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Astron. Astrophys. 332, 643-650 (1998)

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Be stars in open clusters

III. A uvby calibration for the astrophysical parameters of Be stars

J. Fabregat and J.M. Torrejón

Departamento de Astronomía, Universidad de Valencia, E-46100 Burjassot, Valencia, Spain

Received 16 July 1997 / Accepted 17 December 1997


We present linear relations between the equivalent widths of the Balmer lines of Be stars and the anomalies in the uvby photometric indices produced by continuum circumstellar emission. A similar relation exists when the emission in the H line is measured through the photometric index.

These relations have been used to elaborate an empirical calibration of the uvby photometric system to determine the intrinsic colours and indices, the relevant astrophysical parameters and the absolute magnitude of the underlying B star, valid for Be stars of spectral types earlier than B5. The calibration is based on the study of 27 Be stars in 3 open clusters. The proposed calibration procedure allows the determination of the interstellar reddening with an accuracy of 0.033 mag. (rms) and the absolute magnitude with an accuracy of 0.7 mag.

Our calibration independently confirms the previously known result that Be stars of spectral types in the range B0-B5 are overluminous by a mean of 0.3 mag. with respect to their absorption-line counterparts of the same spectral type.

Key words: stars: fundamental parameters – techniques: photometric – stars: emission-line, Be – open clusters and associations: general

Send offprint requests to: J. Fabregat (juan@pleione.uv.es)

© European Southern Observatory (ESO) 1998

Online publication: March 23, 1998