bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Rotating Stellar Collapse Model for Supernova 1987a
Authors: Nakamura Takashi , Fukugita Masataka 
Published: July 2016

It is shown that the bunch structure of the Kamiokande neutrino events associated with SN1987a can be naturally understood, if one assumes that the core of the progenitor star was rotating moderately with q(≡ Jc/GM2) ≈ 3 with J the total angular momentum and M the gravitational mass of the core.We assume that the presence of the observed gap, at least that between the second and the third bunch, is real and consider its implications in the dynamics of the core collapse. Let us define a nondimensional angular momentum q(≡ Jc/GM2) with J the total angular momentum and M the gravitational mass of the core. We assume that the value of q for the core of SN1987a was about 3. Then we expect that the effect of the angular momentum plays an important role when the size of the core r shrinks to < 107cm. In the spherically symmetric collapse model, the size of the unshocked homologous core is of the order of 107cm. Hence we expect that the core at the bounce is essentially governed by the spherically symmetric dynamics. To verify this point we may refer to the simulation by Symbalisty1. Our model almost corresponds to Model ROT2 in which one obtains a neutrinosphere with a roughly spherical radius of approximately 50km. We then expect that the infalling nonhomologous matter onto the core will liberate a gravitational energy of the order of 1052ergs.
The Light Curve of SN 1987 A
Authors: Schaeffer R. , Cassé M. , Mochkovitch R. , Cahen S. 
Published: July 2016

AbstractWe use a semi–analytical model of supernova light curves that extends Arnett’s scheme [1,2] to include the effect of recombination of hydrogen, helium and heavy elements in the expanding ejecta. Introducing in the model the physical parameters of Sanduleak −69 202, the salient characteristics of the light curve of SN 1987 A are reasonably reproduced over 100 days.
An X-Ray Investigation of Crab-Like Supernova Remnants
Authors: Wang Z. R. , Seward F. D. 
Published: July 2016

The Crab Nebula is the most noticeable object in our Galaxy, and the remnant of the famous Chinese guest star appeared in 1054AD, the best association between supernova remnants(SNR) and ancient guest stars. Before seventies, the Crab Nebula was considered as a special SNR with different morphology and physical features from that of most SNRs, Now more and more Crab-like SNRs have been detected(Weiler 1985). It is necessary to make a systematical investigation for the Crab-like SNRs, especially for those with central pulsars because they offer us more physical messages than others.The two associations SNR and PSR, the Crab Nebula with PSR 0531+21 and the Vela SNR with PSR 0833-45, were confirmed at the end of sixties and still were the only two associations before eighties. Recent years, PSR 1509-58 in MSH 15-52 and PSR 0540-69 in a SNR of LMC(Seward & Harnden 1984, Seward etal. 1984) as well as PSR 1951+32 in CTB 80 (Clifton et al. 1987, Fruchter etal. 1987) were discovered. On the other hand, the X-ray emission of PSR 1055-52 and others were detected (Cheng & Helfand 1983, Helfand 1983). Recently, we searched for the X-ray emission of isolated pulsars over more than thirty fields in Einstein observation. By use of the same instrument calibrstions, the X-ray luminosities of ten isolated pulsars and their surrounding nebulae are obtained. Let Lx be the total X-ray luminosity of a pulsar and its nebula in the 0.2-4.0 kev band, and E be the rotating energy loss rate of the pulsar, the following statistical relation is obtained by linear regression and shown as the line in Fig. 1.
Infrared observations and mass loss of the binary system V861 Sco
Authors: Tanzi E.G. , Maraschi L. , Tarenghi M. , Treves A. 
Published: July 2016

V 861 Sco (HD 152667) is a well known single line binary(1,2).The proposed association with a variable X-ray source(3,4) has triggered renewed interest in the system. Recent optical, infrared and ultraviolet observations(5 - 12) have provided a better knowledge of its characteristics. A first estimate of the mass loss was given by Hutchings(13).Here we report on a series of photometric observations in the infrared (from 1.25 to 4.8 µ) taken at various orbital phases which improve and extend previous measurements by Tanzi et al.(12)The results give evidence of a phase modulated infrared excess which can be interpreted in terms of a non isotropic mass flow in the system or, alternately, of a contribution from a colder secondary component.
Stellar mass loss and galactic chemical evolution
Authors: Serrano A. , Peimbert M. 
Published: July 2016

