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Vol 45, No 8 (2019)
- Year: 2019
- Articles: 6
- URL: https://journal-vniispk.ru/1063-7737/issue/view/12020
Article
The Seyfert Galaxy NGC 1275: Superfine Structure
Abstract
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).
475-489
Spectral Properties of Heavily Obscured Seyfert Galaxies from the INTEGRAL All-Sky Survey
Abstract
We have investigated the X-ray spectral properties of the ten heavily obscured nearby (z < 0.1) active galactic nuclei (AGNs) IGR J00256+6821, NGC 1194, CGCG 420−015, IGR J09253+6929, NGC 3281, NGC 4939, IGR J14175−4641, NGC 5643, NGC 5728, and ESO 137−G034 from the catalogue of hard X-ray sources detected during the INTEGRAL seven-year all-sky survey. Based on data from the NuSTAR space telescope supplemented with XMM-Newton and Chandra data at low energies, we have estimated the intrinsic absorption column densities, photon indices, and intrinsic luminosities of these AGNs. In three objects (NGC 5643, NGC 3281, and ESO 137−G034) the absorption column density (NH) exceeds 2 × 1024 cm−2, while the observed spectrum is dominated by the emission from the central source scattered in the surrounding gas-dust torus. In five objects (IGR J00256+6821, IGR J14175−4641, CGCG 420−015, NGC 1194, and NGC 5728) NH = 1−2 × 1024 cm−2, while the emissions transmitted through the torus and reflected from it make comparable contributions to the recorded X-ray flux. Two more sources (IGR J09253+6929 and NGC 4939) manifested themselves as Compton-thin (NH < 5 × 1023 cm−2) AGNs during the NuSTAR observations. The intrinsic luminosities of the investigated AGNs exceed the observed ones by up to a factor of 7. Given the results obtained now for almost the entire sample of AGNs from the catalogue of the INTEGRAL seven-year all-sky survey, there are reliable absorption column density and intrinsic luminosity estimates, which make it one of the best samples for investigating the population of AGNs in the local Universe.
490-520
Evolution and Pulsations of Population I Post-AGB Stars
Abstract
Evolutionary calculations of population I stars with initial masses M0 = 1 M⊙, 1.5 M⊙ and 2 M⊙ were carried out up to the stage of the proto-planetary nebula. Selected models of post-AGB evolutionary sequences with effective temperatures 3.6 × 103 K ≲ Teff ≲ 2 × 104 K were used as initial conditions in calculations of self-excited stellar oscillations. For the first time the sequences of hydrodynamic models of radially pulsating post-AGB stars were computed using the self-consistent solution of the equations of radiation hydrodynamics and time-dependent convection. Within this range of effective temperatures the post-AGB stars are the fundamental mode pulsators with period decreasing as the star evolves from Π ≈ 300 day to several days. Period fluctuations are due to nonlinear effects and are most prominent at effective temperatures Teff < 5000 K. The amplitude of bolometric light variations is ΔMbol ≈ 1 at Teff ≲ 6000 K and rapidly decreases with increasing Teff. The theoretical dependence of the pulsation period as a function of effective temperature obtained in the study can be used as a criterion for the evolutionary status of pulsating variables suspected to be post-AGB stars.
521-527
High Resolution Optical Spectroscopy of a B-type Abundance Standard Candidate in Ori OB1—HD 35039
Abstract
We present LTE analysis of high resolution optical spectra for the B-type abundance standard candidate HD 35039 (HR 1765, 22 Ori) with an ambigous binary nature. The spectra were obtained with the 3.9-m Anglo-Australian Telescope (AAT) and the UCLES spectrograph. The standard 1D LTE analysis with line-blanketed LTE model atmospheres and spectral synthesis provided fundamental atmospheric parameters of Teff = 22000 ± 1300 K, log g = 3.5 ± 0.3, ξ = 6.0 ± 3.0 km s−1, v sin i = 5.0 ± 1.0 km s−1, [Fe/H] = −0.3 dex, and the photospheric abundances of eleven elements. The FEROS spectrum of the star from the public spectra archive were also obtained and used to test the model parameters of the star: Hydrogen Paschen lines (P12, P13, and P14) provided a good fit for the reported model parameters. We have also acquired high resolution HIDES and HERMES spectra of the star. The error margins in the reported model parameters as well as their degeneracies were tested by the Bayesian inference method. We detect for the first time the P III 4059, 4222, and 4246 Å lines and determine the phosphorus abundance, log ϵ(P)= 4.95 ± 0.3 dex (i.e., [P/Fe] = −0.15 dex), from line synthesis. The obtained argon abundance, log ϵ(Ar) = 6.55 ± 0.19 dex, agrees well with the literature measurements. For the remaining elements, abundances determined in this study for HD 35039 are lower than the average abundances of B dwarfs of well studied OB associations as well as the mean abundances of a sample of early B-type stars in the solar neighbourhood, by up to 0.3 dex. In the FEROS, HIDES, and HERMES spectra, we observe the emission in the high-excitation lines of Si II and Al II. We find a variable radial velocity, with a peak-to-peak amplitude of about 10 km s−1.
528-545
Constraints on the Regimes of Electron Acceleration in Solar Flares
Abstract
Based on the observations of microwave impulsive bursts recorded at the Nobeyama Radio Observatory, we have obtained constraints on the regimes of electron acceleration in solar flares. By analyzing the evolution of the growth rate of the radio flux, we have established that the electron acceleration during a solar flare occurs in a slow regime compared to the exponential one.
546-550
An Analytical Model for the Current Structure of the Magnetosheath Boundary in a Collisionless Plasma
Abstract
We have constructed an analytical model of a quasi-stationary current sheet in a collisionless plasma that describes the boundary of the magnetosheath formed by the solar (stellar) wind. The model significantly extends the scope of the magnetohydrodynamic approach and provides a kinetic match between the nonuniform anisotropic distribution functions of electrons and ions at various effective temperatures. According to our estimates, it allows the current structure of the bow shock and the magnetopause to be qualitatively described for a wide class of objects, including the planetary magnetospheres modified by the incoming stellar wind, the boundary layers of the magnetic clouds filled with a plasma and moving away from the star through the surrounding wind plasma, and the high coronal magnetic loops blown around by the wind on late-type stars.
551-564