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Issue A&A
Volume 469, Number 3, July III 2007
Page(s) 1069 - 1076
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20065563



A&A 469, 1069-1076 (2007)
DOI: 10.1051/0004-6361:20065563

A study of the $\beta$ Cephei star $\gamma$ Pegasi: binarity, magnetic field, rotation, and pulsations

V. V. Butkovskaya1 and S. I. Plachinda1, 2

1  Crimean Astrophysical Observatory, Nauchny, Crimea, 98409, Ukraine
    e-mail: varya@crao.crimea.ua
2  Institute for Astronomy, University of Vienna, Tuerkenschanzstrasse 17, 1180 Vienna, Austria

(Received 6 May 2006 / Accepted 2 April 2007)

Abstract
Aims.We provide observational material to study the magnetic field variability of the classical $\beta$ Cep-type star $\gamma$ Peg .
Methods.The observations were carried out in the $\ion{He}{i}$ 6678 line in the course of 23 observing nights from 1997 to 2005 with using the Coudé spectrograph in spectropolarimetric mode at the Crimean 2.6 m telescope. The behavior of stellar wind was studied in the UV region using data from the IUE satellite (the INES database).
Results.It is shown that the UV stellar wind exhibits a variability. A variation of the wind due to stellar pulsations has been detected. In the $\ion{He}{i}$ 6678 line, the abnormally blueshifted radial velocities ($\gamma$ = -60.57 $\pm$ 0.29 km s-1) were detected during a single night in 2005. We do not confirm the 370.5-day orbital period. The most probable orbital period was estimated as $P_{\rm orb}$ = 6.81608 $\pm$ 0.00012 day. The ratio $P_{\rm orb}/P_{\rm puls}$ = 44.92 appeared to be very close to integer. We have detected the presence of a weak magnetic field on the star. The longitudinal component of the field varies from -10 G to 30 G with the stellar rotation. The most probable rotational period is $P_{\rm rot}$ = 6.6538 $\pm$ 0.0016 days. Both the orbital and the rotational periods are integral multiples of the difference between them: $P_{\rm orb}/\vert P_{\rm orb} - P_{\rm rot}\vert$ = 42.002, and $P_{\rm rot}/\vert P_{\rm orb} - P_{\rm rot}\vert$ = 41.002. Variation in the longitudinal magnetic field during the pulsation period with an amplitude about 7 G was detected.


Key words: stars: magnetic fields -- stars: early-type -- stars: oscillations -- stars: binaries: spectroscopic -- stars: individual: $\gamma$ Pegasi



© ESO 2007

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