Deuterium chemistry and D/H ratios in Class 0/I proto-brown dwarfs

Riaz, B. und Thi, W.-F. (2022): Deuterium chemistry and D/H ratios in Class 0/I proto-brown dwarfs. In: Monthly Notices of the Royal Astronomical Society, Bd. 511, Nr. 4: S. 6110-6125

Abstract

We have conducted the first extensive observational survey of several deuterated species in 16 Class 0/I proto-brown dwarfs (proto-BDs) and 4 Class Flat/Class II brown dwarfs. Observations were obtained with the IRAM 30m telescope in the DCO+ (3-2), DCN (3-2), DNC (3-2), and N2D+ (3-2) lines. The DCO+/(HCO+)-C-13, DCN/(HCN)-C-13, and DNC/(HNC)-C-13 ratios are comparatively higher and show a narrower range than the DCO+/HCO+, DCN/HCN, and DNC/HNC ratios, respectively. The mean D/H ratios for the proto-BDs derived from these molecules are in the range of similar to 0.02-3. Both low-temperature gas-phase ion-molecule deuteron transfer and grain surface reactions are required to explain the enhanced deuterium fractionation. The very dense and cold (n(H2) >= 10(6) cm(-3), T <= 10 K) interior of the proto-BDs provide the suitable conditions for efficient deuterium fractionation in these cores. There is no correlation between the D/H ratios and the CO depletion factor, with the exception of the DCN/HCN ratios that show a strong anti-correlation possibly due to the difference in the peak emitting regions of the DCN and HCN molecules. Over a wide range in the bolometric luminosities spanning similar to 0.002-40 L-circle dot, we find a trend of higher DCO+/HCO+ and DCN/HCN ratios, nearly constant DNC/HNC and DNC/(HNC)-C-13 ratios, and lower N2D+/N2H+ ratios in the proto-BDs compared to protostars. Only one Class II brown dwarf shows emission in the DCO+ (3-2) line. No correlation is seen between the D/H ratios and the evolutionary stage.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Physik
• Themengebiete: 500 Naturwissenschaften und Mathematik > 530 Physik
• ISSN: 0035-8711
• Sprache: Englisch