Statistics of magnetic field measurements in OBA stars and the evolution of their magnetic fields

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim We review the measurements of magnetic fields of OBA stars. Based on these data, we confirm that magnetic fields are distributed according to a lognormal law with mean log B = − 0.5 (B in kG) with a standard deviation σ = 0.5. The shape of the magnetic field distribution (MFD) is similar to that for neutron stars. This finding favors the hypothesis that the magnetic field of a neutron star is determined mainly by the magnetic field of its predecessor, namely the massive OB star. Further, we model the evolution of an ensemble of magnetic massive stars in the Galaxy. We use our own population synthesis code to obtain the distribution of stellar radii, ages, masses, temperatures, effective magnetic fields, and magnetic fluxes from the pre-main-sequence (PMS) via zero-age main sequence (ZAMS) up to the terminal-age main sequence stages. A comparison of the MFD obtained in our model with that obtained from the recent measurements of the stellar magnetic field allows us to conclude that the evolution of magnetic fields of massive stars is slow if not absent. The shape of the real MFD shows no indications of the magnetic desert proposed previously. Based on this finding, we argue that the observed fraction of magnetic stars is determined by physical conditions at the PMS stage of stellar evolution

Statistics of Magnetic Fields for OB Stars

Based on an analysis of the catalog of magnetic fields, we have investigated the statistical properties of the mean magnetic fields for OB stars. We show that the mean effective magnetic field ${\cal B}$ of a star can be used as a statistically significant characteristic of its magnetic field. No correlation has been found between the mean magnetic field strength ${\cal B}$ and projected rotational velocity of OB stars, which is consistent with the hypothesis about a fossil origin of the magnetic field. We have constructed the magnetic field distribution function for B stars, $F({\cal B})$, that has a power-law dependence on ${\cal B}$ with an exponent of $\approx -1.82$. We have found a sharp decrease in the function $F({\cal B})$F for {\cal B}\lem 400 G that may be related to rapid dissipation of weak stellar surface magnetic fields.Comment: 22 pages, 7 figures, accepted Astronomy Letters, 2010, vol.36, No.5, pp.370-379, contact E-mail: [email protected]

Comprehensive study of the magnetic stars HD 5797 and HD 40711 with large chromium and iron overabundances

We present the results of a comprehensive study of the chemically peculiar stars HD 5797 and HD 40711. The stars have the same effective temperature, Teff = 8900 K, and a similar chemical composition with large iron (+1.5 dex) and chromium (+3 dex) overabundances compared to the Sun. The overabundance of rare-earth elements typically reaches +3 dex. We have measured the magnetic field of HD 5797. The longitudinal field component Be has been found to vary sinusoidally between -100 and +1000 G with a period of 69 days. Our estimate of the evolutionary status of the stars suggests that HD 5797 and HD 40711, old objects with an age t \approx 5 \times 108 yr, are near the end of the core hydrogen burning phase.Comment: 26 pages, 5 Encapsulated Postscript figure

ADAPTIVE MODE OF THE MSS BTA

The study of instability of the Main stellar spectrograph of the 6-m Telescope together with system of registration of a spectrum by means of the CCD shows that there is a drift of a spectrum along a dispersion, corresponding to the tenth of a pixel (the hundredth part of Α) in an hour. To eliminate this drift, i.e. to keep a spectrum from displacement, the plane-parallel glass plate was installed behind a slit of the spectrograph. The angle of inclination of this plate changes depending on a mismatch of positions of the current and comparison basic spectra. A lamp of hollow cathode is used. The scheme of this device is described. The results of tests are presented. The time of correction takes about one minute that allows to keep the position of the ThAr spectrum within +-0.0006 Α.The study of instability of the Main stellar spectrograph of the 6-m Telescope together with system of registration of a spectrum by means of the CCD shows that there is a drift of a spectrum along a dispersion, corresponding to the tenth of a pixel (the hundredth part of Α) in an hour. To eliminate this drift, i.e. to keep a spectrum from displacement, the plane-parallel glass plate was installed behind a slit of the spectrograph. The angle of inclination of this plate changes depending on a mismatch of positions of the current and comparison basic spectra. A lamp of hollow cathode is used. The scheme of this device is described. The results of tests are presented. The time of correction takes about one minute that allows to keep the position of the ThAr spectrum within +-0.0006 Α