bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bright Giants with Small Amplitude Long Period Velocity Variability
Authors: Beavers Willet I. 
Published: July 2016

AbstractObservations during the first eight years of operation of the Fick Observatory photoelectric radial velocity spectrometer have led to the development of a list of approximately seventy bright late giant stars with suspected small amplitude long period velocity variations. Some of these stars have been identified as variable velocity objects by other observers, and a few of them have previous low quality orbit determinations or estimations. Preliminary SB1 orbits are reported for eight of the list members which have been observed through at least one complete cycle. Estimates of the period (P) and velocity semiamplitude (K) are made for other confirmed variables. Generally, the sample contains long P (2 to 8 years), small K (4 to 14 km/sec), late giant systems.
Radial-Velocity Standards
Authors: Batten Alan H. 
Published: July 2016

AbstractThe writer reviews the presently available lists of standard-velocity stars approved by IAU Commission 30 and suggests that the time has arrived for major revisions. Many of the currently adopted standards are known or suspected to be variable in velocity at the level of precision to which we can now work. The writer suggests that we need three levels of standards. Some half-dozen or so bright solar-type stars, visible from all major observatories, should be chosen as fundamental standards, after extensive testing by many observers in various places. A larger group of secondary standards, in various parts of the sky and of a wider range of spectral type and brightness, should be chosen for everyday use by observers working at moderate dispersions. Those stars in the current IAU lists not yet suspected of having variable velocities might form the nucleus of this group. Finally, reference stars should be chosen for special purposes (e.g. cross-correlation, objective-prism determinations) in consultation with the users of these techniques. Standards of accuracy for this last group of stars need not be so strict as for the others.
Summary
Authors: Freeman K.C. 
Published: July 2016

We have seen at this meeting how technical advances In devices and detectors have made it possible to measure accurate radial velocities for faint stars and very accurate velocities for brighter stars. People are working on a wide range of frontier problems that were out of reach only a few years ago. Stellar radial velocity work is making an outstanding contribution to our understanding of stars, star clusters and the Galaxy, and I believe that this work has a very rosy future.I would like now to pick out some topics that seemed particularly important for the present and the future.
Heavy Remnants in Globular Cluster Cores
Authors: Mayor M. , Meylan G. 
Published: July 2016

With a mean precision of 0.6 km/s per measurement, the radial velocities of 169 giants in 47 Tue (published in Mayor et al., 1983) added to the further measures of 25 stars in the core, have permitted the determination of rotation V(r,z) and velocity dispersion σ(r) in this globular cluster. With a mean precison of 0.9 km/s per measurement, the radial velocities of 298 giants in ω Cen (to be published in Mayor et al., 1985), distributed up to the centre, have also permitted the determination of V(r,z) and σ(r) (for both clusters, see Meylan and Mayor, 1984).The ratios νo/σo of ordered to random motions and the ellipticities of ω Cen and 47 Tue point to a global isotropy of the velocity dispersion.
The Whole Earth Telescope
Authors: Nather R. Edward 
Published: July 2016

AbstractThe history of our galaxy and the detailed history of star formation in the early universe is written in the white dwarf stars. Recently we have learned how to reach beneath their exposed surfaces by observing white dwarfs that are intrinsic variables. We use the stellar equivalent of seismology to probe their interiors, and thus to unravel the history they hold inside. We have designed and placed into operation an observational technique that uses the whole earth as a telescope platform, defeating the effects of daylight which, until now, had seriously limited the length of a single light curve, and therefore the amount of information we could hope to extract from it. This paper describes our new telescope and presents preliminary results from our first observing run in March, 1988.
The Effects of Time Dependant Convection on White Dwarf Radial Pulsations
Authors: Starrfield S. , Cox A. N. 
Published: July 2016

AbstractWe have investigated the effects of relaxing the normal assumption of frozen in convection on studies of radial instabilities in 0.6M⊙ carbon-oxygen white dwarfs with either pure hydrogen layers overlying pure helium layers or 0.6M⊙ carbon-oxygen white dwarfs with pure helium surface layers. In this paper we assume that convection can adjust to the pulsation at a rate determined by the time scale of a convective eddy. Using this assumption in our analysis stabilizes most of the modes in both the DA and DB radial instability strips. We also find that the blue edge of the DA radial instability strip, assuming frozen in convection, is between 12,0O0K and 13,000K. The blue edge for the DB radial instability strip (frozen in convection) is between 32,000K and 33,000K.
Observations of Cold Degenerate Stars
Authors: Ruiz Maria Teresa , Anguita Claudio , Maza Jose 
Published: July 2016

