2019MNRAS.483.1139R -
Mon. Not. R. Astron. Soc., 483, 1139-1157 (2019/February-2)
Chemical tracers in proto-brown dwarfs: CO, ortho-H2CO, para-H2CO, HCO+, CS observations.
RIAZ B., THI W.-F. and CASELLI P.
Abstract (from CDS):
We present a study of the CO isotopologues and the high-density tracers H2CO, HCO+, and CS in Class 0/I proto-brown dwarfs (proto-BDs). We have used the IRAM 30m telescope to observe the 12CO (2-1), 13CO (2-1), C18O (2-1), C17O (2-1), H2CO (3-2), HCO+ (3-2), and CS (5-4) lines in seven proto-BDs. The hydrogen column density for the proto-BDs derived from the CO gas emission is ∼2-15 times lower than that derived from the dust continuum emission, indicating CO depletion from the gas-phase. The mean H2CO ortho-to-para ratio is ∼3 for the proto-BDs and indicates gas-phase formation for H2CO. We have investigated the correlations in the molecular abundances between the proto-BDs and protostars. Proto-BDs on average show a factor of ∼2 higher ortho-to-para H2CO ratio than the protostars. Possible explanations include a difference in the H2CO formation mechanism, spin-selective photodissociation, self-shielding effects, or different emitting regions for the ortho and para species. There is a tentative trend of a decline in the HCO+ and H2CO abundances with decreasing bolometric luminosity, while the CS and CO abundances show no particular difference between the proto-BDs and protostars. These trends reflect the scaled-down physical structures for the proto-BDs compared to protostars and differences in the peak emitting regions for these species. The C17O isotopologue is detected in all of the proto-BDs as well as the more evolved Class Flat/Class II BDs in our sample, and can probe the quiescent gas at both early and late evolutionary stages.
Abstract Copyright:
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
Journal keyword(s):
astrochemistry - brown dwarfs - stars: evolution - stars: formation - ISM: abundances - ISM: molecules
Status at CDS
:
Large table(s) will be appraised for possible ingestion in VizieR.
Simbad objects:
14
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