bluuebunny/crossref_metadata_2025_split huggingface dataset:
Resonance Effects in Fundamental Mode, First-Overtone, and Double-Mode Cepheids
Authors: Antonello Elio 
Published: June 2019

AbstractLinear adiabatic periods, period ratios and frequencies of Cepheid models with. P0 less than about 10 days have been computed, taking into account standard and nonstandard mass-luminosity relations and the new (or augmented) opacities. A comparison of the results with the observed properties of Cepheids has yielded the following conclusions:(a)A non-standard mass-luminosity relation is needed in order to have good agreement between observed stars and models on the temperature-period (or luminosity) diagram; ‘standard’ models have much lower temperatures and luminosities than observed stars.(b)The linear models predict the following resonances: f2/f0 = 2 (well known) at P0 ∼ 10 days, f4/f0 = 3 at P0 ∼ 6.8 days, f4/f1 = 2 at P1 ∼ 3.2 days, and f1 + f0 = f3 at P0 ∼ 6.5 days.(c)All these resonances yield effects which have been observed in light curves of Cepheids at the predicted periods: f2/f0 = 2 and f4/f0 = 3 in classical Cepheids; f4/f1 = 2 in first-overtone Cepheids; and f4/f1 = 2 and f1 + f0 = f3 in double-mode Cepheids.The discussion will include comparison with the results obtained with nonlinear models by Moskalik et al. (1992) for fundamental-mode Cepheids, and by Aikawa (1992) for first-overtone Cepheids.
A new pulsating white dwarf in the Wide Field Camera?
Authors: Wonnacott D. 
Published: June 2019

AbstractRecent observations in the extreme ultraviolet have shown that the binary companion of the pulsating metallic-lined A8m: star IK Peg is a hot DA white dwarf. The EUV light curve is shown to be subject to too much photon noise to identify any periods, and simulations of the effect of a hotspot on the compact object indicate that it is unlikely that the observed photometric variability is not intrinsic to the A8m: star.
B,V Photometry of the Variable Star V9 in the Globular Cluster 47 Tuc
Authors: Corwin Michael , Carney Bruce 
Published: June 2019

AbstractWe present BV CCD photometry of the variable star V9 in the globular cluster 47 Tuc. V, B, and (B – V) light curves are given. A colour-magnitude diagram based on four V and four B frames is given. V9's location on the diagram is considerably brighter and bluer than the edge of the red horizontal branch. Its radial velocity indicates that V9 is a member of the cluster.
Some Observational Limitations of Extinction Measurements in the Rocket Ultraviolet
Authors: Borgman Jan 
Published: June 2019

Even Before any Measurement of stellar fluxes in the ultraviolet had been obtained, predictions were being made on the basis of stellar atmosphere models. At the moment, it seems that such com-putations (for example, see ref. 1) are in reasonable agreement with actual observations from rockets (ref. 2) in the spectral region down to about 2000 Å. At shorter wavelengths it is necessary to take into account the appreciable blanketing by spectral lines which unavoidably is present in the transmission bands of any wide-band photometric system, even in the case of early B stars, as has been shown in reference 3.It must be anticipated that the reduction of extinction measurements in the UV from spaceborne instruments will follow the same procedure that has been used so far: stars with the same intrinsic energy distribution but with different amounts of reddening material in the line of sight are compared, the difference in energy distribution being attributed to the wavelength dependence of interstellar extinction.
Color and Polarization of Reflexion Nebulae NGC 2068, NGC 7023, and Merope Nebula in Three Spectral Regions
Authors: Elvius Aina , Hall John S. 
Published: June 2019

A Survey of the Polarization of Light by the nebulosity within 67 regions of the Pleiades cluster was made in early 1962. The survey was made without color filters. On two nights, however, some preliminary polarization measures were made with color filters; the results obtained in this investigation seemed to be promising enough to justify a more thorough study of polarization in three colors. The polarimeter used in 1962 was not suited for observations in the UV, however, because its polaroid analyzer would have absorbed most of the ultraviolet light.In early 1963 color measures of nebulosity were made within the Pleiades cluster in the blue and yellow spectral regions. Later that year a few more observations of polarization were made in three colors with a polarimeter which contained a Glan-Thompson analyzer. An entirely new polarimeter with a Glan-Foucault prism was built in 1964.
High Angular Resolution Binary Star Interferometry
Authors: McAlister Harold A. 
Published: June 2019

