Astrophysical Bulletin最新文献

In the present paper, we study HD 144941, a EHe-r magnetic star with a very strong magnetic field and unique abundance of helium. We determined the magnetic field variability period equal to 6.969 days and proposed the most probable model of the magnetic field structure. The average surface magnetic field (B_{s}=11,226) G, the magnetic field structure can be described by the theoretical magnetic dipole model located in the center of the star. The inclination angle of the dipole axis to the rotation equator plane is unusually great: (alpha=65^{circ}). The star’s age after the ZAMS is about (10^{6}) yr. We suppose that in terms of a very strong magnetic field, the wind ‘‘blows out’’ significant amount of helium to the surface according to the diffusion theory.

This paper presents the results of magnetic field measurements for 19 chemically peculiar stars in three open star clusters IC 4756, (alpha) Per, NGC 7092. More than 80 spectra of circularly polarized radiation were obtained with the Main Stellar Spectrograph (MSS) at the 6-m BTA telescope of SAO RAS. It was found that the magnetic field value in these clusters is more than three times less than in the young Orion OB1 association. Apparently, unique conditions developed in this association allowed the generation of super-strong magnetic field during the formation of stars.

Based on Gaia DR3 data, a new revision of the stellar content isperformed within the (20^{prime})-radius field centered on theyoung open cluster vdB 130, which is a part of the Cyg OB1stellar association. A total of 97 stars and 39 protostars ofluminosity classes I/II/III are identified that have proper-motionbased cluster membership probabilities (P>0.98). The totalnumber of possible cluster members with membership probabilities(P>0.50) is equal to about 300, and the cluster age estimated byfitting theoretical isochrones does not exceed 10 Myr. Thetrigonometric-parallax based cluster distance is (Dapprox 1670pm 60) pc, and the cluster color excess, (E(BP-RP)approx 0overset{textrm{m}}{.}85pm 0overset{textrm{m}}{.}02) withevidence for strong differential extinction.

We present the second part of the review of spectroscopic observations of Mira variables in the optical and near infrared. The role of various structures (atmosphere, envelopes) in the formation of the optical spectrum is estimated. The thickness of the molecular layer that creates the observed effects of distortion of the emission spectra is estimated based on two model approximations. Assuming that a significant part of the optical spectrum is formed in the circumstellar envelopes, the known photometric and spectroscopic effects are discussed.

Based on the available photometric data spanning almost 8000 days (21.9 years) of observations of a bright G5 V dwarf, solar-type star HD 4915, we carried out a study of the manifestations of its activity, probably transitioning to a state similar to the Maunder Minimum. To estimate the duration of the possible activity cycles of the star, we used three independent data sets. We obtained evidence of HD 4915 light variations, including the interval of time corresponding to a decrease in its chromospheric activity variations. Based on the constructed power spectrum, we can suggest the existence of possible cycles of the order of 1640 and 630 days (4.5 and 1.7 years) for the object’s brightness, which are comparable with the chromospheric activity cycle estimate of 4–4.2 years, significantly shorter than the duration of the magnetic activity cycle of the Sun, which is a distinguishing feature of HD 4915. Using photometric observations of the star from Kamogata Wide-field Survey, including data from the measurements taken after 2018, when it could have been starting an activity phase similar to the Maunder Minimum, we obtained indications of possible 450, 1260 and 2000 day cycles (1.23, 3.5 and 5.5 years) and made a conclusion about the presence of cyclic light variations during this supposed lower activity state of HD 4915. We discuss the probable estimate of the star’s rotation period. A consideration of the HD 4915 data available in the TESS archive for four observing sets led us to conclude that they are unsuitable for determining its rotation period.

We present the measurement results for the spectral flux densities of 19 calibration sources observed with the RT-22 single-dish telescope of the Crimean Astrophysical Observatory of the Russian Academy of Sciences at 22.2 and 36.8 GHz in 2017–2020. About half of them belong to the commonly accepted secondary standards with periodically monitored flux densities at radio frequencies. The measurements were carried out to refine the calibration measurements of the RATAN-600 radio telescope at high frequencies. The specificity of RATAN-600 meridian observations requires a ‘‘grid’’ of calibration objects distributed over declinations from (-35^{circ}) to (+90^{circ}) instead of 1–3 conventional calibrators which are sufficient for observations at different heights with a single-dish antenna. The radio variability of the objects was estimated taking into account the literature measurements, the results were interpolated to a frequency of 30 GHz. It was found that radio variability at 22 GHz at time scales of about 20–30 years exceeds 10(%) for the calibrators 4C (+)16.09 and 3C 309.1. We discuss a possibility of verifying the calibration sources at the RT-22 by a new method that uses a noise signal generator as an indicator of their relative flux density accuracy.

We searched again for a radial (vertical) gradient of the longitudinal magnetic field of the chemically peculiar star (alpha^{2}) CVn. We considered the history of magnetic studies of this object demonstrating large differences in the data obtained with different methods. Such differences can be explained by the fact that the magnetic field sharply drops (by 2 orders stronger than in the case of a dipole structure) with height in the atmosphere. The spectroscopic, spectropolarimetric, and photometric data indicate that the large- and small-scale structure of the atmosphere of (alpha^{2}) CVn has not changed over more than 90 years of observations.

The nonlinearity of the transfer function of photon detection by a CCD receiver of an echelle fiber-optic spectrograph of high spectral resolution at the BTA SAO RAS is studied. Local analysis of signals in the image of the emission spectrum and correction of data are carried out.

We present the results of model analysis of the optical spectra of SU UMa and WZ Sge-type dwarf novae TY Psc, FL Psc, and V455 And. Spectroscopic observations were carried out at the SAO RAS 6-m BTA telescope in 2013. The selection criterion for the systems under study is their existence in a quiescent state with an optically thin accretion disk and dominance of white dwarf radiation. The fulfillment of the criterion was verified by observing the H I Balmer series broad absorption lines simultaneously with two-peak H I, He I, and Fe II emissions. A technique for automated fitting of model spectra of white dwarfs and observed spectra of dwarf novae based on quantitative criteria for their matching is proposed and implemented. The atmospheric parameters (effective temperature (T_{textrm{eff}}) and surface gravity (log g)) of accretors in TY Psc, FL Psc, and V455 And were determined applying it and used further to obtain their masses and radii. Due to the technique proposed here we obtained the estimates of the fundamental parameters of the secondaries using the theoretical ‘‘mass–radius’’ relationships for brown and red main-sequence dwarfs. As a result, we demonstrate the possibility in principle of determining all the main parameters of the SU UMa and WZ Sge dwarf novae based on modeling and the analysis of a small number of their spectra in the quiescent state.