http://arxiv.org/abs/2201.07064
We report the first detection in the ${\it J}{{\it K}}$ = 1${0}$ – 0${0}$ rotational transition line of CH${3}$D towards three Class 0/I proto-brown dwarfs (proto-BDs) from IRAM 30 m observations. Assuming a rotational temperature of 25 K, the CH${3}$D abundances (relative to H${2}$) are in the range of (2.3–14.5) $\times$ 10$^{-7}$. The CH${4}$ abundances derived from the CH${3}$D abundances and assuming the DCO$^+$/HCO$^+$ ratios are in the range of (0.05–4.8) $\times $10$^{-5}$. The gas-phase formation of CH${3}$D via CH$_2$D$^+$ is enhanced at high densities of 10$^{8}$–10$^{10}$ cm$^{-3}$ and our observations are likely probing the innermost dense and warm regions in proto-BDs. Thermal and/or non-thermal desorption can return the CH${3}$D and CH$_{4}$ molecules formed at an early stage on grain surfaces to the gas-phase. The gas phase abundances are indicative of warm carbon-chain chemistry in proto-BDs where carbon-chain molecules are synthesized in a lukewarm ($\sim$20-30 K) region close to the central source.
B. Riaz and W. Thi
Wed, 19 Jan 22
56/121
Comments: Accepted in MNRAS Letters
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