We summarize here some of the results that we have obtained from chemical evolution models. In particular, we discuss those aspects related to stellar mass loss, helium production, a varying heavy element yield and the very light stars.The observed value of the helium to heavy element abundance ratio ΔY/ΔZ is about 3 (e.g. Lequeux et al. 1979). First theoretical estimates gave ΔY/ΔZ= 0.4 (Hacyan et al. 1976).
On the Accuracy of Frequency Determination by an Autoregressive Spectral Estimator
Authors: Kovács G. 
Published: July 2016

AbstractThe accuracy of frequency determination by a least squares technique for an autoregressive spectral estimator is studied and compared with the Fourier method. Using numerical tests the probability distribution function of the peak location is calculated. The autoregressive filter order is optimized in the sense of minimum variance of the peak location. Simple sinusoidal signals with additive Gaussian noise are considered and the effect of other components is only indicated. Generally, a filter order between 1/3 and 1/2 of the total data number and a not very dense data sampling, gives the most stable spectrum. The results are numerical.
Radiative Transfer and Solar Oscillations
Authors: Christensen-Dalsgaard Jørgen , Goode Philip R. 
Published: July 2016

AbstractWe consider the atmospheric behaviour of solar oscillations in a model including a detailed, semi-empirical atmosphere. Equations of radial and non-radial oscillation, with consistent treatment of the radiation field, are derived. These equations are solved in the radial, grey case; the results show that departure from the Eddington approximation has little effect on the properties of the oscillations. Preliminary results are presented for the non-radial case, indicating substantial deviations from the Eddington approximation when the optical thickness across a horizontal wavelength is of the order of or less than unity.
A New Method for determining the Helium Abundance in the Solar Atmosphere
Authors: Isaak G. R. 
Published: July 2016

AbstractRecent observations of a cut-off frequency in the acoustic modes of the Sun (Claverie et al., 1981b) should help determine the mean molecular weight and, thereby, the helium abundance in the visible layers of the solar atmosphere. A first preliminary result of Y = 0.42 ± 0.04 is obtained for an assumed minimum photospheric temperature of 4400 K ± 200 K.
Solar Models with Low Opacity
Authors: Kuzurman P.A. , Pamyatnykh A.A. 
Published: July 2016

AbstractEvolutionary models of the present Sun with standard and artifically low opacity of stellar matter are obtained and adiabatic nonradial oscillations of the models are computed. The opacity x in nonstandard model (which is the first in a series of future models with low χ) was taken half as much as the Cox-Stewart opacity. The central temperature in such model is approximately 10% below the ‘standard’ values, which can explain the neutrino experiment results. Unlike solar models with very low heavy element abundance, the low χ model has approximately standard mass concentration and distribution of the matter in the outer layers – specifically, the standard characteristics of the convection zone. Hence, the spectrum of adiabatic oscillations is similar to that of the standard models and has the same capabilities for the explanation of the observed pulsations.
Theoretical Eigenfrequencies of Solar Oscillations of Low Harmonic Degree l in Five-Minute Range
Authors: Shibahashi H. , Osaki Y. 
Published: July 2016

AbstractWe have calculated eigenfrequencies of radial and nonradial p-mode oscillations with low harmonic index l (l = 0, 1, 2, 3, and 4) for a standard solar model with normal composition and appoximately the correct age. It is found that theoretical eigenfrequencies calculated for our standard model agree approximately with observed peaks in the power spectra for the full-disk five minute oscillation of the Sun (Claverie et al., 1980; Grec et al., 1983; Scherrer et al., 1983) in agreement with other recent works (Christensen-Dalsgaard and Gough, 1980; Scuflaire et al., 1981). However, there still remains a slight discrepancy between theory and observations in such a sense that the theoretical eigenfrequencies are slightly lower than observations (see Figure 1).
The Study of Velocity Oscillations in the Solar Photosphere Using the Velocity Substraction Technique
Authors: Kobanov N.I. 
Published: July 2016

