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

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.

We present the results of our identification of 11 X-ray sources detected on the half of the sky (0^{circ}<l<180^{circ}) in the 4–12 keV energy band on the combined map of the first five all-sky surveys with the Mikhail Pavlinsky ART-XC telescope onboard the SRG observatory. All these sources were also detected by the SRG/eROSITA telescope in the 0.2–8 keV energy band, whose data have allowed us to improve their positions and to investigate their X-ray spectra. Five of them have been detected in X-rays for the first time, while the remaining ones have already been known previously, but their nature has remained unknown. We have taken optical spectra for nine sources with the 1.6-m AZT-33IK telescope at the Sayan Observatory (the Institute of Solar–Terrestrial Physics, the Siberian Branch of the Russian Academy of Sciences); for two more objects we have analyzed the archival spectra from SDSS and the 6dF survey. The objects are classified as Seyfert galaxies (seven Sy1, three Sy1.9, and one Sy2) at redshifts (z=0.029{-}0.258). Our analysis of the X-ray spectra has revealed a noticeable intrinsic absorption ((N_{textrm{H}}sim 10^{22}) cm({}^{-2})) in two of the four Seyfert 2 galaxies (Sy1.9–2). The spectrum of one more of them (SRGA J000132.9+240237) cannot be described within the model of an absorbed Comptonization continuum, which may point to a strong absorption and a significant contribution of the reflected radiation. However, the available SRG all-sky survey data are not enough to obtain reliable constraints on the absorption column density in this object, which is also interesting in that it is radio loud. Longer X-ray observations are required to refine the physical properties of this active galactic nucleus.

We present the results of our optical study of the eclipsing polar Gaia23cer. We analyze the orbital brightness variability in high ((langle rrangleapprox 16.5^{m})) and low ((langle rrangleapprox 19.2^{m})) states. The system has an orbital period (P_{textrm{orb}}=102.0665pm 0.0015) min and exhibits deep eclipses with a duration (Delta t_{textrm{ecl}}=401.30pm 0.81) s. The spectra have a red cyclotron continuum with the Zeeman H(alpha) absorption triplet forming in a magnetic field with a strength (B=15.2pm 1.1) MG. The source of emission lines has a high radial velocity semi-amplitude ((Kapprox 450) km s({}^{-1})), and its eclipse lags behind the eclipse of the white dwarf. The mass (M_{1}=0.79pm 0.03;M_{odot}) and temperature (T=11,350pm 650) K of the white dwarf have been estimated by modelling the spectral energy distribution. The eclipse duration corresponds to a donor mass (M_{2}=0.10{-}0.13;M_{odot}) and an orbital inclination (i=84.3^{circ}{-}87.0^{circ}). The donor temperature was estimated to be (Tapprox 2900) K by modelling the elliptical variability and eclipse depth.

We consider the final evolutionary stages of a neutron star–black hole pair. According to the current paradigm, such systems eventually coalesce, which in some cases is accompanied by neutron-star tidal disruption. Using analytical methods, we show that the scenario of slow (of the order of several seconds) neutron-star stripping by the black hole is also possible, depending on the system parameters (the initial masses and intrinsic angular momenta of the components, the equation of state for the neutron star). Reaching the lower mass limit (about one tenth of the solar mass), the neutron star explodes to produce a comparatively powerful electromagnetic transient. Our population calculations show that the stripping mechanism is possible in 50–90(%) of the cases among all coalescing neutron star–black hole pairs, depending on the model assumptions about the evolution of close binary systems (the common-envelope efficiency parameter, the supernova explosion mechanism) and the initial metallicity of the stellar population. Because of the large mass of the ejected material, the kilonova emission in this scenario has good prospects of detection.

Based on spectrophotometric observations, we have investigated the envelope of Nova V1405 Cas. The spectrophotometric evolution has shown that it belongs in its spectral characteristics to the rare type of hybrid novae. At the optically thick phase in the Balmer lines the profiles had a P Cyg shape; the radial velocities of the absorption components in the profiles pointed to ejecta with velocities reaching (RV=-1800) km s({}^{-1}). We have determined the maximum envelope expansion velocity from the half-width of the line profiles at the continuum level, which reached 3300 km s({}^{-1}) from the H({alpha}) line. We have obtained approximate estimates of the electron density (N_{e}=10^{7}) cm({}^{-3}), temperature (T_{e}=2times 10^{4}) K, and the abundances of some elements. We show that the neon and iron abundances for such electron density and temperature can differ from the solar ones insignificantly. The low neon abundance does not allow one to assert with confidence that the white dwarf in this nova is an oxygen–neon one. The mass of the envelope has been estimated to be ({sim}6times 10^{-5};M_{odot}).