AbstractSpectrophotometry, BVRI CCD photometry and CCD trigonometric parallaxes of the southern DC stars vB3, ER8 and ESO 439-26 are presented. These stars should be considered among the lowest luminosity degenerates known, with absolute visual magnitudes of 15.4, 16.2 and 17.2 respectively.
An Unsuccessful Search for White Dwarf Companions to Nearby Main Sequence Stars
Authors: Shipman Harry L. , Geczi Jeanne 
Published: July 2016

AbstractMany of the nearest white dwarf stars (e.g., Sirius B and Procyon B) are in such binaries and would have remained undiscovered if they were even a little bit further away. White dwarfs which are sufficiently hot (T(eff) > 10,000 K) would, if present in binary systems with a relatively cool (F, G, K, or M) main–sequence secondary, be visible in IUE images as a hot companion to the main sequence star. We systematically examined 318 IUE images of 280 different G, K, and M stars which had been observed for other purposes. No previously undiscovered white dwarf stars were found.
X-ray Emission from Hot DA White Dwarfs; EXOSAT Results, and Implications for Atmospheric Models
Authors: Paerels Frits , Heise John 
Published: July 2016

AbstractWe present the observations of the photospheric X-ray spectra of hot DA white dwarfs, obtained with the 500 lines mm−1 Transmission Grating Spectrometer on EXOSAT. These spectra cover the full soft X-ray band, at high wavelength resolution and statistical quality. They allow us to do an accurate measurement of the photospheric parameters, particularly of effective temperature and chemical composition of the atmosphere.We consider the case of HZ 43 in some detail. Model atmospheric spectra that satisfy all measured absolute optical, UV and X-ray fluxes turn out not to fit the shape of the measured X-ray spectrum. However, from a comparison of model spectra calculated with different model atmospheres codes we infer the existence of a 15% systematic uncertainty in the model fluxes at the shortest wavelengths (λ < 100 Å) in current model calculations. This can explain the fitting problem. Since the systematic uncertainty in the models is larger than the statistical uncertainty in the shape of the measured X-ray spectrum of HZ 43, we cannot at present use this measured shape to derive the effective temperature and gravity. We revert to broad band photometry, using the measured integrated soft X-ray flux and the optical flux, to determine Te = 45,000 – 54,000K, R/R⊙ = 0.0140 – 0.0165. From the absence of the He II Ly edge at 227 Å in the measured spectrum, we set a upper limit on the photospheric helium abundance of He/H = 1.0 × 10−5; this upper limit is independent of the uncertainties in the model calculations mentioned above.
Discovery of the sixth DBV Star: CBS 114
Authors: Winget D. E. , Claver C. F. 
Published: July 2016

Though widely spread across the H-R diagram the compact pulsators have much in common. All are multi-periodic, and most have extremely complex light curves. All appear to be pulsating in nonradial g-modes, with temperature variations responsible for the bulk of the light modulations. The g-modes are global in nature and, typically, many are excited in each pulsator, so they are a rich source of seismological information about the interior regions of the white dwarf stars.The pulsating DB white dwarf stars (DBV’s) form one of the three distinct classes of pulsating compact objects currently known. We find these classes nearly uniformly distributed in log Te spanning virtually the whole range of the white dwarf cooling sequence, from the hot DOV stars at log Te ~ 5 to the DAV (ZZ Ceti) stars at log Te ~ 4; the DBV stars, with logTe ~ 4.5, fall in the middle.
A New Temperature Determination for Sirius B from IUE: Implications for the Observed Soft X-Ray Fluxes
Authors: Kidder K. , Holberg J.B. , Wesemael F. 
Published: July 2016

