A coronal loop model for the production of X-ray and radio flares in the RS CVn binary HR 1099

The RS CVn binary stellar system HR 1099 is a source of both X-ray and radio flares. We present here a model of the system in which the two types of flare are produced by the same population of mildly-relativistic ( 10) electrons, injected into a coronal loop. After reviewing possible radiation mechanisms we conclude that, given the probable conditions in the flaring region, the radio emission is gyrosynchrotron radiation and the X-ray emission is thermal bremsstrahlung. The thermal X-ray source must lie in the stellar chromosphere, but the apparent absence of plasma absorption at radio frequencies indicates that the radio source is located high in the coronal loop. Using the relationships given by Dulk and Marsh (1982) for the radio emission from a power-law electron energy spectrum,N() ( - 1)^–, we conclude that 3 7, with 30% of the electron population trapped in the radio source. Some implications of these results for one particular version of the model are discussed.     

New developments in eclipsing binary light curve modeling

The light curve modeling of binary stars has continued to evolve since its founding by Henry Norris Russell (see Russell and Merrill 1952 and citations therein) nearly a century ago, accelerated in the 1950s by Kopal's introduction of Roche geometry into models and by the development of synthetic light curve computer code in the 1970's. Improved physics and the use of more kinds of observational input are providing another round of important advances that promise to enlarge our knowledge of both binary stars and ensembles containing them. Here we discuss the newer horizons of light curve modeling and the steps being taken toward them.     

High resolution near-IR imaging with arrays

The availability of large format, low noise detector arrays has opened the 1 to 20 m region for sub-arcsecond imaging. Using recent results in the investigation of Galactic star forming regions, the Galactic center and external galaxies as examples, we discuss the various techniques that have been employed. These range from image selection and image sharpening, over speckle techniques and adaptive optics to lunar occultation. These examples demonstrate that sub-arcsecond imaging and spatial interferometry in the near- and mid-infrared has a great future potential.     

A power spectrum description of Galactic neutral hydrogen

Angular power spectra for neutral hydrogen towardsl = 140°,b = 0° on scales from ≈ 1° to 1/10° are presented. The spectra are generally well fitted by a power-law dependence on radius in theuv-plane, with an index between ≈ -2.2 and ≈ -3.0. The more distant hydrogen, which corresponds to larger physical scales, tends to have a more negative index than does the nearer material. There is no preferred angular scale apparent at any velocity. For the distant hydrogen there is no obvious difference between the slope of power spectra for emission aligned perpendicular compared with that parallel to the Galactic plane.     

The spatial distribution of pulsars and the spiral structure of the Galaxy

We have looked for and found a possible spatial correlation between the present pulsar distribution and the estimated locations of the spiral arms at earlier epochs. Through a detailed statistical analysis we find a significant correlation between the present distribution of pulsars and the mass distribution (in the spiral arms) expected about 60 Myr ago for a corotation resonance radius of 14kpc. We discuss the implications of this correlation for the minimum mass of the progenitors of pulsars. Interpreting the spread in the locations of pulsars with respect to the past locations of the spiral arms as predominantly due to their space velocities, we derive an average velocity for the pulsar population.     

Application of INSAT satellite cloud-imagery data for site evaluation work of proposed GRACE observatory

The weather-imageries from the INSAT group of satellites provide reliable and concurrent multistation cloud-cover data — an important input for a proper selection of an observatory site for optical, infra-red and γ-ray astronomy work. Using these data, it is shown that Gurushikar, Mt. Abu, promises to be an excellent site for setting up the proposed GRACE facility for high-sensitivity Gamma-Ray Astrophysics Cerenkov Experiments.     

Apollo 12 ropy glasses revisited

Abstract— We analyzed ropy glasses from Apollo 12 soils 12032 and 12033 by a variety of techniques including SEM/EDX, electron microprobe analysis, INAA, and ³⁹Ar-⁴⁰Ar age dating. The ropy glasses have KREEP-like compositions different from those of local Apollo 12 mare soils; it is likely that the ropy glasses are of exotic origin. Mixing calculations indicate that the ropy glasses formed from a liquid enriched in KREEP and that the ropy glass liquid also contained a significant amount of mare material. The presence of solar Ar and a trace of regolith-derived glass within the ropy glasses are evidence that the ropy glasses contain a small regolith component Anorthosite and crystalline breccia (KREEP) clasts occur in some ropy glasses. We also found within these glasses clasts of felsite (fine-grained granitic fragments) very similar in texture and composition to the larger Apollo 12 felsites, which have a ³⁹Ar-⁴⁰Ar degassing age of 800 ± 15 Ma (Bogard et al, 1992). Measurements of ³⁹Ar-⁴⁰Ar in 12032 ropy glass indicate that it was degassed at the same time as the large felsite although the ropy glass was not completely degassed. The ropy glasses and felsites, therefore, probably came from the same source. Most early investigators suggested that the Apollo 12 ropy glasses were part of the ejecta deposited at the Apollo 12 site from the Copernicus impact Our new data reinforce this model. If these ropy glasses are from Copernicus, they provide new clues to the nature of the target material at the Copernicus she, a part of the Moon that has not been sampled directly.     

