Spectrophotometric investigation of eight galaxies with a UV excess

The results of a spectroscopic and morphological investigation of galaxies with a UV excess Nos. 27, 28, 93, 101, 109, 164, 204, and 217 from the lists of [M. A. Kazarian, 15, 5, 193 (1979)] are given. The equivalent widths, relative intensities, and half- widths of lines are determined. The masses of galaxies Nos. 28, 93, 101, 164, 204, and 217 are also determined. Translated from Astrofizika, Vol. 41, No. 2, pp. 175–184. April-June, 1998.     

V1589 Cyg=B19: A foreground dMe flare star in the direction of NGC 7000

Institute of theoretical Astrophysics, Oslo, Norway; Department of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences; Department of Astronomy and McDonald Observatory, Austin, Texas, USA; Department of Physics and Astronomy, University of Arkansas at Little Rock, Arkansas, USA; Byurakan Astrophysical Observatory Armenian Academy of Sciences, USSR. Published in English in Astrofizika, Vol. 19, No. 1, 67–73, July–August, 1988.     

On string cosmology with a dilaton potential. II

Investigations of string cosmology with a nonperturbative dilaton potential, begun in the first part of this work, are continued. The picture of cosmological evolution of an isotropic, gravi-dilaton model for different cases of the behavior of the potential in the region of strong coupling is analyzed by methods of the qualitative theory of dynamical systems. Features of models with potentials that take negative values in certain ranges of values of the dilaton field are discussed. A specific mechanism of generation of the nonperturbative potential, based on gaugino condensation in a hidden sector of the gauge group, is considered. Translated from Astrofizika, Vol. 40, No. 4, pp. 517–534, October-December, 1997.     

Photometric Geodesy of main-belt asteroids: I. Lightcurves of 26 large,rapid rotators

We present 5 years of lightcurve data on a sample of large, rapidly rotating asteroids selected for a program of “photometric geodysy.” A total of 257 complete or partial lightcurves were obtained for 26 asteroids, numbers 9, 15, 16, 22, 22, 29, 39, 41, 43, 45, 55, 65, 87, 88, 107, 125, 129, 130, 201, 216, 337, 349, 354, 511, 584, and 694. The observing protocol was designed to obtain precise absolute photometry at a wide variety of orbital longitudes and phase angles. The purpose of this data set is to allow determination (in future publications) of pole positions and shapes, and to constrain densities, strength, and other geophysical traits of these bodies.     

人工神经网络在天文学中的应用

人工神经网络具有自学习、自适应、鲁棒性好、动态响应快等特点,并具有较强的非线性处理问题能力,因此在天文学中得到广泛而成功的应用．综述了人工神经网络在天文学中主要应用模型的基本原理和优缺点,阐述了人工神经网络适用于天文学的某些基本特征,着重介绍了人工神经网络在天文学中的具体应用实例,并对其发展和应用前景进行了展望．由于天文数据分布的庞杂和天文数据量的急剧增加,人工神经网络将日益显示出优越性．     

Photometric study of the major satellites of Uranus

In this paper, we analyze the results of ground-based and space-born photometric observations of the major satellites of Uranus—Miranda, Ariel, Umbriel, Titania, and Oberon. All sets of photometric observations of the satellites available in the literature were examined for uniformity and systematic differences and summarized to a unified set by wavelength ranging from 0.25 to 2.4 μm. This set covers the interval of phase angles from 0.034° to 35°. The compound phase curves of brightness of the satellites in the spectral bands at 0.25, 0.41, 0.48, 0.56, 0.75, 0.91, 1.4, and 1.8 μm, which include a pronounced opposition surge and linear part, were constructed. For each satellite, the geometric albedo was found in different spectral bands taking into account the brightness opposition effect, and its spectral dependence was studied. It has been shown that the reflectance of the satellites linearly depends on the wavelength at different phase angles, but has different spectral gradients. The parameters of the phase functions of brightness, including the amplitude and the angular width of the brightness opposition surge, the phase coefficient, and the phase angle at which the nonlinear increase in brightness starts, were determined and their dependences on wavelength and geometric albedo were analyzed. Our investigations show that, in their optical properties, the satellites Miranda and Ariel, Titania and Oberon, and Umbriel present three types of surfaces. The observed parameters of the brightness opposition effect for the Uranian satellites, some ice satellites of Jupiter and Saturn, and the E-and S-type asteroids are analyzed and compared within the framework of the coherent backscattering and mutual shadowing mechanisms.     

