Optical Photometric Variable Stars towards the Galactic \hii region NGC 2282

Abstract

We report here CCD $I$-band time-series photometry of a young (2$-$5 Myr) cluster NGC 2282 to identify and understand the variability of pre-main-sequence (PMS) stars. The $I$-band photometry, down to $\sim$ 20.5 mag, enables us to probe the variability towards the lower mass end ($\sim$ 0.1 M$_\odot$) of the PMS stars. From the light curves of 1627 stars, we identified 62 new photometric variable candidates. Their association with the region was established from H$\alpha$ emission and infrared (IR) excess. Among 62 variables, 30 young variables exhibit H$\alpha$ emission, near-IR (NIR)/mid-IR (MIR) excess or both, and they are candidate members of the cluster. Out of 62 variables, 41 are periodic variables with the rotation rate ranging from 0.2 to 7 days. The period distribution exhibits a median period at $\sim$ 1-day as in many young clusters (e.g., NGC~2264, ONC, etc.), but it follows a uni-modal distribution unlike others having bimodality with the slow rotators peaking at $\sim$ 6$-$8 days. To investigate the rotation-disk and variability-disk connection, we derived NIR excess from $\Delta$(I$-$K) and MIR excess from $Spitzer$ [3.6]$-$[4.5] $\mu$m data. No conclusive evidence of slow rotation with the presence of disks around stars and fast rotation for diskless stars is obtained from our periodic variables. A clear increasing trend of the variability amplitude with the IR excess is found for all variables.