The (C-12)/(C-13) abundance ratio in the envelope of R Scuti

Details The (C-12)/(C-13) abundance ratio in the envelope of R Scuti The (C-12)/(C-13) abundance ratio in the envelope of R Scuti

Aug 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990a%26a...234..355b&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 234, no. 1-2, Aug. 1990, p. 355-358. Research supported by CICYT.

Astronomy and Astrophysics

Astrophysics

15

Abundance, Carbon Monoxide, Carbon 12, Carbon 13, Stellar Envelopes, Stellar Mass Ejection, Astronomical Maps, Late Stars, Radio Waves, Stellar Composition, Stellar Models, Variable Stars, Rv Tau Variables, Radio Lines: Molecular, Stars: Circumstellar Matter, Stars: Late-Type, Stars: R Sct

Scientific paper

We have made maps of the 12C0 and 13C0 J=2-1 line emission associated to the RV Tau variable R Scuti. It is shown that the CO cloud constitutes a circumstellar envelope, probably ejected by the star in the past. The CO clouds show a slight bipolar symmetry. After taking into account possible opacity and excitation effects, we conclude that, in order to explain the observed (12COJ=2-1)/(13COJ=2-1) intensity ratio of ˜3, we must assume a 12CO/13CO abundance ratio ≲10. This limit is confirmed by a fit of the observed profiles by a model of molecular excitation in the envelope. We argue that the chemical fractionation effects are not very important in this context and can be easily accounted for in the models, and, therefore, that the above value also holds for the 12C/13C ratio. Such a low value of the relative abundance ratio is similar to those usually found in the atmospheres of evolved stars and approaches the relative abundances expected for material processed by the CNO cycle. This result indicates that the circumstellar envelope is formed by material already processed in the stellar interior. Finally, we also determine other physical conditions in the envelope from model fitting to the lines.

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