Reconstructing the orbital history of the Veritas family

The family of (490) Veritas is a young, dynamically heterogeneous asteroid family, located in the outer main belt. As such, it represents a valuable example for studying the effects of chaotic diffusion on the shape of asteroid families. The Veritas family can be decomposed into several groups, in terms of the principal mechanisms that govern the local dynamics, which are analyzed here. A relatively large spread in proper eccentricity is observed, for the members of two chaotic groups. We show that different types of chaos govern the motion of bodies within each group, depending on the extent of overlap among the components of the corresponding resonant multiplets. In particular, one group appears to be strongly diffusive, while the other is not. Studying the evolution of the diffusive group and applying statistical methods, we estimate the age of the family to be τ=(8.7±1.7) Myr. This value is statistically compatible with that of 8.3 Myr previously derived by Nesvorný et al. [Nesvorný, D., Bottke, W.F., Levison, H.F., Dones, L., 2003. Astrophys. J. 591, 486-497], who analyzed the secular evolution of family members on regular orbits. Our methodology, applied here in the case of the Veritas family, can be used to reconstruct the orbital history of other, dynamically complex, asteroid families and derive approximate age estimates for young asteroid families, located in diffusive regions of the main belt. Possible refinements of the method are also discussed.     

Redshifts of 19 Shakhbazian compact groups of galaxies

By observations at Calar Alto (Spain), La Silla (Chile) and Cananea (Mexico), we measured redshifts of 108 candidate members in 19 Shakhbazian compact galaxy groups ShCG 44, 105, 149, 168, 270, 276, 278, 279, 298, 303, 304, 310, 317, 331, 339, 340, 345, 358, and 359. Redshifts of another ten members were taken from the NED. We found that nine out of 118 candidate member galaxies are stars, and twelve galaxies are not members of the corresponding groups and are projected over them. The group ShCG 168 is the core of a cluster. The groups ShCG 276, ShCG 298, and ShCG 303 are either strongly contaminated by field galaxies with redshift differing not very much from that of the corresponding group, or are the results of a chance projection of field galaxies.     

Natural MHD oscillations of a neutron star

Natural, low-frequency, hydromagnetic oscillations of an isolated, nonrotating neutron star, which are localized in the peripheral crust, the structure of which is determined by the electron-nuclear plasma (the Ae phase), are studied. The plasma medium of the outer crust is treated as a homogeneous, infinitely conducting, incompressible continuum, the motions of which are determined by the equations of magnetohydrodynamics. In the approximation of a constant magnetic field inside the crust (the magnetic field outside the star is assumed to have a dipole structure), the spectrum of normal poloidal and toroidal hydromagnetic oscillations, due to presumed residual fluctuations of flow and their associated fluctuations in magnetic field strength, is calculated. Numerical estimates given for the periods of MHD oscillations fall in the range of periods of radio pulsar emission, indicating a close connection between the residual hydromagnetic oscillations and the electromagnetic activity of neutron stars. Translated from Astrofizika, Vol. 40, No. 1, pp. 77–86, January–March, 1997.     

