The early-type chemically peculiar stars often show strong magnetic fields on their surfaces. These magnetic topologies are organized on large scales and are believed to be close to an oblique dipole for most of the stars. In a striking exception to this general trend, the helium-strong star HD 37776 shows an extraordinary double-wave rotational modulation of the longitudinal magnetic field measurements, indicating a topologically complex and, possibly, record strong magnetic field. Here we present a new investigation of the magnetic field structure of HD 37776, using both simple geometrical interpretation of the longitudinal field curve and detailed modeling of the time-resolved circular polarization line profiles with the help of magnetic Doppler imaging technique. We derive a model of the magnetic field structure of HD 37776, which reconciles for the first time all magnetic observations available for this star. We find that the local surface field strength does not exceed ≈ 30 kG, while the overall field topology of HD 37776 is dominated by a non-axisymmetric component and represents by far the most complex magnetic field configuration found among early-type stars.

Spectropolarimetric observations of 96 chemically peculiar (CP) main‐sequence stars have been carried out at the 6‐m telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) with the aim of searching for the presence of stellar magnetic fields. The stars selected for investigation were CP stars known to have strong anomalies in the wavelength region of the continuum flux depression around λ 5200 Å. This selection was conducted with the aid of low‐resolution spectral observations, made with the SAO RAS 1‐m telescope, and of published differential photometric data. Magnetic fields have been successfully detected in 72 stars of which only three stars were previously known to have magnetic fields. For two stars, the longitudinal component of the magnetic field Be exceeds 5 kG: HD 178892 – 7.4 kG, and HD 258686 – 6.7 kG. We failed to reliably detect the magnetic field in the other 24 CP stars. These stars are mostly fast rotators, a feature which hampers accurate measurements of Be. It is demonstrated in this paper that selecting candidate magnetic stars by considering their photometric indices Z or Δa, or alternatively, by inspecting low‐resolution spectra around the λ 5200 Å flux depression, considerably increases the detection rate.

No abstract

No abstract

No abstract

Abstract. Starspots are usually associated with the action of magnetic fields at stellar surfaces. However, an inhomogeneous chemical distribution of mercury was found recently for the mercury-manganese (HgMn) star α And -a well-established member of a non-magnetic subclass of the chemically peculiar stars of the upper main sequence. In this study we present first results of the high-resolution survey of the Hg  3984 Å resonance line in the spectra of rapidly rotating HgMn stars with atmospheric parameters similar to those of α And. We use spectrum synthesis modelling and take advantage of the Doppler resolution of stellar surfaces to probe the horizontal structure of mercury distribution. Clear signatures of spots are found in the Hg  3984 Å line profiles of HR 1185 and HR 8723. Two observations of the latter star separated by two days give evidence for line profile variability. We conclude that inhomogeneous distribution of Hg is a common phenomenon for the rapidly rotating HgMn stars in the 13 000-13 800 K effective temperature range independent of the stellar evolutionary stage. These results establish the existence of a new class of spectrum variable spotted B-type stars. It is suggested that the observed Hg inhomogeneities arise from dynamical instabilities in the chemical diffusion processes and are unrelated to magnetic phenomena.

No abstract

We report a discovery of the Zeeman resolved spectral lines, corresponding to the extremely large magnetic field modulus B s = 17.5 kG, in the cool Ap star HD 178892. The mean longitudinal field of this star reaches 7.5 kG, and its rotational modulation implies the strength of the dipolar magnetic component B p ≥ 23 kG. We have revised rotation period of the star using the All Sky Automated Survey photometry and determined P = 8.2478 d. Rotation phases of the magnetic and photometric maxima of the star coincide with each other. We obtained Geneva photometric observation of HD 178892 and estimated T eff = 7700 ± 250 K using photometry and the hydrogen Balmer lines. Preliminary abundance analysis reveals abundance pattern typical of rapidly oscillating Ap stars.