Yu. V. Glagolevskij

Magnetic field structures in chemically peculiar stars

We report the results of magnetic field modelling of around 50 CP stars, performed using the “magnetic charges” technique. The modelling shows that the sample reveals four main types of magnetic configurations: 1) a central dipole, 2) a dipole, shifted along the axis, 3) a dipole, shifted across the axis, and 4) complex structures. The vast majority of stars has the field structure of a dipole, shifted from the center of the star. This shift can have any direction, both along and across the axis. A small percentage of stars possess field structures, formed by two or more dipoles.

Evolution of the Magnetic Fields of Main-Sequence CP-Stars. IV

A possible scenario is proposed for the origin and evolution of magnetic stars based on the observational data accumulated up to now. The large difference in magnetic structures and the predominant orientation of the magnetic dipoles are explained, along with the mechanism by which 10% of the magnetic stars differ from normal. A reason is discovered for the slow axial rotation of the stars and a cause is found for the absence of strong magnetic fields in Ae/Be Herbig stars.

Magnetic configurations of the fast CP rotators HD3360, HD4778, HD5737, HD112413, and HD215441

The method of “magnetic charges” is used to model magnetic fields of five rapidly rotating stars (P < 25d) and to find the basic parameters of their magnetic fields. A table containing all the modeling results obtained using the adopted method as well as the parameters obtained for the same stars by other authors is presented. Significant discrepances are found in a number of cases, which can apparently be explained by insufficient accuracy of the estimated inclinations of the stars to the line of sight.

Complex structure of the magnetic field of the CP star HD32633

The method of “virtual magnetic charges” is used to analyze the structure of the magnetic field of the CP star HD32633. The phase relation of its magnetic field differs strongly from a sine wave. The structure of the star’s field can be described fairly well by two dipoles located in the opposite regions of the star near its rotation equator. Each of these dipoles produces two pairs of magnetic spots of opposite polarity similar to sunspots. The dipoles are located at a distance of Δa=0.6 R from the center, where R is the radius of the star. The field strength at the poles is equal to ±42 and ±19 kG.

The atmospheres of helium-deficient Bp stars

Based on spectra taken with a 6-m telescope, we analyzed the abundances of chemical elements in the He-weak stars HD 21699 and HD 217833, estimated their surface magnetic fields (Bs = 4000 and 4500 G, respectively) from the magnetic intensification of spectral lines, and determined their microturbulences (Vt = 0.80 and 0.75 km s−1, respectively). The low values of Vt show that the stellar atmospheres are stabilized by a magnetic field, which explains the presence of diffusion processes that lead to chemical anomalies. Helium is strongly underabundant, and its deficiency is −1.50 and −1.81 dex in HD 21699 and HD 217833, respectively. We used model atmospheres to determine the effective temperatures, Teff = 16 000 and 15 450 K, and surface gravities, log g = 4.15 and 3.88, for the stars from the Hδ line, implying that they lie on the main sequence near the stars of luminosity class V.

Magnetic field models of nine CP stars from “accurate” measurements

The dipole models of magnetic fields in nine CP stars are constructed based on the measurements of metal lines taken from the literature, and performed by the LSD method with an accuracy of 10–80 G. The model parameters are compared with the parameters obtained for the same stars from the hydrogen line measurements. For six out of nine stars the same type of structure was obtained. Some parameters, such as the field strength at the poles Bp and the average surface magnetic field Bs differ considerably in some stars due to differences in the amplitudes of phase dependences Be(Φ) and Bs(Φ), obtained by different authors. It is noted that a significant increase in the measurement accuracy has little effect on the modelling of the large-scale structures of the field. By contrast, it is more important to construct the shape of the phase dependence based on a fairly large number of field measurements, evenly distributed by the rotation period phases. It is concluded that the Zeeman component measurement methods have a strong effect on the shape of the phase dependence, and that the measurements of the magnetic field based on the lines of hydrogen are more preferable for modelling the large-scale structures of the field.

Spot system and stratification of some chemical elements in the atmosphere of He-weak star HD 21699

Surface helium and silicon distribution of a He-weak CP star HD21699 was examined using the spectra obtained at different phases of the star’s rotational period. The abundance of helium over the whole surface is weak, but in the magnetic polar regions it is strong, apparently due to the impact of stellar wind. Silicon accumulates in the region with a horizontal alignment of the magnetic lines, as follows from the theory. The abundance of helium and silicon increases with depth. Moreover, the boundary of the abundance variation is very sharp and its depth practically does not change with the rotational period phase. Accounting for the stratification of chemical elements considerably changes the deduced temperature distribution with depth as well as the form of the hydrogen line profile.

Magnetic field models of CP stars. II: HD11503, HD12098, HD12447, HD14437, HD34452, HD40312, HD178892

We model magnetic fields of seven magnetic stars using a program for studying the structure of magnetic fields in CP stars. It appears that five of them clearly manifest the structure of a central dipole, and the remaining two can be explained by a shifted dipole model. Our previous research and the results of this study demonstrate that the dipole orientation inside the stars relative to the rotation axis can vary from 0° to 90°, both for fast and slow rotators. We can not yet solve the question of the existence of a dominant orientation due to lack of statistics. Our modeling results are consistent with those calculated using Preston’s technique in the case of a dipole field configuration.

Magnetic-field dependence of chemical anomalies in CP stars

The dependence of the degree of anomaly of parameter Z of Geneva photometry (Z0 = ZCPℒZnorm.) on the average surface magnetic field Bs is analyzed. The Z0 value is proportional to the degree of anomaly of chemical composition. It was found that Bs → 0 corresponds Z0 → −0.010÷ −0.015, i.e., part of CP stars are virtually devoid of magnetic field, but exhibit chemical anomalies. This effect may be due to selection whereby only objects with strong chemical anomalies are classified as CP stars, thereby producing a deficit of stars with relatively weak anomalies. Moreover, CP stars have other sources of stabilization of their atmospheres besides the magnetic field, e.g., slow rotation. Formulas relating Z0 to Bs are derived.

General properties of magnetic CP stars

We present the review of our previous studies related to observational evidence of the fossil field hypothesis of formation and evolution of magnetic and non-magnetic chemically peculiar stars. Analysis of the observed data shows that these stars acquire their main properties in the process of gravitational collapse. In the non-stationary Hayashi phase, a magnetic field becomes weakened and its configuration complicated, but the fossil field global orientation remains. After a non-stationary phase, relaxation of young star’s tangled field takes place and by the time of joining ZAMS (Zero Age Main Sequence) it is generally restored to a dipole structure. Stability of dipole structures allows them to remain unchanged up to the end of their life on the Main Sequence which is 109 years at most.