HCN and HNC mapping of the protostellar core Chamaeleon-MMS1

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, HNC, and HN 13 C. The column densities of H 13 CN, HN 13 C, H 15 NC and NH 3 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 ± 0.1 K. The HN 13 C/H 13 CN column density ratio is between 3 and 4, i.e. similar to values found in several other cold cores. The HN 13 C/H 15 NC column density ratio is ∼7. In case no 15 N fractionation occurs in HNC (as suggested by recent modelling results), the HNC/HN 13 C abundance ratio is in the range 30−40, which indicates a high degree of 13 C fractionation in HNC. Assuming no differential 13 C fractionation the HCN and HNC abundances are estimated to be ∼7 × 10 −10 and ∼2 × 10 −9 , respectively, the former being nearly two orders of magnitude smaller than that of NH 3 . 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: χ(NH 3 ) > χ(HC 3 N) > χ(HNC) > χ(HCN) > χ(N 2 H + ). 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 13 C isotopic substitutes cannot be excluded on the basis of the present and other available data.

An upper limit of gaseous water abundance in Chamaeleon-MMS1 as observed with ODIN

“…This paper presents a comprehensive analysis of the nature of the core, and gives an overview of previous molecular line and continuum studies of the region. The chemical properties of the core have been also discussed by Kontinen et al (2000) and Tennekes et al (2006). The main conclusion of Belloche et al (2006) is that Cha-MMS1 is not powering the molecular outflow and that it therefore represents either a prestellar core or a transitional object between the prestellar and Class 0 stages.…”

Nitrogen Isotopic Fractionation of Interstellar Nitriles

“…The results of these models must then be compared with observations. Although 15 N-substituted species have been observed in a few interstellar sources (e.g., Linke et al 1983;Hermsen et al 1985;Ikeda et al 2002;Tennekes et al 2006), in many cases only weak limits can be placed on the 15 N/ 14 N ratios, in part due to the fact that the lines of the main isotopomer are often optically thick.…”

Nobeyama 45 m mapping observations toward Orion A. III. Multi-line observations toward an outflow-shocked region, Orion Molecular Cloud 2 FIR 4

“…For example, in warm dense gas in OMC-1, it is measured to be much smaller than unity (Goldsmith et al 1981(Goldsmith et al , 1986). On the other hand, in cold dense gas, Tennekes et al (2006) derived a somewhat large ratio of 3 − 4 toward Cha-MM1. Colzi et al (2018) showed that for high-mass starless cores, the Schilke et al 1992;Talbi et al 1996).…”