AbstractThe benefits and limitations of the application of high angular resolution interferometry to the study of binary stars are considered. The principle advantage of such observations is that they provide data complementary to parameters determined by other techniques and permit the direct determination of masses, angular diameters and distances to systems which would otherwise be inaccessible to such complete analysis. These values then directly lead to linear diameters, absolute magnitudes, absolute emergent fluxes and effective temperatures. The prospects for significantly increasing our knowledge of these fundamental astrophysical parameters are extremely promising. The applications of interferometry to surveys for new binary stars, to star clusters, and to wider visual binaries with the goal of detecting planetary perturbations are also briefly considered.
Effects of Ground Motions on Amplitude Interferometry
Authors: Bender Peter L. 
Published: June 2019

AbstractSome examples are given of types of ground motion which hs.ve been observed with seismic and geodetic instruments. In general, away from sources of man-made noise, the amplitudes of ground strains and tilts in the microseism band with periods of a few seconds normally are of the order of a few times 10-10. Strain and tilt tides give amplitudes of a few times 10-8, and long term average strain and tilt rates at relatively good sites may be roughly 10-7/yr. Superposed on such relatively long wavelength motions can be larger local pier motions, which are likely to be irregular. However, very high ground stability has been demonstrated at a few sites The limitations of ground motions on long term amplitude interferometer stability are serious if applications such as earth rotation and polar motion measurements are considered, but at shorter periods the environmental problems will be almost completely atmospheric.
The Scope of the Lunar Occulation for Measurement of Stellar Angular Diameters
Authors: Ridgway Stephen T. 
Published: June 2019

AbstractThis review of the lunar occultation technique summarizes results of 94 diameter measurements for 62 stars. The range of angular diameters measured, the coverage of spectral types, and the wavelengths studied are illustrated and discussedo Comparison with other techniques, magnitude limits and possible future developments are also considered.
Extended Atmospheres of Planetary Nuclei
Authors: Böhm K. H. , Cassinelli J. 
Published: June 2019

AbstractExploratory calculations on nongray, hydrostatic-equilibrium model envelopes for central stars of planetary nebulae of high temperature and possibly near the instability limit are reported. It is conjectured that these may be related to Wolf-Rayet type nuclei; it appears possible to obtain an OV absorption, and OVI emission, spectrum even in an LTE calculation.
The Central Star of the Planetary Nebula LMC-N66: A Massive Accreting White Dwarf?
Authors: Реñа M. , Hamann W.-R. 
Published: June 2019

AbstractThe central star of the PN LMC-N66 showed an impressive outburst in 1993 - 1994, returning to its initial conditions about 8 years later. Its spectrum resembles that of a WN4.5 star, being the only confirmed central star of planetary nebulae showing such a spectral type. Recent analysis for the central star parameters, performed by Hamann et al. (2003) is presented. They have found that the bolometric luminosity increased by a factor larger than 6, during the outburst. We discuss the possible scenarios which have been proposed to explain the exceptional stellar parameters and the outburst mechanism. The stellar characteristics and the morphology and kinematics of the planetary nebula suggest the presence of binary system (massive star with a less massive companion or, a white dwarf accreting matter in a close-binary system). These cases pose the least severe contradictions with observational constraints.
Chandra Monitoring Observation of the Antennae Galaxies: The X-Ray Source Populations and the Shape of their Luminosity Function
Authors: Zezas A. , Fabbiano G. , Baldi A. , King A. R. , Ponman T. J. , Raymond J. C. , Schweizer F. 
Published: June 2019

AbstractWe present the X-ray luminosity function (XLF) of the Antennae galaxies based on 8 observation performed with Chandra. We detect between 37 and 49 sources in each observation. After combining all observations we detect a total of 120 sources down to a limiting luminosity of ~ 2 x 1037 erg s–1. Comparison between the XLFs of the individual observations shows that they are not affected by source variability. The cumulative XLF of the coadded observations is well represented by a single power-law with a slope of ~ –0.5.
X-Ray Binaries in Early Type Galaxies and the Globular Cluster Connection
Authors: Maccarone T. J. , Kundu A , Zepf S. E. , Puzia T. H. 
Published: June 2019

