Volume 413, Number 1, January I 2004
|Page(s)||241 - 249|
|Section||Interstellar and circumstellar matter|
|Published online||17 December 2003|
Australia Telescope Compact Array imaging of circumstellar HCN line emission from R Scl
CSIRO Australia Telescope National Facility, PO Box 76, Epping NSW 1710, Australia
2 Sterrewacht Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
3 Stockholm Observatory, AlbaNova, 106 91 Stockholm, Sweden
4 Onsala Space Observatory, 439 92 Onsala, Sweden
Corresponding author: T. Wong, Tony.Wong@csiro.au
Accepted: 19 September 2003
We present radio-interferometric observations of HCN line emission from the carbon star R Scl, obtained with the interim 3-mm receivers of the Australia Telescope Compact Array. The emission is resolved into a central source with a Gaussian FWHM of ~1´´, which we identify as the present mass loss envelope. Using a simple photodissociation model and constraints from single-dish HCN spectra, we argue that the present mass-loss rate is low, yr-1, supporting the idea that R Scl had to experience a brief episode of intense mass loss in order to produce the detached CO shell at ~10´´ radius inferred from single-dish observations. Detailed radiative transfer modelling yields an abundance of HCN relative to H2, , of in the present-day wind. There appears to be a discrepancy between model results obtained with higher transition single-dish data included and those from the interferometer data alone, in that the interferometer data suggest a smaller envelope size and larger HCN abundance than the single-dish data. The lack of HCN in the detached shell, , is consistent with the rapid photodissociation of HCN into CN as it expands away from the star.
Key words: circumstellar matter / stars: carbon / stars: AGB and post-AGB / stars: mass-loss
© ESO, 2004
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