bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculated Energy Distributions for SN II
Authors: Hauschildt P.H. , Spies W. , Wehrse R. , Shaviv G.
Published: July 2016

We have calculated a large grid of hydrogen-rich supernova photospheres, in which radii, effective temperatures, density profiles, and expansion velocities have been varied. Spherical geometry, radiative equilibrium and LTE level populations are assumed. In the quasi-exact radiative transfer, the dilution of the radiation field, and scattering as well as absorption (by all relevant continuous processes and up to 150 000 lines in some models) are accurately considered. Good agreement can be obtained with the UV and IR spectra of supernovae 1979C, 1980K, and 1987A as observed during the coasting phase. Potential methods of parameter determinations for SN II are briefly discussed.
Thermal Radiation from a Neutron Star in SN 1987A
Authors: Nomoto Ken’ichi , Tsuruta Sachiko
Published: July 2016

The supernova 1987A in the Large Magellanic Cloud has provided a new opportunity to study the evolution of a young neutron star right after its birth. A proto-neutron star first cools down by emitting neutrinos that diffuse out of the interior within a minutes. After the neutron star becomes transparent to neutrinos, the neutron star core with > 1014 g cm−3 cools predominantly by Urca neutrino emission. However, the surface layers remain hot because it takes at least 100 years before the cooling waves from the central core reach the surface layers (Nomoto and Tsuruta 1981, 1986, 1987).

From the hot surface, thermal X-rays are emitted. The detection limit for X- rays from SN 1987A by the Ginga satellite is 3 ×1036 erg s−1 (Makino 1987; Tanaka 1987). If the thermal X-rays are to be observed by Ginga, the surface temperature should continue to be as high as Ts > 8 ×106 (R/10km)−1/2 K until the ejecta becomes transparent. The exact value of the initial surface temperature depends on various factors during the violent stages of explosion, cooling stages of the proto-neutron star through diffusive neutrinos, and possible re-infalling of the ejected material. Therefore, until the surface layers become thermally relaxed Ts may satisfy the above condition.
Mass loss from central stars of planetary nebulae
Authors: Perinotto Mario , Benvenuti Piero , Cacciari Carla
Published: July 2016

From a high resolution spectrum taken with IUE, the central star of the planetary nebula IC 2149 is found to exibit a wind with edge velocity of 1440 ± 100 km s-1. Our preliminary evaluation of the associated mass loss rate gives 10-8 M0 yr-1. Other planetary nebulae nuclei are studied with low resolution IUE spectra and indications are found of mass loss rates consistent with the above value.
Narrow components in UV line profiles as evidence for a two component stellar wind for 0 and B stars
Authors: Lamers Henny J.G.L.M.
Published: July 2016

The UV resonance lines of early type stars show narrow absorption components, with a width of the order of 300 km s-1, superimposed on the wider P Cygni profiles. Such narrow components have been detected in the Copernicus spectra of a few early type stars by Morton (1976) and Snow and Morton (1979). The variability of these components was studied by Snow (1977) who compared two scans of the UV line profiles of 15 stars taken about four years apart. He found that the narrow components do not change in velocity (except for the CIII λ 1175 line in ζ, Pup) but that the strength of the components can change drastically. In some stars the narrow components were present in only one of the two spectra. We studied the characteristics of these narrow components in the Copernicus spectra (Snow and Jenkins, 1977). The stars are listed in Table 1. Examples of these narrow components are shown in Figure 1.
Evolutionary effects of mass loss in low-mass stars
Authors: Renzini Alvio
Published: July 2016

The effects of mass loss on the evolution of low-mass stars (actual mass smaller than 1.4 Mʘ) are reviewed. The case of globular cluster stars is discussed in some detail, and it is shown that evolutionary theory sets quite precise limits to the mass-loss rate in population II red giants. The effects of mass loss on the final evolutionary stages of stars producing white dwarfs is also discussed. In particular, the interaction of the wind from the hot central star with the surrounding planetary nebula is considered. Finally, the problem of the origin of hydrogen-deficient stars is briefly discussed.
Structure of the Solar Oscillation with Period near 160 Minutes
Authors: Scherrer Philip H. , Wilcox John M.
Published: July 2016

The solar oscillation with period near 160 min is found to be unique in a spectrum computed over the range of periods from about 71 to 278 min. Our best estimate of the period is 160.0095 ± 0.001 min, which is different from 160 min (1/9 of a day) by a highly significant amount. The width of the peak is approximately equal to the limiting resolution that can be obtained from an observation lasting 6 years, which suggests that the damping time of the oscillations is considerably longer than 6 years. A suggestion that this peak might be the result of a beating phenomenon between the five minute data averages and a solar oscillation with period near five minutes is shown to be incorrect by recomputing a portion of the spectrum using 15 s data averages.
Observation of Five-Minute-Period Gravity Waves in the Solar Photosphere
Authors: Stebbins R.T. , Goode Philip R. , Hill Henry A.
Published: July 2016

Vertically propagating traveling waves have been observed in the solar photosphere. These waves have a period of 278 ± 41 seconds and a vertical phase velocity of about 2 km s-1. It is noted that these waves also have approximately the same period as the well-studied five-minute-period acoustic mode, which is evanescent in the photosphere. The only consistent interpretation of the traveling waves implies that they are gravity waves. About half the time the gravity waves are outgoing, while the remainder of the time they are ingoing.

