The Influence of Superflares of Host Stars on the Dynamics of the Envelopes of Hot Jupiters

Results of a study of the influence of solar-type host stars superflares on the gas dynamics of the extended envelopes of giant exoplanets are presented. During flare events, the radiation intensity of the host star in the extreme ultraviolet and soft X-ray can increase by several orders of magnitude for a short time, leading to strong local heating of the exoplanet atmosphere on the side facing the star, with the formation of shocks in the atmosphere. Computations of the gas-dynamical response of the atmosphere of the hot Jupiter HD 209458b to characteristic superflares of solar-like stars were carried out earlier in [1] using a one-dimensional aeronomical model correctly taking into account heating and chemical processes in the atmosphere. To investigate the outflow of atmospheric gas, the results obtained with this onedimensional model were used as simple boundary conditions for computations of the three-dimensional flow structure after a flare. The results of these three-dimensional gas-dynamical computations show that the mass ejection of the flare increases the size of the envelope over several hours, which could be detected with existing observing facilities. It is shown that the mass-loss rates for the most powerful superflare considered could be enhanced by an order of magnitude over several tens of hours after the flare.

     

Formation of Two-ring Polycyclic Aromatic Hydrocarbons via the Recombination of Benzyl and Propargyl Radicals under the Circumstellar Envelopes Conditions of Asymptotic Giant Branch Stars

Astronomy Reports - The mechanisms and kinetics of the formation of two-ring polycyclic aromatic hydrocarbons via the recombination of benzyl (C7H7) and propargyl (C3H3) radicals under the...     

Spots and Activity of Am Stars

The results of a detailed analysis of spot activity on metallic-line A (Am) stars are presented. Two ROTD stars, KIC 8323104 and KIC 8703413, whose power spectra are characterized by a narrow peak and numerous lower-amplitude features at lower frequencies are considered. KIC 12253106, which is not an ROTD star, but undoubtedly has spots on its surface, is also studied. The rotation periods of the surface spots have been found, and the evolution of the spot positions explored. The differential-rotation parameter ΔΩ has been estimated. An analysis of the light curve to reconstruct maps of temperature inhomogeneities on the surface of KIC 8703413 has been performed. These maps indicate concentrations of the active regions at two longitudes. One of these longitudes was active about twice as often as the other one during our observations. The cyclical pattern of the variability of the spot positions on the stellar surface is determined, which may be related to oscillations due to Rossby waves.     

Statistics of Stars with Relativistic Velocities

The scenario for the dynamical capture of a binary system in the neighborhood of a supermassive black hole used byHills in 1988 to predict the existence of hypervelocity stars (~1000 km/s) allows the existence of stars with relativistic velocities attaining (1/3?2/3)c, where c is the speed of light. The increase of the kinetic energy of these stars by more than a factor of 100 is due to the replacement of one component of the binary with a supermassive black hole. This scenario takes candidate of relativisti©velocity stars outside our Galaxy, into intergalactic space, where they could be ejected from merging galaxies populated by supermassive black holes. At present, this is a hypothetical class of stars with anomalous kinematics, but it is already posing a serious challenge for modern astrometry, which, like 300 years ago, is still concerned with the detection of proper motions. While this was related to stars in the solar neighborhood at the time of Halley, is now a problem for studies of the most remote and weakest stars in intergalactic space. Possibilities for detecting such stars must be based on estimates of their abundances, that is, on their statistics. This paper is based on a presentation made at the conference “Modern Astrometry 2017,” dedicated to the memory of K.V. Kuimov (Sternberg Astronomical Institute, Moscow State University, October 23–25, 2017).

     

A Catalog of Variable Stars based on the new name list

We present a new electronic version of the General Catalog of Variable Stars (GCVS) based on the new IAU name list of confirmed variable stars. The catalog contains 1270 stars, most of them contained earlier in the New Catalog of Suspected Variable Stars or its supplement. A number of recent studies—including those by authors of the catalog, who investigated many stars using data from modern automatic surveys, determined light-curve elements for periodic stars, and plotted numerous light curves—have made it possible to move these stars to the GCVS. Among the catalog objects, 24 stars are novae or other unusual variable stars that acquired their GCVS names out of the usual order, upon communication from the Bureau of Astronomical Telegrams of the International Astronomical Union. We present the GCVS names, coordinates, classifications (in two forms: the GCVS system and a new, proposed system), brightness-variation limits, and light-curve elements for the catalog stars, as well as bibliographic references and remarks when necessary. We discuss several catalog stars that are of astrophysical interest or caused problems during the compilation of the catalog.     

