8.621±0.024 +177 +295.798972 +23.398806 +- +- +14.623±0.040 +13.622±0.040 +13.154±0.036 +201 +295.806361 +23.392806 +18.651±0.129 +1.686± - +- +- +- +213 +295.678611 +23.391889 +18.583±0.133 +1.531±0.099 +15.949±0.093 +15.302±0.128 +14.913±0.129 +238 +295.856583 +23.385806 +- +- +9.096±0.022 +7.248±0.033 +6.386±0.027 +239 +295.793083 +23.386500 +17.564±0.063 +2.161±0.036 +13.328± - +12.411±0.044 +11.853±0.034 +240 +295.913278 +23.384861 +16.320±0.033 +1.113±0.034 +14.480±0.035 +14.178±0.051 +14.074±0.052 +264 +295.759250 +23.382944 +- +- +14.953±0.040 +14.097±0.043 +13.771±0.045 +298 +295.707806 +23.376667 +17.367±0.056 +1.772±0.040 +14.216±0.034 +13.319±0.040 +12.605±0.030 +369 +295.889056 +23.363222 +- +- +13.520±0.026 +12.672±0.033 +12.243±0.031 +377 +295.880000 +23.361417 +18.610±0.127 +2.027± - 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+11.322± - +11.205±0.037 +1262 +295.775250 +23.238000 +17.173±0.050 +2.100±0.030 +13.351±0.034 +12.474±0.041 +11.998±0.032 +1266 +295.802833 +23.236806 +18.656±0.134 +2.123±0.069 +14.808±0.038 +14.078±0.049 +13.694±0.045 +1268 +295.699250 +23.237972 +- +- +9.148±0.019 +7.211±0.034 +6.303±0.026 +1295 +295.812361 +23.232472 +- +- +14.982±0.043 +13.783±0.040 +12.963±0.032 +1298 +295.671972 +23.234000 +18.572±0.133 +2.430±0.059 +14.280±0.049 +13.287±0.055 +12.611±0.042 +1317 +295.899889 +23.227722 +- +- +15.778±0.081 +14.299±0.063 +13.344±0.038 +1352 +295.816861 +23.222944 +12.586±0.011 +0.693±0.012 +11.411±0.022 +11.168±0.030 +11.106±0.026 +1389 +295.718444 +23.218000 +16.432±0.031 +1.683±0.025 +13.25 ±0.027 +12.387±0.034 +11.659±0.027 +1405 +295.778889 +23.214194 +18.752±0.142 +1.817±0.090 +15.644±0.069 +14.713±0.071 +14.516±0.090 +1406 +295.844722 +23.213083 +17.981±0.088 +1.589±0.063 +15.113±0.122 +14.442±0.237 +13.856±0.283 +1459 +295.758944 +23.204833 +- +- +15.208±0.056 +14.355±0.055 +13.932±0.060 +1500 +295.892056 +23.195889 +15.993±0.033 +1.365±0.031 +13.631±0.038 +13.176±0.051 +13.053±0.042 +1506 +295.738167 +23.197333 +15.499±0.024 +1.237±0.021 +13.540 ± - +13.123±0.036 +13.088± - +1508 +295.846250 +23.195111 +- +- +14.502±0.043 +13.425±0.050 +12.769±0.036 +1511 +295.813722 +23.194889 +16.513±0.034 +1.795±0.026 +13.734±0.028 +13.124±0.037 +12.874±0.033 +1525 +295.817722 +23.191972 +13.517±0.015 +1.170±0.015 +11.520 ±0.023 +11.221±0.028 +11.071±0.026 +1526 +295.740750 +23.192917 +8.846±0.024 +0.721±0.019 +7.610 ±0.029 +7.327±0.036 +7.256±0.024 +1548 +295.840667 +23.186917 +18.460±0.141 +6.181±0.018 +8.177±0.023 +6.609±0.017 +5.875±0.020 +of the detector whereas a few stars contains spurious data +points. The derived periods of stars are given in Table 2. +3 +CLUSTER MEMBERSHIP OF VARIABLE +STARS +For each variable star, its UBV I plus 2MASS photometry +along with Gaia EDR3 proper motion and parallax have +been used to assess the likelihood of cluster membership. +The UBV , JHK, and mid infrared (MIR) data at wave- +© 0000 RAS, MNRAS 000, 1–?? + +Variable stars in NGC 6823 +5 +lengths 3.6, 4.5, 5.8 and 8 micron, are taken from Massey +et al. (1995), Cutri et al. (2003), and GLIMPSE survey, re- +spectively. +3.1 +Gaia Characterization of the Variable Stars +The 88 variable stars reported in this work have been char- +acterized with the Gaia EDR3 parallax and proper motion +measurements. Fig. 8 plots the sky positions of all the Gaia +sources (in gray) within 30′ toward NGC 6823. This covers +the field of the Tenagra images (variable stars marked in +black crosses) and is much wider than the cluster’s angular +size of ∼ 3.′6 (red circle) (Morales et al. 2013). The stellar +density is clearly enhanced toward the center. +Each variable star was matched with Gaia counterparts +within a radius of 2.′′5 as the compromise of the seeing of the +Tenagra images, leading to 91 Gaia sources. Fig. 9 presents +the proper motion vector plot of all the stars (gray) and +those within 4′ nominal cluster region (black small circles, +1294 stars) for which the members should be concentrated, +serving as the sample of cluster members. This 4′ (posi- +tional) sample has a mean of µα ≈ −1.7 mas yr−1 and +µδ ≈ −5.3 mas yr−1, which agrees well with the litera- +ture values (Cantat-Gaudin & Anders 2020). Shown in the +bottom panel are the proper motions for variable stars (in +black with error bars). One sees that the majority of our +variable stars share the same proper motion ranges. +Gaia measures repeatedly the astrometry of a source +from which the parallax and proper motion are solved simul- +taneously. Parallax, however, does not serve as a constraint +for membership as stringently as the proper motion, because +given the uncertainties, negative average values may result, +rendering the reciprocal to estimate the distance possible +only if a statistical inference is exercised (Bailer-Jones et al. +2021). For our work the parallax value was used directly. The +parallax of the 4′ sample exhibits a peak around 0.45 mas, +indeed consistent with the literature value (Cantat-Gaudin +& Anders 2020), and so does the variable star sample, as +demonstrated in Fig. 10. If the 4′ sample is further di- +vided by proper motion ranges, one finds no star within 1– +2 mas yr−1 from the cluster’s mean having parallax between +0.4 mas and 0.6 mas. This signifies the sufficiency as mem- +bership criteria of (1) a radius of 1 mas yr−1 in the proper +motion from the cluster average proper motion, and (2) a +parallax value 0.35–0.55 mas. A variable satisfying both (1) +and (2) is therefore considered a “highly probable” mem- +ber, whereas one that fulfills only (1) or (2) is classified as +a “possible” member. Table 4 lists information about the +proper motions, parallax, and magnitudes for the 88 vari- +ables identified in the present work. +Fig. 11 shows the Gaia G versus BP − RP CMD for +the highly probably members (in red) and possible mem- +bers (in blue). Overlapped in the diagram is the PARSEC +isochrones of 1, 2, and 4 Myr, respectively, each shifted by +a distance modulus of 11.753 (parallax of 0.446 mas) and +reddening of E(B −V ) = 0.8 (Sagar & Joshi 1981) adopting +the reddening law of AV = 3.1 E(B −V ), AG = 0.83627 AV , +ABP = 1.08337 AV , and ARP = 0.63439 AV . The highly +probable members indicate an age of roughly 2 Myr. +Three variables have ambiguous Gaia counterparts +within the matching radius. Star No. 478 has two possible +matches, equally faint thereby with relatively large uncer- +tainties in Gaia data but either one is consistent with being +a member. The star was not detected in our V band im- +age and appears progressively brighter from I = 14.47 mag, +to 2MASS J = 13.42 mag, H = 13.42 mag, and Ks = +13.00 mag. +Star No. 1063 is the second brightest star in our variable +list, with the brightest one (No. 1526) being clearly not a +member. The star also has two Gaia matches, with contrast- +ing brightness (G = 9.72 mag versus 12.87 mag). Given its +V = 9.70 mag, the fainter one, having an outlying parallax +of 0.282 mas, is eliminated. The other counterpart, however, +has a negative parallax value with a large uncertainty. This +compromises its membership determination. Its optical and +NIR colors both suggest an early-type star and its position +in the CMD suggests a main-sequence member. +Star No. 1262 has V += 17.173 mag, 2MASS J = +13.351 mag, H = 12.474 mag, and Ks = 11.998 mag. The +brighter Gaia match has G = 16.379 mag but has a neg- +ative parallax value and inconsistent proper motion. The +other Gaia star is faint, with G = 19.291 and no measure- +ments in the other two Gaia bands, has parallax and proper +motion values well consistent with being a member. +3.2 +Colors and Magnitudes +3.2.1 +U − B vs B − V TCD +To identify probable MS variables, we have plotted in Fig. 12 +the U − B versus B − V for variable stars identified in the +cluster region with the photometric data of 22 stars found +in Massey et al. (1995). Reddening in terms of color excess +E(B−V ) ranges from 0.7 to 1.1 mag (Erickson 1971; Guetter +1992; Massey et al. 1995; Pigulski et al. 2000). Pigulski et +al. (2000) recognized the highest extinction in the eastern +part of the cluster where a trapezium system, i.e., of O, B +spectral types, is located. The eastern part of their observed +field is the direction to the reflection nebula NGC 6820, and +their study suggested more than half of the total absorption +to arise from nearby interstellar matter toward NGC 6823. +It is inferred that there is significant differential reddening +within the cluster, manifest that the cluster is located behind +at least AV = ∼ 3 mag (Riaz et al. 2012). Rangwal et al. +(2017) studied the interstellar extinction of open clusters +and found that NGC 6823 follows a normal extinction law in +optical as well as in the NIR wavelengths. The U −B versus +B − V TCD shows that the stars exhibiting within E(B − +V ) = 0.7–1.1 mag could be MS members of the cluster, +indicating a nonuniform reddening across the cluster. The +reddened theoretical ZAMS of Girardi et al. (2002) is