AbstractWe summarize the key observations made in recent observations of X-ray sources in early-type galaxies. Typically about half of the X-ray binaries in early-type galaxies are in globular clusters, they are preferentially found in metal rich globular clusters, and there is no indication that cluster-age is an important parameter. Theoretical challenges are presented by these results.
The Formation and Evolution of Compact Stars in Binaries
Authors: Taam Ronald E. 
Published: June 2019

AbstractThe stellar evolutionary processes responsible for the formation of compact objects in interacting binary systems and their evolution are described. The common envelope phase plays a crucial role in their formation and angular momentum losses associated with magnetic braking and/or mass loss are important for their evolution. An application of these processes provides the evolutionary link between classes of interacting binary systems.
Accretion Processes in Mira AB
Authors: Karovska M. , Wood B. , Marengo M. , Raymond J. C. , Hack W. , Guinan E. 
Published: June 2019

AbstractThe Mira AB interacting binary provides an ideal laboratory for studying mass loss and accretion processes in systems containing an AGB star and a compact accretor, because its components have been resolved and can be studied individually. We present here results from our long term study of accretion processes in this system. Those include recent HST observations suggesting that the accretion rate onto Mira B is much lower than before, indicating possible disruption of the accretion disk.
High Speed Photometry of AM CVns with the UCT CCD
Authors: Woudt Patrick A. , Warner Brian 
Published: June 2019

AbstractFollowing our high speed photometric survey of faint cataclysmic variables, two CVs were recognised to be helium-transferring double degenerates; these are ES Cet (Рorb – 620.21144 s) and 2003aw (Psh= 2041.5 s). We have now observed ES Cet photometrically for over two years in order to follow the evolution of the orbital period. We oiler an alternative; explanation for the nature of V407 Vul (which was classified as an ultra-compact together with RX J0806 and ES Cet); this will take V407 Vul out of the AM CVn classification.
The Mysterious Nature of HS 2331+3905
Authors: Aranjo-Betancor S. , Gänsicke B. T. , Hagen H.-J. , Marsh T. R. , Thorstensen J. , Harlaftis E. T. , Fried R. E. , Engels D. 
Published: June 2019

AbstractWe report the discovery of one unique cataclysmic variable drawn from the Hamburg Quasar Survey, HS 2331 + 3905. Follow-up observations obtained over three years unveiled a very unusual picture. The large amplitude 3.5 h radial velocity variations obtained from our optical spectroscopy is not the orbital period of the system, as one would normally expect. Instead, extensive CCD photometry strongly suggests that HS 2331 + 3005 is a short orbital period cataclysmic variable with Рorb = 81.09 min, containing a cold white dwarf which appears to exhibit ZZ Ceti pulsations.
CH Cygni and Other Symbiotic Stars with Low Luminosity Hot Components
Authors: Leedjärv L. , Tomov T. , Mikołajewski M. , Burmeister M. 
Published: June 2019

Some aspects of the recent activity period of the peculiar symbiotic binary CH Cyg, which has ejected both bipolar jets and discrete centrifugal outflows, are discussed.In symbiotic binaries, the red giant's wind is accreted onto the white dwarf. High luminosity of the hot components (Lhot ~103L⊙, reaching ~104L⊙ in the outbursts) (Mikołajewska 2003; Sokoloski 2003) indicates that the accreted matter undergoes thermonuclear burning. There are about 10 symbiotic stars which have ejected high-velocity, collimated, bipolar jets. Some of them show flickering of the optical light on the time scale of minutes. Both jet ejection and flickering indicate that an accretion disk should be present in those systems. Jet emitting symbiotic stars seem to have lower luminosity of the hot component ( ~1 – 100 L⊙) than in most other symbiotics.
Modeling He-Rich Disks in AM CVn Binaries
Authors: Nagel T. , Dreizler S. , Rauch T. , Werner K. 
Published: June 2019

