Abstract
We present radio-interferometric observations of HCN J = 1 → 0 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, ∼2 × 10-7 M⊙ 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, fHCN, of ∼10-5 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 J = 1 → 0 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, f HCN ≲ 2 × 10-7, is consistent with the rapid photodissociation of HCN into CN as it expands away from the star.
Original language | English (US) |
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Pages (from-to) | 241-249 |
Number of pages | 9 |
Journal | Astronomy and Astrophysics |
Volume | 413 |
Issue number | 1 |
DOIs | |
State | Published - Jan 2004 |
Externally published | Yes |
Keywords
- Circumstellar matter
- Stars: AGB and post-AGB
- Stars: carbon
- Stars: mass-loss
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science