bluuebunny/crossref_metadata_2025_split huggingface dataset:
Low Mass Hydrogen Envelopes and the DB Gap
Authors: MacDonald James 
Published: July 2016

The existence of a gap in the distribution of helium atmosphere white dwarfs at the effective temperature interval 30,000 K ≤ Te ≤ 45,000 K is well documented (Wesemael, Green and Liebert 1985; Liebert et al 1986; Green and Liebert 1987).To explain the presence of this gap and other variations of the non-DA to DA ratio, it has been proposed (Fontaine and Wesemael 1987; Liebert, Fontaine and Wesemael 1987) that the helium-rich PG 1159 stars are the progenitors of essentially all white dwarfs. Some minute quantity of hydrogen of total mass, MH, is assumed to be mixed in the outer helium envelope, and settle upward as the star cools from the PG 1159 stage. Eventually enough hydrogen is at the surface to make the star appear a DA. The star has to become DA before it cools down to ≈ 45,000 K and cools to ≈ 30,000 K as a DA. At this temperature, depending on MH, the underlying helium convection zone may break into the hydrogen layer, diluting it and making the star a DB.
Optical Frequencies in V471 TAU
Authors: Winget D. E. , Claver C. F. 
Published: July 2016

V471 Tau is a spectroscopic and eclipsing binary system located in the Hyades cluster. The binary consists of a K2V and a hot DA white dwarf star (Nelson and Young 1970). Soft x-ray observations reveal strong modulation at periods of 554.7 ± 0.3s and 277.5 ± 0.1s (Jensen 1985, Jensnen et al. 1986).Robinson et al. (1988) reported the detection of the 555 s period in the optical. This period was about a factor of 20 reduced in mean amplitude in their data relative to the soft x-ray amplitude. They also found that it varied in amplitude from run to run by more than a factor of 2.5, dropping below detectability on several runs. They found some evidence for the 277.5 s period in several runs, but never at high enough amplitude to measure reliably. In addition, they noted that several of their runs had statistically significant power at other frequencies, but noted that in their six runs none of the additional frequencies repeated themselves. Robinson et al. also used observations near the eclipse of the white dwarf to demonstrate that most of the pulsed light is coming from the white dwarf.
The Search for Close Binary Evolved Stars
Authors: Saffer Rex A. , Liebert James 
Published: July 2016

AbstractWe report on a search for short-period binary systems composed of pairs of evolved stars. The search is being carried out concurrently with a program to characterize the kinematical properties of two different samples of stars. Each sample has produced one close binary candidate for which further spectroscopic observations are planned. We also recapitulate the discovery of a close detached binary system composed of two cool DA white dwarfs, and we discuss the null results of Hα observations of the suspected white dwarf/brown dwarf system G 29–38.
White Dwarf – Accretion Disk Boundary Layers
Authors: Regev Oded 
Published: July 2016

AbstractThe method of matched asymptotic expansions is used to calculate the detailed structure of white dwarf- accretion disk boundary layers. Both optically thick and thin boundary layers are investigated for various values of the relevant parameters, as long as the layer’s vertical extension remains very much smaller than the white dwarf’s radius. Detailed, self consistent solutions for the boundary layer’s and disk’s structure are calculated and used to find the amount of energy radiated onto the accreting white dwarf (recently recognized to be an important factor in nova outburst modelling).
High Resolution Optical Spectra of 120 White Dwarfs
Authors: Tytler David , Rubenstein Eric 
Published: July 2016

AbstractHigh quality optical spectra of 120 white dwarfs have been obtained to search for double degenerate systems, some of which might become type I supernovae. No systems with high amplitude velocity variations have been found. However several exceptionally cool DA white dwarfs have been found to show weak Helium absorption lines, and four stars have split H-alpha line cores indicative of binary systems.
A Mass-Eccentricity Correlation in Spectroscopic and Visual Binary Orbits
Authors: Dommanget J. 
Published: July 2016

Looking for a possible explanation for the debated existence of a correlation between period and eccentricity in binary orbits [of which a diagramme is given in fig. 1.) we made the assumption that the orbital evolution of the binaries could be the consequence of a substantial mass-loss of their components even when these components are late type main sequence stars.This led first to the consideration of various classes of the areal constant. But it.immediately appeared much better to consider for each of such classes, the total mass of each system instead of its orbital eccentricity and thus to consider the mass-period diagramme rather than the period-eccentricity diagramme. Eleven such diagrammes were considered.
Quasi-Simultaneous Photometric and Polarimetric Observations of T Tau And Ry Tau
Authors: Red’kina N.P. , Chernova G.P. 
Published: July 2016

