SMA millimeter observations of hot molecular cores

Abstract

We present Submillimeter Array observations in the 1.3 mm continuum and the CH3CN (12K–11K) line of 17 hot molecular cores associated with young high-mass stars. The angular resolution of the observations ranges from 1. 0 to 4. 0. The continuum observations reveal large (>3500 AU) dusty structures with gas masses from 7 to 375 M , which probably surround multiple young stars. The CH3CN line emission is detected toward all the molecular cores at least up to the K = 6 component and is mostly associated with the emission peaks of the dusty objects. We used the multiple K-components of the CH3CN and both the rotational diagram method and a simultaneous synthetic local thermodynamic equilibrium model with the XCLASS program to estimate the temperatures and column densities of the cores. For all sources, we obtained reasonable fits from XCLASS by using a model that combines two components: an extended and warm envelope and a compact hot core of molecular gas, suggesting internal heating by recently formed massive stars. The rotational temperatures lie in the range of 40–132 K and 122–485 K for the extended and compact components, respectively. From the continuum and CH3CN results, we infer fractional abundances from 10−9 to 10−7 toward the compact inner components, which increase with the rotational temperature. Our results agree with a chemical scenario in which the CH3CN molecule is efficiently formed in the gas phase above 100–300 K, and its abundance increases with temperature.