AbstractA method of measurement of local line-of-sight velocities in the solar atmosphere by means of polarization optics is described. No spurious signals due to instrumental displacements of the spectrum arise with this method. The sensitivity of the method obtained is 0.3 m s-1, with a time constant τ = 5 s and input aperture 1.4ʺ x 4.5ʺ. Some preliminary results of the assessment of spatial characteristics of 5-min oscillations are included. Data are given to illustrate a center-to-limb variation of the spectrum of 5-min oscillations.
A New System for Observing Solar Oscillations at the Mount Wilson Observatory. I: System Design and Installation
Authors: Rhodes Edward J. , Howard Robert F. , Ulrich Roger K. , Smith Edward J. 
Published: July 2016

AbstractIn this paper we describe a new observing system which is currently nearing completation at the Mount Wilson Observatory. This system has been designed to obtain daily measurements of solar photospheric and subphotospheric rotational velocities from the frequency splitting of non-radial solar p-mode oscillations of moderate to high degree (i.e. l > 150). The completed system will combine a 244 x 248 pixel CID camera with a high-speed floating point array processor, a 32-bit minicomputer, and a large-capacity disc storage system. We are integrating these components into the spectrograph of the 60-foot solar tower telescope at Mount Wilson in order to provide a facility which will be dedicated to the acquisition of oscillation data.
Resonant Coupling between Solar Gravity Modes
Authors: Dziembowski W. 
Published: July 2016

AbstractIt is shown that in consequence of the parametric resonance, g modes of low spherical harmonic degree l are strongly coupled to the modes of high degree. The coupling limits the growth of lowl modes to very small amplitudes. For g1, l = 1 mode, the final amplitude of the radial velocity is of the order of 10 cm s-1. A mixing of solar core as a result of a finite-amplitude development of linear instability of this mode is thus highly unlikely.
On the Excitation of Oscillations of the Sun (Numerical Models)
Authors: Kosovichev A.G. , Severny A.B. 
Published: July 2016

AbstractNumerical solutions of the general time-dependent gas-dynamical equations in linear adiabatic approximation are given for initial conditions imitating: (a) a central perturbation, (b) a boundary perturbation (in the convective envelope), and (c) a ‘shrinking’ of the Sun as a whole. For a variety of models of the Sun it is found that at the surface the radial component vr of velocity is much greater than the tangential component vt, and that the period T of stationary oscillations does not exceed 131m. The appearance at the surface of a g mode with period 160m is found to be improbable.With the initial conditions adopted, a propagating wave is produced which is reflected successively from the centre to the periphery and back, producing 5-min oscillations at the surface of the Sun. Expansion of this wave into separate modes leads to a power spectrum qualitatively similar to that observed.
Excitation of the Solar Oscillations by Objects Consisting of y-Matter
Authors: Blinnikov S. I. , Khlopov M. Yu. 
Published: July 2016

AbstractModern development of particle physics makes it probable that new, still undiscovered, particles exist interacting with the ordinary matter by means of gravitation only. Okun suggested to call such particles the y-particles and to call the matter consisting of them the y-matter. We show that planet-like object orbiting inside the Sun and consisting of y-matter may explain 160 min nonradial solar oscillations.
Maunder Convection Mode on the Sun and Long Solar Activity Minima
Authors: Dogiel V. A. 
Published: July 2016

AbstractA model of velocity field oscillations in the solar convective zone is suggested. The system of convective equations is investigated for a thin rotating spherical envelope when the rotation velocity is depended on the coordinates. It is shown that two different structures of convective cells (longitudinal, or latitudinal) can exist in the envelope depending on gradients values of the rotation velocity and Prandtl number.It is supposed that two different regimes of convection (stationary and autofluctuating) are possible in the envelope when the angular velocity gradients are determined by the convection itself. In the case of autofluctuating regime the alternation of longitudinal and latitudinal structure of convection is realized.If one assumes that on the Sun there exists an autooscillating convection regime, then the periods of the existence of latitudinal convection structure may be associated with long periods of activity minima since according to Cowling’s theorem, the action of the axisymmetric magnetic field generation mechanism isimpossible under conditions of axisymmetric velocity structures.
An Essay on Stellar Oscillations and Evolution
Authors: Iben Icko 
Published: July 2016