The data were collected by Stebbins et al. (1980) to study the vertical structure of the photosphere. They examined velocity pertubations at nine altitudes in the photosphere using a Doppler shift technique. The current work represents a reanalysis of that data which uncovered the five-minute-period traveling waves.

The mean velocity amplitude of disturbances at a given altitude, as registered in the observed Doppler shift, was found to be directly proportional to the mean velocity amplitude at the base of the photosphere. This was the expected relationship between the velocity amplitudes. It was not expected that the standard deviation of the velocity amplitude at a particular altitude would be independent of the velocity amplitude at the base of the photosphere. In addition, the phase difference between velocities at different altitudes is, unexpectedly, inversely proportional to the velocity amplitude at any altitude. These two traits of the data are consistent with a five-minute-period nonacoustic traveling wave being superimposed on the five-minute-period acoustic mode. This supposition is borne out by a detailed examination of the data in the complex plane of amplitude and phase and by a calculation of the power spectrum of the traveling waves as a function of their vertical wavenumber (see Hill et al., 1982).
Mean Colors and Effective Temperatures of K and M Dwarfs
Authors: Wing Robert F.
Published: July 2016

Many applications of multicolor wideband photometry depend upon the existence of a table of mean colors, i.e. a listing of the average values of the color indices B–V, V–R, etc. for each spectral type. Such a table relates the observed colors of unreddened stars to their temperature classes and enables one to draw a reference line representing the main sequence on any color-color diagram.
Spots, Spot-Cycles, and Magnetic Fields of Late-Type Dwarfs
Authors: Vogt Steven S.
Published: July 2016

A review is presented of the current state of observational knowledge concerning spots, spot-cycles and surface magnetic fields on active late-type dwarfs. The discussion centers primarily on the physical characteristics of starspots on BY Dra-type stars, including spot sizes, temperatures, structural morphology, migratory motions, and activity cycles. The discussion will also include some references to similar spot phenomena on the RS CVn stars. Observational evidence for surface magnetic fields on these stars, and on chromospherically-active G and K dwarfs, is also reviewed.
Multiple Wavelength Observations of Flaring Active Regions
Authors: Lang Kenneth R.
Published: July 2016

The radio emission of quiescent active regions at 6 cm wavelenght marks the legs of magnetic dipoles, and the emission at 20 cm wavelength delineates the radio wavelength counterpart of the coronal loops previously detected at X-ray wavelengths. At both wavelengths the temperatures have coronal values of a few million degress. The polarization of the radio emission specifies the structure and strength of the coronal magnetic field (H 600 Gauss at the heigths h 4 x 109 cm above sunspot umbrae). At 6 cm and 20 cm wavelength the solar bursts have angular sizes between 5" and 30" brightness temperatures between 2 x 107 K and 2 x 108 K, and degrees of circular polarization between 10% and 90%. The location of the burst energy release is specified with second-of-acr accuracy. At redio wavelength the burst occur within the central regions of magnetic loops, while the flaring Hα kernels are located at the loop footpoints. Coronal loops exhibit enhanced radio emission (preburst heating) a few minutes before the release of burst energy. The radio polarization data indicate magnetic changes before and during solar bursts.
A Flare-Like Event from the Short-Period System XY UMa
Authors: Zeilik M. , Elston R. , Henson G. , Smith P.
Published: July 2016

XY UMa (+55°1317, SA027143) is a short-period (P 0.48 d) cousin of the RS CVn stars. The primary star is G2-G5V; the secondary K5 (Geyer, quoted by Lorenzi and Scaltriti, 1977). Geyer (1977) has done the bulk of the observational work to date, including the first photoelectric observations. The rapid, annual changes in XY UMa's light curve, and the fact that the last published light curves was from the 1977 season convinced us to reobserve this active system.
On Activities of UV Cet-Type Flare Stars and of T Tau-Type Stars
Authors: Gershberg R.E.
Published: July 2016

Comparisons of the activities of UV Cet-type flare stars and of T Tau-type stars with solar activity permits the conclusion that non-sta-tionary processes in the UV Cet-type stars and in the Sun are of an indent ical physical nature but that they differ qualitatively from active events in the T Tau-type stars. The identity of the activity in flare stars and the Sun makes it possible to study successfully stellar activity with the help of known models of various solar events and, on the other hand, to have a more general approach to the physics and evolution of solar activity on the basis of established features of numerous flare stars of different ages and masses. The hypothesis on hydromagnetic activity of the T Tau-type stars is sketched; within this framework, one supposes that the main feature of such stars is an occurrence at every point of the stellar surface, of conditions necessary for the existence of dark spots, i.e. a lowering of the photospheric brightness due to strong local magnetic fields.
Dynamo Theory in the Sun and Stars
Authors: Belvedere G.
Published: July 2016

Complementarity of solar and stellar observations should increase our knowledge of the basic facts and mechanismsof activity. The great development of stellar activity observations has enhanced theoretical study, most of which is in the framework of dynamo theory.

