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

The source BL Lac exhibited an enhanced activity from August 2020 to July 2022. This activity peaked in July–August 2021. In this period the source reached historic brightness maxima in various energy ranges. Observations of this nonstandard maximum were carried out by the SAI staff of the Crimean Station of SAI and with the telescopes of the Caucasus Mountain Observatory (CMO SAI MSU). Optical and near-infrared photometric data as well as optical polarimetric data were obtained. When investigating the correlation between the optical and gamma-ray fluxes and between the optical and infrared fluxes, its high degree with an almost zero lag was confirmed—this means that the emission regions spatially coincide or are very close together. The degree of linear polarization in the investigated period changed in a wide range, reaching 20({%}), with an anticorrelation between the degree of linear polarization and the brightness of the object having been observed. A similar pattern of variation was also observed in the preceding flares of this object. The changes in the electric vector position angle (EVPA) show a dependence on the rate of change of the object’s brightness. The EVPA changed greatly during flares and slowly at the times of a slow change in the intensity.

Using long-slit and panoramic spectroscopy at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences and by mapping emission lines in a narrow passband of 13 Å with the MaNGaL instrument at the 2.5-m telescope of the Caucasus Mountain Observatory of the Sternberg Astronomical Institute of the Lomonosov Moscow State University, we have investigated the gaseous component of the giant lenticular galaxy NGC 934. The gas kinematics in the galaxy has turned out to disagree completely with the stellar kinematics, suggesting recent accretion of a large amount of cold gas by the galaxy. Weak star formation proceeds in the accreted gas on the periphery of the galaxy, mainly in a ring of radius 26 kpc, which may promise the buildup of a giant low-surface-brightness stellar disk in this early-type galaxy. The gas metallicity in the star formation ring is nearly solar: the accretion source is most likely the swallowing of a massive gas-rich satellite.

I explore the possibility of estimating an upper limit for the present-day iron abundance in the baryonic matter at which the gamma-ray background from the decay of ({}^{56})Ni synthesized in the Universe to date comes into conflict with the observed MeV gamma-ray background. I calculate the brightness of the gamma-ray background from SNe Ia and SNe II by taking into account the gamma-ray scattering and absorption in supernova ejecta. The model brightness of the gamma-ray background is shown to be consistent with the observed MeV gamma-ray background if the iron abundance in the baryonic matter is less than 15({%}) of the solar one.

We present the results of the analysis of the SRG/ART-XC observation of the Supergiant Fast X-ray Transient IGR J16195-4545 performed on March 3, 2021. Six bright flares are present in the light curve, with no significant change in hardness occuring during these flares. The spectrum is described with an absorbed power law model with a high energy exponential cutoff showing heavy absorption, with (N_{textrm{H}}=(12pm 2)times 10^{22}text{ cm}^{-2}) and (Gamma=0.56pm 0.15), (E_{textrm{cut}}=13pm 2) keV. Adopting the Bayesian block decomposition of the light curve, we measured the properties of the observed flares (duration, rise time, waiting time, released energy and pre-flare luminosity), which are consistent with the quasi-spherical subsonic accretion model. The stellar wind velocity of the supergiant is estimated to be (v_{w}approx 500) km s({}^{-1}). Additionally, the system was found to have an unusual near-IR variability.

We present the first results of the SRG observation of the pulsar 4U 1538–52 based on ARC-XC and eROSITA data. An extended emission in the form of a halo is detected around the source in the 0.5–8 keV energy band. Our simulation has shown that its surface brightness distribution can be described by a two-component model composed of a flat disk ({sim}250^{primeprime}) in radius and a (beta)-model with a characteristic size ({sim}480^{primeprime}). We have constructed a broadband spectrum of 4U 1538–52 in the energy range 0.5–30 keV, which can be fitted by a weakly absorbed ((N_{textrm{H}}simeq 0.7times 10^{22}) cm({}^{-2})) power law with a high-energy cutoff. In addition, iron emission lines are detected in the pulsar spectrum at 6–7 keV. We show that the observed halo spectrum is considerably softer (a power-law index ({simeq}2.8)) than the pulsar spectrum (a power-law index ({simeq}0.9)), consistent with the predictions of theoretical models for the X-ray scattering by dust.

