Magnetic field models of CP stars HD18296, HD19832, HD22470, HD24712

We model the magnetic fields of four magnetic stars using published longitudinal (Be) field measurements. The structure of the magnetic field of each of the four stars is close to that of the central dipole. Unfortunately, the number of measurements for each star is insufficient for accurate finding of the field parameters, and therefore we find no dipole shift exceeding its error Δa ≈ 0.1, expressed as a fraction of the stellar radius. Our data support the opinion that the results of modeling depend most strongly on the adopted inclination of the star’s rotation axis i.     

Magnetic field of CP stars in the Ori OB1 association. II. HD36540, HD36668, HD36916, HD37058

We present the results of magnetic field measurements of four chemically peculiar (CP) stars with helium abundance anomalies which are the members of the Orion stellar association OB1. The stars under study were classified as magnetic by other authors earlier. The present paper contains the results of the extensive study of the stars. Magnetic field measurements allowed us to conclude that HD36540 has a weak field and the longitudinal component B _e does not exceed 500 G. The longitudinal field of HD36668 varies with the period P = 2_. ^d 11884 and the amplitude from ?2 to +2 kG. The magnetic field of HD36916 has mainly negative polarity and varies within the range from 0 to ?1 kG with the period P = 1.d 565238. HD37058 is a magnetic star, the longitudinal field of which varies from ?1.2 to +0.8 kG with the period P = 14_. ^d 659. The B _e field variability pattern for the stars HD36916 and HD37058 is of a simple harmonic type. The longitudinal field of HD36668 is best described with two combined harmonic functions (“a doublewave”). The variability period of HD36540 is still undetermined. For all the stars from this paper, we measured radial velocities V _r, axial rotation rates v _e sin i, and determined basic parameters of atmospheres (effective temperatures T _eff and gravity acceleration log g). We also estimated masses M, luminosities L, and radii R of the stars.     

Chemical composition of the He-w stars HD 37058, 212454, and 224926

Our spectrophotometric analysis of the atmospheres of HD 37058, HD 212454, and HD 224926 shows these objects to be typical He-w stars with close-to-zero microturbulence velocities, very different magnetic fields, and wide scatter of chemical anomalies. However, one of the main manifestations of separation is that helium moves from the outer layers of the atmosphere into the star’s interior.Our analysis of the stars HD 212454 and 224926 with Be<100 G shows that despite their weak magnetic fields they have the same degree of chemical anomaly as highly magnetized stars. Chemical composition varies over a wide range for stars with the same magnitude of magnetic field. We find the conditions in the temperature interval 13000–16000 K to be the most favorable for the formation of He-w type stars. Helium underabundance is the strongest near the maximum of the distribution and it is observed in stars with weak as well as strong fields. Because of the scatter mentioned above the degree of chemical anomalies is not strictly related to the magnitude of the magnetic field, although the field has an appreciable effect on the formation of chemical inhomogeneities at the star’s surface. Its influence is minimal in stars with very weak magnetic fields and the presence of strong chemical anomalies indicates that microturbulence in these stars is sufficiently weak even without the effect of the magnetic field. It is plausible to assume that the anomalies arise due to slow rotation.The temperature dependences of rotation velocity vsini for stars with weak magnetic fields show no apparent trends associated with the magnitude of magnetic field. The rotation velocities vsini of almost all stars are lower than those of normal stars, except for HD 131120, 142096, 142990, and 143669, which rotate with the same velocity or even faster than normal stars. These objects do not obey the general rule and their example shows that stable atmospheres can also be found among fast rotators and that magnetic field takes no part in the spin-down of CP stars. We believe that CP stars inherited their slow rotation from protostellar clouds.     

Magnetic Models of HD 115708 and HD 119419

The magnetic fields of the chemically peculiar stars HD 115708 and HD 119419 were modeled using observed curves of variation of the magnetic field with the phase of the rotational period. It turned out that the field of HD 115708 is described, in a first approximation, by a central dipole, while the field of HD 119419 is described by an off-center dipole. The main parameters of the magnetic fields of both stars and maps of the surface field-strength distribution were obtained. The dipole axis of the first star lies in the equatorial plane while that of the second is almost parallel to the axis of rotation.     