AbstractWe have used IUE archive observations to obtain a new and independent estimate of the effective temperature of Sirius B. In this effort we have modeled the observed Lyman alpha profile of Sirius B as a function of effective temperature and find; Teff = 24,500 ± 500 K. This temperature is in good agreement with a recent result obtained from analysis of EXOSAT soft X-ray spectra of Sirius B. In addition to providing confirmation of the soft X-ray result, this temperature implies that Sirius B is significantly cooler and larger in radius than most previous estimates. The radius, R = 0.090 ± 0.005 R⊙, implied by the lower temperature is well in excess of the radius of fully degenerate star having the mass of Sirius B. This investigation employed a unique set of SWP archive spectra, acquired with Sirius B in the small aperture, which have proved to be free of scattered light contamination from Sirius A.
H-Alpha Emission in Hot Degenerates and OB Subdwarfs
Authors: Reid Neill , Wegner Gary 
Published: July 2016

Based on observations obtained using the 60-inch telescope at Palomar Observatory which is jointly owned by the California Institute of Technology and the Carnegie Institution of Washington and on observations obtained with the 200-inch Hale telescope which is owned by the California Institute of Technology.The intial observations of white dwarf stars and their immediate precursors, the hot subdwarfs, suggested that these stars possess the simplest (and, aesthetically, the most pleasing) spectra of any astronomical object. The high gravity leads to the spectrum being dominated, in the most stars, by broad lines of either hydrogen or helium, depending on the composition of the photospheric layers, with a few stars exhibiting lines from both species. However, the more detailed observations of recent years have revealed a higher degree of complexity. In particular, absorption lines of high excitation species (N V, C IV, etc.) have been detected in the ultraviolet spectra of several hot white dwarfs (Bruhweiler & Kondo, 1982) and, most recently, high resolution optical spectra have shown that one of the latter stars, the hottest known DA, G191-B2B, exhibits significant emission in the core of the H-alpha absorption line (Reid &: Wegner, 1988). Following up the latter observation, we have obtained high resolution spectra of a number of hot subdwarfs, with temperatures ranging from ~ 20,000K to more than 60,000 K. Most of these stars also exhibit Baimer emission, at Hβ as well as Hα in at least one case. We suggest the temperature reversal in the stellar atmosphere may be a function of the He/H ratio at the level of the photosphere.
Gravitational Redshifts and the Mass-Radius Relation
Authors: Wegner Gary 
Published: July 2016

The gravitational redshift is one of Einstein’s three original tests of General Relativity and derives from time’s slowing near a massive body. For velocities well below c, this is represented with sufficient accuracy by:As detailed by Will (1981), Schiff’s conjecture argues that the gravitational redshift actually tests the principle of equivalence rather than the gravitational field equations. For low redshifts, solar system tests give highest accuracy. LoPresto & Pierce (1986) have shown that the redshift at the Sun’s limb is good to about ±3%. Rocket experiments produce an accuracy of ±0.02% (Vessot et al. 1980), while for 40 Eri B the best white dwarf, the observed and predicted VRS agree to only about ±_5% (Wegner 1980).
The Frequency of Cepheid Binaries
Authors: Russo G. 
Published: July 2016

AbstractWe summarize the methods now available to detect the presence of companions to Cepheids, and then we analyze the results of the application of the recent photometric method proposed by Fernie (1980). If applied to the set of VBLUW observations of southern Cepheids carried out by Pel (1976), this method gives a frequency of about 25%, which is consistent with the more recent spectroscopic determinations (Gieren, 1981). The importance of the IUE satellite to directly observe the U flux emitted by the B-companion is emphasized.
On the Distribution of Young Spectroscopic Binary Stars Over the Major Semiaxes of their Orbits
Authors: Popova E.I. , Tutukov A.V. , Shustov B.M. , Yungelson L.R. 
Published: July 2016

About 60% of stars of the disc population in our Galaxy are close binary systems (CBS). Half of the known CBS are spectroscopic binary stars (Kraitcheva et al., 1978).To know the distribution of a correlation between the masses of CBS components and semiaxes of their orbits is necessary for the investigation of the origin and evolution of CBS. For such statistical investigations, a catalogue of CBS was compiled at the Astronomical Council. The catalogue is based on the 6th Batten catalogue (Batten, 1967), its extensions (Pedoussant and Ginestet, 1971; Pedoussant and Carquillat, 1973) and data published up to the end of 1980 (Popova et al., 1981). Now it is recorded on magnetic tape and contains data on 1041 spectroscopic binaries; 333 of them are stars with two visible spectra. The latter are mostly systems prior to mass exchange and the distribution of physical parameters in these systems reflects the distribution and presumably conditions at the time of formation. Using some assumptions, we can obtain for spectroscopic binaries masses of the components M1 and M2 (or the ratio q = M1/M2) and semiaxes of their orbits. Masses of components with the known sin i were obtained by the usual technique; when sin i was not known, masses were estimated from the spectra. We shall discuss here the distribution of CBS in the M-a plane.
Mass Loss in Algol-Type Stars: Implication on their Evolutionary Stage
Authors: Mardirossian F. , Giuricin G. 
Published: July 2016

