The nature of terrains of different types on the surface of Venus and selection of potential landing sites for a descent probe of the <Emphasis Type="Italic">Venera-D</Emphasis> Mission     

M.?A.?IvanovEmail author  L.?V.?Zasova  M.?V.?Gerasimov  O.?I.?Korablev  M.?Ya.?Marov  L.?M.?Zelenyi  N.?I.?Ignat’ev  A.?G.?Tuchin 《Solar System Research》2017,51(1):1-19

We discuss a change in the resurfacing regimes of Venus and probable ways of forming the terrain types that make up the surface of the planet. The interpretation of the nature of the terrain types and their morphologic features allows us to characterize their scientific priority and the risk of landing on their surface to be estimated. From the scientific point of view, two terrain types are of special interest and represent easily achievable targets: the lower unit of regional plains and the smooth plains associated with impact craters. Regional plains are probably a melting from the upper fertile mantle. The material of smooth plains of impact origin is a well-mixed and representative sample of the Venusian crust. The lower unit of regional plains is the most widespread one on the surface of Venus, and it occurs within the boundaries of all of the precalculated approach trajectories of the lander. Smooth plains of impact origin are crossed by the approach trajectories precalculated for 2018 and 2026.  相似文献   

Method for Validation of the Onboard Attitude Control System Software of the <Emphasis Type="Italic">Auriga</Emphasis> Earth Remote Sensing Small Spacecraft     

P.?E.?RozinEmail author 《Solar System Research》2017,51(7):646-653

The paper considers a digital modeling complex for the attitude control system of the Auriga Earth remote sensing small spacecraft. Mathematical models of measuring and executive devices are described. The results of spacecraft orbital attitude tests are presented.  相似文献   

Change in the activity character of the coronae of low-mass stars of various spectral types     

B.?A.?NizamovEmail author  M.?M.?Katsova  M.?A.?Livshits 《Astronomy Letters》2017,43(3):202-209

We study the dependence of the coronal activity index on the stellar rotation velocity. This question has been considered previously for 824 late-type stars on the basis of a consolidated catalogue of soft X-ray fluxes. We carry out a more refined analysis separately for G, K, and M dwarfs. Two modes of activity are clearly identified in them. The first is the saturation mode, is characteristic of young stars, and is virtually independent of their rotation. The second refers to the solar-type activity whose level strongly depends on the rotation period. We show that the transition from one mode to the other occurs at rotation periods of 1.1, 3.3, and 7.2 days for stars of spectral types G2, K4, and M3, respectively. In light of the discovery of superflares on G and K stars from the Kepler spacecraft, the question arises as to what distinguishes these objects from the remaining active late-type stars. We analyze the positions of superflare stars relative to the remaining stars observed by Kepler on the “amplitude of rotational brightness modulation (ARM)—rotation period” diagram. The ARM reflects the relative spots area on a star and characterizes the activity level in the entire atmosphere. G and K superflare stars are shown to be basically rapidly rotating young objects, but some of them belong to the stars with the solar type of activity.  相似文献   

Spatial environment of polar-ring galaxies from the SDSS     

S.?S.?Savchenko  V.?P.?ReshetnikovEmail author 《Astronomy Letters》2017,43(3):146-151

Based on SDSS data, we have considered the spatial environment of galaxies with extended polar rings. We used two approaches: estimating the projected distance to the nearest companion and counting the number of companions as a function of the distance to the galaxy. Both approaches have shown that the spatial environment of polar-ring galaxies on scales of hundreds of kiloparsecs is, on average, less dense than that of galaxies without polar structures. Apparently, one of the main causes of this effect is that the polar structures in a denser environment are destroyed more often during encounters and mergers with other galaxies.  相似文献   

Diffusion of elements in the interstellar medium in early-type galaxies     

P.?S.?MedvedevEmail author  S.?Yu.?Sazonov  M.?R.?Gilfanov 《Astronomy Letters》2017,43(5):285-303

The role of diffusion in the redistribution of elements in the hot interstellar medium of earlytype galaxies is considered. It is well known that gravitational sedimentation can affect significantly the abundances of helium and heavy elements in the hot intergalactic gas of massive galaxy clusters. The universal temperature profile in cool-core clusters and the theoretical mass–temperature relation suggest that the maximum effect of sedimentation must take place in the most massive virialized objects in the Universe. However, observational data from the Chandra and XMM-Newton observatories demonstrate more complex scaling relations between the masses of early-type galaxies and other parameters, such as the mass fraction and temperature of the interstellar gas. An important fact is that the radial temperature profile can have both falling and rising patterns. We have calculated the diffusion based on the observed gas density and temperature distributions for 13 early-type galaxies that have different envelope types and cover a wide range of X-ray luminosities. To estimate the maximum effect of sedimentation and thermal diffusion, we have solved the full set of Burgers equations for a non-magnetized interstellar plasma. The results obtained demonstrate a considerable increase of the He/H ratio within one effective radius for all galaxies of our sample. For galaxies with a falling or constant temperature profile the average increase of the helium abundance is 60% in one billion years of diffusion. The revealed effect can introduce a significant bias into the metal abundance estimate based on X-ray spectroscopy and can affect the evolution of stars that could be formed from a gas with a high helium abundance.  相似文献   

