G. A. Chuntonov

Possible Variability of the Magnetic Field of T Tau

Using the Main Stellar Spectrograph of the 6-m Special Astrophysical Observatory telescope equipped with a polametric analyzer, we measured the longitudinal magnetic field component B∥ for the T Tauri stars T Tau and AS 507 on January 16 and 18 and February 15, 2003. For both stars, we determined only the upper limits on B∥ from photospheric lines: +15±30 G for T Tau and −70±90 G for AS 507. The magnetic field of AS 507 was not measured previously, while B∥ for T Tau is lower than its values that we obtained in 1996 and 2002 (B∥≂150±50G), suggesting that the longitudinal magnetic field component in the photosphere of T Tau is variable. We also measured the longitudinal magnetic field component for T Tau in the formation region of the He I 5876 Å emission line. We found B∥ in this region to be ⋍+650, ⋍+350, and ⋍+1100 G on January 16, 18, and February 15, 2003, respectively. Our observations on January 18 and February 15 correspond to virtually the same phase of the stars rotation period, but the profiles of the He I 5876 Å line differ markedly on these two nights. Therefore, we believe that the threefold difference between the B∥ values on these nights does not result from observational errors. We discuss the possible causes of the B∥ variability in the photosphere and the magnetosphere of T Tau.

Magnetic field of the young star RW Aur

Results of ourmeasurements of the longitudinal magnetic field Bz for the young star RWAur A are presented. Bz measured from the so-called narrow component of the He I 5876 line varies in the range from −1.47 ± 0.15 to +1.10 ± 0.15 kG. Our data are consistent with a stellar rotation period of }~5.6 days and the model of two hot spots with opposite magnetic field polarities spaced about 180° apart in longitude. Relative to the Earth, the spot with Bz < 0 lies in the hemisphere above the midplane of the accretion disk, while the spot with Bz > 0 is below the midplane. The upper limit for Bz (at the 3σ level) obtained by averaging all observations is 180 G for the photosphere and 220 and 230 G for the Hα and [OI] 6300 line formation regions, respectively. We have also failed to detect a field in the formation region of broad emission line components: the upper limit for Bz is 600 G. In two of 11 cases, we have detected a magnetic field in the formation region of the blue absorption wing of the Na I D doublet lines, i.e., in the wind from RW Aur A: Bz = −180 ± 50 and −810 ± 80 G. The radial velocity of the photospheric lines in RW Aur A averaged over all our observations is }~+10.5 km s−1, i.e., a value lower than that obtained by Petrov et al. (2001) ten years earlier by 5.5 km s−1. Therefore, we discuss the possibility that RW Aur is not a binary but a triple system.

Main stellar spectrograph of the 6-meter telescope. Analysis, reconstruction, and operation

The Main Stellar Spectrograph (MSS) of the 6-m telescope of the Special Astrophysical Observatory was developed in the early 1970s and has been in permanent operation since 1975. This instrument has been successfully kept operational for a long time by equipping it with modern detectors and significantly upgrading its optical layout. In this paper we present the main parameters of the optomechanical layout of the MSS, the design features of auxiliary devices, operational experience and statistics of the use of the instrument with various detectors, and the characteristics of the corresponding observational techniques.

New results of magnetic field measurements for BP tau

We present measurements of the longitudinal magnetic field component B‖ of the young star BP Tau in the He I 5876 emission line formation region, i.e., in the accretion flow near the stellar surface. The values obtained (≃1.7 kG and ≃1.0 kG in 2000 and 2001, respectively) agree with the results of similar measurements by other authors. At the same time, we show that the previously obtained field strength at the magnetic pole, Bp, and the inclination of the magnetic axis to the rotation axis, β, are untrustworthy. In our opinion, based on the B‖ measurements available to date, it is not possible to conclude whether the star’s magnetic field is a dipole one or has a more complex configuration and to solve the question of whether this field is stationary. However, we argue that at least in the He I 5876 line formation region, the star’s magnetic field is not stationary and can be restructured in a time of the order of several hours. Nonstationary small-scale magnetic fields of active regions on the stellar surface and/or magnetospheric field line reconnection due to the twisting of these field lines as the star rotates could be responsible for the short-term magnetic field variability. It seems highly likely that there are no strictly periodic variations in brightness and emission line profiles in BP Tau due to the irregular restructuring of the star’s magnetic field.

