Bp stars in OrionOB1 association

A total of 85 CP stars of various types are identified among 814 members of the Orion OB1 association. We selected 59 Bp stars, which account for 13.4% of the total number of B type stars in the association. The fraction of peculiar B type stars in the association is found to be twice higher than that of peculiar A type stars. Magnetic field are found in 22 stars, 17 of them are objects with anomalous helium lines. No significant differences are found between the field strengths in the Bp type stars of the association and Bp type field stars. We identified 17 binaries, which make up 20% of the total number of peculiar stars studied which is the standard ratio for CP stars.Comment: Proceedings of IAUS 30

The extraordinary complex magnetic field of the helium-strong star HD 37776

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.Comment: 9 pages, 8 figures; accepted for publication in The Astrophysical Journa

Spectropolarimetry of Magnetic Chemically Peculiar Stars in the Orion OB1 Association

We summarise the results of a spectropolarimetric survey of 56 chemically peculiar (CP) stars in the association of Orion OB1. We uniformly collected the observational material with the 6-m telescope BTA of the Special Astrophysical Observatory in 2013-2021. We identify 14 new magnetic CP stars with a longitudinal magnetic field exceeding approximately 500 G. The studied sample contains 31 magnetic stars or 55% of the whole CP population in Orion OB1. We show that the percentage of the magnetic CP stars and the field strength drops sharply with age. The mean longitudinal magnetic field in the young subgroup OB1b ($\log t=6.23$) is confidently almost three times stronger than in the older subgroups OB1a ($\log t=7.05$) and OB1c ($\log t=6.66$). In the Orion Nebula, a place with the youngest stellar population ($\log t < 6.0$), we detect the magnetic field only in 20% of CP stars. Such occurrence drastically differs from 83% of magnetic CP stars in the nearby subgroup OB1c. We consider this effect an observational bias caused by a significant portion of a very young population with the signatures of Herbig Ae/Be stars. The technique we used for magnetic measurements, and the quality of available data do not allow us to detect weak fields in the case of stars with a limited number of lines and emissions in spectra.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journal. Contains 14 pages, 11 figure

Studies of Magnetic Chemically Peculiar Stars Using the 6-m Telescope at SAO RAS

We present a survey of the most important results obtained in observations with the 6-m telescope in the studies of magnetic fields of chemically peculiar stars. It is shown that we have found more than 200 new magnetic chemically peculiar stars, which is more than 30% of their total known number. Observations of ultra-slow rotators (stars with rotation periods of years and decades) have shown that there are objects with strong fields among them, several kG in magnitude. In the association of young stars in Orion, it has been found that the occurrence and strength of magnetic fields of chemically peculiar stars decrease sharply with age in the interval from 2 to 10 Myr. These data indicate the fossil nature of magnetic fields of chemically peculiar stars. About 10 magnetic stars were found based on ultra-accurate photometry data obtained from the Kepler and TESS satellites. A new effective method of searching for magnetic stars was developed. In addition, the exact rotation periods make it possible to build reliable curves of the longitudinal field component variability with the phase of the star’s rotation period, and hence to create its magnetic model. The survey is dedicated to the memory of Prof. Yuri Nikolaevich Gnedin

Studies of Magnetic Chemically Peculiar Stars Using the 6-m Telescope at SAO RAS

We present a survey of the most important results obtained in observations with the 6-m telescope in the studies of magnetic fields of chemically peculiar stars. It is shown that we have found more than 200 new magnetic chemically peculiar stars, which is more than 30% of their total known number. Observations of ultra-slow rotators (stars with rotation periods of years and decades) have shown that there are objects with strong fields among them, several kG in magnitude. In the association of young stars in Orion, it has been found that the occurrence and strength of magnetic fields of chemically peculiar stars decrease sharply with age in the interval from 2 to 10 Myr. These data indicate the fossil nature of magnetic fields of chemically peculiar stars. About 10 magnetic stars were found based on ultra-accurate photometry data obtained from the Kepler and TESS satellites. A new effective method of searching for magnetic stars was developed. In addition, the exact rotation periods make it possible to build reliable curves of the longitudinal field component variability with the phase of the star’s rotation period, and hence to create its magnetic model. The survey is dedicated to the memory of Prof. Yuri Nikolaevich Gnedin.</jats:p

Magnetic Doppler imaging of early-type stars

Doppler imaging of early-type magnetic stars is the most advanced method to interpret their line profile variations. DI allows us to study directly a complex interplay between chemical spots, magnetic fields, and the mass loss. Here we outline the general principles of the surface mapping of stars, discuss adaption of this technique to early-type stars and present several recent examples of the abundance and magnetic mapping performed for rapidly rotating early-B stars. In particular, we present the first Doppler images for the very fast rotating He-rich star HR 7355 and a reconstruction of magnetic field for the well-known Bp star a On E. We also present new magnetic maps for the He-strong star HD 37776, which possesses one of the most complex magnetic field topologies among the upper main sequence stars.</p