Analysis of physical processes in eruptive YSOs with near-infrared spectra and multiwavelength light curves

The decade-long Vista Variables in the Via Lactea (VVV) survey has detected numerous highly variable young stellar objects (YSOs). We present a study of 61 VVV YSOs ($\Delta K_s$ = 1-5 mag), combining near infrared spectra from Magellan and VLT with NEOWISE light curves to investigate physical mechanisms behind eruptive events. Most sources are spectroscopically confirmed as variables (typically Class I YSOs) but extinction is also seen. Among them, magnetically controlled accretion, identified by H{\sc i} recombination emission (usually accompanied CO emission), observed 46 YSOs. Boundary layer associated FU Ori-like outbursts overtone H$_2$O absorption, only longer duration events ($\ge$5 yr total duration). However, even long events, accretion mode predominates, amplitudes similar boundary mode. Shorter (100-700 days) usually have lower these generally either periodic accretors or multiple timescale wherein large photometric changes occur on timescales weeks years. find that ratio $K_s$ $W2$ can distinguish between extinction. Several quasi-periodic variables. identify examples extinction-driven periodicity among them (with periods up 5 yr) though more data needed classify some cases. suggest dynamic interactions companion may control rate substantial proportion systems, although star-disc should be considered.