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

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.

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.