(Proposal ID) S17A-086

(PI) Lucas, Philip

(Proposal Title)
A study of eruptive variable YSOs in Cygnus

(Abstract)
Some YSOs exhibit optical/IR outbursts due to episodic mass accretion. This 
accretion phase may occur in every low mass protostar, and be responsible for 
a large fraction of the final mass. Using the VVV and UKIDSS Galactic Surveys 
we have recently discovered that outbursts above the 1 mag level are far more 
common in embedded protostars than in optically brighter, slightly more evolved
T Tauri stars. We call this new class MNors, to complement the optically 
brighter FUors and EXors. The MNors have diverse spectra that are not yet 
understood. The nature of the mechanism that triggers the sudden increase in 
mass accretion remains uncertain, though our recent Subaru/HiCIAO imaging 
results for FUors support theories involving gravitational instability. We 
propose AO imaging and spectroscopy of a sample of nearby MNors in Cygnus with 
IRCS, as the first step in characterising this numerous new population. We will
combine spatial and spectroscopic data on disk and envelope structure and 
system inclination in order to develop a unified picture.