fitted +to the TCD. The value of color excess E(V − I) was taken +as 0.88 mag which has been calculated using the minimum +reddening value of E(B − V )=0.70 mag. +3.2.2 +J − H vs H − K TCD +Fig. 13 shows the J − H versus H − K TCD for NGC 6823. +Only 86 stars were cross-matched between the present sam- +ple of variable stars and the 2MASS catalog, with the JHK +counterparts of two stars No. 201 and No. 377 not found +during the match. In the 2MASS TCD, the “F” and “T” +regions are locations of probable Class III/���eld stars and +Class II sources, respectively. The filled squares plotted in +© 0000 RAS, MNRAS 000, 1–?? + +6 +Sneh Lata et al. +Figure 4. The I and V band phased light curves of variable stars identified in the region of NGC 6823. +blue and green colors represent, respectively, probable PMS +and MS members. Circles in the diagram represents field +stars. Riaz et al. (2012) from their NIR CCD found early- +type MS dwarfs concentrating close to (H −Ks) ∼ 0.7 mag, +and (J − H) ∼ 1.5 mag, having extinction AV +⩾ 10. +These authors have noticed another population near the +classical TTS locus close to (H − Ks) ∼ 0.6 mag and +(J − H) ∼ 1.0 mag, presumably being young disk-bearing +members. In the 2MASS TCD, about half the detected vari- +ables are in the “T” or “F” regions hence could be T Tauri +variables. A few PMS stars located below the TTS locus are +probably Herbig Ae/Be stars. We note that star No. 679 +occupies the position where Herbig Ae/Be stars are placed, +while in U − B versus B − V TCD it lies close to the MS +locus; it could thus be either a reddened MS star or a Herbig +Ae/Be member. +Following Gutermuth et al. (2008) to classify young stel- +lar sources, Riaz et al. (2012) used MIR IRAC data and +found 2 Class I, 94 Class II, and 394 Class III or field stars +in the region. The figure 4(a) of Riaz et al. (2012) is plot- +ted with the (H − Ks) and [4.5] − [8] TCD for the 490 +sources. This shows both YSOs and the diskless sources +© 0000 RAS, MNRAS 000, 1–?? + +135v +103v +103i +135i +-0.6 +-0.3 +-1.0 +-0.6 +-0.4 +-0.4 +-0.211 +-0.5 +-0.2 +-0.2 +-0.1 +0.0 +m +m +m +m +0.0 +0.0 +0.0 +0.2 +0.5 +0.2 +0.1 +0.4 +1.0 +0.4 +0.2 +0.6 +0.6 +0.3 +1.5 +0.8 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +147v +147i +154v +154i +-0.6 +0.4 +-0.6 +.0.4 +Tpo +-0.4 +0.2 +.0.2 +-0.2 +0.0 +m +m +m +m +0.0 +0.0 +0.0 +0.2 +0.2 +0.2 +0.2 +0.4E +0.4 +0.4E +0.6 +0.4 +0.6 +0.6 +0.00.5 1.01.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +201v +201i +213v +213i +-0.6 +-0.6 +-0.4 +-0.8E +-0.6 +-0.4 +-0.2 +-0.4 +-0.4 +-0.2 +0.0 +-0.2 +m +m +m +m -0.2 +0.0 +0.2 +0.0 +0.0 +0.2 +0.4 +0.2 +0.2 +0.4 +0.6 +0.4 +0.4 +0.6 +0.8 +0.6 +0.6 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +239v +239i +240v +240i +.1.0 +-0.3 +1.0 +0.3 +-0.5 +-0.5 +-0.2 +-0.2 +0.0 +0.0 +-0.1 +-0.1 +m +m +m +m +0.5 +0.5 +0.0 +0.0 +1.0 +1.0 +0.1 +0.1 +1.5 +1.5E +0.2 +王 +2.0 +2.0 +0.3 +0.2 +0.00.5 1.0 1.52.0 +0.00.5 1.01.52.0 +0.00.5 1.01.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase298v +298i +377v +377i +-0.6 +0.4 +0.4 +-0.4 +.0.2 +-0.5 +0.2耳 +-0.2 +0.0 +m +m +m +m +0.0 +0.0 +0.0 +0.2 +0.2 +0.5 +0.2 +0.4 +0.4 +0.6 +0.6 +1.0 +0.4 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +385v +385i +449v +449i +1.0 +-0.6 +0.2 +0.2 +-0.4 +-0.5 +.0.1 +0.1 +-0.2 +m +m +m +m +0.0 +0.0 +0.0 +0.0 +0.2 +0.5 +0.1 +0.1 +0.4 +1.0 +0.6 +0.2 +0.2 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +502v +502i +510v +510i +-0.4 +-0.2 +-0.2 +0.2 +0.5 +-0.1 +.0.1 +0.0 +m +m +m +m +0.0 +0.0 +0.0 +0.2 +0.5 +0.1 +0.1 +0.4 +1.0 +0.6 +0.2 +0.2 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +527v +527i +531v +531i +.0.4 +0.4 +-0.6 +0.4 +-0.4 +.0.2 +0.2 +-0.2 +-0.2 +m +m +m +m +0.0 +0.0 +0.0 +0.0 +二 +0.2 +0.2 +0.2 +0.2 +0.4 +0.4 +0.4 +0.6 +0.4 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase546v +546i +561v +561i +-0.6 +0.3 +-0.6 +0.4 +0.2 +-0.4 +-0.4 +-0.2 +-0.1 +0.2 +-0.2 +m +0.0 +m +m +0.0 +0.0 +0.1 +0.0 +0.2 +0.2 +0.2 +0.2 +0.4 曲 +0.3 +0.4 +0.4 +0.6 +0.4 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +614v +614i +619v +619i +-0.3 +-0.3 +-0.2 +0.2 +-0.2 +-0.2 +-0.1 +-0.1 +-0.1 +0.0 +m +m +m +m +0.0 +0.0 +0.0 +0.1 +0.1 +0.1 +0.1 +0.2 +0.2 +0.2 +0.3 +0.3 +0.2 +0.00.5 1.01.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +623v +623i +655v +655i +-0.2 +-0.2 +-0.5 +-0.4 +-0.2 +-0.1 +-0.1 +0.0 +0.0 +m +m +m +m +0.0 +0.0 +0.2 +0.5 +0.4 +0.1 +0.1 +14 +0.6 +0.2 +0.2 +1.0 +0.8 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +679v +679i +706v +706i +-0.2 +0.3 +.0.4 +-0.3 +-0.2 +-0.2 +-0.1 +0.2 +-0.1 +.0.1 +m +m +m +m +0.0 +0.0 +0.0 +0.0 +0.1 +0.1 +0.1 +0.2 +0.2 +0.2 +0.2 +0.3 +0.4 +0.3 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase731v +731i +733v +733i +-0.6 +0.4 +-0.2 +-0.3 +-0.4 +-0.2 +.0.1 +-0.2 +-0.2 +.0.1 +0.0 +m +m +m +m +0.0 +0.0 +0.0 +0.1 +0.2 +0.1 +0.2 +0.2 +0.4 +0.2 +0.6 +0.4 +0.3 +0.3 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +752v +752i +757v +757i +-0.4 +0.4 +0. 2 +0.3 +-0.2 +-0.2 +-0.2 +0.2 +.0.1 +m +m +m +m +0.0 +0.0 +0.0 +0.0 +0.1 +0.2 +0.2 +0.2 +0.2 +0.4 +0.4 +0.4 +0.3 +0.00.5 1.01.52.0 +0.00.5 1.01.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +765v +765i +822v +822i +-0.6 +-0.6 +-0.2 +-0.2 +-0.4 +-0.4 +-0.1 +0.1 +-0.2 +-0.2 +0.0 +m +m +m +m +0.0 +0.0 +0.0 +0.1 +0.2 +0.2 +0.1 +0.2 +0.4 +0.4 +0.6 +0.6 +0.2 +0.3 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +860v +860i +886v +886i +（ +-0.4 +-0.2 +-0.2 +-0. +-0.5 +0.1 +0.0 +0.0 +m +m +m +m +0.0 +0.0 +0.2 +0.1 +0.5 +0. +0.4 +0.2 +1.0 +0.6 +0.3 +. +0.00.5 1.01.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +PhaseVariable stars in NGC 6823 +7 +Figure 5. Continued. +to have similar NIR colors, but from their IRAC TCD +the photospheric and the disk population at IRAC color +[4.5] − [8] ∼ 0.4 mag are readily distinguishable. They have +noted that a few Class III/field stars are mixed with Class II +sources. Their IRAC TCD in figure. 4(b) shows different lo- +cales of Class I and Class II sources. The protostars (Class I) +are located in the top-right corner and exhibit the reddest +in the [3.6] − [5.8] color, whereas the Class II sources are +placed at [4.5] − [8] ⩾ 0.5 mag, [3.6] − [5.8] ⩾ 0.4 mag, and +the Class III/field stars are found to be near [4.5] − [8] and +[3.6] − [5.8] ∼ 0.2 to 0.3 mag. +3.2.3 +NIR and MIR TCDs +To see the distribution of young variable sources we have +plotted them in the NIR and MIR TCD (left panel) and MIR +TCD (right panel) in Fig. 14. To obtain these plots we have +cross-matched the coordinates of variable stars with those +from the Spitzer Galactic Legacy Infrared Mid-Plane Survey +Extraordinaire (GLIMPSE), yielding MIR counterparts of +all 88 variable stars. A few stars, namely Nos. 154, 238, 313, +1405, and 1406 do not have magnitudes at [4.5] and other +wavelengths. The H − K versus [4.5] − [8] TCD shows most +young stellar sources to have H − K ≳ 0.3 mag whereas the +© 0000 RAS, MNRAS 000, 1–?? + +1064v +1064i +1066v +1066i +-0.2 +-0.3 +-0.2 +-0.15 +-0.10 +-0.2 +-0.1 +.0.1 +0.05 +-0.1 +0.0 +m +m +1.. +m +m +0.0 +0.00 +0.0 +0.1 +0.05 +0.1 +0.1 +0.2 +0.10E +0.2 +0.2 +0.3 +0.15 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +1072v +1072i +1094v +1094i +0.15 +-0.3 +-0.3 +-0.10 +-0.2 +-0.2 +0.1 +.0.05 +.0.1 +.0.1 +m +m +m +0.00 +0.0 +0.0 +0.0 +0.05 +0.1 +0.1 +0.1 +0.10E +0.2 +0.2 +0.15 +0.2 +0.3 +0.3 +0.00.5 1.0 1.52.0 +0.00.5 1.01.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +1122v +1122i +1155v +1155i +-0.2 +-0.2 +-0.6 +-0.4 +-0.4 +-0.2 +-0.1 +0.1 +0.2 +0.0 +m +m +m +m +0.0 +0.0 +0.0 +0.2 +0.2 +0.1 +0.1 +0.4 +0.4 +0.2 +0.2 +0.6 +0.6 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +1230v +1230i +1235v +1235i +-0.2 +0.2 +-0.4 +-0.4 +-0.2 +-0.2 +-0.1 +0.1 +0.0 +0.0 +m +m +m +m +0.0 +0.0 +0.2 +0.2 +0.4 +0.4 +0.1 +0.1 +0.6F +0.6E +0.2 +0.2 +0.8 +0.8 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase1262v +1262i +1266v +1266i +-0.4 +-0.3 +-0.6F +-0.6 +0.2 +.0.4 +-0.4 +-0.2 +-0.1 +-0.2 +-0.2 +m +m +0.0 +m +0.0 +m +0.0 +0.0 +0.1 +0.2 +0.2 +0.2 +0.4 +0.2 +0.4 +0.3 +0.6 +0.4 +0.4 +0.8 +0.6 +0.00.5 1.01.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +1298v +1298i +1352v +1352i +2.0 +1.0 +0.2 +0.2 +1.5 +-0.5 +0.1 +-0.1 +-1.0 +m -0.5 +m +m +m +0.0 +0.0 +0.0 +0.0 +0.5 +0.5 +0.1 +0.1 +1.0 +.5 +1.0 +0.2 +0.2 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +1389v +1389i +1405v +1405i +-0.4 +-0.4 +-0.6 F +-0.6 +-0.4 +-0.4 +0 +-0.2 +-0.2 +.0.2 +-0.2 +m +m +m +m +0.0 +0.0 +0.0 +0.0 +0.2 +0.2 +0.2 +0.2 +0.4 +0.4 +0.4 +0.4 +0.6 +0.6 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +1406v +1406i +1500v +1500i +-0.8 +-0.3 +-0.4 +-0.2 +-0.6 +-0.2 +-0.2 +-0.1 +-0.4 +.0.1 +0.0 +0.0 +m -0.2 +m +m +m +0.0 +0.0 +0.2 +0.1 +0.1 +0.2 +0.4 +0.2 +0.2 +0.4 +0.6 +0.6 +0.3 +0.3 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.01.