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Astron. Astrophys. 317, L23-L26 (1997)


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Letter to the Editor

Calibrating horizontal-branch stars with Hipparcos *

K.S. de Boer , H.-J. Tucholke and J.H.K. Schmidt

Sternwarte, Univ. Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany

Received 1 October 1996 / Accepted 5 November 1996

Abstract

Parallaxes from the Hipparcos satellite allow for the first time to calibrate parameters of horizontal-branch (HB) like stars based on geometric distances. We present absolute magnitudes and luminosities for 8 such stars. Using [FORMULA] and log g values available from the literature, we also can calculate the mass of the HB stars. We find an average value of [FORMULA] = 0.38 [FORMULA] M [FORMULA] for stars with 7500 < [FORMULA] < 9000 K, well below the value from stellar evolution theory, which predicts masses near 0.6 M [FORMULA]. Recent investigations of HB stars in globular clusters indicated similarly low mass values. The likely cause for the discrepancy of the mass values lies in the low gravities derived from Balmer line profiles.

Key words: astrometry; stars: horizontal branch; stars: fundamental parameters; stars: evolution

* Based on data from the HIPPARCOS Astrometry Satellite

Send offprint requests to: deboer@astro.uni-bonn.de


© European Southern Observatory (ESO) 1997

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