Astronomy Letters-A Journal of Astronomy and Space Astrophysics最新文献

The rotational modulation of the radial velocities of narrow emission lines in four classical T Tauri Stars has been studied. The previously declared shift in the mean velocity of neutral and ionized helium lines relative to the mean velocity of the star has been found to be not related to the inflow of accreting gas into the spot, since the radial velocity curves for lines with different velocity shifts must experience phase shifts relative to one another, whereas the observed phase shifts are absent within the uncertainties and do not correspond to the observed line velocity shifts. This means that the line shifts are not caused by the real gas motion. In the case of neutral helium lines, the shifts can be explained by a large optical depth of the lines and the Stark effect for plasma parameters that correspond to the expected ones at the base of the accretion column in T Tauri stars.

The Gnevyshev–Ohl rule is considered for a new series of sunspot areas on a four-century time scale (Nagovitsyn and Osipova 2021). The hypothesis of Usoskin et al. (2001) about the existence of an additional small cycle on the descending branch of Zürich cycle 4 is accepted. This leads to a change in the parity of the cycles earlier than 5. Eleven-year cycles in the 17th century have been distinguished. Their average duration, from minimum to minimum, is (T=8.9pm 1.4) years. New data and approaches have led us to conclude that the Gnevyshev–Ohl rule holds for the 410-year interval as a whole without the exclusion of the pair of Zürich cycles 4 and 5 adopted in the rule previously.

A new approach to calculating the electrostatic energy of solid interiors of degenerate stars has been developed. It is applicable to systems with any ionic composition. The proposed method is used to study ordered Coulomb crystals formed by two types of ions with charge numbers (Z_{1}) and (Z_{2}). Eight different body-centered cubic lattices are considered at (x_{1}geq 1/2), where (x_{1}) is the relative number of ions with charge number (Z_{1}). Six of them are new, while for (x_{1}=1/2) and (1/4) the results for electrostatic energy coincide with those known earlier. All obtained results are approximated by an expression convenient for practical use.

We studied the model of the Galaxy with a bar which reproduces well the distributions of the observed radial, (V_{R}), and azimuthal, (V_{T}), velocities derived from the Gaia DR3 data along the Galactocentric distance (R). The model profiles of the distributions of the velocity (V_{R}) demonstrate a periodic increase and the formation of a hump (elevation) in the distance range of 6–7 kpc. The average amplitude and period of variations in the velocity (V_{R}) are (A=1.76pm 0.15) km s({}^{-1}) and (P=2.1pm 0.1) Gyr. We calculated angles (theta_{01}), (theta_{02}), and (theta_{03}) which determine orientations of orbits relative to the major axis of the bar at the time intervals: 0–1, 1–2, and 2–3 Gyr from the start of simulation. Stars whose orbits change orientations as follows: (0^{circ}<theta_{01}<45^{circ}), (-45^{circ}<theta_{02}<0^{circ}), and (0^{circ}<theta_{03}<45^{circ}), make a significant contribution to the hump formation. The fraction of orbits trapped into libration among orbits lying both inside and outside the outer Lindblad resonance (OLR) is 28(%). The median period of oscillations of librating orbits is 2.0 Gyr. The median period (P) of long-term variations in the angular momentum and total energy of stars increases as the Jacobi energy approaches the values typical for the OLR but then sharply drops. The distribution of model stars over the period (P) has two maxima located at (P=0.6) and (1.9) Gyr. Stars with orbits lying both inside and outside the corotation radius (CR) concentrate to the first maximum. The distribution of stars whose orbits lie both inside and outside the OLR depends on their orientation: orbits elongated perpendicular to the bar concentrate to the first maximum but those stretched parallel to the bar concentrate to the second maximum. The fact that the observed profile of the (V_{R})-velocity distribution derived from the Gaia DR3 data does not show a hump suggests that the age of the Galactic bar, counted from the moment of reaching its full power, must lie near one of two values: (2.0pm 0.3) or (4.0pm 0.5) Gyr.

