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

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.

The characteristics of the spiral structure of galaxies in compact groups (from the HCG and SDSSCGA catalogs) and in isolation (from the CIG catalog) have been obtained and analyzed. The dependence of the type of spiral pattern on the spatial environment of galaxies has been studied. The conclusions about how a tidal interaction affects the spiral structure have been drawn. The fraction of grand design spirals in compact groups is shown to be considerably higher than that in a sample of isolated objects. Grand design galaxies in the field, on average, have bluer and narrower spiral arms. This may probably due to the absence of a tidal interaction that has a strong effect on the structure of galaxies in a crowded environment.

A homogeneous set of calcium and scandium abundances has been obtained for 54 A-type stars with strong metal lines (Am stars) by taking into account the departures from local thermodynamic equilibrium. A correlation of the Ca and Sc abundances with the effective temperature ((T_{textrm{eff}})) has been revealed, with the Ca and Sc abundances in stars with a surface gravity (log g<4) growing with increasing (T_{textrm{eff}}) faster than in stars with (log ggeq 4). No correlation of the Ca and Sc abundances with the iron abundance and the stellar rotation velocity has been found. Am stars exhibit, on average, a higher value of [Ca/H] than that of [Sc/H] and ([textrm{Ca}/textrm{Sc}]=0.41pm 0.30). However, for (T_{textrm{eff}}>9500) K there is a hint at a systematic difference between stars with (log ggeq 4) and (log g<4). The iron overabundance is, on average, the same in the range (7200leq T_{textrm{eff}}leq 10,030;textrm{K}). It is shown that when atomic diffusion is taken into account, evolution computations with the MESA code for stellar masses of 1.5–2.2 (M_{odot}) give surface abundances that are consistent with the Ca and Fe abundances in Am stars in three open clusters with an age greater than 600 Myr. Additional mechanisms for the separation of chemical elements are required to explain the Am phenomenon in young stars in the Pleiades cluster. Published diffusion models have been tested. The turbulent models of Richer et al. (2000) and Hui-Bon-Hoa et al. (2022) are consistent with the observations of Am stars in open clusters at large values of the free parameter (omega): 1000 for Ca and Fe and 500 for Sc. None of the diffusion models corresponding to the mass and age of the Am star Sirius reproduces the abundances of the elements from He to Ni observed in it. The results obtained are important for a better understanding of the chemical peculiarity mechanisms in Am stars.

We have carried out multiwavelength spectroscopic and photometric studies of the object SRGe J194401.8+284452 (2RXS J194401.4+284456, XMMSL2 J194402.0+284451, 2SXPS J194401.7+284450), the brightest X-ray source in the position uncertainty ellipse of the unidentified gamma-ray source 4FGL J1943.9+2841, with the goal of determining its nature and the possible association with the gamma-ray source. The object is shown to be a cataclysmic variable with an orbital period of about 1.5 h and clear evidence for the presence of an accretion disk around the white dwarf. It can be classified by its properties as an intermediate polar whose association with the gamma-ray source is unlikely. SRGe J194401.8+284452 exhibits abrupt transitions between its high and low luminosity states simultaneously in the optical and X-ray bands, which remain relatively stable on time scales of several months/years. This may be related to the change in the accretion rate by an order of magnitude. We have obtained constraints on the mass (0.3–0.9 (M_{odot})) and temperature ((14,750pm 1250) K) of the accreting white dwarf in the low state, the mass of the donor star (({leq}0.08pm 0.01;M_{odot})), and the orbital inclination of the binary system ((40^{circ}{-}75^{circ})). In the low state we have detected an 8-min brightness variability in the optical band that is most likely related to the white-dwarf spin and not to the nonradial pulsations. In the high state we have revealed stochastic brightness variations on time scales of 1–15 min with amplitudes of 0.2–(0.6^{m}). SRGe J194401.8+284452 replenishes the small group of intermediate polars with the shortest orbital periods lying below the gap in the period distribution of these systems and exhibiting transitions between the states with high and low accretion rates. The brightness of the source at a level of (17{-}20^{m}) in the 2000–8000 Å range and ((5{-}50)times 10^{-13}) erg s({}^{-1}) cm({}^{-2}) in the range 0.3–10 keV makes it an interesting object for a detailed study of the physics of such systems.