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 and chemical composition of the peculiar star HD 10221

We analyzed the chemical composition of the chemically peculiar (CP) star HD 0221=43 Cas using spectra taken with the NES spectrograph of the 6-m telescope with a spectral resolution of 45 000. The Hβ line profile corresponds most closely to T_eff = 11 900 K and log g = 3.9. The rotational velocity is v_e sin i = 27 ± 2 km s^?1, and the microturbulence is ξ_t = 1 km s^?1. The results of our abundance determination by the method of synthetic spectra show that the star has chemical anomalies typical of SrCrEu stars, although its effective magnetic field is weak, B_e < 100 G. For silicon, we obtained an abundance distribution in atmospheric depth with a sharp jump of 1.5 dex at an optical depth of log τ₅₀₀₀ = ?0.3 and with silicon concentration in deep atmospheric layers. Similar distributions were found in the atmospheres of cooler stars with strong and weak magnetic fields. A comparison of the chemical peculiarities in HD 10221 with known CP stars with magnetic fields of various strengths leads us to conclude that a low rotational velocity rather than amagnetic field is the determining factor in the formation mechanism of chemical anomalies in the atmospheres of CP stars.     

Magnetic field of CP stars in the Ori OB1 association. I. HD35456, HD35881, HD36313 A,HD36526

We present the results of magnetic field measurements of four chemically peculiar (CP) stars, the members of the Orion stellar association OB1. Observations were carried out with the circular polarization analyzer at the Main Stellar Spectrograph of the 6-m telescope. All the studied stars refer to the subtype of Bp stars with weak helium lines. Canadian astronomer E. F. Borra detected a magnetic field in three of them (HD35456, HD36313, and HD36526) from the Balmer line magnetometer observations. HD35881 was observed for the first time for the purpose to search for a magnetic field. We obtained the following results: HD35456 is a magnetic star with longitudinal field variation range from +300 to +650 G and a period of 4.9506 days; HD35881 is possible a new magnetic star, the longitudinal component of which varies from?1 to +1 kGwith a period of 0.6998 days, however, a small number of lines broadened by rotation does not allow us to conduct measurements more accurately; HD36313 is a binary star with the components similar in brightness, the primary component is a magnetic star with broad lines, the magnetic field of the secondary component (the star with narrow lines) was not detected. Measurements in the Hβ hydrogen line showed the variations of the longitudinal component from ?1.5 to +2 kG with a period of 1.17862 days; a strong longitudinal field was detected in HD36526 (from 0 to +3000 G) varying with a rotation period of the star of 3.081 days. In all the cases, we observe considerable discrepancies with the data on magnetic fields of these objects obtained earlier.     

The exceptional Herbig Ae star HD 101412: The first detection of resolved magnetically split lines and the presence of chemical spots in a Herbig star

In our previous search for magnetic fields in Herbig Ae stars, we pointed out that HD 101412 possesses the strongest magnetic field among the Herbig Ae stars and hence is of special interest for follow‐up studies of magnetism among young pre‐main‐sequence stars. We obtained high‐resolution, high signal‐to‐noise UVES and a few lower quality HARPS spectra revealing the presence of resolved magnetically split lines. HD 101412 is the first Herbig Ae star for which the rotational Doppler effect was found to be small in comparison to the magnetic splitting and several spectral lines observed in unpolarized light at high dispersion are resolved into magnetically split components. The measured mean magnetic field modulus varies from 2.5 to 3.5kG, while the mean quadratic field was found to vary in the range of 3.5 to 4.8 kG. To determine the period of variations, we used radial velocity, equivalent width, line width, and line asymmetry measurements of variable spectral lines of several elements, as well as magnetic field measurements. The period determination was done using the Lomb‐Scargle method. The most pronounced variability was detected for spectral lines of He I and the iron peak elements, whereas the spectral lines of CNO elements are only slightly variable. From spectral variations and magnetic field measurements we derived a potential rotation period P_rot = 13.86 d, which has to be proven in future studies with a larger number of observations. It is the first time that the presence of element spots is detected on the surface of a Herbig Ae/Be star. Our previous study of Herbig Ae stars revealed a trend towards stronger magnetic fields for younger Herbig Ae stars, confirmed by statistical tests. This is in contrast to a few other (non‐statistical) studies claiming that magnetic Herbig Ae stars are progenitors of the magnetic Ap stars. New developments in MHD theory show that the measured magnetic field strengths are compatible with a current‐driven instability of toroidal fields generated by differential rotation in the stellar interior. This explanation for magnetic intermediate‐mass stars could be an alternative to a frozen‐in fossil field (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnetic,chemically peculiar (CP2) stars in the SuperWASP survey

