Photometric variable stars in the young open cluster NGC 6823

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 UBVI 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 colour and magnitude, as well asthe 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 disc-locking mechanism in the presentsample of TTSs, one TTS with larger (I − K) isfound to be a slow rotator