UV flux distributions of γ Doradus stars ^*

¹ Institut d'Astrophysique de Paris, UMR 7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France e-mail: gerbaldi@iap.fr
² Dipartimento di Astronomia, Università degli Studi di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy e-mail: faraggiana@oats.inaf.it
³ Observatoire de Paris-Meudon, GEPI, 92195 Meudon Cedex, France e-mail: Elisabetta.Caffau@obspm.fr

Received: 3 July 2006
Accepted: 25 April 2007

Abstract

Context.It seems that the recently identified class of pulsating stars, the γ Dor type-variables, includes objects with different metal abundances and a large percentage of binaries.

Aims.We looked for indicators of metal abundance peculiarities and stellar binarity in a sample of 40 confirmed γ Dor stars.

Methods.Absolute magnitudes from Hipparcos parallaxes and UV magnitudes, from the S2/S68 experiment on board the TD1 satellite, are retrieved from databases and compared with predicted values. A set of non variable normal stars is used to check the consistency of this analysis and also serve as reference stars.

Results.Twenty-nine stars of the γ Dor star sample, which is 73% of it, are discovered having abnormal UV fluxes constantly showing UV flux excesses compared to those computed with the atmospheric parameters (T_eff , log g, and metallicity) determined from calibration of the indices. The reason for this UV excess of flux at 196.5 nm and at 236.5 nm, which was previously known only for HD 209295, cannot be ascribed to binarity alone. An extra source of UV flux or less UV absorption – yet unknown – must be present.