Journal Article

Chemical differentiation in regions of high-mass star formation – II. Molecular multiline and dust continuum studies of selected objects

I. Zinchenko, P. Caselli and L. Pirogov

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 395, issue 4, pages 2234-2247
Published in print June 2009 | ISSN: 0035-8711
Published online May 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14687.x
Chemical differentiation in regions of high-mass star formation – II. Molecular multiline and dust continuum studies of selected objects

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The aim of this study is to investigate systematic chemical differentiation of molecules in regions of high-mass star formation (HMSF). We observed five prominent sites of HMSF in HCN, HNC, HCO+, their isotopes, C18O, C34S and some other molecular lines, for some sources both at 3 and 1.3 mm and in continuum at 1.3 mm. Taking into account earlier obtained data for N2H+, we derive molecular abundances and physical parameters of the sources (mass, density, ionization fraction, etc.). The kinetic temperature is estimated from CH3C2H observations. Then, we analyse correlations between molecular abundances and physical parameters and discuss chemical models applicable to these species. The typical physical parameters for the sources in our sample are the following: kinetic temperature in the range ∼30–50 K (it is systematically higher than that obtained from ammonia observations and is rather close to dust temperature), masses from tens to hundreds solar masses, gas densities ∼105 cm−3 and ionization fraction ∼10−7. In most cases, the ionization fraction slightly (a few times) increases towards the embedded young stellar objects (YSOs). The observed clumps are close to gravitational equilibrium. There are systematic differences in distributions of various molecules. The abundances of CO, CS and HCN are more or less constant. There is no sign of CO and/or CS depletion as in cold cores. At the same time, the abundances of HCO+, HNC and especially N2H+ strongly vary in these objects. They anticorrelate with the ionization fraction and as a result decrease towards the embedded YSOs. For N2H+ this can be explained by dissociative recombination to be the dominant destroying process. N2H+, HCO+ and HNC are valuable indicators of massive protostars.

Keywords: astrochemistry; stars: formation; ISM: clouds; ISM: molecules; radio lines: ISM

Journal Article.  7962 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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