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Astron. Astrophys. 325, 585-600


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Obscured Asymptotic Giant Branch stars in the Magellanic Clouds

III. New IRAS counterparts*

Jacco Th. van Loon1,2, Albert A. Zijlstra1, Patricia A. Whitelock3, L.B.F.M. Waters2, Cecile Loup4,5,
and Norman R. Trams6

1European Southern Observatory, Karl-Schwarzschild Straße 2, D-85748 Garching bei München, Germany
2Astronomical Institute, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
3South African Astronomical Observatory, P.O.Box 9, 7935 Observatory, South Africa
4European Southern Observatory, Casilla 19001, Santiago 19, Chile
5Institut d'Astrophysique de Paris, 98bis Boulevard Arago, F-75014 Paris, France
6ISO Science Operations Centre, Astrophysics Division of ESA, Villafranca del Castillo, P.O.Box 50727, E-28080 Madrid, Spain

Received 29 January 1997 / Accepted 1 April 1997

Abstract

We have searched for near-infrared stellar counterparts of IRAS point sources in the Large Magellanic Cloud (LMC), in J- and K-bands. This resulted in the detection of 21 counterparts, of which 19 are new discoveries. Using colour-magnitude and colour-colour diagrams, we identify 13 Asymptotic Giant Branch (AGB) stars with thick circumstellar dust envelopes, 7 possible early post-AGB stars or stars recovering from a thermal pulse, and 1 red supergiant or foreground star. For 10 of the IRAS targets we do not succeed in detecting and/or identifying a near-infrared counterpart. We serendipitously detect 14 other red sources, of which 2 are known Long Period Variables, and a few galaxies. The near-infrared and optical colours of the galaxies may indicate considerable interstellar extinction through the LMC, as much as FORMULA 2-4 mag. The relative number of AGB carbon stars over oxygen stars is shown to decrease as the luminosity increases. Yet amongst the faintest mass-losing AGB stars oxygen-rich stars still exist, which puts constraints on current convection theories that predict the occurrence of third dredge-up and Hot Bottom Burning. We investigate the nature of some LMC stars that have infrared properties very similar to suspected Galactic post-AGB stars.

Key words: stars: mass loss - stars: AGB and post-AGB - dust, extinction - Magellanic Clouds - infrared: galaxies - infrared: stars

*based on observations collected at the European Southern Observatory, La Silla, Chile (proposal ESO 56.E-0681)


© European Southern Observatory (ESO) 1997

Online publication: September 9, 1997
Last change: April 28, 1998
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