The observational effects of the circumstellar gas around the superluminous supernova SN 2018ibb are investigated. The narrow Fe II absorption lines are reproduced in the model of a fragmented cold dense shell between the forward and reverse shocks. The unusual selective absorption in the [O I] emission doublet is explained by the scattering of radiation in the Si II doublet lines in the supernova envelope. It is shown that the [O III] emission doublet at (t_{mathrm{max}}+565) days can be radiated by the supernova envelope, with the asymmetry of the [O III] doublet being explained by the formation of dust in the supernova. Supernova–circumstellar gas interaction modeling in combination with observational data leads to an estimate of the circumstellar shell mass (({sim}0.14 M_{odot})).

The absorption of a gamma-ray burst (GRB) afterglow in the X-ray wavelength range in a dense molecular cloud is investigated. We present the results of our numerical simulations of the propagation of GRB radiation in the cloud for various gas densities, metallicities, and distances from the GRB progenitor star to the cloud. We consider a sample of 45 GRBs with known redshifts in which the isotropic-equivalent gamma-ray energy corresponds to the value adopted in our numerical simulations. For these GRBs we have analyzed the Swift/XRT energy spectra of their afterglows at late times, (tgeq 4times 10^{3}) s. We show that the hydrogen column densities estimated using the absorption model in which the ionization of metal ions is ignored and solar metallicity is used are a factor of 1–3 lower than the actual values if the molecular cloud is near the GRB progenitor star. If the gas cloud is located at a distance (Rgeq 10) pc from the GRB source or the gas metallicity ([M/H]leq-1), then the influence of the could ionization structure on the afterglow absorption is minor.

We explore the origin of the broad component of the [Ar II] 7 (mu)m line emission related to the ejecta excitation by the neutron star of SN 1987A. We argue that the line broad wings are emitted at the temperature of ({sim}300) K. The flux excess in the red wing of [Ar II] line is reproduced by the line photons scattering off the optically thin uniform dust component with the grain size of 1–2 (mu)m and the total mass of (textrm{(several)}times 10^{-3})  (M_{odot}). The dusty opaque clumps containing almost all the dust of SN 1987A have a low occultation optical depth and line photon scattering on dusty clumps do not contribute noticeably in the red wing. The additional heating might be related to ionization losses of relativistic protons.

We propose a new approach to the detection of pulsed radio-astronomical signals based on multichannel reception instead of traditional threshold detection. We show that for weak and super-weak pulsed signals this approach is preferable, since it allows one to work with signals that would be rejected as insignificant ones in the case of threshold detection. We propose a new interpretation of the false alarm probability based on random ordering of the signal in a multichannel receiver. Based on this probability, we introduce an equivalent signal-to-noise ratio as if a single-channel receiver were used. The theoretical dependences log (N{-}textrm{log}F) for noise variations obeying the Gaussian and Laplace distributions are shown for the first time. We show that noise variations cannot explain the (-3/2) law that corresponds to a uniform distribution of sources in space. The proposed new approach is applied to radio-astronomical data from the BSA telescope of the Lebedev Physical Institute.

The pattern of nucleosynthesis during the explosion of a low-mass neutron star formed in a close binary system in the stripping scenario is considered. In the scenario considered the shock arising during the explosion is shown to strongly heat the expanding neutron star matter. The heavy nuclei produced at the preceding stage of nucleosynthesis are partially destroyed as a result of a sharp increase in the role of photonuclear reactions. It is shown that even short-term heating of the matter by the shock can exert a noticeable influence on the results of the synthesis of elements in the r-process in the inner crust matter, while explosive nucleosynthesis gives rise to new elements in the outer crust matter with mass numbers (A) from (50) to (130).

The influence of a dark matter halo around binary primordial black holes on the orbit evolution and the black hole merger rate is considered. Because of the nonspherical contraction of dark matter shells, each shell upon the first contraction passes through the halo center in the direction of the radius vector corresponding to zero angular momentum. Since the shell contraction is a continuous process, at each instant of time there is a nonzero dark matter density at the halo center. This density is determined by the influence of the tidal gravitational forces from inflationary density perturbations and from other primordial black holes. The scattering of dark matter particles by a pair of black holes leads to a loss of the energy of its orbital motion and to an accelerated pair merger. In the case of primordial black holes with masses ({sim};30;M_{odot}), the black hole merger rate in the presence of a dark matter halo is several times higher than that without such a halo.