Astron. Astrophys. 332, 155-164 (1998)

Rotation modulation or/and pulsation in o Andromedae

I. The photometric results of an international multisite multitechnique campaign

J.P. Sareyan ¹, S. Gonzalez-Bedolla ², G. Guerrero ³, J. Chauville ⁴, L. Huang ⁵, J.X. Hao ⁵, Z.H. Guo ⁵, S.J. Adelman ⁶, D. Briot ⁴ and M. Alvarez <sup>7

1</sup> Observatoire de la Côte d'Azur, Département Fresnel, B.P. 229, F-06003 Nice Cedex, France
² Instituto de Astronomia, UNAM, Apdo.Postal 70-264, 04510, Mexico D.F., Mexico
³ Osservatorio di Merate, Via E. Bianchi 46, I-22055 Merate, Italy
⁴ Observatoire de Paris-Meudon, URA 335 du CNRS, F-92195 Meudon Cedex, France
⁵ Beijing Astronomical Observatory, Chinese Academy of Sciences, Beijing 100080, P.R. China
⁶ Department of Physics, The Citadel, 171 Moultrie Street, Charleston, SC 29409, USA
⁷ Observatorio Astronomico Nacional, UNAM, Apdo 877, Ensenada, B.C. 22800, Mexico

Received 17 October 1996 / Accepted 9 December 1997

Abstract

We present the photometry of a month-long international campaign on the variable Be star o Andromedae. Excellent time coverage and photometric precision permit a critical comparison for the first time between the pulsational and the rotational modulation hypotheses. A multiperiodic analysis of data taken many years apart shows sets of close frequencies. The amplitude ratio between the ultraviolet and visible variations is what is expected for early-type star pulsation. But, the total amplitude and the order of importance of the frequencies is very different between observation campaigns.

A simple double wave periodic curve accounts for most of the light variation: a rotation/modulation model is considered, with activity variations in or just above the photosphere. Any model must explain the observed changes in the amplitudes of the frequence corresponding to the period and its first harmonic. A very simple model with two stable photospheric activity "features" is insufficient to explain the small variations observed around the mean values of the period and its light amplitude. Thus we propose that the photosphere, which is very probably oblate and seen almost equator-on, is divided into zonal bands undergoing differential rotation.

Key words: stars: individual: oAnd stars: emission line, Be stars: variables: other

Send offprint requests to: J.P. Sareyan

© European Southern Observatory (ESO) 1998

Online publication: March 10, 1998
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