Even if dynamo theory seems plausible and successful in capturing the essential processes, several uncertainties and intrinsic limits do still exist and are discussed here together with alternative or complementary suggestions.
MHD Thermal Instabilities in Inhomogeneous Atmospheres
Authors: Bodo G. , Ferrari A. , Massaglia S. , Rosner R.
Published: July 2016

The Einstein Observatory survey of stellar coronae (Vaiana et al. 1981) and, specifically, the results on cool, low luminosity stars has suggested a correlation between stellar X-ray luminosity and stellar rotational velocity (Pallavicini et al. 1982, Walter 1981, Vaiana et al. 1981). In addition the Skylab observations of the solar corona have demonstrated a tight correlation between photospheric surface magnetic structures, which emerge from the interior in the form of “loops” above the photosphere by, viz., buoyancy instabilities, (Parker 1979; see also Acheson 1979, Schmitt & Rosner 1982, and references therein), and coronal X-ray emission (Golub et al. 1980). It therefore becomes important to ask how a coronal state (i.e. low density and high temperature plasma) of a stellar atmosphere is formed , presumably from a pure radiative equilibrium configuration.
A Re-Consideration of the Evolution Hypothesis of the Origin of the Resonances Among Saturn's Satellites
Authors: Sinclair A.T.
Published: July 2016

The hypothesis that the origin of the resonances among Saturn's satellites is due to orbital evolution is critically reviewed. It is concluded that the hypothesis provides a plausible explanation of the origin of the Mimas-Tethys resonance, but it is unsatisfactory for Bnceladus-Dione, since their resonance is having little effect on the relative evolution rate of these satellites at present.
Regularization of the Equations of Motion in a Central Force-Field. Application to the Zonal Earth Satellite
Authors: Cid R. , Ferrer S. , Elipe A.
Published: July 2016

Within the framework of linear and regular celestial mechanics, we revise a recent method of Belen'kii (1981). We generalize some of his results, giving a new regularizing function.

We make an application to the zonal earth satellite, considering the hamiltonian function through the harmonic J4. After the angular variable u has been removed, we introduce a new time and we reduce the problem to a linear equation.
Capture of the Comet P/Boethin by Jupiter
Authors: Daniel Benest , Reinhold Bien , Hans Rickman
Published: July 2016

The possible effects of non-gravitationnal forces on the motion of the comet P/Boethin are investigated for various values of the orbital period. A time interval of 2000 years backward and forward is treated. The authors find in all cases that the comet librates temporarily around the 1/1 resonance with Jupiter as a remote jovian satellite during at least two centuries.
Regions of Stability of Asteroids
Authors: Szebehely Victor , Vicente Raimundo , Lundberg John
Published: July 2016

Using Hill's modified stability criterium, regions of orbital elements are established for conditions of stability. The model of the three-dimensional restricted problem of three bodies is used with the Sun and Jupiter as the primaries. Four different cases are studied: direct and retrograde, outside and inside asteroidal orbits. The directions of the asteroidal orbits refer to the synodical reference frame and the positions refer to Jupiter's orbit. The orbital parameters of the asteroids are the semi-major axis (a), the eccentricity (e), and the inclination from Jupiter's orbital plane (i). The effects of the other orbital elements are not investigated in this paper. The argument of the perihelion and the longitude of the ascending node are fixed at Ω = ω = 90° and the time of perihelion passage is T = 0 for all orbits.
Symmetric Periodic Orbits in the Anisotropic Kepler Problem
Authors: Casasaya Josefina , Llibre Jaume
Published: July 2016

The anisotropic Kepler problem has a group of symmetries with three generators; they are symmetries respect to zero velocity curve and the two axes of motion’s plane. For a fixed negative energy level it has four homothetic orbits. We describe the symmetric periodic orbits near these homothetic orbits. Full details and proofs will appear elsewhere (Casasayas-Llibre).
Capture/Escape Boundary in the Collinear Restricted Three-Body Problem
Authors: Gómez Gerard , Llibre Jaume
Published: July 2016

We study the cantorian structure of the successive intersections of the invariant manifolds of infinity (parabolic orbits) with a certain surface of section. The first of these intersections is computed numerically. The structure of the set of orbits of capture or escape after n binary collisions is given.
Near IR spectra of symbiotic stars
Authors: Andrillat Y.
Published: July 2016

It is very well known that symbiotic stars are displaying at the same time spectral characteristics of hot stars, cool stars (principally of M type), nebulae and circumstellar dust envelopes.

The investigation of the near IR is particularly interesting because one finds there important features of these different objects.
The ultraviolet spectrum of AG Draconis
Authors: Altamore A. , Baratta G.B. , Cassatella A. , Giangrande A. , Ponz D. , Ricciardi O. , Viotti R.
Published: July 2016

The high resolution ultraviolet spectrum of AG Dra was observed with IUE in April and August 1981 at phases 0.50 and O.69 according to the Meinunger (1979, Inf. Bull. Var. Stars No.1611) U-light curve. The UV spectrum of the star appears rather different from that of the other classical symbiotic stars. The low resolution IUE spectrum of AG Dra shown in figure 1. The continuum is rather strong with respect to the emission lines and detectable at high resolution. Many intense interstellar lines are present, in spite of the low reddening of the star (E(B-V)=0.06, according to the depth of the 2200A interstellar band).
The peculiar star RX Puppis
Authors: Kafatos M. , Michalitsianos A.G.
Published: July 2016