AbstractQuasi-simultaneous photometric and polarimetric observations of T Tau and RY Tau show that the proper polarization of these stars barises in the visual region in their gaseous emitting envelopes. The polarization of T Tau shows cyclic variations with a period of 5h18. That of RY has two different modes of variation at brightnesses V > 11m and V < 11m; it is possibly connected with the suspected binary nature of this star.
A Possible Explanation of Distortions in the Light Curves of VW Cep By Starspots
Authors: Yamasaki A. 
Published: July 2016

AbstractAn attempt is made to explain the variations in the light curve of VW Cep in terms of a starspot model. Based upon Kwee's (1966) observations, an unperturbed light curve without spots is constructed and analysed for the geometrical elements of VW Cep. Then, by assuming that starspots exist on the surface of the primary component, Kwee's individual light curves are further analysed for locations and intensities of the starspots.
The IUE Observations Of W UMa
Authors: Rucinski S.M. , Pringle J.E. , Whelan J.A.J. 
Published: July 2016

AbstractThe low resolution, phase averaged SWP spectra reveal the trend of increased transition-region line intensities for higher temperatures of ion formation which was previously observed for other active systems. Two series of low resolution LWR spectra covering two full orbital periods have been used to check the photometric results from the ANS satellite and a good agreement is found for the 2200 Å band. Wavelength shifts and changes in the intensity of the blended Mg II emission feature are not inconsistent with the ANS result that the more massive component is the more active one in the W UMa system.
Recent Observational Evidence on W Ursae Majoris Stars
Authors: Rovithis-Livaniou H. , Rovithis P. 
Published: July 2016

During the four last years (1978–1981), some close binaries of W Ursae Majoris type have been observed from the National Observatory of Athens.In all cases a two-beam, multi-mode, nebular-stellar photometer has been used, attached to the 48-inch Cassegrain reflector at the Kryonerion Station.The observed systems are: 44i Boo, VW Cep, AB And, BV Dra, BW Dra, U Peg, V508 Oph. Especially VW Cep and 44i Boo, are very interesting objects; in addition to the light curves that have already been published (Rovithis and Rovithis-Livaniou, 1980–1981), other observations were obtained during the last year and are now at computational stage. The observations of these two systems will be continued during the next years.
Does the Cataclysmic Binary Z Cha Contain a Black Dwarf Secondary?
Authors: Faulkner John , Ritter Hans 
Published: July 2016

AbstractIt is shown that the assumption of a black dwarf secondary in Z Cha leads to a number of contradictions with well established theoretical and observational facts. In particular the model predicts the radial velocity K1 to be much smaller than is observed, the radius of the accretion disk to be smaller than is physically possible and a white dwarf mass which is inconsistent with the white dwarf's radius derived from eclipse analysis. Using the same arguments as for Z Cha it is also possible to exclude a black dwarf secondary in the similar systems OY Car and HT Cas.
Microwave emission from Saturn’s rings
Authors: Muhleman D.O. , Berge G.L. 
Published: July 2016

ABSTRACTPassive radio measurements of Saturn’s Rings are reviewed and new interferometric measurements at λ = 2.7 mm are presented. The brightness temperatures of the A plus B rings at a ring angle of B ⋍ 10° were found to be 17 K and 38 K in two separate experiments, the latter being the more reliable. These results are interpreted in terms of ring particle emission and scattering of the planet’s disk emission by the rings.
Saturn’s E-ring in the red spectral region
Authors: Feibelman W.A. 
Published: July 2016

ABSTRACTObservations of the 1966 edge-on presentation of Saturn’s E-ring in the red spectral region are presented. Techniques to suppress the glare from the planet are briefly described. The E-ring profile did not exhibit a maximum near the orbit of Enceladus in 1966. Some historical comments concerning the E-ring are included to illustrate that important planetary work can be done by ground-based observations.
Infrared observations of the Uranian rings
Authors: Nicholson P.D. , Jones T.J. , Matthews K. 
Published: July 2016

