bluuebunny/crossref_metadata_2025_split huggingface dataset:
Meeting the Public: Popular Observatories
Authors: Kleczek Josip 
Published: July 2016

“L’homme est infiniment petit par son corps, mais il est infiniment grand par son esprit”. Blaise PascalPopular observatories (PO) are an important link between astronomers and the public. Fig.1 represents the flow of information about the Cosmos and the role of POs.The flow of information about celestial bodies starts with photon emission. The emitted photons carry the information about the moment when they are born. They transfer the encoded information through cosmic space in all directions, among others towards our planet. By ground-based or space-based instruments astronomers decode the information in the photons. The size and shape of celestial bodies are determined with great precision (by photography and interferometry). Direction from which the photons arrive determines the position of their source (astrometry). The amount of photons (photometry), their frequency (spectrophotometry) and the direction of their oscillation (polarimetry) are other information decoded from the incident photons. The observational instruments are the interface between the Cosmos and astronomers’ minds.
Abundances in J-Type Carbon Stars
Authors: Utsumi Kazuhiko 
Published: July 2016

It has been found by Utsumi(1985a,b) that in J-type carbon stars of C4-5 and WZ Cas(C9,2J Li), abundances of s-process elements with respect to Fe are nearly normal, while in normal carbon stars of C5-8, heavy metals are overabundant by factors of 10-100, and rare-earth elements are overabundant by a factor of about 10.In the MK system, most J-type stars are classified as C4-5,4-5 stars which show very strong C2 and CN bands. Yamashita(l972,1975) classified many C7-9 stars most of which are CS or SC stars. His classification of C7-9J stars is mainly based on Cl2C13(0,1)band at 6168 A, C13N(4,0)band at 6260 A, and LiI 6708 A line. In most of C7-9 stars, lines of s-prooess elements are greatly enhanced. It is a question if in all J-type stars abundances of s-process elements are nearly normal or not.
Helium Flashes Through the NCO Reaction
Authors: Arai K. , Kaminisi K. , Hashimoto M. , Nomoto K. 
Published: July 2016

It is generally accepted that the helium flash occurs when the 3α reaction commences in the degenerate helium core of low mass stars. In this core, original CNO isotopes have been converted into 14N and the electron Fermi energy becomes large enough to approach the threshold energy for e-capture on 14N. Hence Kaminisi et al. (1975) have pointed out that in these circumstances the 14N(e−, v)14C(α,γ)18O (NCO) reaction may play an important role for igniting the helium flash.We, therefore, examine the effects of the NCO reaction on the evolution of low mass stars. A key ingredient of the NCO reaction is that the density reaches the threshold for e-capture (ρth≃ 106 g cm−3). Evolutionary sequences are presented for the cases of accreting helium white dwarfs (Hashimoto et al. 1986) and a 0.7 M⊙, Population II star ascending the giant branch.
Evolutionary Helium and CNO Anomalies in the Atmospheres and Winds of Massive Hot Stars
Authors: Walborn Nolan R. 
Published: July 2016

AbstractThe ubiquitous evidence for processed material in the atmospheres, winds, and circumstellar ejecta of massive stars will be reviewed. A broad array of normal and peculiar evolutionary stages is considered, up to and including Type II supernova progenitors. The quantitative analysis of these spectra is difficult, and until recently for the most part only qualitative or approximate results have been available. However, several important current programs promise reliable abundance determinations, which will enable detailed comparisons with recent evolutionary calculations. A significant emerging result is that the morphologically normal majority of both hot and cool supergiants may already display an admixture of CNO-cycle products in their atmospheres. It may become possible in this way to identify blue supergiants returning from the red supergiant region, as appears to have been the case for the SN 1987A progenitor.
NLTE Analysis of the Wolf-Rayet Star HD193077 (WN5+abs)
Authors: Schmutz W. , Hamann W.-R. , Wessolowski U. 
Published: July 2016

A model atmosphere code that accounts for the special physical conditions in Wolf-Rayet atmospheres (Hamann and Schmutz, 1986; Wessolowski et al., 1987) is used to analyse the spectrum of the Wolf-Rayet star HD193077 (WN5+abs). The stellar parameters are determined such that the profiles of the helium lines He I λλ4471, 5876, He II λ5412, and the absolute visual magnitude are reproduced.In order to estimate the systematic errors introduced by the model assumptions, we perform some test calculations. Instead of the velocity-law exponent of ß=1, another fit is obtained with ß=0.5 (Fig. 1). This fit yields an effective temperature of about 3000K higher than with ß=1. In order to simulate the effect of the suspected hydrogen content, a further fit (Fig. 2) is made when one free electron per helium atom is added artificially. This has only marginal influence on the derived temperature (+100K). Thus, we conclude that our model assumptions may introduce a systematic error of the order of 5000K.
Dust Driven Winds in Late Supergiants
Authors: Sedlmayr Erwin , Dominik Carsten , Gail Hans-Peter 
Published: July 2016

