演講資訊

摘要：

Episodic accretion is proposed to solve the long-standing luminosity problem in star formation, but its detailed process is still poorly understood. We present N2H+ and CO isotopologue observations with the Atacama Large Millimeter/submillimeter Array (ALMA) in the envelopes of eight Very Low Luminosity Objects (VeLLOs). The spatial distributions of N2H+ and CO isotopologues show clear anti-correlation, tracing the CO snow line, in five out of the eight sources; N2H+ is depleted toward the center where the emission of CO isotopologues show their peak. The CO snow lines traced from the N2H+ distribution are located at much larger radii than those expected from the current luminosities of the central sources. This implies that these five sources experienced a recent accretion burst, which could push the CO snow line outward due to the increasing luminosity of the central source. The N2H+ and CO isotopologues emission from DCE161, one of the other three sources, is most likely tracing a transition disk in a later evolutionary stage. If we exclude DCE161, five out of seven sources (i.e., ~70%) show signatures of a recent accretion burst. This fraction is larger than that of Class 0/I sources studied by J?rgensen et al. (2015) and Frimann et al. (2016), suggesting that the interval of episodic accretion in VeLLOs could be shorter than that in Class 0/I sources.