We have obtained the first high dispersion observations of RX Puppis in the wavelength region 1200 - 3200 A with the “International Ultraviolet Explorer” (IUE). The anomalies we observed in lines such as He II, C III], C IV, N III], N IV], 0 III], and Si III], that show split line profiles, Doppler displaced component(s) suggest dynamic activity in circumstellar material that probably has the form of rings and/or gas streamers between the cool giant and the hot companion, the Mg II lines show P-Cygni structure arising in the Mira primary. The continuum cannot be due to a star earlier than A0 II and it may arise in an accretion disk around the hot secondary. Moreover, the line emission requires photoionization either from a hot subdwarf or the inner accretion disk.
On the model of symbiotic stars
Authors: Tutukov A. V. , Yungelson L. R.
Published: July 2016

We discuss conditions necessary for appearance and discovery of the symbiotic star phenomenon within the model of a binary consisting of a red (super)giant 3 Mʘ not filling the Roche lobe and of an accreting hot degenerate CO-dwarf 0.8 Mʘ. Within this model “classical” symbiotic stars may exist only within a narrow region of mass accretion rates and separations of components: 10-7 ≲ Ṁ ≲ 3.10-7 Mʘ/y and 3.1013 ≲ a ≲ 2.1014 cm. The evolutionary status of symbiotic stars and related objects and the mechanisms of their variability are discussed.
Synthesis of Data on the Local Interstellar Medium
Authors: York Donald G. , Frisch Priscilla C.
Published: July 2016

During this workshop, a considerable amount of data was presented, some refined versions of earlier results and some entirely new. While no completely definite picture of the local interstellar medium can be presented yet, some general conclusions can be drawn. We attempt to draw together the most relevant data in Section III. Some new UV results are collated with published results to help state the physical properties of the gas. A morphological view of the local medium is given in Section III. We confine ourselves to the region within 100 pc with the caveat that the distance of much of the material under discussion is poorly known.
Observations of Interstellar HI Toward Nearby Late-Type Stars
Authors: Landsman Wayne B. , Henry Richard C. , Moos H. Warren , Linsky Jeffrey L.
Published: July 2016

High-dispersion Copernicus and IUE observations of chromospheric Ly α emission are used to study the distribution of HI in the local interstellar medium. Interstellar parameters are derived toward 3 stars within 5 pc of the sun, and upper limits are given for the Ly a flux from 9 other stars within 10 pc.
Probe of the Nearby Interstellar Medium by the Vacant Line of Sight to β CMa
Authors: Gry C. , York D.G. , Vidal-Madjar A.
Published: July 2016

The line of sight to βCMa has been probed by Copernicus observations. This particular line of sight is remarkable for the low mean densities. We find n̄H ∼ .002 cm-3. However we can distinguish two separate regions:

1) A local nearby HI region extends over a few parsecs from the sun with a density of the order of 0.1 cm-3 and a temperature of 11000 to 12500 K.

2) An HII region lies somewhere beyond the HI region and is spread over about 60pc. Its total hydrogen mean density is of the same order as the HI region, i.e. of ∼0.1 cm-3 and it contains only elements in low ionization state. All the data are coherent with the picture of a cloud in ionization equilibrium at T ∼ 23 000° K.
The Smallest Sizes of Diffuse Interstellar Clouds
Authors: Dickey John M. , Crovisier J. , Kazes I.
Published: July 2016

By observing the difference in optical depths between absorption spectra toward the two components of double sources we have measured the variations in opacity over lengths of less than 0.1 up to 10 pc inside diffuse interstellar clouds. Significant variations are detected on scales larger than about 0.2 pc, but not less. This may represent the minimum size for diffuse cloud structure. By comparing the variations of Gaussian fitted line parameters we find that variations in the internal velocity field of diffuse clouds explain the data rather better than tiny independent “cloudlets.”
Nearby Molecular Hydrogen
Authors: Lebrun F.
Published: July 2016

If the gas-to-dust ratio is sufficiently uniform throughout the local interstellar medium, galaxy counts may provide a useful probe of the large scale structure of the interstellar gas. This idea substantiated by gamma-ray observations has led to the discovery of nearby molecular cloud complexes. The reddening studies indicate that one of them lies between 80 and 140 pc from the sun. From CO observations, its molecular mass is estimated to be a few 103 M⊙.
A Model of the Soft X-Ray Background as a Blast wave Viewed from Inside
Authors: Edgar Richard J. , Cox Donald P.
Published: July 2016

The suggestion that the soft x-ray background arises In part from the Sun being inside a large (R ∼ 100 pc) supernova blastwave is examined by producing models of spherical blastwaves. Such models can produce quantitative fits to both surface brightnesses and energy band ratios (for the lowest energy bands) when t ∼ 105 yr, EO = 5 x 1050 ergs, and nO ≃ 0.004 cm-3.