The oool extended shells of giants and supergiants are well known to be places of copious dust formation as indicated by the occurrence of pronounced extinction, reddening, and polarization of the continuous star light and by the appearance of particular absorption features, both manifesting the interaction of photons with particles considerably larger than atoms or molecules.The accepted explanation of these phenomena is the formation of circumstellar dust, i.e. small solid particles with a typical size of the order of 0.1 micron. However, the analysis of these effects yields only information on the interaction of photons with certain functional groups within the clusters - e.g. Si-O, C-H, C-C bending and Si-O, C-C,... stretching vibrations - and thus allows no definite determination of the “real” physical structure and chemical composition of the grain particles. Therefore, observational conclusions concerning the properties of circumstellar dust can provide only some “mean” information which allows no definitive conclusions regarding the true nature of the observed grains (geometrical shape, crystalline structure,...?).
Atmospheric Evidence of Evolutionary Processes in Interacting Binaries
Authors: Kondo Yoji 
Published: July 2016

The preceding invited paper by Sahade (1987) gave a balanced overall picture for the subject matter. I shall attempt to complement his talk in discussing two classes of atmospheric diagnostics of the evolutionary processes in interacting binary systems. These are: (I) Abnormal abundances of elements in the atmosphere resulting from the nuclear processes in the stellar interior. (II) Mass flow as a consequence of the evolution of either of the components and the Algol type binaries.There are several classes of objects with abundance anomalies, such as Am stars. At least some of these objects are known close binaries. In particular, most Am stars appear to be close binary stars. However, the physical causes of the metallic overabundances in those stars are still unclear. We shall in the following examine Algol type binaries for abundance anomalies.
Light Curve Models for SN 1987A and Diagnosis of Supernova Interior
Authors: Nomoto Ken’ichi , Shigeyama Toshikazu , Hashimoto Masa-aki 
Published: July 2016

AbstractPresupernova evolution of the progenitor of SN 1987A, hydrodynamics of explosion (shock propagation, explosive nucleosynthesis), optical light curve due to shock heating and 56Co decay, and X-ray and γ-ray light curves are calculated and compared with the observations of SN 1987A. Constraints on the mass of the hydrogen-rich envelope Menv (i.e., mass loss history) and the helium abundance in the envelope are obtained from the progenitor’s blue-red-blue evolution as well as from the light curve. The explosion energy E and the mass and distribution of 56Ni are inferred from the light curves. Models and observations are in reasonable agreement for E/Menv = 1.5 ± 0.5 × 1050 erg/M⊙, Menv = 5 - 10 M⊙, and MNi ∼ 0.07 M⊙. Mixing of 56Ni into the envelope is indicated.Light curves of exploding bare helium stars are also calculated to see whether the observed Type Ib supernova light curves can be accounted for.
A Simple Treatment of the Problem of Radiative Transfer in Supernova-Like Envelopes
Authors: Isern J. , López R. , Simonneau E. 
Published: July 2016

Since the only direct information, on the physics of supernova explosions comes from spectrophotometry of their light curves, it is wortwhile to put considerable effort on understanding the properties of supernova atmospheres. Two problems appear, however, in doing so. First, the mean free path of a photon in the region where the Spectrum forms (the atmosphere) is an important fraction of the supernova size and the plane parallel approximation breaks down. Second, the roles of scattering and absorption in the formation of the continuum are not clearly determined.The complications introduced by spherical geometry arise from the angular derivative terms in the transfer equation and from the high degree of anisotropy introduced by the geometry. The complications introduced by scattering arise from the presence of the mean intensity in the source term of the transfer equation. As an outcome, its numerical solution is time consuming, and classical simplifications are not possible due to the strong anisotropy of the radiation field. In hydrodynamical calculations it is better to calculate the moments of the radiation field, but the success of this method depends on the possibility of replacing the infinite set of differential equations by the equations of low order moments plus a closure relationship that keeps all the properties of the higher moments.
Is a stellar wind inherent in WR–stars throughout the whole of their evolution?
Authors: Gershberg R.E. 
Published: July 2016

In addition to certain manifestation of a stellar wind during steady states of WR-stars that we have heard here about I have two notes on their extremal stages of evolution which may be also connected to such a hydrodynamical event.The first note. There is a pecular object, HM Sge that had brightened for several magnitudes during several months. It has a strong emission spectrum that is similar to a planetary nebula spectrum in general, and it was suggested that we register a planetary nebula birth. However, in Crimea we have found that a total width of H-alfa emission line is ~ 2000 Km/sec and a central part of its profile is asymmetric significantly. These features exclude a genetic, relationship between HM Sge and Planetary nebulae.
Mass loss from α Ori
Authors: Tanabe T. , Kamijo F. 
Published: July 2016

