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

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 x 10(3) M-circle dot and a bolometric luminosity of 2.3 x 10(4) L-circle dot. Both the mass and luminosity are dominated by the cold component (Td = 20 K). The molecular lines of (CO)-O-18, (CS)-S-34, DCN and thermally excited CH3OH are detected in this core. Prominent infall signatures are observed in the (CO)-C-12 (1 - 0) and (2 - 1). We estimated an infall velocity of 0.45 km s(-1) and a mass infall rate of 7 x 10(-4) M-circle dot 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.