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

We have determined the fundamental parameters (effective temperature (T_{textrm{eff}}), surface gravity, and radius) and chemical composition for six stars of spectral types A–B: HD 186689 ((upsilon) Aql), HD 58142 (21 Lyn), HD 145788, HD 192907 ((kappa) Cep), HD 85504 (7 Sex), and HD 38899 (134 Tau), based on the analysis of high-resolution spectra and spectrophotometric observations. The chemical abundances were determined in the approximation of local thermodynamic equilibrium (LTE) for 25 elements from Li to Nd and for 18 of them by taking into account the departures from LTE (non-LTE). In (upsilon) Aql, 21 Lyn, and (kappa) Cep, which are classified as normal stars in the literature, the non-LTE abundances of the elements from He to Fe are indeed consistent with their solar values within 0.1 dex, but overabundances of Co, Ni, Zn, Sr, Y, Zr, and Ba relative to their solar abundances are observed and their values correlate with the stellar temperature (T_{textrm{eff}}). Thus, we have confirmed the temperature dependence of the Zn, Sr, Y, Zr, and Ba overabundances revealed in our previous papers for normal stars and for the first time have found an analogous dependence for Co and Ni. HD 145788 with an overall overabundance of iron-group elements of 0.17 dex is at the initial stage of transformation into an Am star. The line profiles in the spectra of 7 Sex and 134 Tau suggest that these are rapidly rotating stars seen pole on, and their analysis requires using the methods that take into account the non-sphericity of the star.

The data from the FAST and MeerKAT surveys has significantly increased the number of radio pulsars for which the polarization characteristics of their mean profiles have been determined in detail. This has allowed us to confirm earlier conclusions both about the nature of propagation of two orthogonal modes in the pulsar magnetospheres and about the mechanism of particle production in neutron star polar regions and their evolutionary features. We can now say with even greater confidence that mean profiles formed by the O-mode are significantly wider than those formed by the X-mode. Moreover, the observations confirm the validity of the classical Ruderman-Sutherland vacuum model of particle generation, as well as the evolution of the inclination angles of the magnetic axis to the rotation one in the direction of (90^{circ}).

The most complete sample of galactic maser sources and radio stars with trigonometric parallaxes, proper motions and radial velocities measured by the VLBI method has been compiled based on literature data. These sources are associated with young stars located in high mass star forming regions. The rotation parameters of the Galaxy have been determined based on 156 masers with relative parallax errors less than 10(%), located further than 3 kpc from the galactic center. The linear rotation velocity of the Galaxy at the solar distance (R_{0}) is (V_{0}=243.9pm 3.9) km s({}^{-1}). A very narrow chain of masers (3{-}4) kpc long, elongated in the (lsim 40^{circ}) direction, passing from a segment of the Carina-Sagittarius spiral arm to the Scutum arm, has been studied. A number of authors have hypothesized that this is a possible analogue of the Radcliffe wave. In the present work, no noticeable periodic perturbations of vertical coordinates and velocities were found in this structure. On the other hand, on the diagram ‘‘(ln(R/R_{0}){-}theta)’’ this chain of masers has the form of a segment of a logarithmic spiral with a pitch angle of (-48^{circ}). Perhaps this chain of masers belongs to a jet extending from the end of the bar, rotating rigidly with the angular velocity of the bar.

We consider the scientific objectives of the Lunar Millimeter and Submillimeter Observatory being planned within the International Scientific Lunar Station. Given that the observatory will be created stage by stage, from a single small-diameter telescope as the first element of the Lunar Interferometric Network to the creation of an antenna array, we separately discuss the objectives for the single telescope and the antenna array, including those incorporated into the Moon–Earth and Moon–Earth–space observatory interferometers.

We have searched for ultra-long (({gtrsim}100) s) gamma-ray transients in the data from the anticoincidence shield (ACS) of the SPI gamma-ray spectrometer onboard the INTEGRAL orbital observatory and classified them by machine learning methods. We have found about 4364 candidates for such events in the SPI-ACS data by the ‘‘blind’’ threshold search method. We have developed an algorithm for automatic processing of their light curves that distinguishes a candidate for transients on various time scales and allows its duration and fluence to be determined. The algorithm has been applied to calculate (and compare) the fluxes in the light curves recorded by various INTEGRAL detectors: IREM, SPI-ACS, SPI, ISGRI, and PICsIT. These fluxes have been used to train the classifier based on gradient boosting. Subsequently, we have performed a cluster analysis of the candidates found by the dimensionality reduction and clustering methods. In conclusion we have compared the remaining candidates with the data from the Konus-WIND gamma-ray detectors. Thus, we have confirmed 16 candidates for astrophysical transients, including four candidates for ultra-long gamma-ray bursts from the events detected by the SPI-ACS detector. Out of the probable events, but unconfirmed by other experiments, up to 270 events can be classified as real gamma-ray bursts.

