Astrophys. J., 854, 15-15 (2018/February-2)
Probing episodic accretion in very low luminosity objects.
HSIEH T.-H., MURILLO N.M., BELLOCHE A., HIRANO N., WALSH C., VAN DISHOECK E.F. and LAI S.-P.
Abstract (from CDS):
Episodic accretion has been proposed as a solution to the long-standing luminosity problem in star formation; however, the process remains poorly understood. We present observations of line emission from N2H+ and CO isotopologues using the Atacama Large Millimeter/submillimeter Array (ALMA) in the envelopes of eight very low luminosity objects (VeLLOs). In five of the sources the spatial distribution of emission from N2H+ and CO isotopologues shows a clear anticorrelation. It is proposed that this is tracing the CO snow line in the envelopes: N2H+ emission is depleted toward the center of these sources, in contrast to the CO isotopologue emission, which exhibits a peak. The positions of the CO snow lines traced by the N2H+ emission are located at much larger radii than those calculated using the current luminosities of the central sources. This implies that these five sources have experienced a recent accretion burst because the CO snow line would have been pushed outward during the burst because of the increased luminosity of the central star. The N2H+ and CO isotopologue emission from DCE161, one of the other three sources, is most likely tracing a transition disk at a later evolutionary stage. Excluding DCE161, five out of seven sources (i.e., ∼70%) show signatures of a recent accretion burst. This fraction is larger than that of the Class 0/I sources studied by Jorgensen et al. and Frimann et al., suggesting that the interval between accretion episodes in VeLLOs is shorter than that in Class 0/I sources.
© 2018. The American Astronomical Society. All rights reserved.
astrochemistry - ISM: clouds - stars: formation - stars: low-mass - stars: protostars
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