bluuebunny/crossref_metadata_2025_split huggingface dataset:
Distance Determination of Mass Losing Carbon Stars from CO and HCN Radio Observations
Authors: Unno Wasaburo , Tsuji Takashi , Koyama Kou-ichi , Izumiura Hideyuki , Ukita Nobuharu , Kaifu Norio 
Published: July 2016

AbstractA method of distance determination of evolved carbon stars is proposed and applied to six stars for which the terminal velocity of expansion and the angular size are obtained from the CO and HCN radio observations made at the Nobeyama Radio Observatory. The method assumes the radiation driven wind in spherical geometry. Within those small samples, however, two types of mass losing stars that are systematically different in the antenna temperature ratio TA (CO)/TA(HCN) ≷1, in the velocity ratio υ(CO)/υ(HCN)≶1, and in the angular size ratio θ(CO)/θ(HCN)≷1 seem to be present, suggesting nonspherical geometry of the outflow.
Photospheres of Mira Variables
Authors: Bessell M.S. , Brett J.M. , Scholz M. , Takeda Y. , Wehrse R. , Wood P.R. 
Published: July 2016

Mira variables form an important subgroup of the red giant stars which are typical representatives of stars showing burnt material at their surfaces. Since the photospheres of Miras are not in hydrostatic equilibrium but are characterized by spherically very extended density stratifications, their properties and emitted spectra differ substantially from those of non-Miras, and any attempts to analyse Mira spectra by means of conventional techniques must fail. Non-hydrostatic models are needed for analysis work.We computed a small set of exploratory M type (solar abundances) Mira model photospheres whose density distributions were taken from an improved modification of a pulsation model proposed by wood (1979). Besides the fundamental model parameters, i.e. mass, luminosity and radius (or effective temperature), the parameters of the density stratification (e.g. the heights of the density discontinuities at the shock front positions, or the effective gravity acting between two successive shock fronts) must be treated as free parameters within certain limits, owing to insufficient knowledge of the velocity stratification entering the pulsation model. Typical density and temperature stratifications are shown in Fig. 1 of Scholz (1987). Both CO lines, measuring the outflow and infall velocities of matter between the shock fronts, and selected moleculer band features (colors) were found to react sensitively to adjustments of the model parameters. As an example, Fig.1 shows the differences between CO line profiles computed from the near-maximum model of Fig.1 of scholz (1987) (Fig.1a) and those computed from a model in which the effective gravity between the shock fronts was increased by a factor of 1.5 (Fig. 1b). The same velocity stratification was adopted in of monochromatic radii proves to be a powerful tool of diagnostics of Mira photospheres (Scholz and Takeda 1987; Bessell et al. 1987).
W Ursae Majoris Star Models: Observational Constraints
Authors: Linnell Albert P. 
Published: July 2016

W Ursae Majoris stars can be understood as contact binary stars with a common envelope (Lucy 1968). They subdivide into two types: The A-type are earlier inspectral class than about F5, are believed to have radiative envelopes, and associate primary (deeper) eclipse minimum with transit eclipse. The W-type have spectral classes later than F5, are believed to have convectlve envelopes, and associate primary minimum with occultation eclipse. Controversy has surrounded the explanation of W-type light curves.Four distinct models have been introduced to describe the envelopes or photospheres of W UMa stars. (1) The Rucinski hot secondary model directly explains W-type light curves on a postulational basis. Since 70%-90% of the emitted radiation from the secondary (less massive) component is believed to reach the secondary via circulation currents from the primary, there is an apparent thermodynamic mystery why the secondary should be hotter. (2) The Lucy Thermal Relaxation Oscillation (TRO) model argues that the secondary component is perpetually out of thermal equilibrium and that the components are in contact only during part of a given TRO cycle. During contact the photosphere is supposed to be barotropic. In this case primary minimum always associates with transit eclipse, in disagreement with observation for W-type systems. (3) The Shu et al. thermal discontinuity (DSC) model also argues for a barotropic photosphere but differs from Lucy on the gravity brightening exponent. The changes are insufficient to produce W-type light curves, (4) Webbink (1977), and, separately, Nariai (1976), argue for a baroclinic envelope. If the baroclinicity extends to the photosphere there is a possibility that W-type l i g h t curves could be explained. In particular, the Webbink scenario produces a hot secondary.
Carbon Abundance in Mass-Exchanging Binaries
Authors: Cugier H. , De Greve J.P. 
Published: July 2016

