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Astron. Astrophys. 362, 1020-1040 (2000)


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Stellar and circumstellar activity in the Be star EW Lacertae from the 1993 multi-site campaign

M. Floquet 1, A.M. Hubert 1, R. Hirata 2, D. McDavid 3,4, J. Zorec 5, D. Gies 6, M. Hahula 6, E. Janot-Pacheco 7,1, E. Kambe 8,9, N.V. Leister 7, S. tefl 10, A. Tarasov 11 and C. Neiner 1

1 Dasgal, UMR 8633 du CNRS, Observatoire de Meudon, 92195 Meudon, France
2 Department of Astronomy, Kyoto University, Kyoto 606-01, Japan
3 Limber Observatory, Timber Creek Road, P.O. Box 63599, Pipe Creek, TX 78063-3599, USA
4 Guest Observer, McDonald Observatory, The University of Texas at Austin, USA
5 Institut d'Astrophysique, 98bis Boulevard Arago, 75014 Paris, France
6 Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303-3083, USA
7 Instituto Astronomico e Geofisico, Universidade de São Paulo, Caixa Postal 3386, 01060-970 São Paulo, Brazil
8 Department of Geoscience, National Defense Academy, Yokosuka, Kanagawa 239-8686, Japan
9 Observer at the Dominion Astronomical Observatory (Canada) during the campaign
10 Astronomical Institute, Academy of Sciences, 251 65 Ondejov, Czech Republic
11 Crimean Astrophysical Observatory, Nauchny, Crimea, 334413, Ukraine

Received 4 February 2000 / Accepted 19 July 2000

Abstract

A multi-site, multi-technique campaign on the Be star EW Lac was held for about 9 days in August-September 1993. We present results of the analysis of visual, high S/N spectroscopic data (He I 6678 Å and H[FORMULA]). Search for short-term variability was carried out on He I 6678 (line profiles, radial velocity (RV), equivalent width (EW), full width at half-maximum (FWHM) on the absorption part of the line profile and on violet (V) and red (R) emission peaks) and on H[FORMULA] emission line (line profiles, EW, V, R and V/R ratio). The presence of multi-periodicity is confirmed and we detected the frequencies found in 1989 by Floquet et al. (1992) during a 8-day mono-site campaign. Possible non-radial pulsation solutions for the main frequencies detected are [FORMULA], [FORMULA]. We found evidence on the He I 6678 line of episodic matter outflows through the presence of relatively broad, variable absorption line-profile variations. At least one sharp absorption feature was also observed slowly crossing the stellar disc. It is attributed to a blob of matter temporarily orbiting the star. A brief account is given of broad-band polarimetric observations, performed over 6 nights. A correlation is found between the variation in intrinsic polarization level in the B-band and He I 6678 Å strength. Finally, we present a simple model that reproduces rather well the additional "pseudo-photosphere" contribution in 1993 as opposed to 1989.

Key words: stars: circumstellar matter – stars: emission-line, Be – stars: oscillations – stars: individual: EW Lac – stars: variables: general

Send offprint requests to: M. Floquet (michele.floquet@obspm.fr)

© European Southern Observatory (ESO) 2000

Online publication: October 30, 2000

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