Issue |
A&A
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 | |
Published online | 06 September 2006 |
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
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.
Key words: ISM: individual objects: Chamaeleon-MMS1 / ISM: abundances / ISM: molecules
© ESO, 2006
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