Radio Astronomy Division

Colloquium information

Title Episodic Accretion in VeLLOs
DateTime 2019-01-18  15:00~16:00
Place JYS 331-2
Host Chang Won Lee and Woojin Kwon
Speaker Dr. Tien-Hao Hsieh (ASIAA)
Abstract We will present our recent studies about episodic accretion. Episodic accretion is proposed to solve the long-standing luminosity problem in star formation, but its detailed process is still poorly understood. We observed N2H+ and CO isotopologue using ALMA toward eight Very Low Luminosity Objects (VeLLOs). The spatial distributions of N2H+ and CO isotopologues show clear anti-correlation, highlighting the CO snow line. The CO snow lines are located at much larger radii than those expected from the current luminosities of the central sources. This implies that these sources have experienced a recent accretion burst, which could push the CO snow line outward due to the increasing luminosity of the central source. As a result, about ~70% of sources show signatures of a recent accretion burst. This fraction is larger than that of Class 0/I sources studied by Jørgensen 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. I would further discuss a case study toward IRAS16253 out of these sample. We found a quadruple pattern of CO emission at low velocity; these pattern can be explained by refreeze-out of CO at the disk midplane after the burst or originate from the outflow cavity. We speculate a dusty disk may shield the midplane from the central heating source, resulting in a cold disk at the embedded phase.

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