Such models can be generalized by varying the relative importance of such factors as thermal conduction, Coulomb heating of electrons, and external pressure; by allowing the explosions to occur In pre-existing cavities with steep density gradients, or by examining the effects of large obstructions or other anlsotroples in the ambient medium.
Radial Velocity Information in Sour-Type Spectra
Authors: Merline W.J.
Published: July 2016

Recent advances in instrumentation and technique have provided hope that changes in stellar radial velocities can be measured with an accuracy of 10 m/s. This tremendous increase in the precision of radial velocity measurements should yield a wealth of new information from studies of stellar oscillations and surface phenomena, as well as offer clues to help answer perhaps the most exciting question, that of the existence of extra-solar planetary systems. The stringent requirements of light scrambling, high signal-to-noise ratio, and the need for frequent or simultaneous calibration (Griffin and Griffin 1973; Serkowski 1978) mean that these new techniques are inherently inefficient. This has limited studies to bright stars and to the use of large telescopes. Without a priori knowledge of the inclination of the rotation axes of the stars under study, searches for planetary systems will require a relatively large number of stars to statistically determine the probability that any of these stars harbor planets. Therefore, it is necessary to extend the limits for precise radial velocity studies to 5th or 6th blue/visual magnitude. Efficient extraction of radial velocity information from the spectrum is essential. Furthermore, attempts to increase limiting precision or decrease limiting magnitudes using conventional techniques will also benefit from increased efficiency.
Radial-Velocity Work at Cambridge and Palomar
Authors: Griffin R.F.
Published: July 2016

The Cambridge radial-velocity spectrometer must be the oldest instrument to qualify as relevant to the main theme of this meeting. It was the first instrument to measure radial velocities photoelectrically, and has been the principal source of observational data for more than 100 published papers. Nearly 19 years after it was brought into operation it is still in active use — indeed, I have been observing with it this very week.

The principal observing program is concerned with spectroscopie binaries, and at any given time has about 200 objects on it. Although the weather in Cambridge is poor, the 36-inch telescope has been almost continuously available for radial-velocity work for the last ten years. On the whole, there is as much observing time available as I can use, and its distribution in time is much more favourable for work on spectroscopie binaries than the typical distribution of nights allocated to any one observer on a more popular telescope. Among the orbits written up recently, noteworthy examples are those of HD 210647 (the most eccentric spectroscopie orbit, with e = 0. 904), HR 1105 (the first for an S-type star) and 6 Boo (whose amplitude of little more than 1 km/s is smaller by a factor of two than that of any other orbit that I consider to be reasonably secure).
A Search for Constant Velocity B and A Stars
Authors: Fekel Francis C.
Published: July 2016

Over the past few years high dispersion spectroscopie observations have been obtained for a number of close visual binaries and multiple stars. Because velocity variations in such binaries are relatively small, just a few 10’s of km s−1 at most, and because of the long timespan of the observations, a few years to several decades, the velocities must be very accurate and systematic effects kept to a minimum. This is particularly true since observations have been obtained at several different observatories with several different spectrograph-detector systems. With the advent of solid-state Reticon and CCD detector systems data reduction has primarily been done by cross-correlating the spectrum of a program star with the spectrum of a constant velocity star of similar spectral type. As a result a search for constant velocity stars of B and A spectral type was begun recently. Included in the survey are 6 early B stars, 8 late B stars and 15 early A stars. All have v sin i ≤ 55 km s−1 and about two-thirds have v sin i ≤ 25 km s−1.
Measures of RR Lyrae Stars
Authors: Burki G. , Meylan G. , Mayor M.
Published: July 2016

Four RR Lyrae stars have been measured in Oct.-Nov. 1983 from the Observatoire de Haute Provence in France (radial velocities with CORAVEL) and from La Silla Observatory in Chile (Geneva 7-color photometry). General information on these stars is listed in the following table. The quantities N and σ are the number of measurements and the typical precision of one measurement.

The variation of the radial velocity with the pulsation cycle of each star is shown in Fig. 1. Especially noteworthy is the very quick decrease of the radial velocity in the cases of RR Cet and DX Del.
Masses and Magnetic Fields of White Dwarfs in Cataclysmic Variables
Authors: Lasota J.P. , Hameury J.M. , King A.R.
Published: July 2016

We show that the existence of the AM Her period spike implies (i) a unique white dwarf mass ≃ 0.6 − 0.7M⊙ for most magnetic CV’s (ii) nova explosions remove exactly the accreted mass from magnetic white dwarfs, and (iii) the maximum magnetic field for most CV’s is ≤ 4 × 107 G. The existence of the spike is very strong support for the idea that the period gap results from a drastic reduction of angular momentum losses when the secondary star becomes fully convective.
G117-B15A: How is it Evolving?
Authors: Kepler S.O. , Vauclair G. , Nather R.E. , Winget D.E. , Robinson E.L.
Published: July 2016

The measurement of the rate of change of period with time for the g-mode pulsations in ZZ Ceti stars is a direct measurement of the cooling timescale for a DA white dwarf, which in turn can give a totally independent measurement of the age of the galactic disk. Using asteroseismology, we have obtained a rate of change of the period of the dominant pulsation in the light curve of the ZZ Ceti star G117-B15A of dP/dt = (12.5 ± 5.5) × 10−15s/s, equivalent to a timescale for period change of P/P = (5.5 ± 2.4) × 108 yr, which is consistent with the theoretical value for the cooling timescale of a DA white dwarf around 11,000 K.
The Atmospheric Composition of the Hot Pre-Degenerate Star H1504+65 Revisited
Authors: Vennes S. , Fontaine G. , Wesemael F.
Published: July 2016

