Be stars in open clusters. I. uvby photometry^*

¹ Departamento de Astronomía, Universidad de Valencia, 46100 Burjassot, Valencia, Spain
² Departamento de Ingeniería de Sistemas y Comunicaciones, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain
³ Centro de Cálculo, Universidad Politécnica de Valencia, Camino de Vera 14, 46022 Valencia, Spain
⁴ Círculo Astronómico del Mediterráneo, Fundación Cultural de la Caja de Ahorros del Mediterráneo, Apdo. 616, 03080 Alicante, Spain

Corresponding author: Send offprint request to: J. Fabregat, e-mail: fabregat@evalvx.ific.uv.es

Received: 21 January 1996
Accepted: 5 March 1996

Abstract

We present uvby β photometry for Be stars in eight open clusters and two OB associations. It is shown that Be stars occupy anomalous positions in the photometric diagrams, which can be explained in terms of the circumstellar continuum radiation contribution to the photometric indices. In the - M_V plane Be stars appear redder than the non emission B stars, due to the additional reddening caused by the hydrogen free-bound and free-free recombination in the circumstellar envelope. In the c₀ - M_V plane the earlier Be stars present lower c₀ values than absorption-line B stars, which is caused by emission in the Balmer discontinuity, while the later Be stars deviate towards higher c₀ values, indicating absorption in the Balmer discontinuity of circumstellar origin.