ABSTRACTWe present maps of the Uranian rings at an effective wavelength of 2.2 µm, and spectrophotometric observations covering the ranges 2.0 – 2.4 µm and 2.9 – 3.9 µm. The maps, constructed from data obtained in May 1978 and July 1979, reveal a 2:1 azimuthal brightness variation whose amplitude and phase are consistent with the known width variation and apsidal precession of the eccentric e ring. A detailed comparison of the maps with models based on stellar occultation data leads to an upper limit of ~0.01 on the normal optical depth of any broad (5000 km wide), diffuse component of the ring system. An unexplained feature of the 1978 map is a significant east-west asymmetry, corresponding to a brightening of the near side of the rings relative to the far side.
The C ring of Saturn: A high resolution view of some of its structure
Authors: Lane Arthur L. , Graps Amara L. , Simmons Karen E. 
Published: July 2016

ABSTRACTThe high resolution examination of selected features in Saturn's C-Ring has demonstrated that they are far more complex than previously considered. This brief paper illustrates several classes of the phenomena observed by the Voyager Photopolarimeter star occultation experiment.
Statistical study of Saturnian electrostatic discharges observed by the Voyager planetary radio astronomy experiment
Authors: Zarka P. , Pedersen B.M. 
Published: July 2016

Abstract:During the two Voyager-Saturn missions, the Planetary Radio Astronomy experiment observed sporadic broadband (20 KHz to at least 40 MHz) emissions during a few days around the closest approaches.These emissions are interpreted to arise from short-lived electrostatic discharges in the vicinity of Saturn. Their characteristics have been studied for the experiment's high band (&gt;1.2 MHz).A difference between the periodicity of these Saturn electrostatic discharges (SED) is found, when comparing Voyager 1 and 2 observations.
Viscosity in Saturn's rings
Authors: Lissauer Jack J. , Shu Frank H. , Cuzzi Jeffrey N. 
Published: July 2016

ABSTRACTWe discuss the technique of estimating the viscosity in Saturn’s rings from the damping rate of waves observed to be propagating within the rings. Previously published attempts rely on spiral density waves as a diagnostic, and the wavetrains used in the analyses suffered significant complications that compromised the interpretations. We present a new method that considers the damping of spiral bending waves, a diagnostic which is largely free of,major complications. We deduce a kinematic viscosity of 260 (+150, -100) cm2/s for the middle of the A ring where bending waves have been excited by the 5:3 vertical resonance with Mimas. This value implies upper limits on the particle velocity dispersion and local ring thickness of 0.4 cm/s and 30 m, respectively.
Physical and geological nature of Saturn's larger ring particles
Authors: Chapman Clark R. , Greenberg Richard , Weidenschilling Stuart , Davis Donald R. 
Published: July 2016

ABSTRACTThe evolution and behavior of Saturn’s rings may be influenced by relatively large ring particles. We describe how an important mass fraction of the rings may reside in particles with dimensions of tens of meters to kilometers, which are too few to be seen by radio occultation and too small to be detected in Voyager pictures. We consider the possible physical and geological structure of such bodies and how they influence interactions among ring particles in general.
Effects of shepherd conjunctions on Saturn's F ring
Authors: Showalter M.R. 
Published: July 2016

ABSTRACTSynnott (1982a) has reported that the F-ring braids are often found near the ring segment which was between the shepherds at their last conjunction. We study the possible perturbing effects of such conjunctions on the ring , and find that they are much too small to directly account for the braids.
The gravitational interaction between inclined, elliptical rings
Authors: Yoder C.F. 
Published: July 2016

ABSTRACTThe gravitational torque between two wire rings or within a ring of finite width can prevent differential precession caused by planetary oblateness. Goldreich and Tremaine (1979) proposed this model to explain the observed eccentricity and width variations of the Uranian ε ring. A general expression for the potential for two elliptical and inclined rings is derived in this paper. The stationary solutions and stability of this system are briefly examined.
Applications of three-body resonances to satellites and planetary rings
Authors: Aksnes Kaare 
Published: July 2016

ABSTRACTFormulas have been derived for the strengths and libration/ circulation characteristics of resonances for which qn1- (p+q)n2+ pn3= 0, where p and q are integers and n1, n2, and n3are the mean motions of any three gravitationally interacting bodies in coplanar orbits.The formulas are applied to the well known Laplacian satellite resonances as well as to other possible 3-body resonances in the satellite and ring systems of Jupiter, Uranus, and Saturn.
On planetary rings as sources and sinks of magnetospheric plasmas
Authors: Ip W.-H. 
Published: July 2016