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase1506v +1506i +1511v +1511i +0.3 +-0.3 +-0.2 +-0.3 +-0.2 +-0.2 +-0.2 +-0.1 +.0.1 +-0.1 +-0.1 +0.0 +m +m +m +m +0.0 +0.0 +0.0 +0.1 +0.1 +0.1 +0.1 +0.2 +0.2 +0.2 +0.3 +0.2 +0.3 +0.3 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +1525v +1525i +1526v +1526i +-0.3 +0.2 +-0.5 +0.3 +-0.2 +-0.2 +-0.1 +0.0 +.0.1 +m -0.1 +m +m +m +0.0 +0.5 +0.0 +0.0 +0.1 +0.1 +1.0 +0. +0.2 +0.2 +0.2 +0.3 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +1548v +1548i +1.0 +-0.3 +-0.2 +0.5 +.0.1 +0.0 +m +m +0.0 +0.5 +0.1 +1.0 +0.2 +1.5 +0.3 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase903v +903i +924v +924i +-0.2 +-0.2 +-0.6 +-0.4 +.0.4 +-0.1 +-0.1 +-0.2 +-0.2 +m +m +m +0.0 +m +0.0 +0.0 +0.0 +0.2 +0.4 +0.1 +0.1 +0.2 +0.6 +0.2 +0.2 +0.8 +0.4 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +945v +945i +951v +951i +.0.2 +-0.2 +0.4 +0.3 +-0.2 +0.2 +-0.1 +-0.1 +0.1 +0.0 +m +m +m +m +0.0 +0.0 +0.0 +0.2 +0.1 +0.1 +0.1 +0.4 +0.2 +0.2 +0.2 +0.6 +0.3 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +965v +965i +1000v +1000i +-0.3 +.0.2 +-0.2 +.0.2 +-0.2 +0.1 +-0.1 +0.1 +m +m +m +0.0 +0.0 +0.0 +0.0 +0.1 +0.1 +0.1 +0.1 +0.2 +0.2 +0.2 +0.2 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +1007v +1007i +1063v +1063i +-0.2 +-0.3 +0.4 +-0.4 +-0.3 +-0.2 +T +-0.1 +0.2 +-0.2 +-0.1 +m +m +m -0.1 +0.0 +0.0 +0.0 +0.0 +0.1 +0.1 +0.2 +0.1 +0.2 +0.2 +0.2 +0.4 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase8 +Sneh Lata et al. +Figure 6. The I band phased light curves of probable variable candidates around the cluster. +[4.5] − [8] and [3.6] − [5.8] TCD shows a few young stellar +objects to be positioned as field stars or other populations. +3.2.4 +IPHAS data +To identify the young stellar sources with Hα emission, +i.e., the indicator of accretion disks, we have compared the +present data with Table 3 for IPHAS photometry of Riaz +et al. (2012). We got 29 common stars after the match that +have IPHAS photometry, with stars No. 502, 576, 655, 679, +and 979 having Hα emission with equivalent width greater +than 10 ˚A, judged by the (r′ − i′) versus (r′ − Halpha) TCD +for NGC 6823 (Riaz et al. 2012). The location of these five +stars is shown with the red square in the present (J − H) +versus (H − K) TCD. The Hα emission is found to be vari- +able in nature, therefore, it is necessary to check the location +of the objects in spectral type/color versus magnitude dia- +gram to know their membership and nature (Mart´ın et al. +2000). Two stars Nos. 655 and 979 could be considered as +PMS objects which may possess circumstellar accreting disk. +Barrado y Navascu´es et al. (2001) showed that Hα emission +depends on the spectral type or color in the sense that Hα +emission is found to be larger for cooler objects in a plot +between the Hα emission and (I − J) color. The (I − J) +and (I − K) colors for star no. 655 is about 2.26 mag and +4.682 mag, respectively. In the case of star no. 979, we have +taken I magnitude from Pigulski et al. (2000) to determine +its (I − J) and (I − K) colors due to lack of (V − I) color in +present observations, yielding (I − J) and (I − K) colors as +2.020 mag and 3.789 mag, respectively. Stars Nos. 655 and +979 in particular satisfy both colors and Hα emission be- +ing greater than 10 ˚A, hence are young stars with accretion +disks. +3.2.5 +V vs V − I CMD +Sixty one variable stars were detected in both V and I +bands. Their V magnitudes and V −I color are given in Ta- +ble 2, and Fig. 15 shows their V versus (V − I) CMD. The +PMS isochrones and evolutionary tracks for different masses +are taken from Siess et al. (2000). The solid curve represents +ZAMS by Girardi et al. (2002). We determined the distance +modulus of the cluster to be (V −MV ) = 14.31 mag by com- +paring the ZAMS of Girardi et al. (2002) for solar metallicity +to the V versus V − I CMD, which corresponds to a dis- +tance of 2.59 kpc. The present estimate of distance matches +well with those derived in earlier works of NGC 6823. The +isochrone of age 4 Myr also fits the data well. The CMD is +known to be contaminated by the foreground field stars (e.g. +Guetter 1992; Pigulski et al. 2000; Bica et al. 2008). After +analysis of CMD, Pigulski et al. (2000) and Riaz et al. (2012) +noted two different populations in the cluster, one consist- +ing of older, massive stars which are located near or on the +ZAMS, while the other one being younger objects with ages +less than 10 Myr and are of lower masses (∼ 0.1–0.4 M⊙), +that is, of PMS stars. Pigulski et al. (2000) also concluded +that stars lying in B region of their figure 11(a) are cluster +stars of PMS nature, evolving towards the MS. The present +CMD containing variable stars also shows MS of the cluster +to go up to around V = 16 mag; location of variables in the +CMD suggests the majority of these stars to be probable +members. Most the fainter and redder stars lying between +(V − I) =∼ 2 mag and ∼ 3 mag could be PMS objects. +In this CMD, to maintain clarity we have not plotted star +No. 1548 despite it being detected in the I band, because it +has V − I color more than 6 mag. Star No. 449 may be a +possible PMS star but its placement in the U −B/B−V and +J −H/H −K TCDs suggests a field star, even though it has +proper motions in the range of probable cluster members. +© 0000 RAS, MNRAS 000, 1–?? + +142i +177i +238i +264i +0.4 +-0.4 +-0.3 +-0.6 +-0.2 +-0.4 +-0.2 +-0.2 +-0.1 +-0.2 +m +m +m +m +0.0 +0.0 +0.0 +0.0 +0.1 +0.2 +0.2 +0.2 +0.2 +0.4 +0.4 +0.4 +0.3 +0.6 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +369i +402i +452i +478i +-0.4 +-0.6 +-0.6 +-0.4 +-0.4 +-0.2 +-0.2 +-0.2 +0.0 +m +m +m +m +0.0 +0.0 +0.0 +0.2 +0.2 +0.2 +0.5 +0.4 +0.4 +0.4 +0.6 +1.0 +0.6 +0.6 +0.00.5 1.01.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +529i +576i +753i +826i +0.6民 +-0.6 +-0.6 +-0.6 +0.4 +-0.4 +-0.4 +-0.4 +-0.2 +-0.2 +-0.2 +-0.2 +m +m +m +0.0 +m +0.0 +0.0 +0.0 +0.2 +0.2 +0.2 +0.2 +0.4 +0.4 F +0.4 +0.4 +0.6 +0.6 +0.6 +0.8 +0.6 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +831i +950i +979i +1025i +1.5 +-0.6 +0.6 +.0.4 +-1.0 +-0.4 +0.5 +-0.2 +-0.5 +-0.2 +m +m +m +0.0 +m +0.0 +0.0 +0.0 +0.2 +0.5 +0.2 +三 +0.4 +0.5 +1.0E +0.4 +0.6 +1.5 +0.6 +0.8 +1.0 +0.00.5 1.01.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase1061i +1087i +1151i +1168i +-0.4 +-0.4 +1.0 +-0.6 +-0.4 +-0.2 +-0.2 +-0.5 +-0.2 +m +m +m +m +0.0 +0.0 +0.0 +0.0 +0.2 +0.2 +0.2 +0.5 +0.4 +0.4 +0.4 +1.0 +0.6 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +1191i +1228i +1268i +1295i +0.4 +1.0 +-0.5 +-0.5 +-0.5 +0.2 +0.0 +m +m +m +m +0.0 +0.0 +0.0 +0.5 +0.5 +0.5 +0.2 +1.0 +1.0 +1.0 +0.4 +1.5 +0.00.5 1.01.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +1317i +1459i +1508i +.1.0 +-0.6 +-0.6 +-0.4 +0.4 +-0.5 +-0.2 +-0.2 +0.0 +m +m +m +0.0 +0.0 +0.2 +0.5 +0.2 +0.4 +1.0 +0.4 +0.6 +1.5 +0.6 +0.8 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +PhaseVariable stars in NGC 6823 +9 +3.2.6 +NIR CMDs +The J versus (J − K) and J versus J − H CMDs for the +present sample of variable stars are shown in Fig. 16. it +is seen that the MS is almost vertical and clearly sepa- +rated from the PMS objects/field stars as in the case of +the V versus (V − I) CMD. Bica et al. (2008) described the +same and from statistical cleaned CMD, they found that +two populations are distributed separately where majority +of PMS objects are faint and redder. They found the age +of the cluster in the range from 2 to 7 Myr, a color excess +E(B −V )=∼0.86 mag, and AV =2.7±0.2. In their work af- +ter fitting theoretical models, the absolute distance modulus +of the cluster was found to be (m − M)O = 11.5 mag. +Although stars numbered Nos. 142, 402 826, 950, 924, +1025, 1066, 1087, 1298, and 1548 are nonmembers from +the analysis of the Gaia data, we have considered them as +possible PMS objects based on their positions in different +CMD and TCDs. We note that there are 10 stars, namely, +Nos. 240, 614, 623, 752, 965, 1235, 1352, 1500, 1525, and +1526, that are designated as nonmembers from proper mo- +tion and parallax and, these could be MS stars based on +location in TCDs and CMDs. Star 1506 is located well away +from the MS in U − B/B − V TCD while it is lying on te +MS in V/V −I, J/H −K and J/J −H. The analysis of Gaia +data also found it to be nonmember. This is a doubtful case +for being an MS member. From Gaia data analysis we found +stars Nos. 201, 239, 449, 619, 765, 861, 1151, 1168, 1191 and +1508 as possible or probable members but their locations in +various TCDs and CMDs do not seem to be consistent with +membership. Thus, these are considered field stars. +We looked for the matches of our 8 previously identified +PMS stars based on their 2MASS colors and their spectra +taken at the 2.16 m telescope of Beijing Observatory (Ho- +jaev et al. 2003). The spectra showed the strong H-alpha +in emission, the SED in continuum and other features typi- +cal either for TTS or Herbig Ae/Be stars. The cross-match +yields 3 common stars namely 154, 655 and 679 for two of +them we have already determined their features (their loca- +tion on the diagrams, their proper motions and parallaxes). +In the present work, we have classified 655 as classical