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Astron. Astrophys. 325, 585-600 (1997)

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Obscured Asymptotic Giant Branch stars in the Magellanic Clouds

III. New IRAS counterparts *

Jacco Th. van Loon 1, 2, Albert A. Zijlstra 1, Patricia A. Whitelock 3, L.B.F.M. Waters 2, Cecile Loup 4, 5 and Norman R. Trams 6

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, South Africa
4 European Southern Observatory, Casilla 19001, Santiago 19, Chile
5 Institut d'Astrophysique de Paris, 98bis Boulevard Arago, F-75014 Paris, France
6 ISO 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)

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© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998

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