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

{"title":"Spectroscopy of B and Be Stars in the Very Young Open Star Cluster IC 1805","authors":"A. E. Tarasov","doi":"10.1134/S1063773724700142","DOIUrl":"10.1134/S1063773724700142","url":null,"abstract":"<p>Based on moderate-resolution spectra in the range 4200–5200 Å, we have studied late O–early B stars in the very young open star cluster IC 1805. The temperatures of the stars under study have been derived by the differential method in which simple parameters were chosen for a number of spectral lines and were then compared with the analogous parameters from an extensive sample of O–B stars. Accurate <span>(T_{textrm{eff}})</span> estimates have been obtained for them from model atmospheres. Applying this method for the sample of objects under study has allowed the cluster age <span>(t=2pm 0.5)</span> Myr and distance modulus <span>((v-V)_{0}=11.5^{m})</span> to be determined with confidence. We have studied the spectroscopic variability of the emission spectrum for the sole Be star of early spectral type B MWC 50 that is a member of the cluster. We show that it is a classical Be star probably seen pole-on and has no long-term variability of the profiles typical for many classical Be stars.</p>","PeriodicalId":55443,"journal":{"name":"Astronomy Letters-A Journal of Astronomy and Space Astrophysics","volume":"50 4","pages":"249 - 257"},"PeriodicalIF":1.1,"publicationDate":"2024-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141775119","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Estimation of the Kinematic Age of the (boldsymbol{beta}) Pictoris Moving Group from Up-to-date Data","authors":"V. V. Bobylev,&nbsp;A. T. Bajkova","doi":"10.1134/S1063773724700117","DOIUrl":"10.1134/S1063773724700117","url":null,"abstract":"<p>The kinematics of about 40 single stars belonging to the <span>(beta)</span> Pictoris moving group is studied. The age of the <span>(beta)</span> Pictoris moving group is estimated from these stars with ground-based line-of-sight velocity determinations by two methods. Both estimates are kinematic. In the first method we considered the traceback trajectories of the stars, giving an estimate of <span>(t=13.2pm 1.4)</span> Myr. In the second method, by analyzing the instantaneous velocities of the stars, we show that there is an expansion of the stellar system occurring in the Galactic <span>(xy)</span> plane. Based on this effect, we find the time interval elapsed from the beginning of the expansion of the <span>(beta)</span> Pictoris moving group to the present day, <span>(t=20pm 2)</span> Myr.</p>","PeriodicalId":55443,"journal":{"name":"Astronomy Letters-A Journal of Astronomy and Space Astrophysics","volume":"50 4","pages":"238 - 248"},"PeriodicalIF":1.1,"publicationDate":"2024-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141785242","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Observation of a Helioseismically Active Solar Flare with a Low Hard X-ray Flux up to 50 keV","authors":"I. N. Sharykin,&nbsp;I. V. Zimovets,&nbsp;A. G. Kosovichev,&nbsp;I. I. Myshyakov","doi":"10.1134/S1063773724700026","DOIUrl":"10.1134/S1063773724700026","url":null,"abstract":"<p>We consider the M1.1-class solar flare occurred on July 5, 2012, at <span>(06{:}49)</span> UT. This event is unique in that a helioseismic perturbation was detected in it despite its low hard X-ray flux in the 25–50 keV energy band and its very soft hard X-ray spectrum. As a rule, most of the known sunquakes have been detected in solar flares with large hard X-ray fluxes at high energies (at least up to 100–300 keV). The event under consideration contradicts the popular hypothesis about the generation of sunquakes by beams of accelerated high-energy electrons. An analysis of the available RHESSI X-ray spectra shows that they can be explained in two ways. The X-ray spectrum in the 25–50 keV energy band is explained by a power-law distribution of accelerated electrons with an power-law index of 7–9 or by the presence of a superhot plasma with a temperature <span>(Tsim 30)</span>–60 MK. In both cases, we are dealing with electrons of relatively low energies that either were responsible for the sunquake generation or should be considered as a secondary (accompanying) phenomenon with respect to the true cause of the photospheric perturbation. The results of a joint analysis of the X-ray and microwave spectra are presented for the first time for a helioseismically active solar flare. Our analysis shows that the spectra in both ranges can be well explained by the emission of a superhot magnetized plasma and not by accelerated electrons with a soft spectrum. However, the explanation of the spectra when considering partially magnetically trapped accelerated electrons is also possible. We have