Volume 535, November 2011
|Number of page(s)||7|
|Section||Stellar structure and evolution|
|Published online||18 November 2011|
Carbon isotopic abundance ratios in S-type stars⋆
1 Astronomy DepartmentUniversity of Washington, Seattle, WA 98195-1580, USA
e-mail: email@example.com; firstname.lastname@example.org
2 Observatorio Astronómico Nacional, Apartado 1143, Alcalá de Henares, 28800 Madrid, Spain
e-mail: email@example.com; firstname.lastname@example.org
3 Physical Sciences Dept., Everett Community College, Everett, WA, USA
Received: 24 June 2010
Accepted: 26 September 2011
We have used the IRAM 30 m telescope on Pico de Veleta to observe 11 S-type stars in the J = 1–0 and J = 2–1 transitions of both 12C16O and 13C16O in order to derive the 12CO/13CO ratio in their circumstellar envelopes. Detections of high signal to noise were achieved for 7 stars. A mean isotope ratio of 35.3 ± 6.2 was found. This ratio fits between the ratio for late M stars of about 12 ± 3 and that of carbon stars of 58 ± 17. Hence, we confirm the often proposed evolutionary sequence from late M through type S to carbon stars. Mass loss rates of 5 × 10-8 to 3 × 10-6 M⊙ y-1 are derived from the present CO data using a simple uniform outflow model with line-dependent opacities, in very good agreement with previous mass-loss estimates.
Key words: stars: AGB and post-AGB / stars: abundances
© ESO, 2011
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