SETI public: A CH3CN and HCO+ survey towards southern methanol masers associated with star formation

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Paper: astro-ph/0512589
Date: Fri, 23 Dec 2005 05:42:54 GMT (218kb)

Title: A CH3CN and HCO+ survey towards southern methanol masers associated with
star formation

Authors: C. R. Purcell, R. Balasubramanyam, M. G. Burton, A. J. Walsh, V.
Minier, M. R. Hunt-Cunningham, L. L. Kedziora-Chudczer, S. N. Longmore, T.
Hill, I. Bains, P. J. Barnes, A. L. Busfield, P. Calisse, N. H. M. Crighton,
S. J. Curran, T. M. Davis, J. T. Dempsey, G. Derragopian, B. Fulton, M. G.
Hidas, M. G. Hoare, J.-K. Lee, E. F. Ladd, S. L. Lumsden, T. J. T. Moore, M.
T. Murphy, R. D. Oudmaijer, M. B. Pracy, J. Rathborne, S. Robertson, A. S. B.
Schultz, J. Shobbrook, P. A. Sparks, J. Storey, T. Travouillion

Comments: 29 pages, 16 figures. Accepted for publication in MNRAS. For
associated online figures please see

http://www.phys.unsw.edu.au/~crp/papers/cp...2005_online.pdf>

\\
We present the initial results of a 3-mm spectral line survey towards 83
methanol maser selected massive star-forming regions. Here we report
observations of the J=5-4 and 6-5 rotational transitions of methyl cyanide
(CH3CN) and the J=1-0 transition of HCO+and H13CO+.

CH3CN emission is detected in 58 sources (70 %) of our sample). We estimate
the temperature and column density for 37 of these using the rotational diagram
method. The temperatures we derive range from 28-166 K, and are lower than
previously reported temperatures, derived from higher J transitions. We find
that CH3CN is brighter and more commonly detected towards ultra-compact HII
(UCHII) regions than towards isolated maser sources. Detection of CH3CN towards
isolated maser sources strongly suggests that these objects are internally
heated and that CH3CN is excited prior to the UCHII phase of massive
star-formation.

HCO+ is detected towards 82 sources (99 % of our sample), many of which
exhibit asymmetric line profiles compared to H13CO+. Skewed profiles are
indicative of inward or outward motions, however, we find approximately equal
numbers of red and blue-skewed profiles among all classes. Column densities are
derived from an analysis of the HCO+ and H13CO+ line profiles.

80 sources have mid-infrared counterparts: 68 seen in emission and 12 seen in
absorption as `dark clouds'. Seven of the twelve dark clouds exhibit asymmetric
HCO+ profiles, six of which are skewed to the blue, indicating infalling
motions. CH3CN is also common in dark clouds, where it has a 90 % detection
rate.

\\ ( http://arXiv.org/abs/astro-ph/0512589> , 218kb)

• Previous message: LARRY KLAES: "SETI public: The Ups and Downs of the Hubble Constant"

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