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

TL;DR

This study investigates the molecular emissions and infall motion in the high-mass young stellar object G8.68-0.37 through multi-wavelength observations, revealing a massive cold core with active infall and chemical signatures of deuteration.

Contribution

It provides detailed physical, chemical, and kinematic characterization of G8.68-0.37, highlighting the infall process and molecular abundance ratios in a high-mass star-forming core.

Findings

Massive cold core with 1500 solar masses

Detected infall velocity of 0.45 km/s and high infall rate

Overabundance of DCN indicating past cold deuteration

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 $T_{\rm d}=20$ K and 120 K, respectively. The core has a total mass of up to $1.5\times10^3$ $M_{\odot}$ and bolometric luminosity of $2.3\times10^4 L_{\odot}$. Both the mass and luminosity are dominated by the cold component ($T_{\rm d}=20$ 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 $7\times10^{-4} M_{\odot}$ 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.