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

In the fall of 2019, during the in-flight calibration phase of the SRG observatory, the onboard eROSITA and Mikhail Pavlinsky ART-XC telescopes carried out a series of observations of PG 1634+706 — one of the most luminous (an X-ray luminosity ({sim}10^{46}) erg s({}^{-1})) quasars in the Universe at (z<2). Approximately at the same dates this quasar was also observed by the XMM-Newton observatory. Although the object had already been repeatedly studied in X-rays previously, its new observations allowed its energy spectrum to be measured more accurately in the wide range 1–30 keV (in the quasar rest frame). Its spectrum can be described by a two-component model that consists of a power-law continuum with a slope (Gammaapprox 1.9) and a broadened iron emission line at an energy of about 6.4 keV. The X-ray variability of the quasar was also investigated. On time scales of the order of several hours (here and below, in the source rest frame) the X-ray luminosity does not exhibit a statistically significant variability. However, it changed noticeably from observation to observation in the fall of 2019, having increased approximately by a factor of 1.5 in 25 days. A comparison of the new SRG and XMM-Newton measurements with the previous measurements of other X-ray observatories has shown that in the entire 17-year history of observations of the quasar PG 1634+706 its X-ray luminosity has varied by no more than a factor of 2.5, while the variations on time scales of several weeks and several years are comparable in amplitude.

We have carried out a comprehensive study of the poorly investigated eclipsing polar 1RXS J184542.4(+)483134 with a short orbital period (P_{textrm{orb}}approx 79) min. An analysis of its long-term light curves points to a change in the position and sizes of the accretion spot as the accretion rate changes. Narrow and broad components, which are probably formed on the ballistic segment of the accretion stream and on the magnetic trajectory, respectively, are identified in the emission line profiles. An inversion of the line profiles from emission to absorption due to the obscuration of the accretion spot by the accretion stream is observed. Based on the eclipse duration and the radial velocities of the narrow line component, we impose constraints on the white dwarf mass, (0.49leq M_{1}/;M_{odot}leq 0.89), and the orbital inclination, (79.7^{circ}leq ileq 84.3^{circ}). An analysis of the cyclotron spectra points to the presence of two accretion spots with magnetic field strengths (B_{1}=28.4^{+0.1}_{-0.2}) MG and (B_{2}=30{-}36) MG. The main spot has a complex structure that apparently has a dense core and a less dense periphery emitting a spectrum with cyclotron harmonics. Polarization observations reveal a circular polarization sign reversal during the orbital period and an anticorrelation of the polarization with the brightness of the polar. Our modeling of polarization observations using the simple model of an accreting white dwarf shows that the polarization properties can be interpreted in terms of two-pole accretion with different optical depths of the accretion spots ((tau_{1}/tau_{2}sim 10)). An analysis of the Swift/XRT observations points to a predominance of bremsstrahlung in the X-ray radiation from the system.

Evolutionary sequences of AGB stars with initial masses on the main sequence (M_{textrm{ZAMS}}=1.5;M_{odot}), (2;M_{odot}), and (3;M_{odot}) were computed for the initial metallicity (Z=0.014). Selected models of evolutionary sequences with envelopes under thermal equilibrium were used as initial conditions for calculation of nonlinear stellar pulsations. The hydrodynamic models of each evolutionary sequence are shown to concentrate along the continuous line in the period–radius and period–luminosity diagrams. The theoretical period–radius and period–luminosity relations differ from one another for different main–sequence star masses because the stellar luminosity of AGB stars depends on the degenerate carbon core mass which increases with increasing (M_{textrm{ZAMS}}). In hydrodynamic models of evolutionary sequences (M_{textrm{ZAMS}}=2) and (3;M_{odot}) the periods of the first overtone pulsators are (86leqPileq 123textrm{d}) and (174leqPileq 204textrm{d}), whereas all models of the evolutionary sequence (M_{textrm{ZAMS}}=1.5;M_{odot}) oscillate in the fundamental mode. Fairly regular radial oscillations exist in stars with pulsation periods (Pilesssim 500) d. In models with longer periods the amplitude rapidly increases with increasing (Pi) and oscillations become irregular.

We present the results of our long-term photometric and spectroscopic monitoring with the 1.5-m telescope RTT-150 for the optical counterpart of the high-mass X-ray binary IGR J21343+4738 discovered in 2002 by the INTEGRAL space X-ray observatory. The X-ray source was also repeatedly detected by the telescopes of the SRG observatory during the all-sky surveys in the period 2019–2021. We have investigated the spectroscopic and photometric variabilities of the optical counterpart, a Be star, caused by physical processes in the equatorial disk. The evolution of the equatorial disk parameters over a long time interval of 16 years has been analyzed.

A method for estimating the spatial period of energy release in solar flares is proposed to analyze the present-day satellite observations of arcades of flare coronal loops. The method is based on the application of a Fourier analysis to the difference images of flare arcades in the far ultraviolet. The operation of the method is demonstrated with the observations of the Bastille Day flare from the TRACE spacecraft in the 171 Å channel. The mean spatial period of energy release in the Bastille Day flare determined by the proposed method is 5–8 Mm, in good agreement with the scenario for the development of thermal instability of the preflare current layer in solar flares.