AbstractIt is cautioned that solar models adjusted in such a way as to achieve a match between theoretical solar oscillation characteristics and observed ones may produce neutrino fluxes inconsistent with the observations and that this is likely to be explicable as a deficiency in modeling that portion of the envelope which is most strongly affected by uncertainties in the treatment of convection. Then follows a summary of how the results of pulsation theory and of stellar evolution theory have been used together to learn about the structure and evolution of RRLyrae stars, classical Cepheids, and high luminosity AGB stars.
The Atmosphere of a Probably Very Young by Dra-Type Flare Star
Authors: de la Reza R. , Butler C.J. , Torres C.A.O. , Batalha C.C. 
Published: July 2016

ABSTRACTThe flare star Gliese 182 (dM0.5e) seems to be only known single BY Dra type that presents Li in its atmosphere. This characteristic and others, principally activity, and high rotation, indicate that probably this is a very young object. We analyse in this work the possibility to interpret with a single typical model for a dMe atmosphere, some observed lines of Gliese 182 and to predict others. The lines belong to the following atoms; Li I, H I, He I, He II, C I, C II. A relatively good agreement exists only for neutral lines but not for ionized lines. The upper chromosphere and transition region must be studied in more detail. Some comparison are made with the UV observations of the double star BY Dra. Empirical relatively high X-ray fluxes are predicted for both stars. The Li abundance of Gliese 182 is confirmed to be similar to that of the interstellar medium.
Einstein and IUE Observations of Nearby Red Dwarfs
Authors: Johnson Hugh M. 
Published: July 2016

ABSTRACTThis paper summarizes data for 40 representative nearby stars from one guest observer's coordinated programs with the Einstein observatory or IUE observatory. The coronal X-ray, chromospheric ultraviolet, and auxiliary optical properties of sets of these stars are tabulated or illustrated in several ways. Factors of stellar duplicity are shown to be quite prevalent in presenting the observations. The most luminous X-ray dwarfs below the Sun are strongly prone to binary status. X-ray luminosity, and the ratio of chromospheric flux to X-ray flux, are dependent on photospheric radius. A very long period BY Draconis variable of type dM6e (HH And) is a detected X-ray source, and some presumably quite old (halo) stars are detected.
X-Ray Observations Of Stellar Flares
Authors: Haisch Bernhard M. 
Published: July 2016

ABSTRACTThe history of stellar X-ray flare observations prior to EINSTEIN is reviewed. X-ray light curves as measured by the IPC are then presented for all time resolved flare events discovered as of July 1982 in the EINSTEIN data set. These light curves are analyzed in terms of solar-like loop models to derive densities, temperatures, loop lengths, magnetic field strength lower limits, etc. The failure of the model to adequately represent the observations in the case of the YZ CMi flares is discussed. The relationship of X-ray to optical emission and X-ray to UV emission is considered from both an observational and a theoretical viewpoint. It is concluded that the characterization of a flare by a single, time averaged ratio, Lx /Lopt , is not physically significant.
Perturbations due to the Asteroid Belt
Authors: Fu Tong , Zhen Chen 
Published: July 2016

AbstractA new expansion for the gravitational potential of the asteroid belt is derived in this paper on the basis of binomial expansions. Its advantages are: (1)the unified form both for the inner and for the outer regions of the belt; (2)suitability for discussing the motions of the celestial bodies with perihelions within but apohelions beyond the belt; (3)rapidity of convergence.The perturbations due to the asteroid belt are studied by using our expansion.
Resonant Asteroidal Motion in the Kirkwood Gaps: A Three-Dimensional Study
Authors: Scholl H. , Froeschle C. 
Published: July 2016

AbstractResonant asteroidal motion is investigated over 17 000 years in a three-dimensional elliptical model Sun-Jupiter-Asteroid averaged by Schubart's method à la Poincarè. Orbits remain trapped in the resonance over this period. The various stability mechanisms are discussed. With respect to their behaviour of ω and ῶ, our resulting orbits reveal 5 distinct classes. These 5 classes can be described in Schubart's topology for the planar problem. As compared to the planar case, eccentricities of orbits in the three-dimensional model vary more strongly. This is an important result for the problem of the delivery of meteorites.
Construction of Periodic Orbits, Problems of Stability and Period Determination, in the Elliptical Non-Planar Restricted Problem
Authors: Edelman Colette 
Published: July 2016

