Authors: Lagadec, Eric; Zijlstra, Albert A.¹; Sloan, G. C.²; Wood, Peter R.³; Matsuura, Mikako; Bernard-Salas, Jeronimo²; Blommaert, J. A. D. L.⁴; Cioni, M.-R. L.⁵; Feast, M. W.; Groenewegen, M. A. T.⁶; Hony, Sacha⁷; Menzies, J. W.⁸; van Loon, J. Th.⁹; Whitelock, P. A.

Source: Monthly Notices of the Royal Astronomical Society, Volume 396, Number 1, June 2009 , pp. 598-608(11)

Publisher: Wiley-Blackwell

Abstract:

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 thedustyradiative 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

Document Type: Research article

DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14736.x

Affiliations: 1: Jodrell Bank Centre for Astrophysics, The University of Manchester, School of Physics and Astronomy, Manchester M13 9PL 2: Department of Astronomy, Cornell University, 108 Space Sciences Building, Ithaca, NY 14853-6801, USA 3: Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611, Australia 4: Instituut voor Sterrenkunde, K.U. Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium 5: Centre for Astrophysics Research, University of Hertfordshire, Hatfield AL10 9AB 6: Koninklijke Sterrenwacht van Belgie, Ringlaan 3, 1180 Brussels, Belgium 7: CEA, DSM, DAPNIA, Service d'Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France 8: South African Astronomical Observatory, PO Box 9, 7935 Observatory, South Africa 9: Astrophysics Group, School of Physical and Geographical Sciences, Keele University, Staffordshire ST5 5BG

Publication date: 2009-06-01

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

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