The magnetic chemically peculiar (CP2) stars of the upper main sequence are well‐suited for investigating the impact of magnetic fields on the surface layers of stars, which leads to abundance inhomogeneities (spots) resulting in photometric variability. The light changes are explained in terms of the oblique rotator model; the derived photometric periods thus correlate with the rotational periods of the stars. CP2 stars exhibiting this kind of variability are classified as α² Canum Venaticorum (ACV) variables. We have analysed around 3850000 individual photometric WASP measurements of magnetic chemically peculiar (CP2) stars and candidates selected from the catalogue of Ap, HgMn, and Am stars, with the ultimate goal of detecting new ACV variables. In total, we found 80 variables, from which 74 are reported here for the first time. The data allowed us to establish variability for 23 stars which had been reported as probably constant in the literature before. Light curve parameters were obtained for all stars by a least‐squares fit with the fundamental sine wave and its first harmonic. Because of the scarcity of Strömgren uvbyβ measurements and the lack of parallax measurements with an accuracy better than 20%, we are not able to give reliable astro‐physical parameters for the investigated objects. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Lichtelektrische Untersuchungen der vier Ap-Sterne HD 9531, HD 10221, HD 27309 und HD 184905

The lightcurves in the UBV system are given for the four Ap stars HD 9531, HD 10221, HD 27309 and HD 184905 from 1968 to 1971. The measurements are represented by the periods o^d.6684, 3^d.16, 2^d.7098 and 1^d.845031 respectively.     

Rotating superdense configurations: pulsars and their astrophysical manifestations

This paper is a discussion of some results from papers by followers of V. A. Ambartsumyan, whose fundamental articles serve as the beginning of research on superdense stars: white dwarfs and neutron stars. Solutions of the Einstein equations are given for the case of axial symmetry and are used to determine the integral parameters of rotating neutron stars and white dwarfs. A theory of magnetic field generation in neutron stars has been developed and is consistent with the existence of high, nonuniform magnetic fields on the order of 10¹⁴ G in pulsars. A theory has been proposed for the dynamics of neutron vortices and used to explain the observed relaxation of the angular velocity of pulsars following glitches.     

Magnetic field model for slowly rotating CP-stars. γEqu= HD201601

A magnetic field model is constructed for the extremely slow rotator γEqu based on measurements of its magnetic field over many years and using the “magnetic charge” method. An analysis of γEqu and of all the data accumulated up to the present on the magnetic field parameters of chemically peculiar stars leads to some interesting conclusions, of which the main ones are: the fact that the axis of rotation and the dipole axis are not parallel in γEqu and the other slowly rotating magnetic stars which we have studied previously is one of the signs that the braking of CP stars does not involve the participation of the magnetic field as they evolve “to the main sequence.” The axes of the magnetic field dipole in slow rotators are oriented arbitrarily with respect to their axes of rotation. The substantial photometric activity of these CP stars also argues against these axes being close. The well-known absence of sufficiently strong magnetic fields in the Ae/Be Herbig stars also presents difficulties for the hypothesis of “magnetic braking” in the “pre-main sequence” stages of evolution. The inverse relation between the average surface magnetic field Bs and the rotation period P is yet another fact in conflict with the idea that the magnetic field is involved in the braking of CP stars. We believe that angular momentum loss involving the magnetic field can hardly have taken place during evolution immediately prior “to the main sequence,” rather the slow rotation of CP stars most likely originates from protostellar clouds with low angular momentum. Some of the slowly rotating stars have a central dipole magnetic field configuration, while others have a displaced dipole configuration, where the displacement can be toward the positive or the negative magnetic pole. __________ Translated from Astrofizika, Vol. 49, No. 2, pp. 251–262 (May 2006).     

The delta scuti-star HD 220392: a possible component of a binary system

Physical parameters and distances are determined for the stars HD 220391 and HD 220392, which possibly form a physical pair. Ages and evolutionary masses in the new track system of Schalleret al. (1992) as well as gravitational masses of both stars are evaluated. Distance and age estimates of this possible binary system are obtained: 128(±12) pc and 7.9(±0.8) × 10⁸ yr. Both stars are located within the Delta Scuti instability strip on the H-R diagram, but a variability was only detected in HD 220392 by Lampens (1992). The pulsation mode(s) and the pulsation mass of this variable star cannot be determined at the present time.     