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.

Results of magnetic field measurements in young stars DO Tau, DR Tau, and DS Tau

The results of longitudinal magnetic field measurements Bz in the hot accretion spot in three classical T Tauri stars (CTTS) are reported. In all three stars the magnetic field is detected at a level above 2σ in the formation region of the narrow component of the He I 5876 Å emission line. In the case of DS Tau the longitudinal field Bz in the hot spot was also measured from the narrow emission components of the Na I D lines, implying +0.8 ± 0.3 kG, which is equal to the Bz field component measured from the He I 5876 Å line. Our results suggest that the 6-m telescope of the Special Astrophysical Observatory can be used to study magnetic fields in the hot spots of CTTS with magnitudes down to 13m, making it possible to double the number of stars of this type with measured Bz values in the accretion zone.

Rapid spectral variability of ɛ PerA

The results of high-resolution spectropolari metric observations (R = 60 000) of the B0.5-type subgiant ɛ PerA are reported. Regular components of line profile variations with the frequencies 3.82–12.99 d−1 are found. A possible relation between the non-radial pulsations of the star and the observed regular variations of the line profiles is shown. A wavelet analysis of the difference of line profiles in the spectrum of ɛ PerA is performed. The amplitude of the wavelet spectrum is found to have two maxima at 10–20 and 50–60 km/s velocity scales. It is suggested that the first maxi mum corresponds to the amplitude of fluctuations in the velocity field of large-scale motions in the non-radially pulsating photosphere of the star, whereas the second maximum is associated with the variation of the half widths of spectral line profiles. An upper limit for the effective magnetic field of the star is inferred.

Features of calcium and strontium distribution on the surface of CP star HD49976

Modelling the magnetic field structure in HD49976, we obtained a map of its magnetic field distribution on the surface and its main parameters. Simulating the distribution of Ca and Sr by the phase dependences of the Ca II 3934 Å and Sr II 4215 Å equivalent line widths revealed that their abundances are most likely increased between the magnetic poles. An insufficiently clear result is due to the structure of the magnetic field of HD49976, which proved to be complex, not corresponding to the central dipole. It is modelled by two dipoles, the stronger of them is in the center of the star, and the other, weaker, is at distance of 0.3R* from the center. The synthetic spectrum method yielded abundances of 28 elements in the moments of magnetic field extrema. The carbon and sulfur abundances proved to be close to the solar values, silicon showed a deficit of 1.0 dex, lithium, calcium, iron and the iron peak elements, strontium, rare earths are in excess, especially significant in the case of rare earths. High-resolution spectropolarimetric observations closely covering the entire rotation period are required to investigate the distribution of chemical elements in complex multi-dipole magnetic configurations, applying the Magnetic Doppler Imaging method.

Charge accumulation and cyclic image transfer on CCD: Search for rapid variations of magnetic field in γ Equ

We search for the variable component of themagnetic field in γ Equ by studying four Nd III lines with the Main Stellar Spectrograph of the 6-m BTA telescope of the Special Astrophysical Observatory via accumulation and cyclic transfer of the electronic image of the Zeeman spectrum on the CCD. The single exposure time was set equal to 1/8 of the spectral variability period. We detected no variable component in the magnetic field of γ Equ with a period of 12.1 min in the November 5/6, 2003 observations.

Study of the weakly magnetic star HD 116656

We studied the spectroscopic binary HD 116656 (ζ1 UMa) that has previously been suspected to be a Si-type chemically peculiar star. The magnetic field of each individual component was measured with a high accuracy, but none were found. The upper limit for each field was estimated as 20 G. The abundances of the chemical elements studied in both components proved to be the same. The pattern of their chemical anomalies suggests that they are more likely chemically peculiar Am stars than magnetic CP stars. The rotational velocities of the components slightly differ, 31.7 km s−1 for component A and 37.0 km s−1 for component B. Low rotational velocities are characteristic of both nonmagnetic metallic-line and magnetic chemically peculiar stars.