A study of the β Cephei star γ Pegasi: binarity, magnetic field, rotation, and pulsations^*

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 β Cep-type star γ Peg.

Methods.The observations were carried out in the 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 6678 line, the abnormally blueshifted radial velocities (γ = -60.57 ± 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_orb = 6.81608 ± 0.00012 day. The ratio = 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_rot = 6.6538 ± 0.0016 days. Both the orbital and the rotational periods are integral multiples of the difference between them: = 42.002, and = 41.002. Variation in the longitudinal magnetic field during the pulsation period with an amplitude about 7 G was detected.