Strewn field,mineralogy, and petrology of Al Haggounia 001: A unique enstatite chondrite

In this work, we investigate macroscopic characteristics, magnetic susceptibility, mineralogy, and mineral composition of Al Haggounia 001. The samples were collected during eight field missions in the period between 2015 and 2019. In the strewn field of about 65 km in length, the specimens are found either on the surface or shallowly buried in loose sediments, which rules out the previous suggestions that this meteorite is a fossil meteorite. Macroscopically, the samples exhibit three major lithologies with various colors, porosities, and distributions of oxidized veins. The data obtained using transmitted and reflected light microscopy, scanning electron microscopy, and electron microprobe analysis confirm the macroscopic observations and show a heterogenous distribution of silicates and metal sulfides. Al Haggounia 001 is composed of enstatite, plagioclase, kamacite, taenite, schreibersite, daubreelite, troilite, graphite, sinoite, and silica polymorphs. We identified a new type of chondrules that are flattened and composed of rods of albite and enstatite, as well as elongated nodules of metal and sulfides, in addition to compression fractures in the form of subparallel veinlets. These features presumably reflect the deformation caused by shock. The magnetic susceptibility of Al Haggounia 001 (4.39 ± 0.20) is much lower than that of usual EH (5.48 ± 0.16) and EL (5.46 ± 0.04) chondrites but is in the range of E finds (5.05 ± 0.43). The thermomagnetic and hysteresis measurements are controlled by type, size, distribution of metal-sulfide nodules, arrangement of oxyhydroxide veins, and weathering. Al Haggounia 001 is an anomalous meteorite with a polymict nature. It records multiple events revealing its unique origin which expends the groups of enstatite chondrites and provides insights into the complex formation and evolution history of their parent body.     

The phosphates of IIIAB iron meteorites

Abstract— Thirteen phosphate minerals are found in IIIAB iron meteorites. Four of these (sarcopside, graftonite, johnsomervilleite, and galileiite) constitute the majority of occurrences. The IIIB iron meteorites are confined to occurrences of only these four phosphates. The IIIA iron meteorites may contain one or more of these four phases; they may also contain other rarer phosphates, and silica (in two instances) and a silicate rock (in one instance). Thus, the IIIA lithophile chemistry is more varied than that of the IIIB meteorites. Based on petrographic relations, sarcopside appears to be the first phosphate to form. Graftonite is probably formed by recrystallization of sarcopside. Johnsomervilleite and galileiite exsolved as enclaves in sarcopside or graftonite at lower temperatures, although some of these also nucleated as separate crystals. The IIIAB phosphates are carriers of a group of incompatible lithophile elements: Fe, Mn, Na, Ca, and K, and, rarely, Mg as well as Pb. These elements (and O) were concentrated in a residual, S-rich liquid during igneous fractional crystallization of the IIIAB core mass. The phosphates formed by oxidation of P as the core solidified and excluded O, which increased its partial pressure in the residual liquid. The trace siderophile trends in bulk IIIAB metal are paralleled by a mineralogical trend of the phosphate minerals that formed. For IIIAB meteorites with low-Ir contents in the metal, the phosphates are mainly Fe-Mn phases; at intermediate Ir values, more Na-bearing phosphates appear; at the highest Ir values, the rarer Na-, K-, Mg-, Cr-, and Pb-bearing phosphates appear. The absence of significant amounts of Mg, Si, Al, and Ti suggest depletion of these elements in the core by the overlying mantle.     

Study of the nearest open clusters and the associated moving clusters by numerical simulations

In our previous papers, we showed that at the final phases of the dynamical evolution of an open cluster, an extended population of stars elongated along its Galactic orbit, the stellar tail of the cluster, is formed. The tail stars that escaped from the cluster at different times move in a common orbit with low relative velocities. Experiencing a weak interaction with Galactic field stars, these objects, the relics of open clusters, can exist for a fairly long time. In this paper, we investigate the structures of such stellar tails in the nearest open clusters: Hyades, Pleiades, Praesepe, Alpha Persei, Coma, IC 2391, and IC 2602. To this end, we performed several numerical simulations of the dynamical evolution of these clusters in the tidal field of the Galaxy. Our computations of the dynamical evolution were based on known cluster age estimates and real Galactic orbits. The initial conditions were chosen in such a way that the parameters of the simulated clusters corresponded to their observed parameters. As a result, we obtained models of the stellar tails for the nearest open clusters and estimated such parameters of the tails as their sizes, densities, locations relative to the solar neighborhood, and others.     