Stars with relativistic speeds in the Hills scenario

The dynamical capture of a binary system consisting of a supermassive black hole (SMBH) and an ordinary star in the gravitational field of a central (more massive) SMBH is considered in the three-body problem in the framework of a modified Hills scenario. The results of numerical simulations predict the existence of objects whose spatial speeds are comparable to the speed of light. The conditions for and constraints imposed on the ejection speeds realized in a classical scenario and the modified Hills scenario are analyzed. The star is modeled using an N-body approach, making it possible to treat it as a structured object, enabling estimation of the probability that the object survives when it is ejected with relativistic speed as a function of the mass of the star, the masses of both SMBHs, and the pericenter distance. It is possible that the modern kinematic classification for stars with anomalously high spatial velocities will be augmented with a new class—stars with relativistic speeds.     

Evolution of Stars Paired with Intermediate-Mass Black Holes

Under certain conditions, stars close to intermediate-mass black holes (IMBHs) can form close binary systems with these objects, in which the Roche lobe can be filled by the star and intense accretion of the star’s matter onto the IMBH is possible. Recently, accreting IMBHs have been associated with hyperluminous X-ray sources (HLXs), whose X-ray luminosities can exceed 10⁴¹ erg/s. In this paper, the evolution of star—IMBH binary systems is investigated assuming that the IMBH mainly accretes the matter of its companion star, and that the presence of gas in the vicinity of the IMBH does not appreciably affect changes in the orbit of the star. The computations take into account all processes determining the evolution of ordinary binary systems, as well as the irradiation of a star by hard radiation during the accretion of its matter onto the IMBH. The absorption of external radiation in the stellar envelope was calculated applying the same formalism that is used to calculate the opacity of the stellar matter. The computations also assumed that, if the characteristic time for the mass transfer is less than the thermal time scale of the star, there is no exchange betwween the orbital angular momentum of the system and the angular momentum of the matter flowing onto the IMBH.

Numerical simulations have shown that, under these assumptions, three types of evolution are possible for such a binary system, depending on the mass of the IMBH and the star, as well as on the star’s initial distance from the IMBH. The first type ends with the destruction of the star. For low-mass main sequence (MS) stars, only this option is realized, even in the case of large initial distances from IMBH. For massive MS stars, the star is also destroyed if the mass of the IMBH is high and the initial distance of the star from the IMBH is sufficiently small.

The second type of evolution can occur for massive MS stars, which are initially located farther from the IMBH than in the first type of evolution. In this case, the massive star fills its Roche lobe during its evolutionary expansion, after which a stage of intense mass transfer begins. It is in this phase of the evolution that the star- IMBH system can manifest itself as a HLX, when its X-ray luminosity L_X exceeds 10⁴¹ erg/s for a fairly long time. Numerical simulations show that the initial mass of the donor star in systems with M_BH = (10³?10⁵)M_⊙ must be close to ～10 M_⊙ in this case. The characteristic duration of the HLX stage is 30 000–70 000 years. For smaller initial donor masses close to ～5M_⊙, L_X does not reach 10⁴¹ erg/s in the stage of intense mass transfer, but can exceed 10⁴⁰ erg/s. The duration of this stage of evolution is 300 000–800 000 years. A characteristic feature of this second type of evolution is an increase in the orbital period of the system over time. As a result, after a period of intense mass loss, the star “retreats” inside the Roche lobe. A remnant of the star in the form of a white dwarf is left behind, and can end up fairly far from the IMBH.

The third type of evolution can occur for massive MS stars that are initially even farther from the IMBH, as well as for massive stars that are already evolved at the initial time. In this case, conservative mass exchange in the presence of intense stellar wind leads to the star moving away from the IMBH, without filling its Roche lobe at all. For massive stars with sufficiently strong stellar winds (for example, stars with masses ～50M_⊙), the accretion rate of matter onto the IMBH in this case can reach values that are characteristic of HLXs. As in the case of the second type of evolution, the stellar remnant can remain at a fairly large distance from the IMBH.

     

Motion of Stars in Layered Inhomogeneous Elliptical Galaxies

Astronomy Reports - The problem of the spatial motion of a passively gravitating body (PGB) in the gravitational field of a layered inhomogeneous elliptical galaxy (LIEG) is considered on the basis...     

