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

We propose a model for the origin of the broad He II 4686 Å emission in early spectrum of SN 2020jfo (type IIP). The 4686 Å line is emitted presumably by dense fragments embedded into a hot gas of the forward shock wave. The fragments are produced as a result of a heavy braking of the dense low mass shell, at the ejecta boundary and a simultaneous Rayleigh–Taylor instability. The temperature of line-emitting fragments is ({approx}5times 10^{4}) K. Calculations of ionization and excitation of helium and hydrogen accounts for the He II 4686 Å luminosity, large flux ratio of He II 4686 Å/H(alpha) and a significant optical depth of 4686 Å line. We demonstrate that fragments heating by hot electrons of the forward shock compensates cooling via He II 304 Å emission.

We present the results of the optical identification and spectroscopic redshift measurements of 216 galaxy clusters detected in the SRG/eROSITA all-sky X-ray survey. The spectroscopic observations were performed in 2020–2023 with the 6-m BTA telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences, the 2.5-m telescope at the Caucasus Mountain Observatory of the Sternberg Astronomical Institute of the Moscow State University, the 1.6-m AZT-33IK telescope at the Sayan Solar Observatory of the Institute of Solar–Terrestrial Physics of the Siberian Branch of the Russian Academy of Sciences, and the 1.5-m Russian–Turkish telescope (RTT-150) at the TÜBİTAK Observatory. For all of the galaxy clusters presented here the spectroscopic redshift measurements have been obtained for the first time. Of these, 139 galaxy clusters have been detected for the first time in the SRG/eROSITA survey and 22 galaxy clusters are at redshifts (z_{textrm{spec}}gtrsim 0.7), including three at (z_{textrm{spec}}gtrsim 1). Deep direct images with the rizJK filters have also been obtained for four distant galaxy clusters at (z_{textrm{spec}}>0.7). For these observations we chose the most massive clusters and, therefore, most of the galaxy clusters presented here with the spectroscopic redshifts measured by us will most likely enter in future into the cosmological samples of galaxy clusters from the SRG/eROSITA survey.

The proton capture reaction serves as a valuable tool for exploring the nuclear structure. Specifically, in the p-shell, the radiative proton capture on ({}^{9})Be plays a significant role in the nucleosynthesis of light elements. We have investigated the reaction ({}^{9}textrm{Be}(textrm{p},gamma)^{10})B using the modified potential model. Within this framework, we have examined various electric and magnetic transitions associated with this reaction and have computed the rates for both direct capture and resonance capture. The reaction rate of ({}^{9}textrm{Be}(textrm{p},gamma)^{10})B is evaluated by employing the computed total cross-sections across a temperature range of 0.006 to 1 T9. A comparative analysis is conducted between the calculated rate and the data obtained from NACRE II. The astrophysical S factor and reaction rate are expressed analytically, accompanied by an estimation of the influence of low-lying resonances on the reaction rate.

The detection of radio emission from solar flares at frequencies below ({sim}2) GHz allows the upper limits for the characteristic size of the soft X-ray (SXR) source (L(t)) to be estimated under the assumption that the density (n(t)) is determined by the plasma frequency (nu_{p}). If the SXR source with a higher density is inside the radio source, then the size of the SXR source will be (L(t)<(EM(t)/2n(t)^{2})^{1/3}), where (EM(t)) is the emission measure. For three flares (C7.2 on December 22, 2009, M2.9 on July 6, 2012, and X1.1 on July 6, 2012) we calculate the expansion speeds of the SXR source (V(t)sim dL(t)/dt), which are compared with the estimates of the sound speed and the Alfvén speed. By ‘‘magnetic detonation’’ we mean the process of the propagation of magnetic reconnection with a supersonic speed in eruptive flares. Magnetic detonation and the succeeding coronal mass ejection (CME) were realized in the December 22, 2009 C7.2 and July 6, 2012 X1.1 flares, in which supersonic and super-Alfvén speeds were reached if the density of the SXR source was lower than (2.1times 10^{9}) and (7.4times 10^{8}) cm({}^{-3}) ((nu_{p}<410) and ({<}245) MHz), respectively. There were no magnetic detonation and CME in the July 6, 2012 M2.9 flare, whose radio emission frequencies were only above 1415 MHz ((n>2.5times 10^{10}) cm({}^{-3})). For magnetic detonation in the July 6, 2012 X1.1 flare we have estimated the magnetic field strength, the reconnection electric field strength, the plasma flow, and the CME mass.