The evolution of the carbon abundance at the surface of both components of a mass-exchanging (Algol-type) binary is examined (fig. 1). Distinction is made between case B and case AB (fig. 2) of mass transfer, in view of the different timescales involved. In the mass accreting component thermohaline mixing is adopted when matter with decreasing hydrogen abundance is deposited on the surface.It is shown that at the surface of the loser a very low C-abundance is present, while at the surface of the gainer different regimes occur. On the average the expected C-abundance on the gainer is clearly lower than the observed solar value, but far above the value at the surface of the loser. The variation in time during the mass-exchange process is compared to the values, derived from observation of several Algol-type systems.
Spectral Peculiarities in Nova Vulpeculae 1984 N° 2
Authors: Andrillat Yvette , Houziaux Léo 
Published: July 2016

This slow nova has been observed spectroscopically at Observatoire de Haute-Provence in two wavelengths regions: 330–460 nm (plate factors: 4 and 8 nm), and 750–1100 nm (plate factors: 23 and 26 nm/mm).Time coverage includes the following stages: close to maximum of light, early nebular phase and advanced nebular stage.Spectra are similar to those of classical novae: strong continuum, wide emission bands with double structure, flanked by a moderate strength absorption component at −1400 km/s.The following ions are identified: H I, O I, C I, N I, Mg I and II, Ca I and II, Fe II, Ti II, Si II and Sr II.
Observation of a Neutrino Burst from the Supernova SN1987a: The KAMIOKANDE-II Collaboration
Authors: Totsuka Yoji 
Published: July 2016

A neutrino burst was observed in the KAMIOKANDE-II detector on 23 February, 7:35:35 UT ( ±1 minute) during a time interval of 13 seconds. The signal consisted of 11 electron events of energy 7.5 to 36 MeV, of which the first 2 point back to the Large Magellanic Cloud (LMC) with angles 18° ± 18 ° and 15° ± 27°.A new analysis of the special low threshold trigger counts strongly indicates that KAMIOKANDE did not observe any signals at 2:52:36 which is the time claimed by the Mont Blanc group.
Calculated Energy Distributions for SN II
Authors: Hauschildt P.H. , Spies W. , Wehrse R. , Shaviv G. 
Published: July 2016

AbstractWe 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

AbstractFrom 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.
Evolutionary effects of mass loss in low-mass stars
Authors: Renzini Alvio 
Published: July 2016

AbstractThe 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

AbstractThe 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

AbstractVertically 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).
Spots, Spot-Cycles, and Magnetic Fields of Late-Type Dwarfs
Authors: Vogt Steven S. 
Published: July 2016

AbstractA 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

Abstract.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.
Dynamo Theory in the Sun and Stars
Authors: Belvedere G. 
Published: July 2016

ABSTRACTComplementarity 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.
A Re-Consideration of the Evolution Hypothesis of the Origin of the Resonances Among Saturn's Satellites
Authors: Sinclair A.T. 
Published: July 2016

AbstractThe 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

AbstractWithin 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

AbstractThe 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

AbstractUsing 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

AbstractThe 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

AbstractWe 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.
The peculiar star RX Puppis
Authors: Kafatos M. , Michalitsianos A.G. 
Published: July 2016

AbstractWe 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

AbstractWe 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.
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

AbstractHigh-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

AbstractThe 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

AbstractBy 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

AbstractIf 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⊙.