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Astron. Astrophys. 329, 169-185 (1998)


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Obscured Asymptotic Giant Branch stars in the Magellanic Clouds

IV. Carbon stars and OH/IR stars *

Jacco Th. van Loon 1, 2, Albert A. Zijlstra 1, Patricia A. Whitelock 3, Peter te Lintel Hekkert 4, Jessica M. Chapman 5, 6, Cecile Loup 7, 8, M.A.T. Groenewegen 9, L.B.F.M. Waters 2, 10 and Norman R. Trams 11

1 European Southern Observatory, Karl-Schwarzschild Straße 2, D-85748 Garching bei München, Germany
2 Astronomical Institute, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
3 South African Astronomical Observatory, P.O.Box 9, 7935 Observatory, Republic of South Africa
4 Australia Telescope National Facility, Parkes Observatory, P.O.Box 276, Parkes, NSW 2870, Australia
5 Anglo-Australian Observatory, P.O.Box 296, Epping, NSW 2121, Australia
6 Australia Telescope National Facility, P.O.Box 76, Epping, NSW 2121, Australia
7 European Southern Observatory, Casilla 19001, Santiago 19, Chile
8 Institut d'Astrophysique de Paris, 98bis Boulevard Arago, F-75014 Paris, France
9 Max-Planck Institut für Astrophysik, Karl-Schwarzschild Straße 1, D-85740 Garching bei München, Germany
10 Space Research Organization Netherlands, Landleven 12, 9700 AV Groningen, The Netherlands
11 ISO Science Operations Centre, Astrophysics Division of ESA, Villafranca del Castillo, P.O.Box 50727, E-28080 Madrid, Spain

Received 13 March 1997 / Accepted 10 July 1997

Abstract

We present N -band photometry for a sample of 21 dust-enshrouded AGB stars in the Large Magellanic Cloud, and three additional sources in the Small Magellanic Cloud. Together with near-infrared photometry, this is used to give a tentative classification into carbon and oxygen-rich atmospheres. Bolometric luminosities are also estimated for these stars. In addition, we present the results of a survey for OH masers in the LMC, which resulted in the discovery of OH maser emission from IRAS04407-7000. Spectra between 600 and 1000 nm have been obtained for two heavily obscured AGB stars in the LMC, confirming them to be highly reddened very late M-type giants. Because the dust-enshrouded stars are clearly undergoing heavy mass loss they are assumed to be very near the termination of their respective Asymptotic Giant Branch phases. The fraction of mass-losing carbon stars decreases with increasing luminosity, as expected from Hot Bottom Burning. The best candidate carbon star, with [FORMULA] mag, is the most luminous mass-losing carbon star in the Magellanic Clouds, and amongst the most luminous AGB stars. At lower luminosities ( [FORMULA] mag) both oxygen and carbon stars are found. This may be explained by a range in metallicity of the individual mass-losing AGB stars.

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

* based on observations obtained at the European Southern Observatory (La Silla, Chile: proposal ESO 54.E-0135), the South African Astronomical Observatory, and the Australia Telescope National Facility

© European Southern Observatory (ESO) 1998

Online publication: November 24, 1997
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