Excitation of Turbulence in Protoplanetary Disks around Binary Stars

Accretion disks around young binary stars are subject to strong forces exerted by the system components. Gas–dynamical interactions excite strong non-linear perturbations in the disk, which can give rise to turbulence. This study considers a mechanism for the excitation of turbulence based on the instability of non-linear waves in a rotating flow. It is shown that the spectrum of non-linear perturbations excited in the inner part of the disk leads to turbularization of the flow. Estimates of the Shakura–Syunyaev index, α ～ 0.01?0.05, are obtained for use in numerical models of accretion disks.     

Studies of Modern Star Catalogs Based on Photoelectric Observations of Lunar Occultations of Stars

An important area of investigation in astronomy is the relationship between fundamental and dynamical coordinate systems. Valuable material for such studies is provided by photoelectric occultation observations of stars by the Moon, which can provide high precision of detecting rapidly occurring processes and have been carried out over a long time interval. This latter feature is especially important for analyses of the stellar propermotions dynamics. A method has been developed to use photoelectric occultation observations to determine the orientation and rotational parameters of the axes of the coordinate system used for modern star catalogs relative to the coordinate axes of a highly accurate dynamical ephemeris of theMoon. A complete database of photoelectric occultation observations has been created for this purpose, containing data for 57 365 events. The combination of photoelectric occultation observations and other astronomical observations such as lunar laser-ranging data enables the highly accurate determination of parameters of the Moon’s dynamics, such as systematic errors in catalog coordinate systems, including various geodetic reference systems. The parameters of shifts and the rotation of the axes of the Hipparcos Celestial Reference Frame relative to the DE421 dynamical system are obtained. This paper is based on a talk given at the conference “Modern Astrometry 2017,” dedicated to the memory of K.V. Kuimov (Sternberg Astronomical Institute, Moscow State University, October 23–25, 2017).

     

Observability of Single Neutron Stars at SRG/eROSITA

Astronomy Reports - A four-year sky survey with the use of the eROSITA telescope on board the Spektr-RG observatory with focusing optics will provide the best coverage in the soft (0.5–2 keV)...     

Giant Pulses of Radio Pulsars

Astronomy Reports - The parameters of pulsars with detected giant pulses (GPs) and the known models proposed to describe the GP phenomenon have been analyzed. The angles between the magnetic moment...     

姻袭成矿与特大型矿床

姻袭成矿与特大型矿床ＡｆｉｌｉａｔｉｏｎａｌＭｅｔａｌｏｇｅｎｙａｎｄＧｉａｎｔＯｒｅＤｅｐｏｓｉｔｓ裴荣富（中国地质科学院矿床地质研究所，北京）烟袭成矿或称亲缘成矿。这一成矿概念早在中世纪（１６世纪中期以前）的矿石成因猜想年代就已萌芽［１］。例如当...     

Comparison of Venusian Coronae with Giant Circumferential Dyke Swarms on Earth

正The surface of Venus features a large number(500)of quasi-circular tectono-magmatic features known as coronae.Coronae are characterized in part by their topographic characteristics,which can be diverse and     

Spectral Energy Distribution for T Tauri Stars with a Debris Disk

Astronomy Reports - The analysis results of spectral energy distribution (SED) curves in the range 0.36–100 μm for 45 young WTTS-type stars and 9 comparison CTTS-type stars are...     

The Role of Gravitational Radiation in the Evolution of Stars and Galaxies

The conditions for the formation of close binaries containing main-sequence stars, degenerate dwarfs of various types, neutron stars, and black holes of various masses are considered. The paper investigates the evolution of the closest binary systems under the influence of their gravitational-wave radiation. The conditions under which the binary components can merge on a time scale shorter than the Hubble time as a result of their emission of gravitational waves are estimated. A self-consistent scenario model is used to estimate the frequency of such events in the Galaxy, their observable manifestations, the nature of the merger products, and the role of these events in the evolution of stars and galaxies. The conditions for the formation and evolution of supermassive binary black holes during collisions andmergers of galaxies in their dense clusters are studied.

     

Giant Metallic Deposits--a Century of Exponential Progress

Please refer to the attachment(s) for more details.     

地幔柱与巨型放射状岩墙群

当前,在对超大陆和超大陆事件研究过程中,对地幔柱引发的超大陆裂解作用普遍引起了重视.为进一步在国内开展同一领域的研究工作,作者在介绍地幔柱一般特征的基础上,着重阐述了作为地幔柱活动产物之一的巨型放射状岩墙群的特点及国外元古宙基性岩墙群的几个实例,同时对我国古元古代初期、中元古代初期和新元古代等三个时期的基性岩墙群的分布及年代学做了简略小结,指出我国在前寒武纪基性岩墙群研究工作中应在岩相学和地球化学研究的基础上,进一步注意对其产状、形态、规模和精确定年的研究.