Nousek et al. (1986) have recently announced the discovery of a remarkable hot compact star, H1504+65, which appears to have an atmosphere devoid of hydrogen and helium. Although the object seems significantly hotter than the related PG1159 stars, its suggested atmospheric composition remains at variance with the He-rich composition inferred for the latter stars (Wesemael, Green, and Liebert 1985). Nousek et al. (1986) have brought forward convincing arguments against a H-dominated atmosphere in H1504+65; it seems that the object is definitely not an extremely hot DA star. On the other hand, the case against a He-rich atmosphere is much weaker and is based on the following circumstantial arguments: (1) no helium lines are detected in the spectrum of H1504+65 (the detection limit is ≈ 0 5 Å), (2) the ultraviolet continuum slope is steeper than that predicted from pure helium modelsaxtrapolated to effective temperatures larger than the upper limits of available grids (Te = 200 000 K for log g = 7 ), and (3) the EXOSAT observations appear to conflict with the He interpretation, although suitable models (with high effective temperatures) are not readily available in this case also. Because of the lack of appropriate models, Nousek et al. (1986) have been careful not to rule out completely the possibility of a He-rich atmosphere for H1504+65. In particular, they admit that He II lines could probably be undetectable if H1504+65 had an effective temperature substantially larger than Te = 150 000 K. Nevertheless, they have found it tempting to hypothesize an atmosphere devoid of both hydrogen and helium. Coupled with the presence of weak C IV and O VI features in the spectrum of H1504+65, this has led to the suggestion that H1504+65 is actually a bare C/O nucleus (cf. Shipman 1987). Although this suggestion is interesting, it has undeservedly remained unchallenged and we have felt it appropriate to reexamine the case against a He-rich atmosphere with the help of further modelling efforts.
The High Resolution Spectrum of the Pulsating, Pre-White Dwarf Star PG 1159-035 (GW VIR)
Authors: Liebert James , Wesemael F. , Husfeld D. , Wehrse R. , Starrfield S. G. , Sion E. M.
Published: July 2016

First reported at the IAU Colloquium No. 53 on White Dwarfs (McGraw et al. 1979), PG 1159-035 (GW Vir) is the prototype of a new class of very hot, pulsating, pre-white dwarf stars. It shows complicated, nonradial pulsation modes which have been studied exhaustively, both observationally and theoretically. The effective temperature has been crudely estimated as 100,000 K with log g ~ 7 (Wesemael, Green and Liebert 1985, hereafter WGL).
Thomson Scattering in Magnetic Fields
Authors: Whitney Barbara
Published: July 2016

The equation of transfer in Thomson scattering atmospheres with magnetic fields is solved using Monte Carlo methods. Two cases, a plane parallel atmosphere with a magnetic field perpendicular to the atmosphere, and a dipole star, are investigated. The wavelength dependence of polarization from a plane-parallel atmosphere is qualitatively similar to that observed in the magnetic white dwarf Grw+70°8247, and the field strength determined by the calculation, 3.2×l08 G, is quantitatively similar to that determined from the line spectrum. The dipole model does not resemble the data as well as the single plane-parallel atmosphere.
An AD HOC Hypothesis on the Pulsation of Delta Scuti Stars
Authors: Antonello E.
Published: July 2016

Taking into account the possible influence of external factors such as the orbital motion in binary systems and the rotational velocity on the pulsation of δScuti stars, it may be possible to explain some properties of these variables.
Statistical Properties of Algol-Type Systems
Authors: Giuricin G. , Mardirossian F. , Mezzetti M.
Published: July 2016

We have inspected the observational data of 114 Algol-type binaries in order to clarify some general aspects of their evolutionary scenario. Through a comparison with the corresponding available statistical analyses of large sample of eclipsing and spectroscopic binaries, we have found a larger than normal concentration of low values of masses, binary separations and specific orbital angular momenta for Algol-type stars. Furthemore, high mass ratios predominate in massive and early-type Algol systems, whereas high total masses are generally accompanied by less prominent oversized and overluminous properties of the mass-losing components.
The Mass Distribution of White Dwarfs and Central Stars of Planetary Nebulae
Authors: Weidemann Volker
Published: July 2016

Recent results on mass distributions for white dwarfs and planetary nebulae are presented and compared with current theoretical predictions. Whereas single star evolution leads to final masses predominantely in a narrow interval around 0.6μ0 which can be explained by current mass loss schemes degenerate stars in binaries present a larger range of masses. The average mass of the primaries in cataclysmic binaries seems to be more around 0.7 than 1μ0.
UV Spectroscopy of the Novalike Variable TT Arietis
Authors: Wargau W. , Drechsel H. , Rahe J. , Klare G. , Wolf B. , Krautter J. , Vogt N.
Published: July 2016

TT Ari was detected by Strohmeier et al. (1957) and is classified as a novalike variable. It was hitherto unclear whether TT Ari is a special type of dwarf nova (Warner, 1976) or an old nova (Cowley et al., 1975). Our group obtained a total of four IUE spectra between 1979 and 1981 in the short and long wavelength region. The first spectrum was taken in July 1979, when the system had a visual brightness of 11.3 magnitudes. The following two IUE observations in November 1980 revealed TT Ari in the lowest optical state (V = 14m.3) observed so far. The fourth spectrum was obtained during the rise to maximum in January 1981, when the system had an apparent magnitude of V = 11m.8. From this behavior, Krautter et al. (1981) concluded that TT Ari is a dwarf nova with extremely extended standstills as they are typical for Z Cam stars.
On the Possible Short-Period Irregular Light Fluctuations of V1357 CYG =CYG X-1
Authors: Kumsiashvili M.I. , Kraicheva Z.
Published: July 2016