The observed abundances of primordial elements such as D, ({}^{4})He, and ({}^{7})Li are key quantities for studying the physical processes that took place in the early Universe. Obtaining the primordial ({}^{4})He abundance (Y({}_{p})) with sub-percent accuracy is one of the major goals of modern observational cosmology. The most widely used method for determining Y({}_{p}) is based on the analysis of spectra from blue compact dwarf galaxies. This approach involves measuring the fluxes of helium, hydrogen, and metal emission lines, followed by detailed modeling aimed at estimating the physical conditions and chemical composition of their interstellar medium, as well as accounting for systematic effects. One of the most significant systematic effects affecting the estimate of Y({}_{p}) is underlying stellar absorption. This effect arises from the overlap of emission lines from the interstellar medium with the same absorption lines formed in stellar photospheres, which contribute to the stellar continuum of H II regions. As a result, the observed emission line fluxes may be significantly altered. In this paper, we present an improved algorithm for full-spectrum modeling of H II regions. The method incorporates both the stellar and nebular continuum, as well as the emission line profiles. The stellar continuum component is constructed by modeling the integrated spectrum of multiple stellar populations using the pPXF package. This approach eliminates the need to separate the measurement of integrated fluxes from the subsequent modeling process. It provides a more self-consistent framework and allows for a more accurate treatment of the underlying absorption effect, thereby increasing the precision of the derived model parameters. Examples of ({}^{4})He abundance measurements in individual objects demonstrate up to a threefold improvement in precision compared to previous methods. The proposed method can be used to obtain more accurate estimates of the primordial ({}^{4})He abundance, as well as to address other problems related to the analysis of H II region spectra.

A statistical analysis of the anisotropic quasi-periodic features of the spatial distribution of galaxy clusters obtained from spectroscopic and photometric redshifts in the interval (0.1leq zleq 0.47) has been carried out. Based on data from the the SDSS III catalog, we show that the preferential direction previously detected in the northern hemisphere (a narrow cone of directions: (alpha_{0}=170^{circ}pm 5^{circ}), (delta_{0}=29^{circ}pm 5^{circ})), along which the one-dimensional distribution of projections of the Cartesian coordinates of clusters contains a significant (({gtrsim}(4{-}5)sigma)) quasi-periodic component, can also be found using photometric redshifts achieving a certain accuracy ((Delta zlesssim 0.013)). Based on data from the photometric DES(times)unWISE catalog, we have analyzed the spatial distribution of clusters in the southern hemisphere, where a cone of close directions was also detected ((alpha_{0}=346^{circ}pm 5^{circ}), (delta_{0}=-29^{circ}pm 5^{circ})), which are approximately an extension of the directions revealed in the northern hemisphere. The power spectra of the one-dimensional distributions along these directions contain significant (({gtrsim}(4{-}5)sigma)) features in the same interval of wave numbers (0.04lesssim klesssim 0.06;h) Mpc({}^{-1}).

We present the most complete up-to-date sample of supernovae associated with gamma-ray bursts (GRB-SNe) for which the peak time of the SN light curve and the peak absolute magnitude have been found. The sample contains 44 SNe. We have searched for correlations between the parameters of the GRB-SN (V)-band brightness peak (the rest-frame (V)-band absolute magnitude (M_{V})) and the rest-frame (V)-band peak time (T_{textrm{max}}) as well as between them and GRB prompt emission parameters ((T_{90,i}), (E_{textrm{iso}}), (E_{p,i})). Any correlations between any pairs of parameters cannot be confirmed at a statistically significant level. A separation into two groups is observed in the (M_{V}{-}log_{10}(E_{textrm{iso}})) distribution. These two groups may correspond to significantly different initial or final parameters of the SN that is the progenitor of long GRBs. We discuss the selection effects that affect the detectability of GRB-SNe and the possible existence of correlations.

We present the results of our spectroscopic identification of nine highly variable X-ray sources detected by the eROSITA telescope of the SRG observatory during its all-sky survey and published in the first paper of this series (the complete sample consists of 49 objects; Medvedev et al. 2022). For our observations we used the BTA, SAI25, AZT-33IK, and RTT-150 telescopes. One of the objects has turned out to be a cataclysmic variable, and another one has already been known previously as a tidal disruption event. The remaining seven objects have turned out to be active galactic nuclei (AGNs) at redshifts from 0.035 to 0.523. For four objects we have estimated the mass of the central black hole from the width and luminosity of the broad H(alpha) line component. These black holes have turned out to be moderately massive: from ({sim}8times 10^{6}) to ({sim}10^{8}) (M_{odot}).

Using SRG/eROSITA X-ray sky survey data and the optical catalog of 2209 Pleiades cluster members constructed from Gaia data, we have found 850 X-ray sources associated with cluster stars. More than 650 of them have been detected in X-rays for the first time. At the distance of the Pleiades the nominal sensitivity of eROSITA in this sky region corresponds to a (0.3{-}2.3) keV luminosity (L_{X}sim 1.6times 10^{28}) erg s({}^{-1}). The eROSITA sources associated with the Pleiades radiate with a total luminosity (L_{X,textrm{total}}sim 1.3times 10^{32}) erg s({}^{-1}), which exceeds the X-ray luminosity of the quiet Sun by a million times. A strong, more than a factor of 10, X-ray variability has been recorded for 27 sources. Most of them are known as eruptive optical variable dM stars. (R_{X}=log(L_{X}/L_{textrm{bol}})) for Pleiades stars increases with decreasing effective stellar temperature from (R_{X}approx{-}5) to (R_{X}approx{-}2). The (R_{X}) distribution of stars is bimodal. The left peak at (R_{X}sim{-}4.3) is formed by FGK stars, while the right peak at (R_{X}sim{-}3.1) is mostly populated by M stars. The dependence of (R_{X}) on the Rossby number (Ro) is different for different spectral types. At small Rossby numbers for K and M stars (R_{X}sim{-}3) and depends weakly on (Ro). At (Rogtrsim 0.25) a rapid decrease in (R_{X}) is observed for K stars, while there are no M stars with large Rossby numbers in our sample. Most of the F and G stars lie in the range of lower values, (R_{X}sim{-}4.5), but the size of our sample is not enough to characterize in more detail the (R_{X}{-}Ro) relation for them.