Journal Article

Metal-rich carbon stars in the Sagittarius dwarf spheroidal galaxy

Eric Lagadec, Albert A. Zijlstra, G. C. Sloan, Peter R. Wood, Mikako Matsuura, Jeronimo Bernard-Salas, J. A. D. L. Blommaert, M.-R. L. Cioni, M. W. Feast, M. A. T. Groenewegen, Sacha Hony, J. W. Menzies, J. Th. Van Loon and P. A. Whitelock

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 396, issue 1, pages 598-608
Published in print June 2009 | ISSN: 0035-8711
Published online June 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14736.x
Metal-rich carbon stars in the Sagittarius dwarf spheroidal galaxy

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We present spectroscopic observations from the Spitzer Space Telescope of six carbon-rich asymptotic giant branch (AGB) stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph) and two foreground Galactic carbon stars. The band strengths of the observed C2H2 and SiC features are very similar to those observed in Galactic AGB stars. The metallicities are estimated from an empirical relation between the acetylene optical depth and the strength of the SiC feature. The metallicities are higher than those of the Large Magellanic Cloud, and close to Galactic values. While the high metallicity could imply an age of around 1 Gyr, for the dusty AGB stars, the pulsation periods suggest ages in excess of 2 or 3 Gyr. We fit the spectra of the observed stars using the dusty radiative transfer model and determine their dust mass-loss rates to be in the range 1.0–3.3 × 10−8 M yr−1. The two Galactic foreground carbon-rich AGB stars are located at the far side of the solar circle, beyond the Galactic Centre. One of these two stars shows the strongest SiC feature in our present Local Group sample.

Keywords: stars: AGB and post-AGB; stars: carbon; circumstellar matter; stars: mass-loss; galaxies: individual: Sagittarius dwarf spheroidal; infrared: stars

Journal Article.  7309 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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