The majority of a low-mass star's main-sequence mass is accreted while it is a deeply embedded Class 0 protostar. Learning how accretion works in the Class 0 phase is therefore essential for understanding how low-mass stars are assembled. Is most of the mass accreted via quiescent, slowly declining accretion as the circumstellar reservoir depletes? Or is it mostly accreted in large, discrete bursts? Class 0 protostars cannot reliably be detected by ground-based near-IR observations, so space-based mid- to far-IR surveys are required to efficiently survey them in the IR. We present a survey for bursts in 92 Class 0 protostars using Spitzer/IRAC imaging of Orion extending from 2014 to 2017. We found three bursts of more than 2 mag, similar to what was observed in the FU Ori protostar HOPS 223. This implies that Class 0 protostars experience bursts of at least this magnitude every 440 yr, with a 95% confidence interval extending from 160 to 1900 yr. Spitzer/IRAC and WISE data show that the bursts persist for a decade or more with significant variability during each burst. Data from Spitzer/MIPS, SOFIA, and Herschel reveal the burst amplitudes. The rate, durations, and amplitudes of Class 0 bursts suggest that the majority of the main-sequence mass may be accreted in such bursts, but uncertainty in the rate makes this claim tentative. Future surveys are needed to reduce this uncertainty.
[Poster PDF File]