estimated the parameters of the thermal plasma, accelerated electrons, and energy fluxes of various types. We analyze the dynamics of ultraviolet and X-ray emission sources. We also present an analysis of the magnetic field structure based on vector magnetograms and the nonlinear force-free coronal magnetic field extrapolation. We discuss the mechanisms for the generation of the helioseismic perturbation during the solar flare under consideration. An eruptive process could probably be both primary and secondary causes of the sunquake. The appearance of a superhot plasma in the corona could give rise to propagating thermal fronts into the lower layers of the solar atmosphere, where helioseismic waves are excited. Our analysis does not allow the possibility of the sunquake generation by accelerated electrons with a soft spectrum to be ruled out either.</p>","PeriodicalId":55443,"journal":{"name":"Astronomy Letters-A Journal of Astronomy and Space Astrophysics","volume":"50 3","pages":"203 - 219"},"PeriodicalIF":1.1,"publicationDate":"2024-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141610882","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Annihilation of Positrons from AGN Jets As a Possible Source of Cosmic Gamma-Ray Background at Energies below 511 keV","authors":"B. A. Nizamov,&nbsp;M. S. Pshirkov","doi":"10.1134/S1063773724700087","DOIUrl":"10.1134/S1063773724700087","url":null,"abstract":"<p>The origin of the diffuse gamma-ray background in the range from hundreds keV to several MeV is not known conclusively. From current models and observations it is believed that, at least partially, this background is formed by blazars and remnants of supernovae (SN) of type Ia in distant galaxies. However, these contributions are not sufficient to reproduce the observed level of the signal. In this work we propose another source which could contribute to this background, namely the jets of active galactic nuclei (AGN). The composition of jets is not known, but there are observational hints that the fraction of positrons there is substantial. Positrons are partially evacuated to the intergalactic medium and partially mix with the circumgalactic medium and annihilate there comparatively quickly. Using the AGN luminosity function, we estimated the positron production rate and the contribution of the positron annihilation to the cosmic background below 511 keV. We also estimated the analogous contribution from positron annihilation within SN Ia remnants in distant galaxies. The contribution of AGNs is estimated to be a factor of 5–10 smaller than the observed background intensity, and the contribution from SNe is yet smaller by one order of magnitude. Nevertheless, the contribution of AGNs appeared to be larger than the contribution of blazars estimated from <i>Swift</i>-BAT and <i>Fermi</i>-LAT observations. The main uncertainty in our model is the fraction of positrons remaining in the circumgalactic medium which makes our estimation an upper limit.</p>","PeriodicalId":55443,"journal":{"name":"Astronomy Letters-A Journal of Astronomy and Space Astrophysics","volume":"50 3","pages":"186 - 193"},"PeriodicalIF":1.1,"publicationDate":"2024-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141610711","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Erratum to: The Method of Periodic Principal Components for the Dynamic Spectrum of Radio Pulsars and Faraday Rotation of Nine Pulse Components of PSR B0329+54","authors":"V. V. Kocharovsky,&nbsp;V. V. Vdovin,&nbsp;A. S. Gavrilov,&nbsp;E. R. Kocharovskaya,&nbsp;S. V. Logvinenko,&nbsp;E. M. Loskutov,&nbsp;V. M. Malofeev","doi":"10.1134/S1063773724030010","DOIUrl":"10.1134/S1063773724030010","url":null,"abstract":"","PeriodicalId":55443,"journal":{"name":"Astronomy Letters-A Journal of Astronomy and Space Astrophysics","volume":"50 3","pages":"220 - 220"},"PeriodicalIF":1.1,"publicationDate":"2024-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142411449","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Increase in the Brightness of the Cosmic Radio Background toward Galaxy Clusters","authors":"S. A. Grebenev,&nbsp;R. A. Sunyaev","doi":"10.1134/S1063773724700063","DOIUrl":"10.1134/S1063773724700063","url":null,"abstract":"&lt;p&gt;We explore the possibility of detecting the excess of the cosmic radio background toward galaxy clusters due to its Compton scattering by electrons of the hot intergalactic gas. When mapping the background fluctuations at frequencies below &lt;span&gt;({lesssim}800)&lt;/span&gt; MHz, this effect gives rise to a radio source at the location of the cluster. At higher frequencies, where the microwave (relic) radiation dominates in the cosmic background, a ‘‘negative’’ source (a ‘‘shadow’’ on the map of background fluctuations) is observed at the location of