The molecular emissions and the infall motion in the high-mass young stellar object G8.68-0.37

Abstract

We present a multi-wavelength observational study towards the high-mass young stellar object G8.68-0.37. A single massive gas-and-dust core is observed in the (sub)millimeter continuum and molecular line emissions. We fitted the spectral energy distribution (SED) from the dust continuum emission. The best-fit SED suggests the presence of two components with temperature of $T_{\mathrm{d}}=20$ K and 120 K, respectively. The core has a total mass of up to $1.5\times 10^3$ $M_{\odot }$ and bolometric luminosity of $2.3\times 10^4{L}_{\odot }$. Both the mass and luminosity are dominated by the cold component ($T_{\mathrm{d}}=20$ K). The molecular lines of C${}^{18}$O, C${}^{34}$S, DCN, and thermally excited CH${}_3$OH are detected in this core. Prominent infall signatures are observed in the ${}^{12}$CO $(1-0)$ and $(2-1)$. We estimated an infall velocity of 0.45 km s${}^{-1}$ and mass infall rate of $7\times 10^{-4}{M}_{\odot }$ year${}^{-1}$. From the molecular lines, we have found a high DCN abundance and relative abundance ratio to HCN. The overabundant DCN may originate from a significant deuteration in the previous cold pre-protostellar phase. And the DCN should now be rapidly sublimated from the grain mantles to maintain the overabundance in the gas phase.

24 pages, 8 figures, accepted for publication in MNRAS

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