The solar wind (SW) plasma thermodynamics in the solar corona is determined by the energy exchange with external sources and can be studied if information about physical plasma parameters, such as the SW temperature, density, flow velocity, etc., is known. Previously, Parker showed that within the one-fluid model the SW plasma state could be described by a polytropic function in which the pressure (p) and density (rho) are related by the relation (p/rho^{gamma}=textrm{const}) with the polytropic index (gamma). In present-day MHD models the application of a polytropic function instead of an approximate description of the plasma heating mechanisms speeds up the computation considerably. The polytropic index (gamma) can be estimated using the SW plasma parameters, but for the SW flows moving toward the Earth measuring such parameters presents certain difficulties. In this paper we consider a method to determine the polytropic index (gamma) for the SW flows at the stage of expansion in the corona from the SW plasma ion parameters measured in situ: the mean Fe ion charge (langletextrm{Q}_{text{Fe}}rangle) and the (textrm{O}^{7+/}) (textrm{O}^{6+}) ion density ratio. The relation between the ion parameters and the polytropic index (gamma) is established by solving the balance equations for the ionization and recombination processes in the SW plasma. The mean values of (gamma) in the corona at heights of ({approx})1–7 solar radii for the flows of the slow SW, the fast SW from coronal holes, and interplanetary coronal mass ejections have been obtained from the histograms of the SW ion parameters measured with the ACE/SWICS instrument in 2010.

A new N I model atom has been constructed using the energy levels known from laboratory measurements and predicted in N I atomic structure calculations and up-to-date atomic data for calculating the radiative and collisional transition rates. The solar abundance (logvarepsilon_{odot,textrm{N}}text{(1D NLTE)}=7.92pm 0.03) has been determined from N I lines by the synthetic spectrum method with a classical one-dimensional (1D, MARCS) solar model atmosphere and by taking into account the departures from local thermodynamic equilibrium (non-LTE effects). By applying the 3D corrections of Amarsi et al. (2020), we have obtained (logvarepsilon_{odot,textrm{N}}(textrm{NLTE}+textrm{3D})=7.88pm 0.03) for the Sun. Based on high-resolution spectra, we have derived the non-LTE nitrogen abundances for 11 unevolved A–F-type stars with reliably determined atmospheric parameters. Non-LTE leads to a strengthening of N I lines, and the non-LTE effects grow with increasing effective temperature. For each of the stars the departures from LTE lead to a decrease in the root-mean-square (rms) abundance error compared to the LTE case. For superficially normal A stars non-LTE removes the enhancements relative to the solar nitrogen abundance obtained in an LTE analysis. The (lambda) Boo-type star HD 172167 (Vega) also has a nearly solar nitrogen abundance. Four Am stars exhibit a scatter, from a nitrogen underabundance with (textrm{[N/H]}=-0.44) to a nitrogen overabundance with (textrm{[N/H]}=0.39). The nitrogen abundances for the Sun and superficially normal A stars are consistent within the error limits with the nitrogen abundance in the interstellar gas and early B-type stars.

An interpretation of the slow-drift ‘‘bursts in absorption’’ observed against the background of Jovian decameter radio emission with a quasi-harmonic structure is given. According to the proposed model, the quenching of cyclotron instability as a result of filling the ‘‘loss cone’’ of the distribution function of emitting ions is responsible for the formation of bursts in absorption. The ions being injected into the emission generation region at the lower boundary of the source and propagating along magnetic field lines fill the loss cone. The parameters of the injected ions needed for the formation of bursts in absorption are estimated by comparing the model parameters with the observed ones.