Photoelectric observations in U, B, V, were carried out to study the possible rapid (during a night) fluctuations of the close binary system V1357 Cyg, including the X-ray source Cyg X-1. Assuming the existence of irregular fast light fluctuations in the X-ray source Cyg X-1,the conclusion can be drawn that during these observations in 1979 the amplitude of the variations did not exceed 0.04 mag.
Summary of optical groundbased E ring observations at the University of Arizona
Authors: Larson Stephen
Published: July 2016

The faint E ring of Saturn is difficult to observe from groundbased telescopes because of atmospheric and instrumental scattering of light from the disc and rings. The application and refinements of coronagraphic imaging techniques and new detectors have pennitted observations of the E ring with the University of Arizona 154 cm telescope since the ring plane crossing in 1979. The measurements briefly summarized here, are derived from photographic and CCD imaging data obtained over 6 nights in 1980, and 7 nights in 1981. These observations may set constraints on physical models of the E ring . During the 1979-80 apparition, the ring plane was viewed nearly edge-on, while in 1981 and 1982 the ring plane was inclined 5° and 10° respectively.
How a sheperd guides a sheep herd?
Authors: Greenberg Richard
Published: July 2016

The mechanism by which a shepherd satellite exerts a confining torque on a ring is considered from the point of view of a single ring particle. It is still not clear how one might most meaningfully include damping effects and other collisional processes into this type of approach to the problem.
Comments on collision mechanics in ring systems
Authors: Hartmann William K.
Published: July 2016

The nature of collisions within ring systems is reviewed with emphasis on Saturn's rings. The particles may have coherent icy cores and less coherent granular or frosty surface layers, consistent with thermal eclipse observations. Present-day collisions of such ring particles do not cause catastrophic fragmentation of the particles, although some minor surface erosion and reaccretion is possible. Evolution by collisional fragmentation is thus not as important as in the asteroid belt.
Multivalued electrostatic potentials; “ chance or necessity ” for the charge of solid particles near Saturn?
Authors: Meyer-Vernet N.
Published: July 2016

In a plasma with (cold) electrons temperature between typically 10 eV and several KeV, the secondary emission on solid particles plays an important role. In particular, in the presence of suprathermal electrons, the potential can have two stable equilibrium states in a given environment: then, the sign of the charge depends on minor historical accidents of the system, and small environmental perturbations yield important jumps of charge. To illustrate this point, well-known by space-craft charging specialists, we investigate the charge's response to a slight variation of ambient parameters near Saturn (flux of suprathermal electrons ; passage from shadow to sunlit). The results are often opposite to those given by either usual “rules of thumb”, or uncareful numerical calculations. The importance of the process is evaluated for different saturnian environments. Some possible consequences for grains physics (dynamics in electromagnetic fields, agglutination and disruption) are discussed.
Numerical experiment applicable to planet formation
Authors: Cazenave Anny
Published: July 2016

A three-dimensional numerical model has been developed with the goal of studying limited dynamical problems relevant to the latest stage of planet growth in the accretion theory. A small number of large protoplanets (~ moon-size) of different masses, moving around the Sun, are considered. The dynamical evolution and growth of the population is studied under mutual gravitational perturbations, accretion and collisional fragmentation processes. Gravitational encounters are treated exactly by numerical integration of the N-body problem. Outcomes of collisional fragmentation are modeled according to the results of Greenberg et al. (1978).
The asteroid ring
Authors: Dermott S.F. , Murray C.D.
Published: July 2016

The asteroid belt between Mars and Jupiter has some features in common with planetary rings; these include gaps associated with resonances and a tendency for pericenter alignment. While it is tempting to think of the Jupiter-asteroid belt system in terms of satellite-disk interactions, the present low spatial density of the belt limits, for example, the application of the spiral density wave theory, which has achieved some success in explaining the resonant structure of Saturn's rings. However, some authors claim that this process, and some other processes, would have been effective in the belt's early history, if the belt was then both flatter and more massive. It is likely that Jupiter's orbital period was then at least slightly different from the present period. From a statistical analysis of the asteroid orbital period data, we show that the present distribution of asteroids is strongly correlated with the present orbital period of Jupiter (to 1 part in 5000). Furthermore, by analyzing the distribution of orbital eccentricities and inclinations we show that the resonant structure of the belt was formed after the asteroids had dispersed from the near-coplanar disk in which they accreted.
Non-Equilibrium Ionisation in Supernova Remnants - A Case Like Tycho - A case like Tycho
Authors: Brinkmann W. , Fink H.H.
Published: July 2016

X-ray observations of young supernova remnants (SNR) provide the most direct tool to study their evolution, their chemical composition, and their interaction with the interstellar medium. We will show for a SNR with the characteristics of Tycho that great care has to be taken in interpreting spectral data obtained with X-ray detectors with low spatial resolution.
The X-ray Emission from SN 1987A and the Remnant of SN 1572 (Tycho)
Authors: Itoh Hiroshi , Masai Kuniaki , Nomoto Ken’ichi
Published: July 2016

The thermal X-ray emission from SN 1987A may be enhanced to a detectable level when the blast shock hits the circumstellar medium which has formed in the red-supergiant stage of the progenitor.