the cluster due to the transfer of some of the relic photons upward along the frequency axis upon their scattering (into the range &lt;span&gt;(nugtrsim 217)&lt;/span&gt; GHz; Sunyaev and Zeldovich 1970, 1972). We have computed the spectra of the expected radio background distortions for various parameters of clusters and show that in many cases in the wide frequency range &lt;span&gt;(30 textrm{MHz}lesssimnulesssim 3 {textrm{GHz}})&lt;/span&gt; the measurement of the distortions will be hindered by the intrinsic thermal (bremsstrahlung) radiation from the intergalactic gas and the scattered radio emission from cluster galaxies associated with their past activity, including the synchrotron radiation from ejected relativistic electrons. Below &lt;span&gt;({sim}20)&lt;/span&gt; MHz the scattering effect always dominates over the thermal gas radiation due to the general increase in the intensity of the cosmic radio background, but highly accurate measurements at such frequencies become difficult. Below &lt;span&gt;({sim}5)&lt;/span&gt; MHz the effect is suppressed by the induced scattering. We have found the frequency ranges that are optimal for searching for and measuring the Compton radio background excess. We show that hot (&lt;span&gt;(kT_{textrm{e}}gtrsim 8 {textrm{keV}})&lt;/span&gt;) clusters at high (&lt;span&gt;(zgtrsim 0.5)&lt;/span&gt;) redshifts are most promising for its observation. Because of the strong concentration of the bremsstrahlung to the cluster center, the peripheral observations of the Compton excess must be more preferable than the central ones. Moreover, owing to the thermal radiation of the gas and its concentration to the center, the above-noted transition from the ‘‘negative’’ source on the map of background fluctuations to the ‘‘positive’’ one when moving downward along the frequency axis must occur not gradually but through the stage of a ‘‘hybrid source’’—the appearance of a bright spot surrounded by a dark ring. This form of the source in projection is explained by its unusual three-dimensional shape in the form of a narrow radio bremsstrahlung peak rising from the center of a wide deep hole associated with the Compton scattering of the cosmic microwave background. The scattered radiation from an active central cluster galaxy in the past can amplify the effect. An analogous ‘‘hybrid source’’ also appears on the map of background fluctuations near a frequency of &lt;span&gt;(217.5)&lt;/span&gt; GHz—when passing from the deficit of the cosmic microwave backgr","PeriodicalId":55443,"journal":{"name":"Astronomy Letters-A Journal of Astronomy and Space Astrophysics","volume":"50 3","pages":"159 - 185"},"PeriodicalIF":1.1,"publicationDate":"2024-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141610710","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Clumpy Accretion As a Possible Cause of Prolonged Eclipses in UX Ori Stars","authors":"V. P. Grinin,&nbsp;T. V. Demidova","doi":"10.1134/S1063773724700075","DOIUrl":"10.1134/S1063773724700075","url":null,"abstract":"<p>We propose a model of deep and prolonged eclipses in young UX Ori stars. Some of these events last for decades and existing models cannot explain them. We show that such eclipses can be caused by the infall of gas and dust clumps from the remnants of the protostellar cloud onto the protoplanetary disk. The perturbation in the disk caused by the infall of a clump leads to a burst of accretional stellar activity and, as a consequence, to a strengthening of the disk wind. If the circumstellar disk is tilted at a small angle to the line of sight, then the dust raised by the wind from the disk surface can cause a dramatic decrease in the stellar brightness that can last for decades.</p>","PeriodicalId":55443,"journal":{"name":"Astronomy Letters-A Journal of Astronomy and Space Astrophysics","volume":"50 3","pages":"194 - 202"},"PeriodicalIF":1.1,"publicationDate":"2024-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141614659","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Method of Periodic Principal Components for the Dynamic Spectrum of Radio Pulsars and Faraday Rotation of Nine Pulse Components of PSR B0329+54","authors":"V. V. Kocharovsky,&nbsp;V. V. Vdovin,&nbsp;A. S. Gavrilov,&nbsp;E. R. Kocharovskaya,&nbsp;S. V. Logvinenko,&nbsp;E. M. Loskutov,&nbsp;V. M. Malofeev","doi":"10.1134/S1063773724700051","DOIUrl":"10.1134/S1063773724700051","url":null,"abstract":"<p>We have developed the method of periodic principal components for signals with a quasi-periodic dynamic spectrum characteristic of radio pulsars. The method is based on an analysis of the eigenvectors and eigenvalues of the signal frequency–time correlation matrix averaged over many pulsar rotation periods. Using the observations of PSR B0329<span>(+)</span>54 with the radio telescope at Pushchino Radio Astronomy Observatory near a frequency of 111 MHz in a 2.5 MHz band as an example, we show that even for short data intervals (a few minutes) the developed method allows one to identify up to nine pulse components of the pulsar, to estimate the correlation between them, and to find the period of Faraday modulation for each component as well as its relative phase and frequency–time chirp rate, i.e., it allows the structure of the emission source to be judged.