Abstract
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 (CO)-C-12 (2-1), (CO)-C-13 (2-1), (CO)-O-18 (2-1), (CO)-O-17 (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 similar to 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 similar to 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 similar to 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 (CO)-O-17 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.
| Dokumententyp: | Zeitschriftenartikel |
|---|---|
| Fakultät: | Physik |
| Themengebiete: | 500 Naturwissenschaften und Mathematik > 530 Physik |
| ISSN: | 0035-8711 |
| Sprache: | Englisch |
| Dokumenten ID: | 82968 |
| Datum der Veröffentlichung auf Open Access LMU: | 15. Dez. 2021, 15:04 |
| Letzte Änderungen: | 15. Dez. 2021, 15:04 |
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