# # Program information file # PROGRAM_ID 2021A046 PROGRAM_TITLE A ToO study of young stars with major eruptions PROGRAM_INV1 Bo Reipurth PROGRAM_INV2 Michael Connelley PROGRAM_INV3 PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG Newborn stars gain their mass by accretion from their circumstellar environment. This was theoretically predicted to occur in a gradually declining manner, but observations of young low-mass stars in major FUor and EXor outbursts have shown that up to 50% of a star's mass may be gained in sudden major accretion events. Such events, during which a T Tauri star increases 5-6 magnitudes in brightness, remain a mystery, with many flavors of accretion events suggested as triggering mechanisms, divided into two classes: disk instability scenarios and external perturbations from stars, brown dwarfs, or giant planets. Given the importance of such events in the build-up of a star as well as our current state of ignorance, we propose a long-term ToO program to obtain a SpeX spectrum as early as possible in the ascending branch of a FUor or EXor event, which is when the signature of the triggering event is most likely to be observable. We have recently completed a major study of all known FUors using SpeX in cross-dispersed mode across the full z,J,H,K range, so we have a unique basis for picking out discrepancies between spectra taken on the ascending branch and later in the elevated state. Two major all-sky surveys are being carried out at UH now, ATLAS and ASAS-SN, which can produce alerts when certain conditions are met. Our triggering threshold is r>3 mag for optical events [and K>2 mag for embedded objects in case such an object is discovered serendipitously during other observations]. Based on [very incomplete] statistics of such previous rare events, we estimated that we have a 50% chance to witness an eruption per semester. We have submitted this proposal for the past 5 semesters and have observed 4 events. PROGRAM_ABSTRACT_END