We present new three-dimensional (3D) interstellar extinction maps in the (V) and Gaia (G) filters within 2 kpc of the Sun, a 3D differential extinction (dust spatial distribution density) map along lines of sight in the same space, a 3D map of variations in the ratio of the extinctions in the (V) and Gaia (G) filters within 800 pc of the Sun, and a 2D map of total Galactic extinction through the entire dust half-layer from the Sun to extragalactic space for Galactic latitudes (|b|>13^{circ}). The 3D maps have a transverse resolution from 3.6 to 11.6 pc and a radial resolution of 50 pc. The 2D map has an angular resolution of 6.1 arcmin. We have produced these maps based on the Gaia DR3 parallaxes and Gaia, Pan-STARRS1, SkyMapper, 2MASS, and WISE photometry for ({sim}100) million stars. We have paid special attention to the space within 200 pc of the Sun and high Galactic latitudes as regions where the extinction estimates have had a large relative uncertainty so far. Our maps estimate the extinction within the Galactic dust layer from the Sun to an extended object or through the entire dust half-layer from the Sun to extragalactic space with a precision (sigma(A_{textrm{V}})=0.06) mag. This gives a high relative precision of extinction estimates even at high Galactic latitudes, where, according to our estimates, the median total Galactic extinction through the entire dust half-layer from the Sun to extragalactic objects is (A_{textrm{V}}=0.12pm 0.06) mag. We have shown that the presented maps are among the best ones in data amount, space size, resolution, precision, and other properties.

Helioseismology has revealed an increase in the rotation rate with depth in a thin (({sim}30) Mm) near-surface layer. The normalized rotational shear in this layer does not depend on latitude. This rotational state is shown to be a consequence of the short characteristic time of near-surface convection compared to the rotation period and radial anisotropy of convective turbulence. Analytical calculations within mean-field hydrodynamics reproduce the observed normalized rotational shear and are consistent with numerical experiments on radiative hydrodynamics of solar convection. The near-surface shear layer is the source of global meridional flow important for the solar dynamo.

We consider the population of point X-ray sources from the two-year SRG/eROSITA survey in the 1(%) DESI spectroscopic survey region in the eastern Galactic hemisphere (eROSITA–1(%)DESI–East). The data under consideration combine a large survey area (compared to the medium-format Stripe82X and XMM-XXL X-ray surveys) and a record high completeness of spectroscopy for the optical counterparts of X-ray sources. We compare the results of the photometric (SRGz) and spectroscopic/astrometric (DESI EDR, SDSS, HELP, GAIA) measurements of the classes and redshifts of objects in three X-ray-flux-limited eROSITA–1(%)DESI–East samples: (F_{X,0.5-2}geqslant 4times 10^{-14}) erg s({}^{-1}) cm({}^{-2}) (bright), (F_{X,0.5-2}=(1.5{-}4)times 10^{-14}) erg s({}^{-1}) cm({}^{-2}) (medium), and (F_{X,0.5-2}=(0.6{-}1.5)times 10^{-14}) erg s({}^{-1}) cm({}^{-2}) (faint) with a total area of 91.4, 91.4, and 16.62 deg({}^{2}), respectively. We propose a new method of postprocessing the probabilistic photo-z predictions based on a two-temperature correction of the probability density function (PDF(z)). This approach allows the calibration of the probabilistic predictions and confidence intervals of the photometric redshifts for eROSITA X-ray sources obtained by SRGz to be improved significantly.

We present a catalog of sources detected by the Mikhail Pavlinsky ART-XC telescope onboard the SRG space observatory during the observations of the Galactic plane region near a longitude (lsimeq 20^{circ}) (L20 field) in October 2019. The L20 field was observed four times in the scanning mode, which provided a uniform coverage of the sky region with a total area of ({simeq}24text{ deg}^{2}) with a median sensitivity of (8times 10^{-13}) erg s({}^{-1}) cm({}^{-2}) (at 50(%) detection completeness) in the 4–12 keV energy band. As a result, we have detected 29 X-ray sources at a statistically significant level, 11 of which have not been detected previously by other X-ray observatories. Preliminary estimates show that four of them can presumably be extragalactic in nature. We also show that the source SRGA J183220.1(-)103508 (CXOGSG J183220.8(-)103510) is most likely a galaxy cluster containing a bright radio galaxy at redshift (zsimeq 0.121).

Atmospheric muons of high energy constitute the major event yield in modern deep large-volume neutrino telescopes. Examining their properties at sea level is crucial for accurately deciphering observed signals. This study involves the computation of the flux and charge ratio of the atmospheric muons with energies exceeding 100 GeV at sea level. The calculation employs the Monte Carlo code CORSIKA in conjunction with several state-of-the-art hadronic interaction models. The obtained results are compared with a set of experimental data and with other recent comparable studies.