TTS +and 679 as MS. There was doubt to consider 679 as PMS +because in U − B versus B − V TCD it is lying on MS but +in J − H versus H − K diagram it is placed in the location +of classical TTS. Now, we determined the membership of +star No 154. It might be probable member of the cluster as +Herbig Ae/Be type star while earlier (Hojaev et al. 2003) +it has been classified as classical TTS, though it has very +different position in V versus V − I CMD to be PMS star +but GAIA suggests it to be highly probable member, and +in J − H versus H − K it is located where Herbig Ae/Be +stars are found. Therefore, it could be considered as Herbig +Ae/Be star. +We have considered members those stars which fulfill +criteria like location in TCDs, CMDs, and have consistent +kinematics. Therefore, using proper motion data together +with location in various TCDs and CMDs obtained from +present and available photometric UBV I, NIR, and MIR +data we classify 25, 48, and 15, respectively, as MS, PMS +members of the cluster, and field stars. The classification of +variables is given in Table 3. +Figure 7. Magnitude as a function of rms value of each star +detected in I band. Open circles represent variable stars identified +in this work. +Figure 8. The sky positions of all the Gaia sources (in gray) +within 30′ toward NGC 6823. +4 +CHARACTERISTICS OF VARIABLE STARS +The log(L/L⊙) vs log Teff diagram (H − R diagram) for 21 +members (MS variables) is shown as Fig. 17. We are not +able to locate four MS stars Nos. 240, 752, 1107 and 1500 +in this plot due to lack of their U and B band data. Here, +the effective temperature and bolometric correction (BC) +have been determined from Toress relation (2010) using the +intrinsic (B − V ) color. The Mbol values of stars are ob- +tained from the relation Mbol = MV +BC, where MV is the +absolute V -band magnitude. The luminosity was obtained +from the relation log(L/L⊙) = −0.4(Mbol − Mbol⊙), where +© 0000 RAS, MNRAS 000, 1–?? + +0.8 +0.6 +0 +S +0 +M +R +0.4 +0.2 +00 +0 +0 +0 +0 +8 +10 +12 +14 +16 +18 +instNGC 6823 +23.8 +23.6 +Decl. [deg] +23.4 +23.2 +23.0 +22.8 +296.2 +296.0 +295.8 +295.6 +295.4 +R.A. [deg]10 +Sneh Lata et al. +Figure 9. The upper panel represents proper motion of all the +stars (gray) and those within 4′ cluster region (black small circles, +1294 stars). The lower panel shows proper motions for variable +stars (in black with error bars). +Mbol⊙ is the bolometric magnitude for the Sun. The MS +variable stars have been classified according to their periods +of variability, the shape of light curves, and their positions +in the H-R diagram. We detected one star as β Cep-type. +Four stars Nos. 679, 886, 1122 and 1352 are located in the +instability strip of slowly pulsating B type (SPB) stars. The +positions in the cluster H-R diagram as well as the observed +variability characteristics of nine stars allow us to conclude +that these variables belong to the new class variables. One +star based on its location in the H − R diagram should be +δ Scuti-type variable. +In the present study, we have detected 48 PMS stars +as most likely cluster members in the PMS stage of evo- +lution. Of these, 4, 8, and 36 stars are classified as Herbig +Figure 10. Histogram of parallaxes for stars within 4 arcmin, +where histogram shaded with black is for variable samples iden- +tified in the present work. +Figure 11. The G vs BP − RP CMD for the present sample +of variable stars. The filled and open squares denote probable +and possible cluster members, and dotted points are considered +nonmembers. +Ae/Be stars, classical TTSs, and weak-lined TTSs, respec- +tively. The amplitudes of weak-lined TTSs range from ∼0.05 +to ∼0.2 mag, and most weak-lined TTSs vary with shorter +periods of less than 1.0 days. The periods and amplitudes of +classical TTSs are found to range from ∼ 0.05 to ∼ 30 days +and ∼ 0.2 to ∼ 0.7 mag, respectively. The above results +suggest that stars with disks, i.e., classical TTSs, exhibit +relatively larger amplitudes than the weak-lined TTSs do, +with the stellar variability in classical TTSs arising from the +presence of the spots, hot and cold, on the stellar surfaces +© 0000 RAS, MNRAS 000, 1–?? + +0 +pmDE[mas/yr +4 +-6 +-8 +-10 +-12 +6 +4 +2 +0 +-2 +-4 +9- +-8 +PmRA[mas/yr]2 +0 +-2 +pmDE[mas/yr +-6 +-8 +-10 ++ +-12 +6 +4 +2 +0 +-2 +-4 +-6 +-8 +PmRA[mas/yr]260 +200 +150 +100 +50 +0.0 +0.5 +1.0 +1.5 +2.0 +plx [mas]10 +12 +14 +[eu] +16 +G +18 +20 +2 +3 +1 +4 +5 +BP - RP[mag]Variable stars in NGC 6823 +11 +Figure 12. (U − B)/(B − V ) TCD for variable stars identified in +the present study. All the UBV data are taken from Massey et +al. (1995). The continuous and dotted line represent the ZAMS +(Girardi et al. 2002) which are shifted along the reddening vector +for reddening E(B − V ) = 0.32 mag and 0.45 mag. Triangles are +those stars that are identified as MS variables. +as found in the previous studies (e.g. Bouvier et al. 1993; +Pandey et al. 2019). +4.1 +Known variables +In the CCD search for variable stars in NGC 6823, Pigulski +et al. (2000) demonstrated that all stars with spectral types +later than A0 are PMS objects. They detected two variable +stars of δ Scuti type and these stars could be at the PMS +stage of evolution and suggested that these objects can fur- +ther be used to test the evolutionary changes in this class of +variable stars. The CMD was used to compare and discuss +the position of the two discovered δ Scuti stars with refer- +ence to the theoretical instability strip for PMS stars of this +type. They have also 13 other variables including one bright +cluster eclipsing binary and an SPB candidate. +Of 15 variables identified by Pigulski et al (2000), 14 +were found to be variable in the present work. We could not +detect variability in the star H8 (E88 or BL 4) (B0 V:pe by +Turner 1979), B1.5 V by Massey et al. 1995), and B1 V by +Shi & Hu (1999). Pigulski et al (2000) noted this stars as +the brightest variable member in the observed cluster field +and found to be a binary star where only one eclipse was +detected in the I band. +Now we will describe the nature of all the known 14 +variable stars individually. +Stars BL 50 (822) and HP 57 (1007) with periods +0.0718530 days, 0.10114 days for BL 50 and 0.0785819 days, +0.0644149 days for HP 57 were found to be most likely clus- +ter PMS members by Pigulski et al. (2000). With their po- +sitions in the cluster CMD as well as the observed periods +Figure 13. (J − H)/(H − K) TCD for variable stars detected +in the field of NGC 6823. The JHK data have been taken from +the 2MASS catalog (Cutri et al. 2003). The continuous and long +dashed lines show sequences for dwarfs and giants (Bessell & Brett +1988), respectively. The TTS locus (Meyer et al. 1997) is shown +by a dotted line. The small dashed lines are reddening vectors +(Cohen et al. 1981) and an increment of visual extinction of AV += 5 mag is denoted by crosses on the reddening vectors. Filled +squares with blue colors represents PMS. The MS population are +shown by green squares whereas open circles may be either MS +members of the cluster or field stars. Triangles (black) represent +two MS members BL 50 and HP 57. +Pigulski et al. (2000) concluded that both objects could be δ +Scuti variables. The present membership analysis, i.e., from +kinematics and positions in various CMDs and TCDs, sug- +gests both stars to be MS members. In the H-R diagram star +No. 822 is positioned where new class variables are found +(between the red edge of SPB and the blue edge of δ Scuti +instability strip). Star No. 1007 could not be placed in the H- +R diagram due to unavailability of UBV data. The present +period of stars 822 is derived as 0.143 days and 0.084 days +while the periodogram analysis gives period of 0.064 days +for star 1007. The period derived for star 1007 is in good +agreement with that derived by Pigulski et al. (2000). The +location of these two stars were shown with red and black +triangles in V versus (V −I) CMD and J −H versus H −K +TCD, respectively. +Star No. 903, a probable cluster MS member was dis- +covered as the third pulsator (G 51) by Pigulski et al. (2000). +Its brightness varies with a period of 0.848 days with an am- +plitude about 0.03 mag. The star was classified by Pigulski +et al. (2000) as an SPB variable according to their variability +characteristics. +The brightness of star No. 886 (G52) found to be binary +by Pigulski et al. (2000) varies with period of 0.61 days +with an amplitude 0.03 mag. It is diagnosed as a member of +the cluster from proper motion and its location in various +© 0000 RAS, MNRAS 000, 1–?? + +1063 +-0.5 +881 +0 +1000 679 +1502 +449 +9658 +0.5 +2斤 +B +U +614 +1.5 +2 +1506 +0 +0.5 +1 +1.5 +2 +B-VX +X +2.5 +X +X +2 +0 +F +T +X +X +1.5 +H +1 +0 +0.5 +0 +-0.6 +-0.4 +-0.2 +0 +0.2 +0.4 +0.6 +0.8 +1 +1.2 +1.4 +1.6 +1.8 +2 +H-K12 +Sneh Lata et al. +Figure 14. (H − K) vs [4.5] − [8.0] and [3.6] − [5.8] vs [4.5] − +[8.0] TCDs for variable stars detected in the field