The Divnoe meteorite: Petrology,chemistry, oxygen isotopes and origin

Abstract— The Divnoe meteorite is an olivine-rich primitive achondrite with subchondritic chemistry and mineralogy. It has a granoblastic, coarse-grained, olivine groundmass (CGL: coarse-grained lithology) with relatively large pyroxene-plagioclase poikilitic patches (PP) and small fine-grained domains of an opaque-rich lithology (ORL). Both PP and ORL are inhomogeneously distributed and display reaction boundaries with the groundmass. Major silicates, olivine (Fa_20–28) and orthopyroxene (Fs_20–28 Wo_0.5–2.5), display systematic differences in composition between CGL and ORL as well as a complicated pattern of variations within CGL. Accessory plagioclase has low K content and displays regular igneous zoning with core compositions An_40–45 and rims An_32–37. The bulk chemical composition of Divnoe is similar to that of olivine-rich primitive achondrites, except for a depletion of incompatible elements and minor enrichment of refractory siderophiles. Oxygen isotope compositions for whole-rock and separated minerals from Divnoe fall in a narrow range, with mean δ¹⁸O = +4.91, δ¹⁷O = +2.24, and Δ¹⁷O = ?0.26 ± 0.11. The isotopic composition is not within the range of any previously recognized group but is very close to that of the brachinites. To understand the origin of Divnoe lithologies, partial melting and crystallization were modelled using starting compositions equal to that of Divnoe and some chondritic meteorites. It was found that the Divnoe composition could be derived from a chondritic source region by ～20 wt% partial melting at T ～ 1300 °C and log(fO₂) = IW-1.8, followed by ～60 wt% crystallization of the partial melt formed, and removal of the still-liquid portion of the partial melt. Removal of the last partial melt resulted in depletion of the Divnoe plagioclase in Na and K. In this scenario, CGL represents the residue of partial melting, and PP is a portion of the partial melt that crystallized in situ. The ORL was formed during the final stages of partial melting by reaction between gaseous sulfur and residual olivine in the source region. A prominent feature of Divnoe is fine μm-scale chemical variations within olivine grains, related to lamellar structures the olivines display. The origin of these structures is not known.     

A new titanium-bearing calcium aluminosilicate phase: II. Crystallography and crystal chemistry of grains formed in slowly cooled melts with bulk compositions of calcium- aluminum-rich inclusions

Abstract The crystallography and crystal chemistry of a new calcium-titanium-aluminosilicate mineral (UNK) observed in synthetic analogs to calcium-aluminum-rich inclusions (CAIs) from carbonaceous chondrites was studied by electron diffraction techniques. The unit cell is primitive hexagonal or trigonal, with a = 0.790 ± 0.002 nm and c = 0.492 ± 0.002 nm, similar to the lattice parameters of melilite and consistent with cell dimensions for crystals in a mixer furnace slag described by Barber and Agrell (1994). The phase frequently displays an epitactic relationship in which melilite acts as the host, with (0001)_UNK | (001)_mel and <10T0>_UNK | <100>_mel. If one of the two space groups determined by Barber and Agrell (1994) for their sample of UNK is applicable (P3ml or P31m), then the structure is probably characterized by puckered sheets of octahedra and tetrahedra perpendicular to the c-axis with successive sheets coordinated by planar arrays of Ca. In this likely structure, each unit cell contains three Ca sites located in mirror planes, one octahedrally coordinated cation located along a three-fold axis and five tetrahedrally coordinated cations, three in mirrors and two along triads. The octahedron contains Ti but, because there are 1.3–1.9 cations of Ti/formula unit, some of the Ti must also be in tetrahedral coordination, an unusual but not unprecedented situation for a silicate. Tetrahedral sites in mirror planes would contain mostly Si, with lesser amounts of Al while those along the triads correspondingly contain mostly Al with subordinate Ti. The structural formula, therefore, can be expressed as with Si + Ti = 4. Compositions of meteoritic and synthetic Ti-bearing samples of the phase can be described in terms of a binary solid solution between the end-members Ca₃TiAl₂Si₃O₁₄ and Ca₃Ti(AlTi)(AlSi₂)O₁₄. A Ti-free analog with a formula of Ca₃Al₂Si₄O₁₄ synthesized by Paque et al. (1994) is thought to be related structurally but with the octahedral site being occupied by Al, that is      

Investigation of the kinematics and structure of the Galaxy in the vicinity of the North galactic pole

In the framework of the programme of studying the meridional section of the Galaxy (MEGA) the absolute proper motions of more than 11000 stars with respect to 3000 galaxies and their stellar magnitudes in the B, V Johnson system are determined in two sky regions near the North Galactic Pole (NGP) by means of Tautenburg Schmidt plates. The limiting and completing apparent stellar magnitudes are B = 20.4 and 18.3 mag, the overall and the investigated sky areas are 16.4 and 14.6 square degrees, respectively. Distances have been determined using the stellar magnitudes, colours, proper motions and reduced proper motions. Stellar kinematics, eccentricities of Galactic orbits, spatial distribution and changes of these characteristics with Z-distance from the Galactic plane are obtained up to 15 kpc. Four subsystems distinguished in the NGP direction, respectively with semithicknesses of 0.25, 0.38, 0.67, 1.48 kpc and density ellipsoid axial ratios of 0.09, 0.20, 0.28, 0.49 show mean velocities in the Galactic rotation direction relative to the LSR of 5.6 ± 0.6, − 11.0 ± 0.6, − 62.5 ± 1.2, − 181.6 ± 4.4 km/s, and ages of 0.1, 0.4, 0.9, 1 of the Galaxy age.