Methyl Cyanide Observations Toward Massive Protostars

TL;DR

This survey of massive protostars using CH3CN line observations reveals hot molecular cores with high temperatures and compact emission regions, demonstrating the line's effectiveness as a probe of hot gas near forming stars.

Contribution

First detection of CH3CN J=12-11 transition in several massive protostars, establishing its utility for studying hot molecular cores.

Findings

CH3CN detected in 9 of 21 sources, with 6 being first detections.

Sources exhibit high rotational temperatures above 50 K.

CH3CN emission is generally coincident with bright mid-IR sources.

Abstract

We report the results of a survey in the CH3CN J= 12-11 transition toward a sample of massive proto-stellar candidates. The observations were carried out with the 10 m Submillimeter telescope on Mount Graham, AZ. We detected this molecular line in 9 out of 21 observed sources. In six cases this is the first detection of this transition. We also obtained full beam sampled cross-scans for five sources which show that the lower K-components can be extended on the arcminute angular scale. The higher K-components however are always found to be compact with respect to our 36" beam. A Boltzmann population diagram analysis of the central spectra indicates CH3CN column densities of about 10^14 cm^(-2), and rotational temperatures above 50 K, which confirms these sources as hot molecular cores. Independent fits to line velocity and width for the individual K-components resulted in the detection of an increasing blue shift with increasing line excitation for four sources. Comparison with mid-infrared images from the SPITZER GLIMPSE/IRAC archive for six sources show that the CH3CN emission is generally coincident with a bright mid-IR source. Our data clearly show that the CH3CN J= 12-11 transition is a good probe of the hot molecular gas near massive protostars, and provide the basis for future interferometric studies.