of NGC 6823. +Blue circles are PMS young stellar sources while black circles are +MS/field stars. +Figure 15. V/(V −I) CMD for variable stars in the region of the +cluster NGC 6823. The open circles (blue) are MS variables, and +probable PMS variable stars are shown by filled circles (magenta). +The open circles in black color are considered field stars. The +continuous curve is ZAMS by Girardi et al. (2002) while dashed +lines are PMS isochrones taken for 0.1, 1, 2, 5, 10 Myrs (Siess +et al. 2000). The PMS evolutionary tracks for different masses +ranging from 0.7 to 5.0 M⊙ from Siess et al. (2000) are plotted +with dotted curves. BL 50 and HP 57 are shown by red triangles. +Figure 16. J/(H − K) and J/(J − H) CMD for variable stars +detected in the field of NGC 6823. The JHK data have been taken +from the 2MASS catalogue (Cutri et al. 2003). Circles (blue) and +circles (green) represent MS and PMS, respectively. The Open +circles in black color demonstrate the field stars. The locations +of stars No. 822 (BL 50) and 1007 (HP 57) are shown with open +circle in red color. +photometric diagrams. The present estimates for period and +amplitude are consistent with those reported in Pigulski et +al. (2000). +Star No. 733 has proper motion values of µα += +−1.671 mas/yr and µδ = −5.453 mas/yr, hence is a prob- +able member of the cluster. Our analysis suggests possibly +more than one period, with 0.143 d and 0.512 d. In Pigulski +et al. (2000) it is H30, and they found its period of more +than 3 days. +The brightness of star No. 757 was found to be chang- +ing with one single period of 0.553 days. The present work +classified this star to be a probable PMS cluster member. +Pigulski et al. (2000) named it V2 and derived its period of +about 1.24 days, commenting that the true period for this +star corresponds to an alias frequency, and they found this +star to be of PMS type source. The present observations +confirm its variability and its PMS nature. The light curves +and periodogram analysis manifest that it could be an eclips- +ing binary with primary and secondary depths being nearly +equal. Morales-Calderon et al. (2012) found six new can- +didate sources as PMS eclipsing binaries with multi-epoch +data of about 2400 stars associated with the Orion Nebula +Cluster, and it is stated that the PMS eclipsing binaries are +valuable as they are in the stage of PMS evolution which +is highly dynamic, therefore their detection is rare at this +stage. +Star No. 924 may be a PMS variable with light curve +varying with more than one period. The proper motion sug- +gests a nonmember of the cluster but its position in TCDs +© 0000 RAS, MNRAS 000, 1–?? + +2 +2 +0 +0 +00 +0 +1 +0 +0 +0 +[5.8] +Q +0 +K- +二 +1 +0 +0 +0 +H +[3.6] +0 +00 +0 +0 +8 +0 +0 +0 +0 +0 +0 +0 +0 +0 +0 +0 +0 +0 +8 +0 +0 +00 +0 +0 +00 +0 +Q +0 +8 +0 +60 +0 +0 +0 +0 +1 +2 +-1 +0 +1 +2 +[4.5]-[8.0] +[4.5]-[8.0]8 +0 +0 +10 +0.1 Myr +12 +0 +1 Myr +5.0 +14 +2 Myr +4.0 +3.5 +5 Myr +3.0 +/2.5 +10 Myr +1 2.0 +16 +11.7 +Q +>1.4 +11.1 +Q.9 +0.7 +18 +20 +0 +2 +3 +4 +V-I6 +6 +8 +8 +0 +0 +0 +00 +8 +10 +10 +0 +0 +0 +0 +0 +& +& +0 +J12 +0 +0 +0 +0 +0 +000 +Q +00 +14 +0 +0 +14 +00 +0000 +0o0 +8 +00 +8 +0@ +0 +0 +0 +0 +0 +0 +0 +00 +16 +0 +16 +0 +18 +18 +-1 +0 +1 +2 +3 +4 +-1 +0 +1 +2 +3 +J-K +H-Variable stars in NGC 6823 +13 +and CMDs indicates a possible weak-lined TTSs. It is des- +ignated as V4 by Pigulski et al. (2000). +Star V5 of Pigulski et al. (2000) is numbered as No. 1061 +in this work. We considered it a field star based on its loca- +tion in CMDs and TCDs. Its brightness in V and I bands +varies with a period of 0.438 days. The variability of this +star is confirmed in the present work. +Star V8 (979) which could be a classical TTS based on +its location in the J − H versus H − K diagram. It has a +period of about 0.038 days. The kinematic data indicate it to +be a possible member of the cluster of PMS nature. Pigulski +et al. (2000) also found it to be suspected PMS variable. +Star No. 753 was designated as V7 by Pigulski et al. +(2000). The period of V7 could not be found by Pigulski et +al. (2000) due to either irregular brightness or long-period +variations. In our analysis, this star is considered a probable +member of the cluster according to the proper motion study. +Its position in the CMD and TCDs suggests a PMS Class II +object. This star shows periodic brightness variation with +its period and amplitude being 0.036 days and 0.225 mag, +respectively. +Star No. 655 (V3 in Pigulski et al. 2000) is a periodic +variable with two possible periods, of about 17 days and of +0.059 days. The location of this star in the J − H versus +H − K TCD suggests a Class II source while proper motion +data also suggest cluster membership. +Star No. 1087 is found to be nonmember based on its +proper motion values. Its location in TCDs suggests a PMS +source. Its brightness changes periodically with a period of +∼ 0.125 days. In Pigulski et al. (2000) this star (V1) was the +reddest object among their variable sample. +Star No. 831 is referred to as V6 by Pigulski et al. (2000) +and they found this star too red as a member of the cluster. +We confirm this star, with a period of about 1 day, to be a +field star. +Star No. 623, E 100, is a PMS object, though it was +considered as a nonmember of the cluster in Pigulski et al. +(2000) because its proper motion values were different from +those of cluster members (Erickson 1971). They mentioned +that this star might belong to the foreground population +and it is of a late type object. The present estimation of its +membership using Gaia data also finds it to be nonmember. +4.2 +Newly detected variables +Now we present newly identified variables in this work. Star +No. 1235 is classified, on the basis of the shape of its light +curve, to be an eclipsing binary, bearing similarity to that +of an EA (Algol) type. In EA type eclipsing binaries, both +stars are nearly spherical in shape, with an extremely wide +range of periods from 0.2 days to 10000 days, and with a +wide range of amplitude of variability. Star No. 1235 has a +period of 1.622 days and a variation amplitude of 0.211 mag. +In the H −R diagram, this star is found to be located in the +region of new class variables. More observations of this star +are required to confirm its nature. This star is a member of +the cluster based on locations in TCDs. However, Gaia data +suggest a nonmember of the cluster. +The light curves of star No. 449 in both V and I bands +reveal it to be a short-period variable. Its periodogram in +both V and I exhibits peaks around 3.2 days and 0.789 days. +Gaia data suggest it to be a probable member. +[h] +Table 3. Period and amplitude of variable stars. Last column rep- +resents membership classification of stars along with their classifi- +cation based on variability characteristics. The stars with asterisk +are previously known variables. The cTTS, wTTS and HAe/Be +are classical, weak-lined TTS and Herbig Ae/Be star, respectively. +ID +Period +Period (TESS) +Amp. +class. +(days) +(days) +(mag) +103 +1.919 +1.913 +0.087 +PMS, wTTS +135 +0.041, 0.010 +- +0.336 +PMS, cTTS +142 +0.504 +- +0.156 +PMS, wTTS +147 +0.940, 0.071 +- +0.080 +PMS, wTTS +154 +1.008 +- +0.580 +PMS, HAe/Be +177 +0.784 +- +0.129 +PMS, wTTS +201 +0.850, 0.845 +- +0.115 +Field +213 +0.253, 0.509 +- +0.167 +Field +238 +0.497 +- +0.166 +Field +239 +0.506, 0.969 +0.889, 2.429 +1.028 +PMS, wTTS +240 +1.109, 0.067 +2.253 +0.032 +MS +264 +0.546 +- +0.202 +PMS, wTTS +298 +0.357, 0.082 +- +0.107 +PMS, HAe/Be +369 +5.699 +2.400, 0.600, 7.041 +0.288 +PMS +377 +0.0332 +- +0.103 +Field +385 +30.100, 0.958 +5.243, 3.960, 0.939 +0.425 +PMS, HAe/Be +402 +0.804 +- +0.394 +PMS, wTTS +449 +3.852, 0.789 +5.297, 0.713, 4.084 +0.037 +Field +452 +3.572 +- +0.203 +PMS, wTTS +478 +9.199, 0.898 +3.066, 2.622, 0.902 +0.366 +PMS, wTTS +502 +1.138, 0.887 +- +0.238 +PMS, wTTS +510 +0.143, 0.030 +- +0.025 +MS, New +527 +0.671, 2.057 +2.045, 2.879 +0.168 +PMS, wTTS +529 +0.047 +- +0.290 +PMS, wTTS +531 +0.755, 3.064 +3.084, 6.232, 9.713 +0.219 +PMS, wTTS +546 +0.806, 0.057 +- +0.044 +Field +561 +10.300, 0.909 +3.24 +0.149 +PMS, wTTS +576 +0.882 +0.850, 3.715 +0.237 +PMS, wTTS +614 +0.707 +0.705, 1.775 +0.051 +MS +619 +0.852 +3.825, 0.850 +0.030 +Field +623* +0.044, 0.053 +0.153, 1.595 +0.022 +MS +655* +17.716, 0.030 +- +0.236 +PMS, cTTS +679 +1.1242, 0.059, 0.564 +0.565, 3.376 +0.046 +MS +706 +4.336, 0.561 +- +0.049 +PMS, wTTS +731 +0.359, 0.099 +- +0.065 +PMS, wTTS +733* +0.512, 0.143 +- +0.029 +MS +752 +0.153 +0.153, 10.770 +0.257 +MS +753* +0.036 +- +0.225 +PMS, cTTS +757* +0.553 +- +0.125 +PMS, wTTS +765 +0.112, 0.124 +- +0.133 +Field +822* +0.143, 0.084 +- +0.034 +MS, New +826 +0.072 +- +0.139 +PMS, wTTS +831* +1.009 +1.147, 1.545, 1.095 +1.463 +Field +860 +8.517, 0.523 +- +0.197 +PMS, cTTS +886* +0.446, 0.618 +- +0.032 +MS +903* +0.848 +- +0.033 +MS +924* +3.206, 0.59, 0.759 +- +0.123 +PMS, wTTS +945 +0.662, 0.663, 1.965 +1.966, 6.000 +0.026 +MS +950 +0.504 +3.179, 2.442 +0.265 +PMS, wTTS +951 +1.392, 0.775 +- +0.064 +PMS, wTTS +965 +2.661, 0.726 +2.65, 4.805 +0.053 +MS, New +979* +0.036 +0.064, 5.002 +0.185 +PMS, cTTS +1000 +0.042, 0.486 +- +0.016 +MS, New +1007* +0.064 +0.527, 0.064, 4.818 +0.037 +MS +1025 +0.059 +- +0.600 +PMS, wTTS +1061* +0.438 +1.581, 6.269 +0.099 +Field +1063 +1.049, 0.028 +- +0.131 +MS, β Cep +1064 +0.653, 0.059, 0.395 +0.804, 5.291 +0.025 +MS +1066 +0.0518, 0.082 +2.166, 1.203 +0.013 +PMS, wTTS +1072 +0.484, 0.032 +0.819, 11.649 +0.025 +MS New +1087* +0.125 +- +0.103 +PMS, wTTS +1094 +0.815 +- +0.081 +PMS, wTTS +1122 +2.402, 0.705 +0.705, 11.649 +0.039 +MS, SPB +1151 +0.769 +0.153, 4.834 +0.359 +Field +1155 +10.955, 0.100 +- +0.092 +PMS, wTTS +1168 +0.526 +- +0.240 +Field +1191 +0.924 +- +0.481 +Field +1228 +0.902 +- +0.448 +PMS, wTTS +1230 +0.386, 0.629 +0.385, 1.755 +0.019 +MS, New +1235 +1.622, 3.267 +3.243 +0.211 +MS, New +1262 +1.215, 0.446 +- +0.058 +PMS, wTTS +1266 +3.382 +- +0.148 +PMS, wTTS +1268 +63.269 +5.240, 0.996 +0.276 +PMS, wTTS +1295 +0.028 +- +0.495 +PMS, cTTS +1298 +0.983, 0.496 +- +0.438 +PMS, cTTS +1317 +0.485 +- +0.671 +PMS, cTTS +1352 +0.027, 0.336 +- +0.014 +MS, SBP +1389 +0.111, 0.166 +- +0.086 +PMS, HAe/Be +1405 +0.077, 0.064 +- +0.128 +Field +1406 +0.140, 0.082 +- +0.123 +Field +1459 +0.865 +- +0.172 +PMS, wTTS +1500 +0.072 +- +0.046 +MS +1506 +0.259, 0.491 +- +0.031 +MS +1508 +0.027 +- +0.264 +Field +1511 +0.059, 0.110 +- +0.032 +Field +1525 +1.132, 0.063 +- +0.034 +MS, New +1526 +0.058 +- +0.075 +MS +1548 +0.986, 0.329 +- +0.174 +PMS, wTTS +© 0000 RAS, MNRAS 000, 1–?? + +14 +Sneh Lata et al. +Figure 17. +log(L/L⊙)/ log Teff diagram for the probable MS +variable stars identified in the present study. The continuous curve +represents the instability strip of SPB stars whereas dotted curve +shows the instability region of δ Scuti stars. The dashed curve +shows the location of β Cep stars (cf. Balona et al. 2011). +The variability of the star No. 527 suggest that it is a pe- +riodic variable whose light varies with a period of 0.671 days. +It is found to be a probable member of the cluster from +its proper motion measurements. Its location in CMDs and +TCDs indicates a PMS object. +The brightness of star No. 531, a probable PMS member +of the cluster, is found to vary with a period of 0.755 days +or 3.065 days, with the variability characteristics consistent +with TTSs. +The proper motion values are not in favor of star +No. 752 to be a cluster member, though in the V versus +V − I CMD, it is located along the MS. The period is de- +rived as 0.153 days and the amplitude is about 0.2 mag. The +variability characteristics of this star is similar to a pulsat- +ing type star or eclipsing binary. After doubling its period +its light curves show two minima which have almost equal +depth. It could be an EW type eclipsing (W Ursae Majoris +eclipsing system). The EW type variables have periods of +less than one day, with almost equal depths of primary and +secondary minima. +Star No. 1508 has a period of ∼ 0.027 day with an am- +plitude of about 0.2 mag. This variable resembles that of the +SX Phe type (Cohen & Sarajedini 2012), which are similar +to δ Scuti stars but pulsate with amplitudes up to 0.7 mag +according to the variability types listed in the General Cat- +alog of Variable Stars (GCVS). +5 +TESS LIGHT CURVES +A few variables like No. 1235 and No. 752 have times se- +ries data from the Transiting Exoplanet Survey Satellite +(TESS; Ricker et al. 2015). The high-quality light curves +from the TESS can be used to understand stellar and plan- +etary evolution and this data provide us opportunity to +study the rotation of stars (Canto Martins et al. 2020). +Here, we present folded light curves, exhibited as Fig. 18 for +32 stars which do not have flux contribution from nearby +brighter sources to account for the low spatial resolution +of TESS. TESS observes the sky in sectors with each sec- +tor observed for about 27 days. The eleanor pipeline to ex- +tract times series data of objects from TESS images has +been used, which is an open-source tool (Feinstein et al. +2019, https://archive.stsci.edu/hlsp/eleanor). We can use +the eleanor package to create light curves for fainter ob- +jects for a more detailed or optimized analysis of individ- +ual objects (Feinstein et al. 2019). The eleanor uses TESS +Full Frame Images (FFIs) to extract systematics-corrected +flux for any given star observed by TESS. It takes TIC ID, +coordinates (RA and DEC) of a star. First, the raw flux +is calculated by aperture photometry as RAW FLUX that +is background subtracted. This raw flux is then corrected +for possible systematic effects, which creates a flux called +CORR FLUX. For isolated stars, to obtain the corrected +flux we have taken default apertures. The eleanor software +also provides the option to define one’s own aperture. We +have extracted light curves of all the detected in the present +photometry. +Out of 32 variables, there are 7 stars which are diag- +nosed as PMS and 14 as MS. The periods of all the 32 stars +have been determined using the method described in the +Section 2.1. The periods for 14 stars (103, 527, 531, 576, +614, 619, 679, 752, 945, 965, 1007, 1122, 1230 and 1235) +are found to be in good agreement with that obtained from +the present ground based optical data. The nature of star +No. 752 and No. 1235 as mentioned earlier is confirmed from +their TESS light curves; that is, star No. 752 shows unequal +maxima, likely due to the O’Connell effect (O’Connell 1951), +for which the maxima between eclipses in some eclipsing bi- +naries are not found equal in brightness (Knote et al. 2022). +The phased light curves of stars Nos. 369, 561, and 619 show +brightness variations similar to Algol type eclipsing binaries. +The light curves of stars 527, 531, 576, 965, 1064, 1072 and +1122 were folded by doubling the value of their derived pe- +riod. Three stars 527, 531 and 576 of them are probable +PMS stars while the remaining 4 stars are cluster members +of MS type. The folded light curves and periods of 1064, +1072 and 1122 are similar to the variability characteristic of +EW type variables. The light curve of star 576 seems to have +properties of EA type variable. The stars 527 and 965 could +be weak-lined TTSs based on their variability characteris- +tics as these sources are of PMS nature and show periodic +variability. The period of star 531 was derived as 3.084 days +using TESS data while its period comes out to be 0.755 days +from V and I band light curves. The variability character- +istics for those stars whose periods determined from present +V and I data do not match with that derived from TESS +observations could be revisited in the future observations +of the cluster NGC 6823. The conflicts between periods for +some cases may arise due to the contribution of flux from +nearby stars in TESS data despite being selected isolated +stars. The present work identified 5 MS, 4 PMS stars and 1 +field variable of eclipsing nature, two of which are confirmed +eclipsing binaries and remaining are suspected ones. Their +© 0000 RAS, MNRAS 000, 1–?? + +5 +1063 +1526 +4 +1 +111 +1 +3 +log +1352 +1122 +17 +606 +30 +10 +Kbr +2 +1506 +614 +4.5 +4 +log + T +leffVariable stars in NGC 6823 +15 +Table 4. The proper motion, parallax and photometry by Gaia. The last column refers to likely or possible membership for each variable +star. +ID +RA +DEC +µra +µDec +plx +gmag +bpmag +rpmag +mem +degree +degree +mas/yr +mas/yr +mas +(mag) +mag +103 +295.667936 +23.412217 +-1.392±0.046 +-5.264±0.077 +0.500±0.074 +17.288±0.003 +18.560±0.015 +16.172±0.006 +2 +135 +295.729818 +23.406842 +-1.335±0.050 +-5.330±0.079 +0.605±0.085 +17.340±0.007 +18.463±0.025 +16.006±0.017 +1 +142 +295.921757 +23.403326 +-4.224±0.059 +-6.330±0.096 +-0.125±0.102 +16.699±0.003 +21.455±0.111 +14.950±0.005 +0 +147 +295.717480 +23.404825 +-1.601±0.043 +-5.533±0.068 +0.154±0.071 +17.151±0.003 +18.555±0.013 +15.988±0.005 +1 +154 +295.729082 +23.404078 +-1.583±0.012 +-5.173±0.018 +0.411±0.019 +13.680±0.003 +15.006±0.006 +12.486±0.006 +2 +177 +295.798833 +23.398720 +-1.430±0.059 +-5.249±0.097 +0.382±0.099 +17.841±0.003 +19.238±0.024 +16.679±0.007 +2 +201 +295.806239 +23.392781 +-1.829±0.065 +-4.434±0.111 +0.764±0.121 +18.017±0.003 +18.879±0.021 +17.098±0.009 +1 +213 +295.678068 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+17.061±0.037 +1 +1298 +295.671363 +23.233613 +-1.763±0.227 +-10.821±0.301 +-1.850±0.289 +18.089±0.021 +18.880±0.071 +16.384±0.040 +0 +1317 +295.899959 +23.227779 +-1.562±0.101 +-5.431±0.123 +0.589±0.137 +18.039±0.010 +19.288±0.036 +16.868±0.028 +1 +1352 +295.816693 +23.222874 +-0.419±0.008 +-4.078±0.011 +1.831±0.012 +12.449±0.003 +12.760±0.003 +11.975±0.004 +0 +1389 +295.717974 +23.217819 +-2.076±0.024 +-5.544±0.032 +0.434±0.035 +15.834±0.004 +16.701±0.010 +14.881±0.008 +2 +1405 +295.778615 +23.214104 +-0.016±0.083 +-4.330±0.113 +0.999±0.120 +18.085±0.003 +19.069±0.014 +17.103±0.007 +0 +1406 +295.844691 +23.213100 +-3.267±0.064 +1.679±0.081 +0.991±0.089 +17.530±0.003 +18.310±0.023 +16.559±0.011 +0 +1459 +295.758607 +23.204733 +-1.710±0.090 +-5.469±0.124 +0.343±0.133 +18.147±0.003 +19.354±0.022 +17.032±0.008 +1 +1500 +295.892106 +23.195945 +3.974±0.049 +-3.001±0.071 +0.924±0.071 +15.646±0.003 +16.328±0.003 +14.820±0.004 +0 +1506 +295.737755 +23.197158 +-1.684±0.022 +-4.291±0.026 +0.674±0.028 +15.219±0.003 +15.857±0.004 +14.435±0.004 +0 +1508 +295.846040 +23.195095 +-2.071±0.089 +-4.858±0.124 +0.392±0.142 +18.061±0.005 +19.437±0.035 +16.831±0.013 +2 +1511 +295.813526 +23.194842 +4.169±0.025 +20.500±0.032 +3.135±0.035 +15.890±0.003 +16.829±0.004 +14.933±0.004 +0 +1525 +295.817542 +23.191915 +-0.781±0.009 +-7.011±0.012 +0.655±0.013 +13.206±0.003 +13.785±0.003 +12.468±0.004 +0 +1526 +295.740382 +23.192673 +59.603±0.010 +-58.093±0.014 +9.066±0.015 +08.663±0.003 +08.977±0.003 +08.173±0.004 +0 +1548 +295.840568 +23.186899 +-1.083±0.043 +-3.305±0.056 +0.248±0.060 +13.737±0.003 +18.375±0.013 +12.116±0.006 +0 +derived parameters are listed in Table 5. The masses and +ages of two suspected PMS binaries could not be obtained +due to unavailability of their V −I color. Since UBV data of +MS star no. 752 are not available, the temperature for this +star has been obtained using theoretical models of Girardi +et al. (2002) and present V magnitude. +© 0000 RAS, MNRAS 000, 1–?? + +16 +Sneh Lata et al. +Figure 18. The phased light curves of variable stars using TESS data. +Figure 19. Amplitude of variability and rotation period of TTSs with ∆(I − K) is shown. +6 +CORRELATION BETWEEN +CIRCUMSTELLAR DISKS AND +VARIABILITY +Accretion onto the stellar surface creates hotspots that +brighten the light curve up to 3 mag, whereas the magnetic +field is responsible for cool and therefore dark spots. Herbst +et al. (1994) studied photometric variability of PMS stars in +the Orion Nebula Cluster, and showed that slower rotators +have larger IR excess than fast rotators, indicating disk lock- +ing, for which the angular momentum is transported through +magnetic field lines from the central star to the circumstellar +disk. This supported the results by Edwards et al. (1993) for +which low-mass young stars with accretion disks have peri- +ods more than 4 days, whereas stars without have periods +ranging from 1.5 to 16 days. Rotation seems to be regulated +after the disk is dissipated, as the star spins up while con- +© 0000 RAS, MNRAS 000, 1–?? + +103 +239 +240 +264 +1230 +160 +230 +100 +1225 +155 +90 +220 +1220 +xni +150 +xni +xnl +80 +Xr +210 +145 +1215 +70 +200 +1210 +140 +60 +1205 +135 +190 +50 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +369 +385 +449 +478 +3000 +340 +1270E +275 +335 +2990 +270 +1260 +330 +2980 +265 +xnl +Xr +xni +325 +1250 +2970 +260 +320 +1240 +2960 +255 +315 +2950 +310 +1230 +250 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +527 +531 +561 +576 +160 +550 +620 +205 F +540 +615 +200 +155 +610 +530 +195 +xnl +xnl +xnl +xn +150 +605 +520 +190 +600 +145 +510 +185 +595 +140 +500 +590 +180 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +614 +619 +623 +679 +06 +345 +2160E +2230 +85 +340 +2220 +2150 +80 +335 +2210 +xn +xn +xn +75 +x +330 +2140 +L +2200 +70 +325 +2130 +2190 +65 +320 +60 +315 +2120 +2180 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase752 +831 +945 +950 +300 +815 +430 +205 +810 +425 +290 +200 +805 +420 +280 +xnl +xnl +195 +xni +xni +800 +415 +270 +190 +795 +410 +260 +185 +790 +405 +250 +785 +400 +180 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +965 +979 +1007 +1061 +355 +6920 +1.784×104 +6940 +350 +1.782×104 +6920 +6900 +345 +xnl +1.780×104 +6900 +xn +xni +340 +6880 +F +1.778×104 +6880 +335 +6860 +1.776×104 +6860 +330 +325 +6840 +1.774×104 +6840 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.01.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +1064 +1066 +1072 +1122 +1110 +415 +1540 +380 +410 +1100 +1530 +370 +405 +xn +xni +1090 +400 +1520 +360 +395 +1080 +1510 +350 +390 +1070 +385 +1500 +340 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase +1151 +1230 +1235 +1268 +540 +2330 +1000 +165 +530 +2325 +900 +160 +520 +2320 +800 +155 +xn +xn +xni +xn +510 +2315 +700 +150 +500 +2310 +600 +490 +145 +2305 +500 +480 +2300 +400 +140 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +0.00.5 1.0 1.52.0 +Phase +Phase +Phase +Phase0.4 +0.3 +(mag +Amp. +0.2 +0.1 +0 +0 +2 +△(I-K)30 +28 +26 +24 +22 +20 +18 +(days) +16 +Period +14 +12 +10 +8 +6 +4 +2 +0 +0 +2 +△(I-K)Variable stars in NGC 6823 +17 +[h] +Table 5. The derived parameters of the confirmed/suspected +eclipsing binaries. The last column refers to binary classification. +ID +Age +Mass +Mbol +log(L/L⊙) +log Teff +class. +Binary +Myrs +M⊙ +mag +class. +369 +- +- +- +- +- +PMS +EA? +561 +1.3 +1.28 +- +- +- +PMS +EA? +576 +- +- +- +- +- +PMS +EA? +619 +- +- +- +- +- +Field +EA? +752 +4.0 +1.95 +- +3.915 +MS +EW +757 +0.4 +1.50 +- +- +- +PMS +EW? +1064 +4.0 +3.40 +-0.794 +2.211 +4.148 +MS +EW? +1072 +4.0 +3.20 +0.1394 +1.837 +4.047 +MS +EW? +1122 +4.0 +4.59 +-1.286 +2.407 +4.141 +MS +EW? +1235 +4.0 +6.75 +-1.272 +2.402 +3.979 +MS +EA +tracting towards the MS (Bouvier et al. 2007). These results +support the magnetic-disk model which controls PMS winds +and angular momentum of young stellar objects during the +PMS evolution. +Models for a disk-star interaction (Ostriker & Shu 1995, +Shu et al. 1994, Ghosh & Lamb 1979) are supported by +the rotation periods of PMS objects in young open star +clusters (Attridge & Herbst 1992, Herbst et al. 2001, 2002, +2004). Kearns & Herbst (1998) and Nordhagen et al. (2006) +determined the rotation periods in two clusters. James et +al. (2010) derived light-curve periods of sun-like sources in +the young cluster NGC 1039. Lamm et al. (2004) presented +the rotation period of PMS objects, which supports the +disk-locking mechanism in young stars. Broeg et al. (2006) +measured rotational periods of young objects to under- +stand the star formation scenario that the off-cloud young +sources should rotate faster if these objects were ejected from +the cloud. They did not find significant period distribution +off-cloud weak-lined TTS south of Taurus-Auriga with re- +spect to weak-lined TTS inside the Taurus-Auriga molecu- +lar cloud. Godoy-Rivera (2021) studied stellar rotation and +found that the distribution of period with mass in the case +of open clusters gives important constraints to study angu- +lar momentum evolution and it is evident that spin down +process depends on the mass. The rotation periods of the +members of cluster have been presented, which are found +to be in range from 0.5 days up to 11.5 days (Meibom et +al. 2009, 2011). Gondoin (2018) concluded that the stellar +rotation evolution in open star clusters could be from loss +of angular momentum, which occurs due to strong winds +during the early evolution of young solar type stars. +A disk-bearing YSO spins down due to magnetic brak- +ing (Koenigl 1991; Ostriker & Shu 1995). The increasing disk +fraction with rotation period in open clusters was reported +by Cieza & Baliber (2007). As discussed above, to explore +a correlation between the variability of classical TTSs with +color excess, mass, and age, we have plotted amplitude of +variability with ∆(I −K) excess in Fig. 19 (left panel), while +the right panel of Fig. 19 shows the rotation period with +∆(I − K) excess. Here the ∆(I − K) excess of PMS sources +is determined using the following relation, +∆(I − K) = (I − K)obs − (AI − AK) − (I − K)0, +where (I −K)obs and (I −K)0 are the observed and intrinsic +colors of stars, whereas AI and AK denote the interstellar +extinction in the I and K bands, respectively. To estimate +the value of (I − K)0 of YSOs, it was necessary to estimate +their masses and ages. These values are available for only 22 +PMS objects from the V versus V −I CMD after comparing +with the theoretical models of Siess et al. (2000). Of the +22 sources, there are 4 classical TTSs for which we could +estimate the age and mass. The AI and AK are estimated +using the relations given by Cohen et al. (1981) by adopting +AV = 2.24 mag. The (I − K)0 value is obtained from the +PMS evolutionary models of Siess et al. (2000) of a given +mass and age. Fig. 19 (left panel) shows that a larger ∆(I − +K) value for classical TTSs corresponds to a relatively larger +amplitude of variability, consistent with those found in the +literature, though we find no clear correlation between ∆(I− +K) and rotation period. However one classical TTS No. 655 +with larger ∆(I − K) excess is found to be rotating with a +longer period. +7 +SUMMARY +This work presents 88 variable stars in the young star cluster +NGC 6823. The association of detected variables to the clus- +ter has been discussed with the Gaia kinematic data, and +the optical and NIR TCDs and CMDs. The membership +of previously known variables has also been discussed. We +have detected 48 stars as PMS stars, of which eight are clas- +sified as classical