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 B _p and the average surface magnetic field B _s differ considerably in some stars due to differences in the amplitudes of phase dependences B _e (Φ) and B _s (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.     

Magnetic fields at the surfaces of stars

Summary Magnetic fields have now been detected in stars in several parts of the Hertzsprung-Russell diagram. Roughly dipolar fields ranging in strength between 3× 10² and 3×10⁴ G are found in many chemically peculiar A and B main sequence stars. Dipolar fields are also found in some 2–3% of white dwarfs, but with strengths between 1×10⁶ and 5×10⁸ G. In both these types of stars, the observed fields vary as the underlying star turns, but do not change in a secular manner. In solartype stars, structurally complex fields of a few kG are found with filling factors of the order of 0.1 to 0.8. Further indirect evidence of fields in cool main sequence stars is provided by detection of visible and ultraviolet line emission (chromospheric activity), x radiation (coronal matter), and giant starspots. In this review, we survey the observations of stellar magnetism in all these types of stars, as well as efforts to model the observed magnetic fields and associated photospheric peculiarities and activity.This article was processed by the author using the Springer-Verlag T_EX AAR macro package 1991.     

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, T _eff = 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 B _e 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 ≈ 5 × 10⁸ yr, are near the end of the core hydrogen burning phase.     

Magnetic fields of chemically peculiar stars. II: Magnetic fields and rotation of stars with strong and weak anomalies in the continuum energy distribution

We make a comparative analysis of magnetic fields and rotation parameters of magnetic CP stars with strong and weak anomalies in the spectral energy distribution. Stars with strong depressions in the continuum at 5200 Å are shown to have significantly stronger fields (the mean longitudinal component of the fields of these stars is 〈B _e〉 = 1341 ± 98 G) compared to objects with weaker depressions (〈B _e〉 = 645 ± 58 G). Stars with stronger depressions are also found to occur more commonly among slow rotators. Their rotation periods are, on the average, about 10 days long, three times longer than these of stars with weak depressions (about three days). This fact is indicative of a decrease of the degree of anomality of the magnetic stars continuum spectrum with increasing rotational velocity. Yet another proof has been obtained suggesting that slow rotation is one of the crucial factors contributing to the development of the phenomenon of magnetic chemically peculiar stars.Magnetic CP stars with weak depressions at 5200 Å are intermediate objects between stars with strong depressions and normal A- and B-type stars both in terms of field strength and rotational velocity.     

Spectroscopic study of the weak magnetic star HD220825-κPsc

The star HD220825 is studied as part of a program to investigate the chemical abundance of CP stars with weak magnetic fields. Its magnetic field is found to be Be < 100 G. The chemical abundance appears to correspond to that of CP stars with high magnetic fields. The present results and other data imply that the magnetic field has little effect on the degree of anomaly in the chemical abundance, although it undoubtedly has an effect. The rotation speed of the star is 37.5 km/s, substantially lower than for normal stars with the same temperature. The weak magnetic field raises difficulties for the hypothesis that the loss of angular momentum involves the magnetic field. __________ Translated from Astrofizika, Vol. 49, No. 4, pp. 585–594 (November 2006).     

The kinematic characteristics of magnetic O‐type stars

Although magnetic fields have been discovered in ten massive O‐type stars during the last years, the origin of their magnetic fields remains unknown. Among the magnetic O‐type stars, two stars, HD 36879 and HD 57682, were identified as candidate runaway stars in the past, and θ¹ Ori C was reported to move rapidly away from its host cluster. We search for an explanation for the occurrence of magnetic fields in O‐type stars by examining the assumption of their runaway status. We use the currently best available astrometric, spectroscopic, and photometric data to calculate the kinematical status of seven magnetic O‐type stars with previously unknown space velocities. The results of the calculations of space velocities suggest that five out of the seven magnetic O‐type stars can be considered as candidate runaway stars. Only two stars, HD 155806 and HD 164794, with the lowest space velocities, are likely members of Sco OB4 and NGC 6530, respectively. However, the non‐thermal radio emitter HD 164794 is a binary system with colliding winds, for which the detected magnetic field has probably a different origin in comparison to other magnetic O‐type stars (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)