Chemical tracers in proto-brown dwarfs: CO, ortho-H${}_2$CO, para-H${}_2$CO, HCO${}^{+}$, CS observations

Abstract

We present a study of the CO isotopologues and the high-density tracers H${}_2$CO, HCO${}^{+}$, and CS in Class 0/I proto-brown dwarfs (proto-BDs). We have used the IRAM 30m telescope to observe the ${}^{12}$CO (2-1), ${}^{13}$CO (2-1), C${}^{18}$O (2-1), C${}^{17}$O (2-1), H${}_2$CO (3-2), HCO${}^{+}$ (3-2), and CS (5-4) lines in 7 proto-BDs. The hydrogen column density for the proto-BDs derived from the CO gas emission is $\sim$2-15 times lower than that derived from the dust continuum emission, indicating CO depletion from the gas-phase. The mean H${}_2$CO ortho-to-para ratio is $\sim$3 for the proto-BDs and indicates gas-phase formation for H${}_2$CO. We have investigated the correlations in the molecular abundances between the proto-BDs and protostars. Proto-BDs on average show a factor of $\sim$2 higher ortho-to-para H${}_2$CO ratio than the protostars. Possible explanations include a difference in the H${}_2$CO formation mechanism, spin-selective photo-dissociation, self-shielding effects, or different emitting regions for the ortho and para species. There is a tentative trend of a decline in the HCO${}^{+}$ and H${}_2$CO 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 C${}^{17}$O 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.

Accepted in MNRAS. arXiv admin note: text overlap with arXiv:1809.10164

References in corpus (21)

• Photodissociation and photoionisation of atoms and molecules of astrophysical interest
• On the reservoir of sulphur in dark clouds : chemistry and elemental abundance reconciled
• A Large Catalog of Accurate Distances to Molecular Clouds from PS1 Photometry
• Can giant planets form by gravitational fragmentation of discs?
• The Gould's Belt Distances Survey (GOBELINS) III. The distance to the Serpens/Aquila Molecular Complex
• Spitzer IRS Spectra and Envelope Models of Class I Protostars in Taurus
• Disks around Brown Dwarfs in the Sigma Orionis Cluster
• IC348-SMM2E: a Class 0 proto-brown dwarf candidate forming as a scaled-down version of low-mass stars
• Brown dwarf formation by binary disruption
• First large scale Herbig-Haro jet driven by a proto-brown dwarf
• Using Chemistry to Unveil the Kinematics of Starless Cores: Complex Radial Motions in Barnard 68
• Silicate Evolution in Brown Dwarf Disks
• Chemical tracers in proto-brown dwarfs: CN, HCN, and HNC observations
• Externally heated protostellar cores in the Ophiuchus star-forming region
• CO abundances in a protostellar cloud: freeze-out and desorption in the envelope and outflow of L483
• Very low-luminosity Class I/Flat outflow sources in sigma Orionis
• Gas and dust in the star-forming region rho Oph A: II. The gas in the PDR and in the dense cores
• The Near-Infrared Outflow and Cavity of the proto-Brown Dwarf Candidate ISO-Oph 200
• A search for pre- and proto-brown dwarfs in the dark cloud Barnard 30 with ALMA
• A multi-wavelength characterization of proto-brown dwarf candidates in Serpens
• Early phases in the stellar and substellar formation and evolution: Infrared and submillimeter data in the Barnard 30 dark cloud

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