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Astron. Astrophys. 323, 827-830 (1997)

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Hipparcos parallaxes and the nature of [FORMULA] Scuti stars *

E. Hog 1 and J.O. Petersen 1, 2

1 Copenhagen University Observatory, NBIfAFG, Juliane Mariesvej 30, DK-2100 Copenhagen O, Denmark (erik@astro.ku.dk)
2 Theoretical Astrophysics Center, Juliane Mariesvej 30, DK-2100 Copenhagen O, Denmark (oz@astro.ku.dk)

Received 10 October 1996 / Accepted 13 January 1997

Abstract

Hipparcos parallaxes give new tests of the nature of [FORMULA] Sct variables. For many individual stars accurate distances are now available, i.e. directly determined luminosities and radii can be used to test theoretical models. Of particular interest are the at present very unclear relations between high-amplitude [FORMULA]  Sct stars and the much more abundant low-amplitude [FORMULA] Sct variables, and the relations between field variables and the SX Phe stars in globular clusters.

Only a few high-amplitude variables have Hipparcos parallaxes sufficiently accurate to provide precise model tests. Here we give a discussion of this group, considering SX Phoenicis and AI Velorum, which have the best parallaxes among the high-amplitude stars, in some detail. It is shown that two new tests based on the improved parallaxes are in good agreement with the (generally accepted) assumption that the high-amplitude variables are normal stars following standard evolution. AD Canis Minoris may be an interesting exception with strongly deviating properties. We briefly comment on globular cluster variables and period-luminosity relations.

Key words: stars: ffi Sct – stars: individual: SX Phe; AI Vel; AD CMi – stars: evolution – stars: distances

* Based on observations made with the ESA Hipparcos satellite

Send offprint requests to: E. Hog

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© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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