We introduce a new polarimeter installed on the high-resolution fiber-fed echelle spectrograph (called BOES) of the 1.8-m telescope at the Bohyunsan Optical Astronomy Observatory, Korea. The instrument is intended to measure stellar magnetic fields with high-resolution (R ∼ 60000) spectropolarimetric observations of intrinsic polarization in spectral lines. In this paper we describe the spectropolarimeter and present test observations of the longitudinal magnetic fields in some well-studied F-B main sequence magnetic stars (m v < 8.8 m ). The results demonstrate that the instrument has a high precision ability of detecting the fields of these stars with typical accuracies ranged from about 2 to a few tens of gauss.Subject headings: Astronomical instrumentation: polarimetry -magnetic fields -stars: magnetic stars IntroductionThe presence of intrinsic linear and circular polarizations in spectra of stellar objects provides an important information for diagnostics of their magnetism, wind surroundings, atmospheric inhomogeneities and other properties. For example, non-zero continuum linear polarization due to Thomson and Rayleigh scattering demonstrates the presence of non-symmetric patterns in the distribution of atmospheric or wind medium. The broad-band circular polarization as well as circular and linear polarizations in spectral lines exhibit information on the magnetic fields. The spectropolarimetric observation is therefore one of the most important tools for the experimental studies of

Isolated cool white dwarf stars more often have strong magnetic fields than young, hotter white dwarfs, which has been a puzzle because magnetic fields are expected to decay with time but a cool surface suggests that the star is old. In addition, some white dwarfs with strong fields vary in brightness as they rotate, which has been variously attributed to surface brightness inhomogeneities similar to sunspots, chemical inhomogeneities and other magneto-optical effects. Here we describe optical observations of the brightness and magnetic field of the cool white dwarf WD 1953-011 taken over about eight years, and the results of an analysis of its surface temperature and magnetic field distribution. We find that the magnetic field suppresses atmospheric convection, leading to dark spots in the most magnetized areas. We also find that strong fields are sufficient to suppress convection over the entire surface in cool magnetic white dwarfs, which inhibits their cooling evolution relative to weakly magnetic and non-magnetic white dwarfs, making them appear younger than they truly are. This explains the long-standing mystery of why magnetic fields are more common amongst cool white dwarfs, and implies that the currently accepted ages of strongly magnetic white dwarfs are systematically too young.

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 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 He i 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 P orb /P 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 rot = 6.6538 ± 0.0016 days. Both the orbital and the rotational periods are integral multiples of the difference between them: P orb /|P orb − P rot | = 42.002, and P rot /|P orb − P rot | = 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: γ Pegasi IntroductionThe classical β Cep-type star γ Peg (HD 886, HR 39, Sp B2 IV) exhibits low-order purely radial pulsations. It has one of the weakest amplitude variations in radial velocity 2K = 7 km s −1 , light ∆m v = 0.017 with short pulsation period of 0.15 day, and de Jager et al. (1982) concluded that γ Peg has a virtually zero rotational velocity component; i.e., the star is seen rotation pole-on. pointed out a possibility that the γ-axis of the 0.15-day velocity curve of γ Peg varies. Harmanec et al. (1979) determined the 6.83-day period for the variations in the γ-axis and concluded that the star is a spectroscopic binary with a circular, slightly inclined orbit. Ducatel et al. (1981) also detected the day-to-day variations of the γ-axis, but they suggest that these variations are associated with stellar oscillations.According to analysis of high-resolution observations of this star that were carried out in a period from 1997 to 2005, Butkovskaya et al. (2006 concluded that γ Peg is a spectroscopic binary as suggested by Harmanec et al. (1979). Recently, Chapellier et al. (2006), combining their radial velocity measurements with data from the literature, confirmed the binarity of this star but with another orbital period of 370.5 days.The first attempt to detect a magnetic field on γ Peg was made by Babcock (1958). He found no evidence of a magnetic field in this sharp-line star. Rudy & Kemp (1978) measured theThe radial velocity data are only availabl...

Results of precision measurements of the net longitudinal component of magnetic Ðeld strength (B e ) performed for Procyon (a CMi, F5 IVÈV) and three solar-type starsÈb Com

Abstract. The complicated and intricate time-dependent behavior of the magnetic field of β Lyrae from 1980 to 2004 is discussed.