ABSTRACTThe presence of satellite and ring systems in the magnetospheres of Jupiter, Saturn and Uranus introduces interesting new physical effects affecting the general dynamics and compositions of these magnetospheres. Besides acting as a sink for the magnetospheric particles via solid-body absorption, the satellites and rings could also emit neutral and ionized gas into the magnetospheres. In the case of the Saturnian rings, because of their especially broad structure and close proximity to the planet, strong exospheric and ionospheric couplings can also take place. Several observed features (e.g. depletion of the ionospheric electron content, generation of the atomic hydrogen cloud in the vicinity of the rings, and a discontinuity in optical depth at 1.64 Rsin the B ring) of the ionosphere and the ring system could result from the related processes of mass transport and exchange between the ionosphere and the rings. Similar effects may also occur in the region of the tenuous E ring leading to peculiar equatorial confinement of the corotating thermal plasma there.
The E-ring of Saturn
Authors: Smoluchowski R. 
Published: July 2016

AbstractThe origin of the E-ring of Saturn and its relationship to Enceladus is a well known problem. Rather than assuming that the ring was formed as a result of one big impact long ago or that it is a consequence of ejection of subcrustal water by tidally induced stresses and cracks of the satellite, it is proposed that the ring is formed as a consequence of micrometeoritic and meteoritic bombardment of Enceladus. It is shown that the mass reaching the ring replaces that lost by erosion, drag and other mechanisms. The effect of the presence of amorphous ice and the possible opposition effect is indicated.
3C58’s Filamentary Radial Velocities, Line Intensities, and Proper Motions
Authors: Fesen R.A. , Kirshner R.P. , Becker R.H. 
Published: July 2016

AbstractOptical spectroscopy on nearly 50 filaments of 3C58 indicates a maximum expansion velocity of 1100 ± 100 km s−1. A considerable range in radial velocity with projected distance from remnant center is found suggesting that the remnant’s optical emission is not confined to a thin shell. Typical filament electron densities are between 200 - 500 cm−3 with Hα/[N II] ratios in the range 0.2 - 0.5. Optical extinction to 3C58 is modest with E[B-V] = 0.68±0.08. Preliminary radial proper motion measurements for a few outlying filaments suggest values of order 0.05” - 0.07” yr−1.
Models for X-ray Emission from Tycho’s Remnant
Authors: Smith Barham W. , Jones Eric M. 
Published: July 2016

AbstractWe reexamine the X-ray emission from Tycho’s remnant using results from hydrodynamic models computed with a detailed spherically symmetric code. The observed synchrotron radio contours (Green and Gull 1983) appear to require a cloudy circumstellar medium (Dickel and Jones, 1985; Dickel, Eilek, and Jones 1987), thus we explore the X-ray emission properties of similar models. We find that they tend to produce broad shells of X-ray emission that resemble the observed X-ray map of Tycho (Seward, Gorenstein, and Tucker 1983). A simple hydrodynamic model can satisfy both radio and X-ray observations, but it has little similarity to the evolution of remnants in cloudy media dominated by thermal conduction (McKee and Ostriker 1977). More work needs to be done to ensure that the spectrum as well as the X-ray map can be modeled with the same cloudy circumstellar medium, although we believe it will not be difficult to obtain as good a statistical agreement with the spectral data as other models have achieved (e.g. Hamilton, Sarazin, and Szymkowiak 1986).
Limits on the Presence of Sulfur in the Young SNRs LMC N132D and SMC 1E0102.2-7219
Authors: Lasker Barry M. 
Published: July 2016

AbstractA new area-spectroscopy search for sulfur as a tracer of the “Si Group” of elements in the ejecta of the young SNRs, LMC N132D and SMC 1E0102.2–7219, yields negative results for [S II]λλ6719, 6731 and [S III]λλ9064, 9532.
G18.95-1.1, A Composite Supernova Remnant Interacting with the Ambient Interstellar Medium
Authors: Fürst E. , Reich W. , Hummel E. , Sofue Y. 
Published: July 2016

AbstractNew radio continuum and spectral line observations of the Galactic radio source G18.95-1.1 are reported. The distance to G18.95-1.1 is 2 kpc as derived from HI-21 cm spectral line observations. These data also indicate an interaction with the interstellar medium. The radio continuum observations classify G18.95-1.1 as a composite supernova remnant.
Effect of Ambient Density on Statistical Properties of SNRs: Σ-D Relation, N-D Relation, Energy Content
Authors: Berkhuijsen Elly M. 
Published: July 2016

