HCN and HNC mapping of the protostellar core Chamaeleon-MMS1

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

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 rotational lines of HCN, HCN, and . The column densities of , , and 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 (1, 1) and (2, 2) inversion lines, is K. The / column density ratio is between 3 and 4, i.e. similar to values found in several other cold cores. The / column density ratio is ∼7. In case no ¹⁵N fractionation occurs in HNC (as suggested by recent modelling results), the HNC/ abundance ratio is in the range , 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 . 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.