β Lyrae: on the magnetic field

β Lyrae shows a complicated and intricate time-dependent behaviour of the magnetic field

A study of the photometric variability of the peculiar magnetic white dwarf WD1953-011

We present and interpret simultaneous new photometric and spectroscopic observations of the peculiar magnetic white dwarf WD1953-011. The flux in the V-band filter and intensity of the Balmer spectral lines demonstrate variability with the rotation period of about 1.45 days. According to previous studies, this variability can be explained by the presence of a dark spot having a magnetic nature, analogous to a sunspot. Motivated by this idea, we examine possible physical relationships between the suggested dark spot and the strong-field magnetic structure (magnetic "spot", or "tube") recently identified on the surface of this star. Comparing the rotationally-modulated flux with the variable spectral observables related to the magnetic "spot" we establish their correlation, and therefore their physical relationship. Modeling the variable photometric flux assuming that it is associated with temperature variations in the stellar photosphere, we argue that the strong-field area and dark, low-temperature spot are comparable in size and located at the same latitudes, essentially overlapping each other with a possible slight longitudinal shift. In this paper we also present a new, improved value of the star's rotational period and constrain the characteristics of the thermal inhomogeneity over the degenerate's surface.Comment: accepted to the Ap

Spectroscopic observations of the exoplanet WASP-32b transit

© 2017, Pleiades Publishing, Ltd.We present first results of spectroscopic observations of transiting exoplanets in the Special Astrophysical Observatory of the Russian Academy of Sciences with the Main Stellar Spectrograph of the 6-m BTA telescope. For the exoplanetWASP-32b, we detected a significant variation of intensity and equivalent width in the Hα spectral line of the parent star at the time of a transit. The equivalent width of the line during transit is by 8–10% larger than outside the planet passage. Residual intensity in the core of the line reveals the following tendency: the line is by 10–15% deeper inside transit than outside it. Observations with the long-slit spectrograph of the Crimean Astrophysical Observatory at the 2.6-m ZTSh telescope also showed a transit event in the Hα line, although, with a smaller amplitude and shape inverted in relation to the data from the 6-m telescope. While in the observations with the BTA the Hα line becomes deeper during the transit, in the ZTSh observations, the residual intensity of the Hα line decreases during the transit. Reducing and analysis of the archive data of WASP-32b observations with the HARPS spectrograph also confirm the Hα line modulation at the time of the transit. The observed data give evidence of the envelope in WASP-32b filling the Roche lobe and a comet-like tail of changing geometry and orientation relative to the observer. These changes determine different depths and shapes of the Hα spectral line at the time of transits

Large-scale magnetic field of the G8 dwarf xi Bootis A

We investigate the magnetic geometry of the active G8 dwarf xi Bootis A, from spectropolarimetric observations obtained in 2003 with the MuSiCoS echelle spectropolarimeter at the Telescope Bernard Lyot (Observatoire du Pic du Midi, France). We repeatedly detect a photospheric magnetic field, with periodic variations consistent with rotational modulation. Circularly polarized (Stokes V) line profiles present a systematic asymmetry, showing up as an excess in amplitude and area of the blue lobe of the profiles. A direct modeling of Stokes V profiles suggests that the global magnetic field is composed of two main components, with an inclined dipole and a large-scale toroidal field. We derive a dipole intensity of about 40 G, with an inclination of 35 degrees of the dipole with respect to the rotation axis. The toroidal field strength is of order of 120 G. A noticeable evolution of the field geometry is observed over the 40 nights of our observing window and results in an increase of the field strength and of the dipole inclination. This study is the first step of a long-term monitoring of xi Bootis A and other active solar-type stars, with the aim to investigate secular fluctuations of stellar magnetic geometries induced by activity cycles.Comment: accepted by MNRA

PROBE OF THE MAGNETIC FIELD IN THE HOT SUPERGIANT ζ Per

At the surface of ∼7% of single hotstars stable mainly dipolar strong magnetic fields havebeen detected. The main hypothesis today is thatthese magnetic fields are of fossil origin. In otherwords, these fields formed from the seed field in themolecular clouds from which the stars were formed.The recent observational and theoretical results confi-rm this theory: the properties of the observed fieldscorrespond to those expected from fossil fields. Massi-ve stars are stars whose initial mass exceeds about8 solar masses. Massive stars play a significant rolein the chemical and dynamical evolution of galaxies.However, much of their variability, particularly duringtheir evolved supergiant stage, is poorly understood.To date magnetic field was registered only at three hotstars of I-II luminosity types: ρ Leo (B1 Ib), ζ OriAa (O9.2 Ib), and ? CMa (B1.5 II). We performedhigh-accuracy spectropolarimetric observation of thehot supergiant ζ Per (B1 Ib) over 26 nights from 1997to 2012 with long-slit spectrograph mounted in thecoude focus of 2.6-m reflector ZTSh at the CrimeanAstrophysical Observatory. We also used circularlypolarized spectra obtained during 2 nights in 2008 wi-th echelle spectrograph ESPADONS mounted at 3.6-m CFHT. Effective magnetic field B e (longitudinalcomponent of the field integrated over visible hemi-sphere) of ζ Per was calculated in the line He I 6678.149 A. Statistically significant longitudinal magnetic field(B e /σ B > 3) was registered in 14 from 199 singlemeasurements. These significant magnetic field valuesare all in the range from −145 to +148 G with themean error 27 G. We suppose the supergiant ζ Per canbe magnetic, but its magnetic field properties is diffi-cult to detect likely due to the insufficient precision ofthe used spectropolarimetric measurements comparedto the expected field strength