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Astron. Astrophys. 346, 805-810 (1999)

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Luminous carbon stars in the Magellanic Clouds *

Jacco Th. van Loon 1, Albert A. Zijlstra 2 and M.A.T. Groenewegen 3

1 Astronomical Institute, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
2 University of Manchester Institute of Science and Technology, P.O.Box 88, Manchester M60 1QD, UK
3 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, D-85740 Garching bei München, Germany

Received 7 December 1998 / Accepted 10 February 1999

Abstract

We present ground-based 3 µm spectra of obscured Asymptotic Giant Branch (AGB) stars in the Magellanic Clouds (MCs). We identify the carbon stars on the basis of the 3.1 µm absorption by HCN and C2H2 molecules.

We show evidence for the existence of carbon stars up to the highest AGB luminosities ([FORMULA] mag, for a distance modulus to the LMC of 18.7 mag). This proves that Hot Bottom Burning (HBB) cannot, in itself, prevent massive AGB stars from becoming carbon star before leaving the AGB. It also sets an upper limit to the distance modulus of the Large Magellanic Cloud of 18.8 mag.

The equivalent width of the absorption band decreases with redder [FORMULA] colour when the dust continuum emission becomes stronger than the photospheric emission. Carbon stars with similar [FORMULA] appear to have equally strong 3 µm absorption in the MCs and the Milky Way. We discuss the implications for the carbon and nitrogen enrichment of the stellar photosphere of carbon stars.

Key words: stars: carbon – stars: circumstellar matter – stars: mass-loss – stars: AGB and post-AGB – galaxies: Magellanic Clouds – infrared: stars

* This paper is based on data obtained at the Cerro Tololo Inter-american Observatories, Chile.

Send offprint requests to: J.Th. van Loon (jvloon@astro.uva.nl)

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© European Southern Observatory (ESO) 1999

Online publication: June 17, 1999
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