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A&A Supplement series, Vol. 129, April II 1998, 289-311

Received March 11; accepted July 24, 1997

Long-term visual spectrophotometric behaviour of Be starsgif

A. Moujtahid tex2html_wrap4813 - J. Zorec tex2html_wrap4815 - A.M. Hubert tex2html_wrap4813 - A. Garcia tex2html_wrap4815 - G. Burki tex2html_wrap4821

Send offprint request: J. Zorec

tex2html_wrap4823  Observatoire de Paris-Meudon, DASGAL, F-92195 Meudon Principal Cedex, France
tex2html_wrap4825  Institut d'Astrophysique de Paris, CNRS, 98tex2html_wrap_inline4769 Bd. Arago, F-75014 Paris, France
tex2html_wrap4827  Observatoire de Genève, CH-1290 Sauverny, Switzerland


The long-term spectrophotometric variations of 49 Be stars are studied using the U and V magnitudes of the UBV system, the total Balmer discontinuity D and the visible gradient tex2html_wrap_inline4779. BCD spectrophotometric and photometric data in five different photometric systems, obtained in most cases since 1950 and reduced to the BCD system, were used. The (U,D), (V,D), (tex2html_wrap_inline4789) and (tex2html_wrap_inline4791) correlations obtained differ from star to star and they can be single or double-valued. They differ clearly for Be phases or Be-shell phases. Be stars with small tex2html_wrap_inline4793 showing the "spectrophotometric shell behaviour'': D > D*, were found. This finding implies either that strongly flattened models of circumstellar envelopes are in doubt for these stars, or that not all Be stars are rapid rotators. Comparison of observed variations with those predicted for model Be stars with spherical circumstellar envelopes of variable densities and dimensions implies that spectrophotometric patterns of Be phases are due to circumstellar envelopes in low opacity regimes, while those of spectrophotometric shell phases are due to circumstellar envelopes in high opacity regimes. In a given star, the envelope regions responsible for the observed variations of D and tex2html_wrap_inline4779 in spectrophotometric shell phases seem to be smaller and denser than those producing the observed variations of these parameters in spectrophotometric Be phases. The high positive RV found in strong shell phases might favor the formation of compact circumstellar layers near the star.

keywords: stars: variable -- stars: Be

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