Systematic error of the Gaia DR1 TGAS parallaxes from data for the red giant clump     

G.?A.?GontcharovEmail author 《Astronomy Letters》2017,43(8):545-558

Based on the Gaia DR1 TGAS parallaxes and photometry from the Tycho-2, Gaia, 2MASS, andWISE catalogues, we have produced a sample of ~100 000 clump red giants within ~800 pc of the Sun. The systematic variations of the mode of their absolute magnitude as a function of the distance, magnitude, and other parameters have been analyzed. We show that these variations reach 0.7 mag and cannot be explained by variations in the interstellar extinction or intrinsic properties of stars and by selection. The only explanation seems to be a systematic error of the Gaia DR1 TGAS parallax dependent on the square of the observed distance in kpc: 0.18R ² mas. Allowance for this error reduces significantly the systematic dependences of the absolute magnitude mode on all parameters. This error reaches 0.1 mas within 800 pc of the Sun and allows an upper limit for the accuracy of the TGAS parallaxes to be estimated as 0.2 mas. A careful allowance for such errors is needed to use clump red giants as “standard candles.” This eliminates all discrepancies between the theoretical and empirical estimates of the characteristics of these stars and allows us to obtain the first estimates of the modes of their absolute magnitudes from the Gaia parallaxes: mode(M _H ) = ?1.49 ^m ± 0.04 ^m , mode(M _Ks ) = ?1.63 ^m ± 0.03 ^m , mode(M _W1) = ?1.67 ^m ± 0.05 ^m mode(M _W2) = ?1.67 ^m ± 0.05 ^m , mode(M _W3) = ?1.66 ^m ± 0.02 ^m , mode(M _W4) = ?1.73 ^m ± 0.03 ^m , as well as the corresponding estimates of their de-reddened colors.  相似文献   

Kinematics of the structure of the active region in Orion-KL     

L.?I.?MatveyenkoEmail author  V.?A.?Demichev  S.?S.?Sivakon’ 《Astronomy Letters》2017,43(6):400-415

The kinematics of the superfine structure of the active star-forming region in the dense molecular cloud Orion-KL has been investigated in the Н₂О maser emission for the period 1998–2003. It has been established that the surrounding gas inflows onto the disk and is transferred in a spiral trajectory to the center. An excess angular momentum as it is accumulated is carried away by a bipolar outflow; a highvelocity central flow surrounded by low-velocity components is formed. The outer low-velocity component observed at the detection limit has a diameter Ø₃ ≈ 4.5 AU, further out, Ø₂ ≈ 0.5 AU and Ø₁ ≈ 0.24 AU. The gas transfer velocity increases exponentially as the center is approached. The maser emission from the central flow is decisive. A rise in the velocity leads to a flow discontinuity and a reduction in the amount of inflowingmaterial and, accordingly, the emission level. The emission in the period under consideration was reduced exponentially for ~6 months, whereupon its restoration began.  相似文献   

Multiple X-ray bursts and the model of a spreading layer of accreting matter over the neutron star surface     

S.?A.?GrebenevEmail author  I.?V.?Chelovekov 《Astronomy Letters》2017,43(9):583-594

We report the detection of series of close type I X-ray bursts consisting of two or three events with a recurrence time much shorter than the characteristic (at the observed mean accretion rate) time of matter accumulation needed for a thermonuclear explosion to be initiated on the neutron star surface during the JEM-X/INTEGRAL observations of several X-ray bursters. We show that such series of bursts are naturally explained in the model of a spreading layer of accreting matter over the neutron star surface in the case of a sufficiently high (? ? 1 × 10^?9 M _⊙ yr^?1) accretion rate (corresponding to a mean luminosity L _tot ? 1 × 10³⁷erg s^?1). The existence of triple bursts requires some refinement of the model—the importance of a central ring zone is shown. In the standard model of a spreading layer no infall of matter in this zone is believed to occur.  相似文献   

IGR J17445-2747—Yet another X-ray burster in the galactic bulge     

I.?A.?MereminskiyEmail author  S.?A.?Grebenev  R.?A.?Sunyaev 《Astronomy Letters》2017,43(10):656-663

The discovery of a type I X-ray burst from the faint unidentified transient source IGR J17445-2747 in the Galactic bulge by the JEM-X telescope onboard the INTEGRAL observatory is reported. Type I bursts are believed to be associated with thermonuclear explosions of accreted matter on the surface of a neutron star with a weak magnetic field in a low-mass X-ray binary. Thus, this observation allows the nature of this source to be established.  相似文献   

Positions of extragalactic objects in the vicinity of M3 and M31 (5C3 radio field) and in the 5C1 radio field     

W. R. Dick  H. Lorenz  P. Notni  E. Schilbach  R.-D. Scholz  G. A. Richter 《Astronomische Nachrichten》1986,307(2):85-88

We have determined the positions of 65 compact extragalactic objects with magnitudes between 16^m and 21^m.7. The mean error of one position is about 0″.3 in α cos δ and in δ. Some hitherto unpublished redshifts are also listed.  相似文献