</p>","PeriodicalId":55443,"journal":{"name":"Astronomy Letters-A Journal of Astronomy and Space Astrophysics","volume":"50 2","pages":"120 - 137"},"PeriodicalIF":1.1,"publicationDate":"2024-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141172517","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Study of the Components of the Double Star ADS 15571 by Speckle Interferometry","authors":"E. N. Sokov,&nbsp;D. L. Gorshanov,&nbsp;I. S. Izmailov,&nbsp;N. A. Shakht,&nbsp;I. A. Sokova,&nbsp;A. S. Beskakotov,&nbsp;V. V. Dyachenko,&nbsp;A. F. Maksimov,&nbsp;A. A. Mitrofanova,&nbsp;D. A. Rasstegaev","doi":"10.1134/S1063773724700038","DOIUrl":"10.1134/S1063773724700038","url":null,"abstract":"<p>Based on the speckle observations of the wide double star ADS 15571 with the 6-m BTA telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences in 2014, we have confirmed the existence of a close companion to component A that was previously detected from astrometric observations at the Pulkovo Observatory. An extension of the BTA observations from 2014 to 2022 has allowed 28 positions of the companion relative to the primary star to be obtained. From this series we have constructed the relative orbit of the companion and determined the sum of the masses of subsystem A (<span>(1.686pm 0.014)</span>\u0000 <span>(M_{odot})</span>). A comparison of this orbit with the orbit of the photocenter of component A constructed from Pulkovo photographic observations has also allowed the mass ratio of the primary star and the companion and their individual masses to be estimated: <span>(M_{textrm{Aa}}=(1.10pm 0.07))</span>\u0000 <span>(M_{odot})</span> and <span>(M_{textrm{Ab}}=(0.59pm 0.07))</span>\u0000 <span>(M_{odot})</span>. Based on the estimates of the magnitude difference between the two stars of the system ADS 15571A, we have estimated the spectral types of the components: ADS 15571Aa—F8V; ADS 15571Ab—K5V–K5.5V. The speckle observations of component B have shown that it has no resolvable companions.</p>","PeriodicalId":55443,"journal":{"name":"Astronomy Letters-A Journal of Astronomy and Space Astrophysics","volume":"50 2","pages":"138 - 147"},"PeriodicalIF":1.1,"publicationDate":"2024-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141172550","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Passage of a Gamma-Ray Burst through a Molecular Cloud: Cloud Ionization Structure","authors":"A. V. Nesterenok","doi":"10.1134/S1063773724700014","DOIUrl":"10.1134/S1063773724700014","url":null,"abstract":"<p>We have constructed a model for the passage of gamma-ray burst radiation through a dense molecular cloud. In our calculations we take into account the main radiation–cloud material interaction processes: the ionization of H and He atoms, the ionization of metal ions with the emission of Auger electrons, the ionization and photodissociation of H<span>({}_{2})</span> molecules, the absorption of ultraviolet radiation in the H<span>({}_{2})</span> lines of the Lyman and Werner bands, and the vaporization of dust grains. The ionization of metal ions by X-ray radiation determines the gas ionization fraction in the region where the gas is predominantly neutral. The photoionization of the inner electron shells of ions is accompanied by the emission of Auger electrons, giving rise to metal ions in a high ionization state. In particular, the column densities of Mg, Si, and Fe ions in the ionization states I–IV are much lower than the column densities of these ions in the ionization state V or higher. The photoionization of metal ions by ultraviolet radiation occurs only at distances smaller than the dust vaporization radius and for neutral atoms with an ionization threshold below 13.6 eV. The results of our calculations have confirmed the previously made assumption that the ionization of He atoms plays an important role in the absorption of radiation in the X-ray wavelength range. For a low metallicity, <span>(textrm{[M/H]}leq{-}1)</span>, the role of helium atoms is dominant.</p>","PeriodicalId":55443,"journal":{"name":"Astronomy Letters-A Journal of Astronomy and Space Astrophysics","volume":"50 2","pages":"99 - 119"},"PeriodicalIF":1.1,"publicationDate":"2024-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141172974","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}