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Astron. Astrophys. 323, 513-523 (1997)


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Giants with infrared excess

H. Plets 1, C. Waelkens 1, R.D. Oudmaijer 2 and L.B.F.M. Waters 3

1 Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 B, B-3001 Heverlee, Belgium (hansp@ster.kuleuven.ac.be; christoffel@ster.kuleuven.ac.be)
2 Imperial College of Science, Technology and Medicine, Blackett Laboratory, Prince Consort Road, London, SW7 2BZ, UK (r.oudmaijer@ic.ac.uk)
3 Sterrenkundig Instituut Anton Pannekoek, Universiteit van Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands (rensw@astro.uva.nl)

Received 30 July 1996 / Accepted 6 January 1997

Abstract

We have correlated optical and infrared catalogs in order to extract a large sample of luminosity class III stars with known infrared flux densities. For a non-negligible fraction of G and K giants, a far-infrared excess emission was found, starting beyond 25 µm. An explanation in terms of present-day mass loss thus becomes unlikely, since the dust should then be warmer and the excess emission less far in the infrared. We believe that the far-infrared excesses of these objects, most likely first-ascent giants, are related to the Vega phenomenon. The dusty disks around these stars, gradually cooled down during their main-sequence phase, could be reheated once the star leaves the main sequence and enters the luminous post-main-sequence phase. The fairly large sample we constructed enables us to derive an estimation for the occurrence of excesses. This fraction of G or K giants with far-infrared excess appears to be distinctly smaller than among main-sequence stars. Since the higher radiation field of giants could lead to a larger evaporation rate of the circumstellar debris, this fact does not conflict with our hypothesis.

Key words: circumstellar matter – stars: evolution – stars: late-type – stars: statistics – infrared: stars

Send offprint requests to: H. Plets

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998

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