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Astron. Astrophys. 338, 919-922 (1998)

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Research Note

Photometry of ET Andromedae and pulsation of HD 219891 *, **

W.W. Weiss 1, R. Kuschnig 1, D.E. Mkrtichian 2, A.V. Kusakin 3, T.J. Kreidl *** 4, S.J. Bus 4, D.J. Osip 4, Z. Guo 5, J. Hao 5, L. Huang 5, J.-P. Sareyan 6, M. Alvarez 7, S.G. Bedolla[FORMULA] 8, J. Zverko 9, J. iovský 9, P. Mittermayer 1, K. Zwintz 1, N. Polosukhina 10, A.V. Mironov 3, N.I. Dorokhov 2, V.P. Goranskij 3, T.N. Dorokhova 2, H. Schneider 11 and F. Hiesberger 1

1 Institut für Astronomie der Universität Wien, Türkenschanzstrasse 17, A-1180 Wien, Austria (e-mail: weiss@galileo.ast.univie.ac.at)
2 Astronomical Observatory, Odessa State University, Shevchenko Park, 270014 Odessa, Ukraine
3 Sternberg State Astronomical Institute, Universitetskij prospect, 13, 119899 Moscow, Russia
4 Northern Arizona University, Box 5100, Flagstaff, AZ 86011, USA
5 Beijing Astronomical Observatory, Zong-guan-cun 100080, Beijing, P.R. China
6 Observatoire de la Cote d'Azur, Le Mont Gros, F-06003 Nice, France
7 Observatorio Astronomico Nacional - UNAM, Apdo. Postal 877, Ensenada, B.C., 22800, Mexico
8 Instituto de Astronomia - UNAM, Apdo. Postal 70-264, 04510 Mexico, Mexico
9 Astronomical Institute of the Slovak Academy of Science, SK-05960 Tatranska Lomnica, Slovakia
10 Crimean Astrophysical Observatory, p/o Nauchny, 334413 Crimea, Ukraine
11 Universitätssternwarte, Geismarlandstrasse 11, D-37083 Göttingen, Germany

Received 8 June 1998 / Accepted 23 July 1998

Abstract

ET And is a binary system with a B9p(Si) star as the main component. We report on the photometric observing campaigns in 1988, 1989 and 1994 which confirmed the rotation period of 1:d618875 for ET And while refuting other published values. Furthermore, the controversial issue of pulsational stability of ET And is resolved since we have discovered pulsation for HD 219891, which was the main comparison star and sometimes exclusively used. The frequency of 10.0816 d-1, a semi-amplitude of 2.5 mmag, [FORMULA] and [FORMULA] suggest this comparison star to be a [FORMULA] Scuti variable close to the blue border of the instability strip. The pulsational stability of ET And could be clearly established and hence no need exists to derive new driving mechanisms for stars between the classical instability strip and the region of slowly pulsating B-type (SPB) stars.

Key words: stars: binaries: spectroscopic – stars: chemically peculiar – stars: individual: ET And – stars: oscillations – stars: rotation

* Based on observations obtained at the Bulgarian National Observatory, Crimean Astrophysical Observatory (Ukraine), Lowell Observatory (USA), Mauna Kea (USA), Mt. Dushak-Erekdak (Turkmenistan), San Pedro (Mexico), Skalnate Pleso (Slovakia), Tien Shan (Kazakhstan) and Wise Observatory (Israel)
** Dedicated to our esteemed colleague S.G. Bedolla whose untimely death greatly saddened us
*** Current address: Northern Arizona University, Box 5100, Flagstaff, AZ 86011, USA

Send offprint requests to: W.W. Weiss

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© European Southern Observatory (ESO) 1998

Online publication: September 17, 1998
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