Photometric variable stars in the young open cluster NGC 6823

TL;DR

This study identifies and characterizes 88 variable stars in the young open cluster NGC 6823, using multi-band photometry and Gaia data, revealing their types, membership, and cluster age around 2 million years.

Contribution

It provides the first comprehensive variability analysis of NGC 6823, classifies new variable types, and refines cluster membership and age estimates using Gaia and TESS data.

Findings

72 cluster members identified among variables

Classified variables into multiple types including $eta$ Cep, $ ext{delta}$ Scuti, T Tauri, and Herbig Ae/Be stars

Cluster age estimated at approximately 2 million years

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 color and magnitude, as well as the shape of the light curve, we have classified the main sequence variables into $\beta$~Cep, $\delta$~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 $\Delta(I-K)$ is found to be slow rotator.