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)millimetre continuum and molecular line emissions. We fitted the spectral energy distribution (SED) from the dust continuum emission. The best-fitting SED suggests the presence of two components with temperature of T_d = 20 and 120 K, respectively. The core has a total mass of up to 1.5 × 10^3 M_⊙ and a bolometric luminosity of 2.3 × 10^4 L_⊙. Both the mass and luminosity are dominated by the cold component (T_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 a mass infall rate of 7 × 10^(−4) M_⊙ yr^(−1). From the molecular lines, we have found a high DCN-to-HCN abundance ratio of 0.07. 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.