We have developed a new code for the calculation of synthetic spectra and vertical structures of accretion disks in cataclysmic variables and compact X-ray binaries. Here we present results for the CV system AM CVn.AM CVn stars are a special type of cataclysmic variables, also called helium cataclysmics. They are systems of interacting binary white dwarfs, consisting of a degenerate C-O white dwarf primary and a low mass semi-degenerate secondary. The secondary loses mass, almost, pure helium, to the primary, forming an accretion disk. They have all in common a helium-rich composition, analoguous to the hydrogen-rich cataclysmic variables. They show photometric variabilities on time scales of ~ 1000s, the prototype of the class, AM CVn, e.g. exhibits a variability of ~ 18 min (Nelemans et al. 2001).
When Might 2P/Encke Have Produced Meteor Storms?
Authors: Steel D.I. , Asher D.J. 
Published: June 2019

Abstract2P/Encke is the only Earth-crossing short-period comet to have a meteoroid/dust trail identified in the data collected by IRAS Such trails have been suggested by Kresák to be the cause of meteor storms, these occurring when the comet/trail node is near 1 AU and the Earth happens to pass through the trail. Here we present the results of integrations of variational orbits of 2P/Encke (the differences in the assumed initial semi-major axes representing the order of changes that could occur due to non-gravitational effects) from which we derive indications of when this comet may have produced meteor storms in the past. Pairs of sets of storms are expected about 300 yr apart, but the effects of chaotic dynamical evolution (and our ignorance of 2P/Encke's non-gravitational forces for any but the last two centuries) mean that we cannot define the epochs in which these may have occurred to better than 200 BC to AD 500 for the last pair, and 3600 to 1800 BC for the previous pair. Looking forwards in time, no meteor storm due to 2P/Encke will occur for at least 600 yr.
Estimating the Asteroidal Component of the Zodiacal Cloud using the Earth's Resonant Ring
Authors: Jayaraman Sumita , Dermott Stanley F. 
Published: June 2019

AbstractThe Earth's resonant ring is populated primarily by asteroidal dust particles because cometary particles have higher Poynting-Robertson drag rates and the Earth's resonances are not strong enough to trap them (Gomes, 1995). It has been shown that asteroidal particles in a limited size range from 5 — 30μm are responsible for the observed trailing/leading flux asymmetry caused by the trailing dust cloud embedded in the ring (Jayaraman and Dermott 1995). The magnitude of the flux asymmetry is a direct function of the area of dust in the ring, which in turn depends upon the number of asteroidal particles in the zodiacal cloud. Using a dynamical model of the ring and the background zodiacal cloud and estimating the surface area of dust needed in the ring to match the observed flux asymmetry in the 25 micron COBE waveband, we have calculated the fraction of asteroidal dust in the zodiacal cloud as a function of p, the slope of the size-frequency distribution of particles.
SIRTF: A Unique Opportunity for Probing the Zodiacal Cloud
Authors: Jayaraman Sumita , Dermott Stanley F. , Werner Michael 
Published: June 2019

AbstractThe Space Infrared Telescope Facility (SIRTF) is planned for launch by NASA in 2001 in a heliocentric orbit at 1.01 AU The spacecraft will drift away from the Earth slowly, reaching a distance of 0.3 AU behind the Earth at the end of its 2.5 year mission. This implies that SIRTF will spiral through the Earth's resonant dust ring (Wright et al., 1995) and, in particular, that it will traverse the dust cloud in the ring that trails the Earth in its orbit. We have used a dynamical model of the ring (Dermott et al., 1994) followed by simulation of the SIRTF orbit to predict the variations in the zodiacal thermal emission due to the trailing dust cloud as seen by SIRTF. Because the dust ring is inclined to the ecliptic, the latitude of peak flux of the trailing cloud will have yearly oscillations about the ecliptic. The amplitude of the oscillations will increase as SIRTF approaches the cloud, reaching a maximum of 20 during the mission. The magnitude of the flux variations can be as high as 4 – 5% or 2–3 MJy/Sr, SIRTF's measurements of these effects will allow us to model the number density and thermal characteristics of asteroidal dust particles near the Earth.
Orbital Evolution of Small Particles Ejected from Martian Satellites
Authors: Ishimoto Hiroshi 
Published: June 2019

AbstractThe dynamical behavior of dust particles ejected from Martian satellites is examined. On the basis of numerical simulations and analytical estimation for the orbital evolution of particles, we have found that there exists two kinds of resonance orbits around Mars. Particles ejected from Phobos and Deimos are influenced by these orbital resonances, and form dust rings with an asymmetrical structure along the orbit of the satellite, i.e., dust rings with a thin disk-like shape for Phobos and with a vertically extended structure for Deimos.
An Optical Instrument to Characterize Individual Dust Particles
Authors: Giovane Frank , Gustafson Bo Å. S. , Lamy Philippe L. 
Published: June 2019

