Mid-infrared Variability of Young Stellar Objects in the Magellanic Clouds (YSOVAR–MC): The Small Magellanic Cloud

Despite significant progress in recent years, the effects of metallicity on star formation remain poorly understood. With a subsolar metallicity environment, the Small Magellanic Cloud (SMC) provides us with an opportunity to study star formation under metal-poor conditions. We present the results of the study on the mid-infrared variability of young stellar objects (YSOs) in three star-forming regions of the SMC: N66 (NGC 346), N83/N84, and N90 (NGC 602). YSOs at a range of evolutionary stages have been identified in these regions by various techniques in multi-wavelength studies. Our variability analysis is mainly based on the Spitzer Space Telescope’s “Young Stellar Object VARiability in the Magellanic Clouds” (YSOVAR-MC) program that imaged N66, N83/N84, and N90 in IRAC 3.6 and 4.5 microns bands. YSOVAR-MC consists of nine epochs of observations over 30 days and was designed to capture time variations of the order of hours to weeks. We constructed a nine-epoch YSOVAR-MC catalog for each region and combined it with additional observing epochs from other surveys (S3MC, SAGE-SMC, SAGE-VAR, and SMC-Last), resulting in 13 epochs for N83/N84 and N90, and 17 epochs for N66 over 12 years. We used this multi-epoch catalog to establish the fraction of massive YSOs that exhibit flux variations, to determine whether they are periodic or stochastic and to search for dependencies on the physical properties of the YSOs and their environments. Variability is one of the most important characteristics of forming stars, thus understanding physical mechanisms responsible for variability over a range of environments is crucial to understand the star formation process.