WISE Discovery of Mid-infrared Variability in Massive Young Stellar Objects

We systematically investigate the mid-infrared (MIR; λ > 3 μm) time variability of uniformly selected ∼800 massive young stellar objects (MYSOs) from the Red Midcourse Space Experiment Source survey. Out of the 806 sources, we obtain reliable 9 yr long MIR magnitude variability data of 331 sources at the 3.4 μm (W1) and 4.6 μm (W2) bands by cross-matching the MYSO positions with ALLWISE and NEOWISE catalogs. After applying the variability selections using ALLWISE data, we identify five MIR-variable candidates. The light curves show various classes, with the periodic, plateau-like, and dipper features. Out of the obtained two color-magnitude diagram of W1 and W1-W2, one shows "bluer when brighter and redder when fainter" trends in variability, suggesting change in extinction or accretion rate. Finally, our results show that G335.9960-00.8532 (hereafter, G335) has a periodic light curve, with an ≈690 day cycle. Spectral energy density model fitting results indicate that G335 is a relatively evolved MYSO; thus, we may be witnessing the very early stages of a hyper- or ultra-compact H ii region, a key source for understanding MYSO evolution.