AbstractWe have examined the observational data of 102 Algols in order to clarify the implications on their evolutionary scenario of various assumptions concerning mass and angular momentum loss during mass transfer. We have found that case B mass exchange is strongly favoured for Algols of relatively low total mass (~ M < 7 Mʘ), while case A predominates, though not so widely as expected in Algols of higher total mass.
Structural Models for Beta Lyrae-Type Disks
Authors: Wilson R.E. 
Published: July 2016

AbstractEquilibrium structural models are computed for a thick, selfgravitating disk in a binary system. Accretion onto the star is limited by the star's rapid rotation (the system is a double-contact binary). The potential formulation is taken from a previous paper, and represents the gravitational potential as that of a massive wire. Corrections to the stellar structure differential equations for the distorted geometry are applied, and the equations are integrated and solved by the fitting point method. The energy is supplied by viscosity. Energy transfer is by convection, and is appreciably superadiabatic throughout the disk. A mass of 0.5 Mʘ is assumed. Representative results are: “central” temperature, 67000 K; “central” pressure, 5 x 1011 dynes/cm2; “equal volume” radius, 17 Rʘ; luminosity, 5 x 103 Lʘ. The model “radius” is in excellent agreement with the observational value for β Lyrae. The model luminosity is slightly higher than the available rate of expenditure of gravitational energy, indicating that a lower disk mass (perhaps 0.25 Mʘ) should be tried.
Origin and Evolution of Contact Binaries of W UMa Type
Authors: Rahunen Timo , Vilhu Osmi 
Published: July 2016

AbstractUsing angular momentum loss estimates from single star studies, it is shown that detached binaries are good candidates as progenitors of contact binaries. Three theories constructed for contact binary evolution (DSC, TRO and AML, see Fig. 1) are discussed. The DSC and TRO theories require a contact binary formation mechanism which produces unequal components (fission) while the AML theory can start from equal components (initially detached binaries). In all theories the end-product is a single star.The stability of unequal entropy models was studied using a formula (2) which couples the energy transfer with the depth of contact and with the entropy difference. The models experience cyclic behaviour on a time scale of 106-107 years (Fig. 2) and the contact never breaks even on the nuclear time scale. This is the important consequence of a formula of type (2). Similar behaviour (with similar formula) is expected also for TRO models and even for DSC models if the discontinuity can be preserved during one cycle period.The DSC and TRO theories, which at first sight look quite different, are in fact complementary. The most probable contact binary theory is perhaps a suitable combination of all three. In this theory angular momentum loss is the new and important factor which may manifest itself in the UV- and X-ray activity observed in W UMa stars.
On the Spatial Density of W UMa Type Stars
Authors: Budding E. 
Published: July 2016

AbstractAttention is directed to the anomalous incidence of W UMa stars, which can be regarded as coming from not only a disproportionately large accumulation among close binary systems with primaries later than around mid-F spectral type, but also as a deficit at early types.Doubt is placed on the necessity of a straightforward identification of W UMa type light curves with contact binaries; and this allows some reduction in the estimated spatial incidence of contact binaries, from the figure of Van't Veer (1975), to 8 x 10-4 of all stars.The incidence is considered, with the aid of some simplifying assumptions, as an example of the general evolution of the distribution of binary systems in the primary spectral type - orbital period plane, subject to some known mechanisms of binary evolution.
A review of radar observations of Saturn’s rings
Authors: Ostro Steven J . , Pettengill Gordon H. 
Published: July 2016

