Issue A&A Volume 456, Number 3, September IV 2006 Page(s) 1037 - 1043 Section Interstellar and circumstellar matter DOI http://dx.doi.org/10.1051/0004-6361:20040294

A&A 456, 1037-1043 (2006)
DOI: 10.1051/0004-6361:20040294

HCN and HNC mapping of the protostellar core Chamaeleon-MMS1

P. P. Tennekes^{1, 2}, J. Harju¹, M. Juvela¹ and L. V. Tóth<sup>3, 4

1</sup>  Observatory, PO Box 14, 00014 University of Helsinki, Finland
    e-mail: peter.tennekes@helsinki.fi
²  Julius Institute, Utrecht University, The Netherlands
³  Department of Astronomy of the Loránd Eötvös University, Pázmány Péter sétány 1, 1117 Budapest, Hungary
⁴  Konkoly Observatory, PO Box 67, 1525 Budapest, Hungary

(Received 18 February 2004 / Accepted 19 June 2006)

Abstract
Aims.The purpose of this study is to investigate the distributions of the isomeric molecules HCN and HNC and estimate their abundance ratio in the protostellar core Cha-MMS1 located in Chamaeleon I.
Methods.The core was mapped in the J=1-0 rotational lines of HCN, HCN, and HN¹³C. The column densities of HN¹³C, HN¹³C, H¹⁵NC and NH₃ were estimated towards the centre of the core.
Results.The core is well delineated in all three maps. The kinetic temperature in the core, derived from the NH₃ (1, 1) and (2, 2) inversion lines, is  K. The HN¹³C/ HN¹³C column density ratio is between 3 and 4, i.e. similar to values found in several other cold cores. The HN¹³C/ H¹⁵NC column density ratio is 7. In case no ¹⁵N fractionation occurs in HNC (as suggested by recent modelling results), the HNC/ HN¹³C abundance ratio is in the range 30-40, which indicates a high degree of ¹³C fractionation in HNC. Assuming no differential ¹³C fractionation the HCN and HNC abundances are estimated to be and , respectively, the former being nearly two orders of magnitude smaller than that of NH₃. Using also previously determined column densities in Cha-MMS1 , we can put the most commonly observed nitrogenous molecules in the following order according to their fractional abundances: .
Conclusions.The relationships between molecular abundances suggest that Cha-MMS1 represents an evolved chemical stage, experiencing at present the "late-time" cyanopolyyne peak. The possibility that the relatively high HNC/HCN ratio derived here is only valid for the ¹³C isotopic substitutes cannot be excluded on the basis of the present and other available data.

Key words: ISM: individual objects: Chamaeleon-MMS1 -- ISM: abundances -- ISM: molecules

© ESO 2006

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