http://arxiv.org/abs/2206.02669
Deuterium fractionation can constrain the physical and chemical conditions at the early stage of brown dwarf formation. We present IRAM 30m observations over a wide frequency range of 213-279 GHz of singly and doubly deuterated species of formaldehyde (HDCO and D${2}$CO) towards Class 0/I proto-brown dwarfs (proto-BDs). Multiple low-excitation HDCO and D${2}$CO transition lines with upper energy level $\leq$ 40 K are detected. The D${2}$CO/HDCO, HDCO/H${2}$CO, D${2}$CO/H${2}$CO abundance ratios range between 0.01 and 2.5 for the proto-BDs, similar to the range seen in low-mass protostars. The highest ratios of D${2}$CO/HDCO $\sim$1.3-2.5 are measured for two Stage 0 proto-BDs. These objects could possess a warm corino, similar to the few hot corino cases reported among Class 0 protostars. The mean D${2}$CO/HDCO, D${2}$CO/H${2}$CO, and HDCO/H${2}$CO ratios for the proto-BDs are comparatively higher than the range predicted by the current gas-grain chemical models, indicating that HDCO and D${2}$CO are formed via grain surface reactions in the dense and cold interiors of the proto-BDs at an early formation stage.
B. Riaz and W. Thi
Tue, 7 Jun 22
35/70
Comments: Accepted in MNRAS
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