Saturn’s rings are the most distant radar-detected planetary entity, and the only radar-detected ring system. Neither distinction is likely to be reinquished during this century.Ten years have passed since the initial detection of radar echoes from Saturn’s rings (Goldstein and Morris, 1973) shattered prevailing notions that typical ring particles were 0.1 to 1 mm in size. (The single fact that microwave radar echoes are detectable requires a substantial density of particles larger than about one centimeter.) During the past decade, additional radar studies of the rings have been conducted, using the λ13.5-cm and λ12.6-cm systems at the Jet Propulsion Laboratory’s Goldstone Tracking Station and the λ112.6-cm system at the National Astronomy and Ionosphere Center’s Arecibo Observatory.
Inclinations of the Uranian rings
Authors: French Richard G. , Elliot James L. 
Published: July 2016

ABSTRACTA kinematic model of the orbits of the nine known Uranian rings was fitted to available stellar occultation data, including a new set of times from the 26 April 1981 occultation obtained from the Anglo-Australian Telescope (AAT). The results of the fit reveal that seven of the nine rings have significant inclinations with respect to the equatorial plane of Uranus. The inclinations are typically a few hundredths of a degree.
Rings around Neptune?
Authors: Elliot James L. 
Published: July 2016

ABSTRACTObservation of two stellar occultations by Neptune in 1981 led to an upper limit of 0.07 on the optical depth of any equatorial rings with radii greater than 31,400 km. An occultation by Neptune on 15 June 1983 will provide an opportunity for a more extensive search for rings.
The eccentric ringlet at 1.29 RS
Authors: Porco C. , Borderies N. , Danielson G.E. , Goldreich P. , Holberg J.B. , Lane A.L. , Nicholson P.D. 
Published: July 2016

We present preliminary results of an examination of the eccentric ringlet near 1.29 R, in Saturn's inner C ring. Situated near the Titan 1:0 apsidal resonance, this feature provides an opportunity to study the behavior of a ring under the influence of both the gravity field of a major planet and the potential of an external satellite.The data sets used for this analysis consisted of seven Voyager images of this ringlet, ranging in resolution from 60 to 5 km/pixel, plus data obtained from three UVS stellar occultations and one Radio Science occultation. Three observations occurred within a day of Voyager 1 closest approach and seven within 5 days of Voyager 3 closest approach. The Voyager encounters were separated by 286 days. Of the seven Voyager images used, only the three highest resolution frames were corrected for geometric distortion. Therefore, the results presented here must be considered preliminary.
An Earth-based attempt to detect S.E.D. at 21 centimeters
Authors: Lecacheux A. , Biraud F. 
Published: July 2016

AbstractWe tried to observe Saturn Electrostatic Discharges at 1420 MHz using the radiotelescope at Nancay, first during Saturn 1981 opposition, the during Voyager 2 fly-by. The obtained flux upper limit indicates a spectrum steeper than about f**(-1).
Resonance identifications in Saturn’s rings
Authors: Wiesel M.E. , Franklin F.A. 
Published: July 2016

AbstractWhen Saturn’s oblateness perturbations are included, a single classical resonance splits into a resonance band structure. We have derived expressions for resonance location, libration region width, and the maximum librator range. We compare these predictions to areas of the C and B rings, the Cassini division, and the F ring, and offer some thoughts on possible mechanisms involved.
A simple model of saturn’s rings – revisited
Authors: Henon M. 
Published: July 2016

ABSTRACTWe describe a crude model of the rings based on a power-law distribution for particle size. The parameters of the model are determined from apparent thickness and radar-radio observations. A number of quantities are derived: mass of the rings, mean surface density, size of largest particle, time scale for dynamical evolution, minimal size of gap-forming particles, number and size distribution of the gaps, kinematic viscosity. Comparisons with observations and with numbers derived in other ways meet with mixed success. The most serious problem lies in the derived time scale for the radial spreading of the disk, which is less than 10 million years.
Diffusion instability in a bi-modal disc
Authors: Ward W.R. , Harris A.W. 
Published: July 2016

ABSTRACTA simplified model of radial diffusion in a particle disc with a bi-modal size distribution is presented. The large particle component excites the small particles’ dispersion velocity via gravitational scattering. The resulting small particle viscous stress goes through a maximum near τ ~ √3 Such a stress profile promotes the development of high and low optical depth zones. The resulting ringlet appearance is due primarily to the distribution of small particles, which produce most of the optical depth but may constitute only a minor portion of the system’s mass.