Astronomy Letters

We have performed a model analysis of the optical radiation from the young pre-cataclysmic variable Lan 30 and determined the set of its fundamental characteristics. Spectroscopic and multiband photometric observations have been carried out with the BTA and Zeiss-1000 telescopes at the Special Astrophysical Observatory of the Russian Academy of Sciences. The technique for modeling irradiated atmospheres of stars in close binary systems has been used for the computations of synthetic spectra and light curves. We have established the dominance of the radiation from an sdB subdwarf with atmospheric parameters $$T_{\textrm{eff}}=30\,500\pm 1100$$ K and $$\log g=5.60\pm 0.10$$ in the optical band under moderate influence of reflection effects on the light curves and HI line profiles. We have analyzed the measured sets of radial velocities of the primary component by taking into account the possible influence of reflection effects on them and refined their semi-amplitude $$K_{1}=56.3\pm 2.0$$ km s $${}^{-1}$$ . We have found that the nearly sinusoidal shape of the light curves of Lan 30 allows only an upper limit on the orbital inclination to be set. Based on agreement between the model and observed light curves, we have estimated the radii of the components at various inclinations. To determine their lower limit, we have used evolutionary estimates of the radii of low-mass main-sequence stars. The mass of the primary component has been taken to be equal to the normal mass of single sdB subdwarfs, $$M_{1}=0.47M_{\odot}$$ . As a result, we have determined the ranges of possible variations of the orbital inclination $$i=33^{\circ}{-}45^{\circ}$$ and semimajor axis, the radii of the components, and the mass $$M_{2}=0.127{-}0.175M_{\odot}$$ of the red dwarf.

Detailed studies of the internal motions of dark clouds using spectral lines of many molecules require a laboratory frequency accuracy of the order of a few m s−1. Based on our laboratory studies of the HNCO rotational spectrum in the ground vibrational state, we have increased significantly the accuracy of frequency calculation in a wide range of quantum numbers. We have achieved an (1σ) uncertainty for rotational transitions in the K a = 0, 1 states recalculated to the Doppler velocity scale ≤2 m s−1 for all frequencies <1.1 THz. This value allows radio-astronomical measurements with an accuracy comparable to that of the highest-precision observations based on spectral lines of other molecules.

We numerically solved the two-dimensional axisymmetric hydrodynamic problem of the explosion of a low-mass neutron star in a circular orbit. In the initial conditions, we assumed a nonuniform density distribution in the space surrounding the collapsed iron core in the form of a stationary toroidal atmosphere that was previously predicted analytically and computed numerically. The configuration of the exploded neutron star itself was modeled by a torus with a circular cross section whose central line almost coincided with its circular orbit. Using an equation of state for the stellar matter and the toroidal atmosphere in which the nuclear statistical equilibrium conditions were satisfied, we performed a series of numerical calculations that showed the propagation of a strong divergent shock wave with a total energy of ∼0.2×1051 erg at initial explosion energy release of ∼1.0×1051 erg. In our calculations, we rigorously took into account the gravitational interaction, including the attraction from a higher-mass (1.9M ⊙) neutron star located at the coordinate origin, in accordance with the rotational explosion mechanism for collapsing supernovae. We compared in detail our results with previous similar results of asymmetric supernova explosion simulations and concluded that we found a lower limit for the total explosion energy.

The formation of hydrogen emission lines in the magnetospheres of young stars is considered. The magnetosphere is assumed to be formed by a dipole magnetic field whose axis is aligned with the stellar rotation axis. The radiative transfer in spectral lines is considered in the Sobolev approximation with nonlocal radiative coupling. We have taken into account the effect of gas ionization fraction transfer when moving in the magnetosphere, demonstrated its influence on the emission spectrum of the magnetosphere for the first time, and estimated the accretion rate from the $$\mathrm{H\alpha}$$ line. We have shown that at low accretion rates $$\dot{M}\lesssim 10^{-9}\ {M_{\odot}}$$ yr $${}^{-1}$$ this effect can exert a significant influence on the model intensities.