AbstractPeriodic orbits in a fixed frame are constructed in the vicinity of nonperiodic solutions of the non perturbed problem. In a first phase, approximate initial conditions are found and in a second phase more accurate initial conditions obtained are used in order to check the periodic orbit by numerical integration of the three-body problem. Some peculiar solutions are found, for example, orbit with nearly zero angular momentum. A study of stability of periodic solutions is proposed with an approximation of the monodromy matrix Φ (T,o),not requiring numerical integration of the 6x6 variational linear system. Finally, some numerical problems of period determination are outlined.
Asymptotic Approach to Mirror Conditions as a Trapping Mechanism in N-Body Hierarchical Dynamical Systems
Authors: Roy Archie E. 
Published: July 2016

AbstractThe consequences for hierarchical stability of almost circular almost coplanar, low perturbation orbits in an n-body hierarchical dynamical system is discussed. It is shown that frequent close approaches to mirror conditions with subsequent reversing of perturbations is ensured by such properties. The part played by near commensurabilities in mean motion is also discussed, the Sun-Jupiter-Saturn case being taken as an example.
Doubly Asymptotic Orbits at the Unstable Equilibrium in the Elliptic Restricted Problem
Authors: Perdios E. 
Published: July 2016

AbstractOutgoing asymptotic orbits at a collinear Equilibrium point of the elliptic restricted three-body problem are constructed analytically and numerically and those which intersect perpendicularly the axis of symmetry are selected by means of a numerical procedure of differential corrections. Due to the symmetry properties of the problem, the latter orbits terminate asymptotically back to the equilibrium point and therefore provide a kind of “asymptotic trapping” at the unstable equilibrium, a trapping mechanism based on "long duration of passage" rather than stability of motion.
The evolutionary status of symbiotic stars
Authors: Rudak Bronislaw 
Published: July 2016

AbstractThe evolutionary relations between symbiotic stars and cataclysmic variables are presented. The symbiotic stars are assumed to be long period detached binaries containing a carbon-oxygen degenerate primary and a red giant losing its mass through a spherically symmetric wind. Such systems can be obtained in Case C evolution, provided a common envelope during a rapid mass transfer phase was not formed. The same way recurrent novae containing a red giant as a secondary component may be produced. The factors influencing the differences between symbiotic stars and nova-type stars are discussed.
Pioneer 10 and Voyager Observations of the Interstellar Medium in Scattered Emission of the He 584 A and H Lyα 1216 A Lines
Authors: Shemansky D.E. , Judge D.L. , Jessen J.M. 
Published: July 2016

AbstractThe combination of Pioneer photometric and Voyager spectrometric observations of EUV interstellar-interplanetary emissions in the region beyond 5 AU have been applied to a determination of atomic hydrogen and helium densities. These density estimates obtained from direct measurement of scattered radiation depend on absolute calibration of the instruments, in the same way as other earlier determinations based on the same method. However, we have combined the spacecraft data with daily full sun averages of the H Lya 1216 A line obtained by the Solar Mesospheric Explorer (SME) satellite, to obtain a measure of atomic hydrogen density independent of instrument absolute calibration. The method depends on observations of long and short term temporal variability of the solar line over a 1 year period, and the fact that the ISM is optically thick. The density estimates from preliminary work on these observations are [H] = 0,12 cm-3 and [He] = .016 cm-3, giving a density ratio close to the cosmic abundance value, in contrast to some earlier results indicating a depletion of atomin hydrogen. We have obtained estimates of galactic background emissions in the signals of both spacecraft.
MgII Spectra of Late Type Stars Used to Probe the LISM
Authors: Beckman J.E. , Crivellari L. , Franco M.L. , Molaro P. , Vladilo G. 
Published: July 2016

AbstractIUE spectra of Mg II h and k in late type dwarfs and giants have been used to detect and measure absorption components due to the LISM. This technique gives a method of probing the awkward range from d = 3 pc to d = 80 pc from the sun . In spite of interpretational uncertainties we can plot the HI component of the LISM well enough to confirm it as a cloud some 20-30 pc in extent, peaking sharply in density towards , moving towards the sun from , at 28 Km/sec. The “hole” towards is confirmed, suggesting a solar position close to the cloud's edge in this direction.