AbstractVariations in ambient density can largely account for: slope and extent of the observed Σ-D relations, the slope of about +1 of the cumulative N-D relation, and the increase of Eo with D as derived from optical line data. Emin increases during the evolution; the behaviour of Ex remains uncertain.
A Search for Shells around Crabs
Authors: Becker R.H. , Helfand D.J. 
Published: July 2016

AbstractPrior to conducting a survey of the galactic plane at 327 MHz using the VLA, we have imaged four fields near galactic longitude of 20 degrees. Each image will cover a 2.5 degree field with ∼1 arcmin resolution. The fields have been chosen to include the remnants G20.0-0.2, G21.5-0.9, and G24.7+0.6. The first two are isolated Crab-like objects, that is, there is no discernible associated shell. Since such shells have relatively steep spectra, images at 327 MHz will be more sensitive to their presence. The absence of a shell can constrain the density of the ISM in the vicinity of the SNR (Reynolds and Aller 1985 A.J.90, 2312). Since ∼50% of Crabs are naked, the implications can be extended to a significant fraction of the ISM.
IRAS Observations of Collisionally Heated Dust in Large Magellanic Cloud Supernova Remnants
Authors: Graham James R. , Evans A. , Albinson J.S. , Bode M.F. , Meikle W.P.S. 
Published: July 2016

AbstractIRAS additional observations show that luminous (104−105 L⊙) far-IR sources are associated with the Large Magellanic Cloud (LMC) supernova remnants N63A, N49, N49B, and N186D. Comparison of the IRAS and X-ray data shows that a substantial fraction of the IR emission from three of the SNRs can be accounted for by collisionally heated dust. The ratio of dust-grain cooling to total atomic cooling is ~10 in X-ray emitting gas (T~106 K). We show why dust cooling does not dominate, but probably speeds SNR evolution in an inhomogeneous interstellar medium.
Differential Imaging of [Fe X] in IC 443
Authors: Brown Larry , Woodgate Bruce E. , Petre Robert 
Published: July 2016

AbstractThis paper presents images of two areas of the supernova remnant IC443 showing emission from the [Fe X] 6374Å red coronal line taken with an emission line differential imaging camera. The areas are in the vicinity of strong soft X-ray emission as observed with the Einstein Observatory. The [Fe X] emission is patchy on the scale of seconds of arc. For the highest emission regions we find an electron density of approximately 100 cm−3 and gas pressures of 108cm−3K. No correlation is found between the X-ray and [Fe X] knots, and the results support a clumpy, multi-temperature region where the [Fe X] knots are balanced between collapse and evaporation.
Supershells
Authors: McCray Richard 
Published: July 2016

AbstractRepeated supernovae from an OB association will, in a few ×107 yr, create a cavity of coronal gas in the interstellar medium, with radius > 100 pc, surrounded by a dense expanding shell of cool interstellar gas. Such a cavity will likely burst through the gas layer of a disk galaxy. Such holes and “supershells” have been observed in optical and H I radio emission maps of the Milky Way and other nearby galaxies. The gas swept up in the supershell is likely to become gravitationally unstable, providing a mechanism for propagating star formation that may be particularly effective in irregular galaxies.
Self-Regulating Star Formation in Isolated Galaxies
Authors: Parravano Antonio 
Published: July 2016

AbstractRecent investigation (Parravano, 1987) shows that the diffuse phases of the ISM condense mainly by the transition from warm gas to small cool clouds (WG → SC). In this work we introduce the new hypothesis that the star formation rate (SFR) in isolated galaxies is self-regulated in such a way that it maintains Pmax close to the ISM gas pressure. Here Pmax is the gas pressure at the marginal state of stability for the transition WG → SC. This hypothesis leads to a relation between global galactic parameters which appears to be applicable to various morphological groups of isolated galaxies.
Ultraviolet Fe II Absorption Lines in HD 59643
Authors: Eaton Joel A. 
Published: July 2016

AbstractThe peculiar red giant HD 59643 (C6,2) has a composite spectrum like a symbiotic star’s except for the absence of highly ionized species. UV observations show a highly variable hot continuum with superimposed absorptions of Fe II and the common emission lines of C IV, Si III], C III], C II], and Mg II. These Fe II absorptions, which are practically ubiquitous in interacting binaries, are an effective diagnostic of turbulence and distribution of scattering gas, even at low resolution.