We discuss the results of our spectroscopy for 17 candidates for distant quasars selected by the SRGz classification system based on data from the first and second sky surveys with the eROSITA telescope onboard the SRG X-ray observatory. Most of the quasar candidates were selected within the DaLeQo observing program, whose goal is a search for the most X-ray luminous quasars with luminosities $$L_{2{-}10\rm keV}\gtrsim 5\times 10^{45}$$ erg s $${}^{-1}$$ at redshifts $$z\gtrsim 3$$ . Our spectroscopic observations were carried out at the 6-m BTA telescope with the SCORPIO-2 spectrograph. We have managed to confirm eight new X-ray quasars at $$z_{\textrm{spec}}\gtrsim 3$$ , including the quasar SRGe J020142.8-015347 at $$z_{\textrm{spec}}=5.02$$ . Owing to the large diameter of the BTA mirror and the high quantum efficiency of the SCORPIO-2 spectrograph in the range 6000–9000 Å, we have managed to measure the С IV (1549 Å) line parameters and to estimate the supermassive black hole masses and accretion rates for seven quasars.

Dựa trên dữ liệu của SDSS, chúng tôi đã xem xét môi trường không gian của các thiên hà có vòng cực mở rộng. Chúng tôi đã sử dụng hai phương pháp: ước lượng khoảng cách chiếu đến bạn đồng hành gần nhất và đếm số lượng bạn đồng hành theo hàm của khoảng cách đến thiên hà. Cả hai phương pháp đều cho thấy rằng môi trường không gian của các thiên hà vòng cực ở quy mô hàng trăm kiloparsec thường ít dày đặc hơn so với những thiên hà không có cấu trúc vòng cực. Rõ ràng, một trong những nguyên nhân chính của hiệu ứng này là các cấu trúc vòng cực trong môi trường dày đặc hơn thường bị phá hủy nhiều hơn trong các trường hợp giao thoa và sát nhập với các thiên hà khác.

The short duration (T 90 < 2 s) gamma-ray bursts (GRBs) detected in the SPI-ACS experiment onboard the INTEGRAL observatory are investigated. Averaged light curves have been constructed for various groups of events, including short GRBs and unidentified short events. Extended emission has been found in the averaged light curves of both short GRBs and unidentified short events. It is shown that the fraction of the short GRBs in the total number of SPI-ACS GRBs can range from 30 to 45%, which is considerably larger than has been thought previously.

We present the results of our abundance analysis for the atmosphere of the chemically peculiar Ap star HD 8441. HD 8441 is interesting in that the lines of rare-earth elements in its spectrum are weak and the longitudinal magnetic field component is small, being only several hundred gauss. Our estimates of the evolutionary status for HD 8441 have confirmed that it belongs to the group of Ap stars with weak lines of rare-earth elements in their spectra that leave the main sequence. A stratification analysis of the atmosphere of HD 8441 assuming a stepwise distribution of elements with depth reveals a nonuniform distribution of Si, Ca, Cr,Mn, and Fe with a significant increase in elemental abundances in deeper layers. The derived distribution qualitatively agrees with predictions of the theory of diffusive separation of elements under the action of radiation pressure forces and gravity. Comparison of the chemical composition and evolutionary status of HD 8441 with those of the stars HD 66318 and HD 144897 with strong magnetic fields shows that their atmospheres differ mainly by the abundances of rare-earth elements. The iron-peak elements exhibit large overabundances irrespective of the magnetic field strength.

Based on VLBA observations (NRAO archive) at λ = 2 cm, we have constructed radio maps of the Seyfert galaxy NGC 1275 with a resolution of 25 µas, the epochs of 1995–2015, and at λ = 7 mm (Boston University archive), the epochs of 2000–2015, with a resolution of 20 µas. We have identified a ring structure with a diameter ϕ ≈ 2 mas (1 pc) inclined at 60° to the plane of the sky that includes three centers of activity, vortices. The surrounding relativistic plasma comes to the main northern center along two arms and is ejected in the southward direction X ≈ −10° of a hollow tube, a jet with a diameter ϕ ≈ 0.12 mas. The second center of activity, a vortex whose plane is parallel to the jet, is located in the remote part of the jet at a distance ρ ≈ 2.5 mas. An excess angular momentum is carried away by a coaxial flow with ∅21 ≈ 0.8 mas and ∅22 ≈ 0.3 mas in the eastward direction X ≈ −90°, where the third center of activity is formed. A coaxial flow with ∅31 ≈ 0.7 mas and ∅32 ≈ 0.35 mas is ejected in the northward direction. The projections of both coaxial flows form mesh points on the plane of the sky. The nozzle splitting in the first system is observed at a resolution of 3 µas. The sizes of the two succeeding centers of activity are 80 × 40 and 80 × 120 µas. The results of our studies of the fine structure of galaxies in polarized emission will be published in the next paper (II).