Basalts from Mare Crisium

The stratified core sample returned from Mare Crisium by the Luna 24 unmanned space probe is composed primarily of a new variety of subophitic to ophitic basalt with very low contents of TiO₂ and MgO. This consists of clinopyroxene, calcic plagioclase, olivine, and minor amounts of silica, chromite, ulvöspinel, ilmenite, troilite, apatite, and Fe-metal. Granular metabasalts have the same bulk composition, but mineral phases exhibit less compositional variation. Fine-grained impact melts have similar compositions and are apparently derived from these basalts. We conclude that the basalts, which are chemically distinct from the very-low-titanium basalts found elsewhere on the Moon, represent the local surface flows of Mare Crisium.Sparse fragments of an olivine vitrophyre that is low in TiO₂ but high in MgO and approaches the composition of the Apollo 15 green glasses may be derived from patches of dark mantling materials 20 km from the landing site.Now at Department of Geology, University of California at Davis, Davis, Calif., U.S.A.Now at Department of Geological Sciences, The University of Tennessee, Knoxville, Tenn., U.S.A.     

Integral field spectroscopy with GEMINI: Extragalactic star cluster in NGC1275

Studies of globular cluster systems play a critical role in our understanding of galaxy formation. Imaging with the Hubble Space Telescope has revealed that young star clusters are formed copiously in galaxy mergers, strengthening theories in which giant elliptical galaxies are formed by the merger of spirals [e.g. Whitmore, B.C., Schweizer, F., Leitherer, C., Borne, K., Robert, C., 1993. Astronomical Journal. 106, 1354; Miller, B.W., Whitmore, B.C., Schweizer, F., Fall, S.M., 1997. Astronomical Journal. 114, 2381; Zepf, S.E., Ashman, K.M., English, J., Freeman, K.C., Sharples, R.M., 1999. Astronomical Journal. 118, 752; Ashman, K.M., Zepf, S.E., 1992. Astrophysical Journal. 384, 50]. However, the formation and evolution of globular cluster systems is still not well understood. Ages and metallicities of the clusters are uncertain either because of degeneracy in the broad-band colors or due to variable reddening. Also, the luminosity function of the young clusters, which depends critically on the metallicities and ages of the clusters, appears to be single power-laws while the luminosity function of old clusters has a well-defined break. Either there is significant dynamical evolution of the cluster systems or metallicity affects the mass function of forming clusters. Spectroscopy of these clusters are needed to improve the metallicity and age measurements and to study the kinematics of young cluster systems. Therefore, we have obtained GMOS IFU data of 4 clusters in NGC1275. We will present preliminary results like metallicities, ages, and velocities of the star clusters from IFU spectroscopy.     

Morphology and geological structure of the western part of the Olympus Mons volcano on Mars from the analysis of the Mars Express HRSC imagery

The images of the western part of Olympus Mons and adjacent plains acquired by the HRSC camera onboard the Mars Express spacecraft were studied. The morphology, topography, and color of the surface were investigated. The surface age was determined by the frequencies of impact craters. The examination of the HRSC images combined with an analysis of the MOC imagery and MOLA altitude profiles have shown that the Olympus Mons edifice, at least in its western part, is composed of not only lavas but also of sedimentary and volcanic-sedimentary rocks consisting of dust, volcanic ash, and, probably, H₂O ice that precipitated from the atmosphere. These data also indicate that glaciations, traces of which are known on the western foot of Olympus Mons (Lucchitta, 1981; Milkovich and Head, 2003), probably also covered the gentle upper slopes of the mountain. It is probable that the ice is still there, protected from sublimation by a dust blanket. Confirming (or rejecting) its presence is a challenge for the scheduled radar sounding with the MARSIS instrument mounted on the Mars Express spacecraft as well.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 2, 2005, pp. 99–116.Original Russian Text Copyright © 2005 by Basilevsky, Neukum, Ivanov, Werner, S. van Gesselt, Head, Denk, Jaumann, Hoffmann, Hauber, McCord, the HRSC Co-Investigator Team.     