TTSs while 36 and 4 as weak-lined TTSs +and Herbig Ae/Be stars, respectively. Three known variables +H30, V2 and V8 are found to PMS variables as suggested +by Pigulski et al. (2000) while two stars BL 50 and HP 57 +previously detected as PMS δ Scuti pulsators are turned out +to be MS members of the cluster from their proper motion, +parallax values and positions on the TCDs and CMDs. TTSs +have periods ranging from 0.01 days to 30 days, and ampli- +tudes of brightness variation from 0.05 mag to 0.7 mag, with +the classical TTSs varying generally with larger amplitudes +than weak-lined TTSs do. It is noted that 3 of the 4 classi- +cal TTSs with larger values of the disk indicator (∆(I −K)) +are found to have relatively larger amplitude variation. The +present results do not support the disk-locking mechanism, +however one classical TTS having large ∆(I − K) is found +to be rotating slowly. In addition, we have identified 25 stars +to be MS variables (SPB stars, δ Scuti, β Cephei and new +class variable stars). Their variability has been characterized +based on the period, amplitude, shape of the light curves, +and location on the H − R diagram. Fifteen variable stars +may belong to the field star population. +8 +ACKNOWLEDGMENTS +We are thankful to Prof. E. L. Mart´ın for the valuable sug- +gestions that improved scientific content of the present work. +Late Dr. A. K. Pandey facilitated this collaboration project +as Director of ARIES during WPC’s visit. He will be for- +ever remembered. SL will always be grateful to him for all +the support and encouragement. We acknowledge the assis- +tance of Michael Schwartz who managed the Tenagra Ob- +servatory in acquisition of the images of this study. ASH +and JCP thanks Ministry of Innovation Development of +Uzbekistan and Department of Science and Technology of +India for financing the joint project (Project References: +UZB-Ind-2021-99 & INT/UZBEK/P-19). This publication +makes use of data products from the 2MASS, which is a +joint project of the University of Massachusetts and the +© 0000 RAS, MNRAS 000, 1–?? + +18 +Sneh Lata et al. +Infrared Processing and Analysis Center/California Insti- +tute of Technology, funded by the National Aeronautics +and Space Administration and the National Science Foun- +dation. This paper includes data collected by the TESS +mission. Funding for the TESS mission is provided by the +NASA’s Science Mission Directorate. We also acknowledge +”Galactic Legacy Infrared Midplane Survey Extraordinaire” +(GLIMPSE) Legacy Program for Spitzer IRAC data. This +work also used data from the European Space Agency (ESA) +space mission Gaia. Gaia data are being processed by the +Gaia Data Processing and Analysis Consortium (DPAC). +Funding for the DPAC is provided by national institutions, +in particular the institutions participating in the Gaia Mul- +tiLateral Agreement (MLA). The Gaia mission website is +https://www.cosmos.esa.int/gaia. The Gaia archive website +is https://archives.esac.esa.int/gaia. +AVAILABILITY OF DATA +The data underlying this article will be shared upon +request +to +the +corresponding +author. +The +2MASS +data +are +available +at +https://vizier.u-strasbg.fr/viz- +bin/VizieR?-source=II/246. The Gaia and Spitzer IRAC +data are obtained from https://gea.esac.esa.int/archive/ +and +https://irsa.ipac.caltech.edu/cgi-bin/Gator/nph- +scan?submit=Select&projshort=SPITZER, +re- +spectively. +We +used +the +following +links +https://archive.stsci.edu/hlsp/eleanor +and +https://adina.feinste.in/eleanor/ to obtain TESS data. +REFERENCES +[] Andre +Philippe, +Ward-Thompson +Derek, +Barsony +Mary, 1993, ApJ, 406, 122 +[] Appenzeller I., Mundt R, 1989A&ARv, 1, 291A +[] Attridge Joanne M., Herbst William, 1992, ApJ, 398, +61 +[] Bailer-Jones C. A. L., Rybizki J., Fouesneau M., Dem- +leitner M., Andrae R., 2021, AJ, 161, 147 +[] Barrado y Navascu´es D., Zapatero Osorio M. R., B´ejar +V. J. S., Rebolo R., Mart´ın E. L., Mundt R., Bailer- +Jones, C. A. L., 2001, A&A, 377, 9 +[] Bessell M. S., Brett J. M., 1988, PASP, 100, 1134 +[] Bica E., Bonatto C., Dutra C. M., 2008, A&A, 489, +1129 +[] Bouvier J., Cabrit S., Fern´andez M., Mart´ın E. L., +Matthews J. M., 1993, A&AS, 101, 485 +[] Bouvier J., Alencar S. H. P., Boutelier T., Dougados +C., Balog Z., Grankin K., Hodgkin S. T., Ibrahimov M. +A., Kun M., Magakian T. Yu., Pinte C., 2007, A&A, +463, 1017 +[] Broeg C., Joergens V., Fernandez M., et al., 2006, A&A, +450, 1135 +[] Canto Martins B. L., Gomes R. L., Messias Y. S, 2020, +ApJS, 250, 20 +[] Cohen J. G., Persson S. E., Elias J. H., Frogel J. A., +1981, ApJ, 249, 481 +[] Cohen R. E., Sarajedini A., 2012, MNRAS, 419, 342 +[] Cutri R. M. et al., 2003 , 2MASS All Sky Cat- +alog of Point Sources, VizieR Online Data Cata- +log, University of Massachusetts and Infrared Process- +ing and Analysis Center (IPAC/California Institute +of Technology), 2246, 0 https://vizier.u-strasbg.fr/viz- +bin/VizieR?-source=II/246 +[] Cantat-Gaudin T., Anders, F. 2020, A&A, 633, A99. +doi:10.1051/0004-6361/201936691 +[] Edwards Suzan, Strom Stephen E., Hartigan Patrick, +Strom +Karen +M., +Hillenbrand +Lynne +A., +Herbst +William, Attridge Joanne, Merrill K. M., Probst Ron, +Gatley Ian, 1993, AJ, 106, 372 +[] Erickson R.R., 1971, Astron. Astrophys., 10, 270. +[] Feinstein Adina D., Montet Benjamin T., Foreman- +Mackey Daniel, 2019, PASP, 131, i4502 +[] Finkenzeller U, Mundt R., 1984, A&A Supp, 55, 109 +[] Gaia +Collaboration +et +al. +2018, +A&A, +616, +13 +https://gea.esac.esa.int/archive/ +[] Girardi L., Bertelli G., Bressan A., Chiosi C., Groe- +newegen M. A. T., Marigo P., Salasnich B., Weiss A., +2002, A&A, 391, 195 +[] Ghosh P., Lamb F. K., 1979, ApJ, 234, 296 +[] Godoy-Rivera Diego, Pinsonneault Marc H., Rebull +Luisa M., 2021, arXiv210101183G +[] Gondoin P., 2017, A&A, 616, 154 +[] Gutermuth R. A. et al., 2008 , ApJ , 674 , 336 +[] Guetter H.H., 1992, Astron. J., 103, 197 +[] Herbst W., Herbst D. K., Grossman E. J., Weinstein +D. 1994, AJ,108, 1906 +[] Herbst W., Booth J. F., Koret D. L., et al., 1987, AJ, +94, 137 +[] Herbst William, Hamilton Catrina M., et al., 2002, +PASP, 114, 1167 +[] Herbst W., Bailer-Jones C. A. L., Mundt R., Meisen- +heimer K., Wackermann R., 2002, A&A, 396, 513 +[] Herbst W., Bailer-Jones C. A. L., Mundt R., 2001, ApJ, +554, 197 +[] Herbst W., Rhode K. L., Hillenbrand L. A., Curran G., +2000, AJ, 119, 261 +[] Hojaev A. S., Chen W. P., Lee H. T., 2003, A&AT, 22, +799 +[] Huang P. C., et al., 2019, ApJ, 871, 183 +[] James D. J., Barnes S. A., Meibom S., et al., 2010, +A&A, 515, 100 +[] Johnstone D., et al. 2018, ApJ, 854, 31 +[] Joy Alfred H., 1945, ApJ, 102, 168 +[] Kearns Kristin E., Herbst William, 1998, AJ, 116, 261 +[] Lada C. J., 1987, Star Forming Regions, IAUS 115, 1 +[] Lamm M. H., Bailer-Jones C. A. L., Mundt R., Herbst +W., Scholz A. 2004, A&A, 417, 557 +[] Knote M. F., Caballero-Nieves Saida M., Gokhale +Vayujeet, et al., 2022, arXiv220604142K +[] Mart´ın E. L., Brandner W., Bouvier J, Luhman K. L., +Stauffer J., Basri G., Zapatero Osorio M. R., Barrado +y Navascu´es D., 2000, ApJ, 543, 299 +[] Massey Philip, Johnson Kelsey E., Degioia-Eastwood +Kathleen, ApJ, 1995, 454, 151 +[] Meibom S., Mathieu Robert D., Stassun Keivan G., +2009, ApJ, 695, 679 +[] Meibom S.; Mathieu Robert D., Stassun Keivan G., +Liebesny Paul, Saar Steven H., 2011, ApJ, 733, 115 +[] Meyer M. R., Calvet N., Hillenbrand L. A., 1997, AJ, +114 , 288 +[] Morales E. F. E., Wyrowski F., Schuller F., et al., 2013, +© 0000 RAS, MNRAS 000, 1–?? + +Variable stars in NGC 6823 +19 +A&A, 560, A76. doi:10.1051/0004-6361/201321626 +[] Morales-Calder´on M., et al., 2011, ApJ, 733, 50 +[] Nordhagen Stella, Herbst William, Rhode Katherine L., +Williams Eric C, 2006, AJ, 132, 1555 +[] Ostriker Eve C., Shu Frank H., 1995, ApJ, 447, 813 +[] O’Connell D. J. K., 1951, Publications of the Riverview +College Observatory, 2, 85 +[] Pandey J. C., Karmakar S., Joshi A., Sharma Saurabh, +Bhushan Pandey S., Pandey A. K., 2019, RAA, 19, 7 +[] Pedrosa Antonio, 1997, IAUS, 182, 306 +[] Pigulski A., Kolaczkowski Z., Kopacki G., 2000, AcA, +50, 113 +[] Ricker George R., Winn Joshua N, Vanderspek R., et +al., 2015, Journal of Astronomical Telescopes, Instru- +ments, and Systems, 1, 014003 +[] Rangwal Geeta, Yadav R. K. S., Durgapal Alok K., +Bisht D., 2017, PASA, 34, 68 +[] Riaz B., Mart´ın E. L., Tata R., Monin J. -L., Phan-Bao +N., Bouy H., 2012, MNRAS, 419, 1887 +[] Sagar R., Joshi U.C. 1981, Astrophys. Space Sci., 75, +465 +[] Siess L., Dufour E., Forestini M., 2000, A&A, 358, 593 +[] Shu Frank, Najita Joan, Ostriker Eve, Wilkin Frank, +Ruden Steven, Lizano Susana, 1994, ApJ, 429, 781 +[] Stone D. G., 1979, Astron. J., 96, 1389 +[] Shi H.M., Hu, J.Y. 1999, Astron. Astrophys. Suppl. +Ser., 136, 313. +[] Stetson P. B, 1992, J. R. Astron. Soc. Can., 86, 71 +[] Stetson P. B., 1987, PASP, 99, 191 +[] Torres G., 2010, AJ, 140, 1158 +[] Turner D. G., 1979, JRASC, 73, 74 +[] Zahajkiewicz E., 2012, AN, 333, 1086 +© 0000 RAS, MNRAS 000, 1–?? +