A straight cylindrical, electrically shielded magnetic flux rope is considered as the upper part of a weakly curved magnetic loop whose footpoints are fixed in the photosphere. All parameters of the flux rope depend on one variable—the distance (r) from the axis of its symmetry. As the flux rope rises into the rarefied solar atmosphere, the external pressure keeping the flux rope from lateral expansion drops continuously. At some critical value of it the longitudinal magnetic field of the flux rope vanishes on the magnetic surface where the longitudinal electric current changes its sign in accordance with the requirement for the total current to be shielded. At the same time, the azimuthal current and the force-free parameter near this surface grow indefinitely. Because of this growth, the electron drift velocity near this surface exceeds the ion-sound speed, leading to the excitation of a plasma ion-sound instability as a trigger of flare energy release. The plasma conductivity in the region of plasma turbulence drops by seven orders of magnitude. Rapid magnetic energy dissipation at the anomalous resistivity generates an inductive electric field in the plasma that exceeds considerably the Dreicer limit. This explains the efficient acceleration of particles in the region where the magnetic field weakens rapidly.

Calculations of stellar evolution at initial abundances of helium (Y=0.28) and heavier elements (Z=0.014) were done for stars with masses on the main sequence (1.7;M_{odot}leq M_{textrm{ZAMS}}leq 5.2;M_{odot}). Evolutionary sequences corresponding to the AGB stage were used for modelling the pulsation period decrease observed for almost two centuries in the Mira-type variable R Hya. Diminution of the period from (Piapprox) 495 d in the second half of the eighteenth century to (Piapprox 380) d in the 1950s is due to stellar radius decrease accompanying dissipation of the radiation–diffusion wave generated by the helium flash. For all the history of its observations R Hya was the fundamental mode pulsator. The best agreement with observations is obtained for eight evolutionary models with initial mass (M=4.8;M_{odot}) and the mass loss rate parameter of the Blöcker formula (0.03leqeta_{textrm{B}}leq 0.07). Theoretical mass estimates of R Hya are in the range (4.44;M_{odot}leq Mleq 4.63;M_{odot}), whereas the mean stellar radius ((421;R_{odot}leqbar{R}leq 445;R_{odot})) corresponding to the pulsation period (Piapprox 380) d agrees well with measurements of the angular diameter by methods of the optical interferometric imaging.

For both periods of the double-mode Cepheid V371 Per and for the Cepheid OGLE-LMC-CEP-2132 we have constructed (O-C) diagrams spanning a time interval of 126 and 119 years, respectively. The (O-C) diagrams have the shape of parabolas, which has allowed us for the first time to determine the quadratic light elements and to calculate the rates of evolutionary changes in their periods: (dP_{Fu}/dt=1.085({pm}{0.007})) s yr({}^{-1}) and (dP_{1O}/dt=0.923({pm}{0.003})) s yr({}^{-1}) for the fundamental mode and the first overtone of V371 Per, respectively, and (dP/dt=15.304({pm}{0.048})) s yr({}^{-1}) for OGLE-LMC-CEP-2132, in agreement with the results of theoretical calculations for the first crossing of the instability strip. The pulsation stability test proposed by Lombard and Koen has confirmed that the increase in the periods is real.

We have investigated the stability of the orbital dynamics of a number of planets detected in binary star systems based on the analysis of data from the TESS orbital observatory. For 20 circumstellar planets we have obtained typical estimates of the Lyapunov time (the time of predictable dynamics). The secular orbital dynamics of 18 planets considered is stable with Lyapunov times greater than 6000 years. For the planets TOI-905b and TOI-1634b the calculated Lyapunov times (less than 3000 years) correspond to unstable dynamics and point to possible inaccuracies in the parameters of the planets found. A detailed analysis of the stability of the secular dynamics of the circumbinary planets TOI-1338 and TIC 172900988 has shown that on the stability diagrams the planets are located in regions with relatively large Lyapunov times (more than 7000 years), confirming the reliability of the derived parameters of the planets.