AbstractThe conceptual design for an optical instrument capable of characterizing dust particles by in situ measurements is described. This instrument, the Integrated Dust Analyzer (IDA), measures the light scattered at several different angles as a particle passes through a pair of polarized light curtains. It is capable of defining or providing an indication of such characteristics as size, index of refraction, absorptivity, and aggregate structure.
Optical and Thermal Properties of Zodiacal Dust
Authors: Levasseur-Regourd A.C. 
Published: June 2019

AbstractRecent progress has been reported in the determination of the zodiacal thermal emission, brightness and polarization. These results, of interest to estimate the foreground sources in astrophysical observations, do not provide immediately information on the dust distribution, and on its optical and thermal properties. To infer local information about the bulk density, and the physical properties of the dust particles, it is necessary to compare the observations with realistic models or to invert the line-of-sight data. The latter approach typically suggests that the bulk density is (in the symmetry plane) inversely proportional to the solar distance, that the particles are not spheroidal, but rather irregular in shape, that their physical properties change with their distance to the Sun and their orbital inclination, and finally that they do not emit like a blackbody. The heterogeneity noticed in the cloud is due to various sources of dust particles, the size, shape or albedo of which evolve as a function of time, under collision and/or evaporation processes.
On the Dielectric Function of Partially Amorphous Olivine Dust
Authors: Lynch David K. , Mazuk S. 
Published: June 2019

AbstractWe present a new technique for computing the optical constants for partially disordered solids based on their crystalline optical constants. The technique assumes that the material is composed of a continuous distribution of oscillators (CDO) and that the degree of atomic disorder can be described by one, or at most two, scalar parameters. We apply the technique to an oft-mentioned solar system material, olivine, and show that its dielectric functions can be predicted for an arbitrary degree of disorder.
Sublimation of Interplanetary Dust
Authors: Mukai Tadashi 
Published: June 2019

AbstractThree topics are briefly reviewed to examine evidence for the nature of dust grains and grain alteration by physical processes related to mainly sublimation. Namely, (1) a change of dust flux detected byin situdust measurements beyond ~ 2 AU from the Sun suggests a disappearance of volatile ices due to sublimation below this distance, (2) an elongation angle dependence of Doppler shifts observed in the zodiacal light can be explained by the introduction of a dependence of the orbital velocity on the radiation pressure forces acting on the grains, taking into account a variation of dust structure with heliocentric distance, and (3) the variation of color temperature observed in cometary coma suggests a loss of carbon content from cometary dust grains due to sublimation. This piece of evidence agrees with the generation of carbon-bearing molecules from extended sources, as infered from observations in cometary comae.
Size Distributions of Asteroidal Dust: Possible Constraints on Impact Strengths
Authors: Durda Daniel D. , Dermott Stanley F. 
Published: June 2019

AbstractWe present results of a numerical collisional model which shows that the slope index of the equilibrium size distribution is dependent upon the size-strength scaling properties of the colliding bodies. This implies that individual asteroid families or distinct taxonomic classes within the mainbelt asteroid population may evolve different equilibrium size distributions. Well constrained observations of the size distribution over particular size ranges may allow constraints to be placed on the impact strengths of particles much larger or smaller than are capable of being measured in laboratory impact experiments.
Chemical Reactions and Dust Destruction in Protoplanetary Accretion Disks
Authors: Finocchi Frédéric , Gail Hans-Peter , Duschl Wolfgang J. , Tscharnuter Werner M. 
Published: June 2019

AbstractA nonequilibrium calculation for the chemistry in a classical protoplanetary accretion disk is presented. Slow radial particle transport moves grains from the cold outer regions of a protoplanetary accretion disk into its warm central part where grains are destroyed. We consider the destruction processes for the silicate and carbon dust component and follow the chemical composition of the gas as a function of the radial distance from the protostar. The main result of this calculation is the presence of huge amounts of methane at a distance of ~ 1 AU from the protostar as product of the carbon dust destruction. It is very likely that more complex organics also are present' in this region.