We propose a universal approximation of the equation of state of superdense matter in neutron star (NS) interiors. It contains only two parameters, the pressure and the density at the center of the maximally massive neutron star. We demonstrate the validity of this approximation for a wide range of different types of equations of state, including both baryonic and hybrid models. Combined with recently discovered correlations of internal (density, pressure, and speed of sound at the center) and external (mass, radius) properties of a maximally massive neutron star, this approximation turns out to be an effective tool for determining the equation of state of superdense matter using astrophysical observations.

We consider the evolutionary status of the recently discovered long-period radio sources PSR J0901-4046, GLEAM-X J1627-52, and GPM J1839-10. It is hypothesized that all three sources are radio pulsars. Within the framework of standard scenarios, it is thought that for the pulsar mechanism to operate, it is necessary to exclude the penetration of external matter into the light cylinder, which corresponds to the ejector stage. We show that for realistic properties of the interstellar medium the 76-second pulsar J0901-4046 must be at this stage, whereas the sources GLEAM-X J1627-52 and GPM J1839-10 with periods ({gtrsim}1000) s can be at this stage only in the case of unrealistically high dipolar magnetic fields ({gtrsim}10^{16}) G. We also show that sources with periods ({sim}100) s and magnetic fields ({lesssim}10^{13}) G cannot be ejectors in a realistic interstellar medium. Thus, we predict that long-period radio pulsars with standard magnetic fields will not be discovered.

We have analyzed the results of our observations of the millisecond pulsar B0329+54 (J0332+5434), which exhibits quasi-periodic variations in the barycentric times of arrival (TOAs) of pulses on long time scales. We have tested the hypothesis about the existence of a planet with a mass close to the mass of the terrestrial planets and an orbital period of 27.8 yr around this pulsar that was proposed previously to explain the variations in its TOAs. We show that this hypothesis is not confirmed when considering the series of TOA residuals over the entire available time interval of observations 1968–2022 and that the TOA variations for this pulsar apparently have a different physical cause.

The detection of radio emission from the gamma-ray pulsar J1836+5925 is reported. Rare events of radio emission from this object have been recorded with the LPA radio telescope at the Pushchino Radio Astronomy Observatory. A two- or three-component integrated profile and very narrow individual pulses are a peculiarity of the radio emission from the pulsar J1836+5925. The presence of an interpulse is also possible. We have measured the dispersion measure, (DM=23pm 1) pc cm({}^{-3}), and estimated the distance to the pulsar, 1.5 kpc. The flux density and the lower limit on the spectral index have been estimated.

In pulsating X-ray sources a magnetized neutron star is surrounded by an accretion disk whose structure requires a study. In particular, the dipole magnetic field of the star can partially penetrate the disk and, freezing into the matter, can give rise to an induced magnetic field in the disk. The field growth can be limited by its turbulent diffusion. In this paper we calculate such an induced field. The problem is reduced to solving the induction equation in the presence of diffusion. An analytical solution of the equation has been obtained, with the radial and vertical structures of the induced field having been calculated simultaneously. The radial structure is close to the previously predicted dependence on the difference of the angular velocities of the disk and the magnetosphere: (bproptoOmega_{textrm{s}}-Omega_{textrm{k}}), while the vertical structure of the field is close to the linear proportionality between the field and the height above the equator: (bpropto z). The possibility of the existence of nonstationary quasi-periodic components of the induced magnetic field is discussed.

We consider the influence of space curvature in the Schwarzschild metric on the contribution of the magnetic field outside the neutron star to the moment of inertia of a radio pulsar. Our consideration is restricted only to the simplest configuration of the magnetic field, when it can be described by only one harmonic. We show that at a fixed magnetic field strength on the stellar surface the influence of space curvature reduces the contribution of the magnetic field outside the star to the departure of the inertia tensor from the spherical one several-fold.