Stellar and circumstellar activity in the Be star EW Lac from
the 1993 multi-site campaign
M. Floquet1,
A.M. Hubert1,
R. Hirata2,
D. McDavid3,4,
J. Zorec5,
D. Gies6,
M. Hahula6,
E. Janot-Pacheco7,1,
E. Kambe8,9,
N.V. Leister7,
S. Stefl10,
A. Tarasov11,
and
C. Neiner1
1
Dasgal, UMR\,8633 du CNRS,
Observatoire de Meudon,
F-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
4Guest 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
8Department of Geoscience,
National Defense Academy,
Yokosuka, Kanagawa 239-8686, Japan
9Observer at the
Dominion Astronomical Observatory (Canada) during
the campaign
10
Astronomical Institute, Academy of Sciences, CZ-251 65
Ond\v{r}ejov, Czech Republic
11
Crimean Astrophysical Observatory, Nauchny, Crimea,
334413, Ukraine
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 ). 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 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 an 8-day
mono-site campaign. Possible non-radial pulsation solutions for the
main frequencies detected are l  2-3, m 2-3. 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.
Accepted by A&A
Preprints from
michele.floquet@obspm.fr
or by anonymous ftp to
ftp://ftp.obspm.fr/outgoing/floquet/ewlac93.ps.gz
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