Mining Young Stellar Objects in unTimely: Probing Variability and Physical Properties

Abstract We present a comprehensive analysis of variability in young stellar objects (YSOs) using a decade-long mid-infrared photometric dataset from the unTimely catalog. With its enhanced sensitivity and extended temporal coverage compared to previous surveys like NEOWISE, the catalog enables the detection of subtle variability patterns and long-term brightness fluctuations in YSOs. We characterize their variability using 12 statistical features and identify 17,795 variable YSOs in the W2 band. Through spectral energy distribution fitting, key physical properties such as mass, age, and luminosity are derived, revealing evolutionary trends. The YSOs are classified into six types of variability: linear (0.4%), curved (16.2%), periodic (2.0%), burst (3.0%), drop (1.0%), and irregular (42.9%), with 15.7% exhibiting combined secular and irregular behaviors. The extended observational baseline significantly improves the detection of stochastic phenomena (e.g., bursts and drops) and complex light-curve morphologies. Our analysis confirms that the mass–luminosity relation of our sample is broadly consistent with Padova and Trieste Stellar Evolution Code pre-main-sequence isochrones; only a small number of low-mass objects deviate at >3 σ , likely reflecting measurement and modeling uncertainties. Combined with the observed correlation between variability types and evolutionary stages, these results advance our understanding of the mechanisms driving the observed brightness changes.