EDP Sciences
Free Access
Volume 456, Number 3, September IV 2006
Page(s) 1037 - 1043
Section Interstellar and circumstellar matter
DOI https://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. Tennekes1, 2, J. Harju1, M. Juvela1 and L. V. Tóth3, 4

1  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)

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 NH
3 (1, 1) and (2, 2) inversion lines, is $12.1 \pm 0.1$ 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 $\sim $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 ${\sim} 7 \times 10^{-10}$ and ${\sim} 2\times 10^{-9}$, 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: $\chi(\mathrm{NH_3}) > \chi(\mathrm{HC_3N}) > \chi({\rm HNC}) > \chi({\rm HCN}) >
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