Erosion by catastrophic floods on Mars and Earth

The large Martian channels, especially Kasei, Ares, Tiu, Simud, and Mangala Valles, show morphologic features strikingly similar to those of the Channeled Scabland of eastern Washington, produced by the catastrophic breakout floods of Pleistocene Lake Missoula. Features in the overall pattern include the great size, regional anastomosis, and low sinuosity of the channels. Erosional features are streamlined hills, longitudinal grooves, inner channel cataracts, scour upstream of flow obstacles, and perhaps marginal cataracts and butte and basin topography. Depositional features are bar complexes in expanding reaches and perhaps pendant bars and alcove bars. Scabland erosion takes place in exceedingly deep, swift floodwater acting on closely jointed bedrock as a hydrodynamic consequence of secondary flow phenomena, including various forms of macroturbulent votices and flow separations. If the analogy to the Channeled Scabland is correct, floods involving water discharges of millions of cubic meters per second and peak flow velocities of tens of meters per second, but perhaps lasting no more than a few days, have occurred on Mars.     

Scaling of melt production in hypervelocity impacts from high-resolution numerical simulations

The volume of melt produced in hypervelocity planetary impacts and the size and shape of the melted region are key to understanding the impact histories of solid planetary bodies and the geological effects of impacts on their surfaces and interiors. Prior work of Pierazzo et al. (Pierazzo, E., Vickery, A.M., Melosh, H.J. [1997]. Icarus 127, 408-423) gave the first estimates of impact melt production in geological materials using a modern hydrocode and equation of state. However, computational limits at the time forced use of low resolution, which may have resulted in low melt volumes. Our simulations with 50 times higher resolution provide independent confirmation of the Pierazzo et al. (Pierazzo, E., Vickery, A.M., Melosh, H.J. [1997]. Icarus 127, 408-423) melt volumes in aluminum, iron, dunite, and granite impacts at velocities between 20 and 80 km/s. In ice/ice impacts, we find that melt volumes depend on target temperature and are lower than predicted by Pierazzo et al. (Pierazzo, E., Vickery, A.M., Melosh, H.J. [1997]. Icarus 127, 408-423). Our melt volumes are directly proportional to impact energy for all materials, over a wide range of impact velocity. We also report new data for melt volume scalings for ice/dunite and iron/dunite impacts and the size and shape of melted region, valuable for interpretation of cratering records and studies of impact-induced differentiation.     

Composition of Coronal Streamers from the SOHO Ultraviolet Coronagraph Spectrometer

The Ultraviolet Coronagraph Spectrometer on the SOHO satellite covers the 940–1350 Å range as well as the 470–630 Å range in second order. It has detected coronal emission lines of H, N, O, Mg, Al, Si, S, Ar, Ca, Fe, and Ni, particularly in coronal streamers. Resonance scattering of emission lines from the solar disk dominates the intensities of a few lines, but electron collisional excitation produces most of the lines observed. Resonance, intercombination and forbidden lines are seen, and their relative line intensities are diagnostics for the ionization state and elemental abundances of the coronal gas. The elemental composition of the solar corona and solar wind vary, with the abundance of each element related to the ionization potential of its neutral atom (First Ionization Potential–FIP). It is often difficult to obtain absolute abundances, rather than abundances relative to O or Si. In this paper, we study the ionization state of the gas in two coronal streamers, and we determine the absolute abundances of oxygen and other elements in the streamers. The ionization state is close to that of a log T = 6.2 plasma. The abundances vary among, and even within, streamers. The helium abundance is lower than photospheric, and the FIP effect is present. In the core of a quiescent equatorial streamer, oxygen and other high-FIP elements are depleted by an order of magnitude compared with photospheric abundances, while they are depleted by only a factor of 3 along the edges of the streamer. The abundances along the edges of the streamer (‘legs’) resemble elemental abundances measured in the slow solar wind, supporting the identification of streamers as the source of that wind component.