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Astron. Astrophys. 330, 145-154 (1998)


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Hipparcos photometry of Herbig Ae/Be stars*

M.E. van den Ancker 1, D. de Winter 2 and H.R.E. Tjin A Djie 1

1 Astronomical Institute "Anton Pannekoek", University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
2 Dpto. Fsica Téorica C-XI, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, E-28049 Madrid, Spain

Received 8 August 1997 / Accepted 12 September 1997

Abstract

The photometric behaviour of a sample of 44 Herbig Ae/Be (HAeBe) candidate stars was studied using a uniform set of optical photometry obtained by the Hipparcos mission. Astrophysical parameters (distance, temperature, luminosity, mass, age) of this sample of stars were derived as well by combining the astrometric data provided by Hipparcos with data from literature. Our main conclusions can be summarized as follows: (1) More than 65% of all HAeBe stars show photometric variations with an amplitude larger than 0:m05; (2) HAeBes with a spectral type earlier than A0 only show moderate (amplitude [FORMULA] 0:m5) variations, whereas those of later spectral type can (but not necessarily have to) show variations of more than 2:m5. We explain this behaviour as being due to the fact that stars with lower masses become optically visible, and hence recognizable as Herbig Ae stars, while still contracting towards the zero-age main sequence (ZAMS), whereas their more massive counterparts only become optically visible after having reached the ZAMS; (3) The Herbig stars with the smallest infrared excesses do not show large photometric variations. This can be understood by identifying the stars with lower infrared excesses with the more evolved objects in our sample; (4) No correlation between the level of photometric variability and the stellar [FORMULA] could be found. If the large photometric variations are due to variable amounts of extinction by dust clouds in the equatorial plane of the system, the evolutionary effects probably disturb the expected correlation between the two.

Key words: circumstellar matter – stars: distances – HR diagram – stars: pre-main sequence – stars: variables

* Based on data from the Hipparcos astrometry satellite.

Send offprint requests to: M.E. van den Ancker (mario@astro.uva.nl)

© European Southern Observatory (ESO) 1998

Online publication: January 8, 1998
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