The X-ray spectrum of Tycho observed with the satellite Tenma can be explained approximately within the context of a carbon deflagration model for Type la supernovae, if the ejecta are assumed to be mixed partially.
HI and CO Observations Towards the SNR Puppis A
Authors: Dubner G.M. , Arnal E.M.
Published: July 2016

The presence of interstellar clouds along the northern and eastern edges of Puppis A is revealed by our HI and CO observations.
CTB80: a SNR with a Neutron-Star Driven Component
Authors: Strom R.G.
Published: July 2016

Pulsar-like emission has been detected from the flat-spectrum component of the galactic radio source CTB80. The consequences for the source are discussed.
Gravitational and Dynamical Instabilities of a Decelerating Plane-Parallel Slab of Finite Thickness
Authors: Voit G. Mark
Published: July 2016

In order to explore how supernova blast waves might catalyze star formation, we investigate the stability of a slab of decelerating gas of finite thickness. We examine the early work in the field by Elmegreen and Lada and Elmegreen and Elmegreen and demonstrate that it is flawed. Contrary to their claims, blast waves can indeed accelerate the rate of
star formation in the interstellar medium. Also, we demonstrate that in an incompressible fluid, the symmetric and antisymmetric modes in the case of zero acceleration transform continuously into Rayleigh-Taylor and gravity-wave modes as acceleration grows more important.
V641 Cas - A Symbiotic Candidate?
Authors: Tomov T. , MiKolajewsKi M.
Published: July 2016

The light variability of V641 Cas was discovered by Guinan et al. (1982). Spectral investigations were made earlier by Barbier(1971,1975), wich classified it as a VV Cep-type star and suggested that the V641 Cas is a binary system consisting of M3Ia supergiant and a B type star. Shaw and Guinan(1985) estimated the spectral class of the companion as B2.5. Recently Guinan et al. (1986) reported about semiregular changes with maximal amplitude of about 1.0mduring 1979–1986. Slow variations in the brightness with a mean period 310d and variable amplitude of 0.3m–0.9m ph are established by Berthold(1983).
Atmospheric Shocks in Mira Variables – MgII Emission
Authors: Brugel Edward W. , Beach T.E. , Willson L.A. , Bowen G.H.
Published: July 2016

We have undertaken an extensive program to investigate atmospheric shock dynamics in Mira variables through monitoring the MgII emission strengths versus phase. Theoretical calculations of Bowen (1987), which represent the structural variations in the extended atmosphere of a pulsating Mira, are presented in addition to the MgII observations. The model calculations generate density, temperature and velocity structures as determined by stellar parameters and by interactions of the driving amplitude, dust opacity and thermal relaxation processes. The main diagnostic provided by the models is the total emitted shock luminosity versus phase, which can be compared to the observed MgII emission. Models and observations are presented for three Miras: S Car, R Car and T Cep.
Thermonuclear Runaways on Accreting Hot White Dwarfs
Authors: Prialnik Dina , Regev Oded
Published: July 2016

Preliminary results of 1–D fully hydrodynamic numerical calculations including accretion and mass loss on a 1M⊙ hot white dwarf are presented. For the case of Ṁ = 10−8M⊙/yr and Teff = 125000°K we get flashes of duration of ∼ 30 – 40 yrs which reccur every ∼ 1500 years. During each flash ∼ 6x10−6M⊙ is lost (∼ 40% of the accreted envelope.
General Discussion on the Physics of Symbiotic Stars
Authors: Kenyon Scott J.
Published: July 2016

This paper reviews the general discussion on the physics of symbiotic stars.
The Observations of AG PEG During 1985–87
Authors: Boyarchuk A.A. , Belyakina T.S. , Tarasov A.E. , Tomov N.
Published: July 2016

The light curves in UBVRI and profiles of the emission lines of Hα, HeII 5411 and HeI 5876, 6678 obtained during 1985–87. The radial velocities of the emission lines HeI 6678 and HeII 5411 demonstrated clear periodic variations in antiphase with the radial velocity defined for the absorption line.
Criteria and Applications of the MK Classification System
Authors: Garrison R. F.
Published: July 2016

A review is given of the present state of MK classification, with a view to future developments in techniques and instrumentation. The principle of the complementarity of quantitative and visual inspection techniques is stressed.

Included in the discussion are examples of problems which are currently outstanding. Among these are variable stars, marginal peculiarities, fundamental standards (with specific reference to the Sun), and representation of the third and higher dimensions.
Some Lessons from the Past and Thoughts on the Future of Spectral Classification
Authors: Walborn N. R.
Published: July 2016

The importance of maintaining the greatest possible independence of spectral classification from theoretical or other external information is emphasized anew, with reference to some historical discussions now seen with the benefit of hindsight. This ideal requirement applies equally to the development and to the application of a classification system, although in practice some well-established information may guide one’s intuition in the initial hypothetical formulation. The fundamental position of this principle in the MK approach to classification is a major reason for the value of its spectral types, and for its continuing success in uncovering new phenomena. The ability of a particular technique to produce interesting or useful results is surely the most significant criterion of its value, and from this viewpoint it appears that new techniques and methods will complement rather than replace traditional spectral classification. Finally, the unique importance at this time of applying both new and traditional methods to spectral classification in the Magellanic Clouds is stressed; they provide the only current opportunity for detailed spectroscopic examination of numerous stars in external systems. It is essential that large telescopes be utilized for this work so that the best attainable observational quality may be maintained, and the many fascinating phenomena revealed by spectral classification in the Galaxy can be comparatively investigated to the maximum extent praticable in the Magellanic Clouds