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

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 Flat/Class II brown dwarfs. Observations were obtained with IRAM 30m telescope DCO+ (3-2), DCN DNC N2D+ (3-2) lines. The DCO+/H13CO+, DCN/H13CN, DNC/HN13C ratios are comparatively higher show a narrower range than DCO+/HCO+, DCN/HCN, DNC/HNC ratios, respectively. mean D/H for proto-BDs derived from these molecules ?0.02-3. Both low-temperature gas-phase ion-molecule deuteron transfer grain surface reactions required to explain enhanced deuterium fractionation. very dense cold ($n_{H_{2}} \ge 10^{6}$ cm?3, T ?10 K) interior provide suitable conditions efficient fractionation cores. There is no correlation between CO depletion factor, exception DCN/HCN that strong anti-correlation possibly due difference peak emitting regions HCN molecules. Over wide bolometric luminosities spanning ?0.002–40 L?, we find trend DCO+/HCO+ (r = -0.7) -0.6) nearly constant -0.4) -0.1) lower N2D+/N2H+ 0.6) compared protostars. Only one dwarf shows emission line. No seen evolutionary stage.