Large amplitude periodic outbursting YSOs in VVV

VISTA Variables in the Via Lactea (VVV) survey obtained near-IR photometry toward the Galactic bulge and the southern disc plane for a decade. In this work, we designed a modified Lomb-Scargle method to search high-amplitude (ΔKs > 1.5 mag) periodic variables (P > 10 d) in the 2nd version of VVV Infrared Astrometric Catalogue (VIRAC2). In total, 1520 periodic sources were discovered, including 61 sources as candidate periodic accreting YSOs, by the unique morphology of the phase-folded light curves, proximity to Galactic HII regions and/or mid-infrared excesses. We employed “skewness” to measure the asymmetry of the phase-folded light curve and found that fast-rise/slow-decay outbursts predominate at the highest amplitude end. The multi-wavelength colour variations are consistent with a variable mass accretion process, as opposed to variable extinction. The cycles are likely to be caused by dynamical perturbations from stellar or planetary companions within the circumstellar disc. An additional search for periodic variability amongst YSO candidates in public Spitzer-based catalogues yielded a further 58 periodic accretors (mostly low-amplitude), enabling wider exploration of the parameter space. Our finding provides an invaluable laboratory to understand the evolution of circumstellar disc under dynamical perturbation, and provides some indirect evidence of planet formation in early stellar ages (< 1 Myr).