High dispersion spectrograms of α Ori are obtained. Several strong absorption lines which have circumstellar components are measured. Assuming the plane-parallel envelope and thermal equilibrium, the mass loss rate is estimated as 1x10-6 Mʘ/yr.To obtain the mass loss rate of red giant stars is very important in connection with the study of the stellar evolution. Several authors have observed circumstellar lines and obtained mass loss rate using precise theories of radiation transfer. However, accuracy of the studies seems to depend not on the adopted theories but on the dispersion of spectrograms, since the structure of the circumstellar space is too complicated to be expressed by,e.g.,single expansion velocity. Because our spectrograms have higher dispersion, compared with others, our study is meaningful, though the assumed model is very simple.
Stellar variability and individuality: observations and implications (invited paper)
Authors: Costero R. , Doazan V. , Stalio R. , Thomas R.N. 
Published: July 2016

AbstractCustomarily, one assumes that the internal structure of the star is not changed by a mass-flux from the atmosphere; thus one changes evolutionary calculations with mass-loss from those without it only by homologously decreasing the mass at each static evolutionary step. Furthermore, it is customary to assume that the mass-flux can be expressed in terms of only the thermal parameters (luminosity, Tepp) or (g, Teff). Sometimes rotation is introduced, but only as a modification of equatorial gravity, not of internal nonthermal structure. The phenomena of large-amplitude variability in times short compared with evolutionary ones, and of individuality (two stars of the same taxonomic class having different atmospheric distributions of Te and density) invalidate such static evolutionary calculations. We summarize the evidence for such large-amplitude variability in Be and la supergiant B stars. We also summarize the evidence for individuality as exhibited by observations: of OVI in OB stars; of x-ray luminosity across the HR diagram; of far-UV spectra of O stars; and of visual and far-UV spectra of Be stars. These observational results require nonthermal fluxes of mass and nonradiative energy to be imposed from below by the subatmosphere; which implies a nonthermal structure of subatmosphere and at least some part of the interior. Such nonthermal structure must then be included in evolutionary calculations. Thus current observations of nonthermal mass-flux from essentially all stars require including a nonthermal internal structure, not simply a mass-loss, in evolutionary calculations.
Winds in late-type stars: Mechanisms of mass outflow
Authors: Linsky Jeffrey L. 
Published: July 2016

AbstractFour basic mechanisms have been proposed to explain the acceleration of winds in late-type stars –– thermal pressure gradients, radiation pressure on circumstellar dust grains, momentum addition by Alfvén waves, and momentum addition by periodic shock waves. In this review I describe recent work in applying these mechanisms to stars, and consider whether these mechanisms can work even in principle and whether they are consistent with recent ultraviolet and X-ray data from the IUE and Einstein spacecraft. Thermally-driven winds are likely important for late-type dwarfs, where the mass loss rates are small, and perhaps also in G giants and supergiants, but they cannot operate alone in the K and M giants and supergiants. Radiatively-driven winds are probably unimportant for all cool stars, even the M supergiants with dusty circumstellar envelopes. In principle, Alfvén waves can accelerate winds to high speeds provided the field lines are initially open or forced open by some mechanism, but detailed calculations are needed. Magnetic reconnection is an interesting suggestion for an acceleration mechanism when the field lines are initially closed. For the Mras and semiregular variable supergiants, periodic shock waves provide a simple way of producing rapid mass loss. Thus we are making some progress in understanding mass loss mechanisms for the cool half of the H-R diagram.
Massive stars burning helium: the numbers of WR stars and red supergiants in galaxies
Authors: Maeder A. 
Published: July 2016

We have calculated evolutionary models of massive stars in the range 15-120 Mʘ from the zero-age sequence up to the end of the carbon burning stage (Maeder, 1981). Three sets of models with different mass loss rates Ṁ have been computed; the adopted parametrisation of Ṁ is fitted on the observations and thus the expression for Ṁ differs according to the location of the stars in the HRD.In this short note we concentrate on the location of the He-burning stars in the HRD. The helium burning phase, which lasts 8 to 10% of the MS phase, is spent mainly as red supergiants (RSG) and as WR stars (note that for low mass loss, the time spent as A-G supergiants becomes longer).
On the evolutionary time scale of the accreting component in massive close binaries: consequences for the supernova event
Authors: Doom C. , De Grève J.P. 
Published: July 2016

AbstractThe remaining core hydrogen burning lifetime after a case B of mass exchange is computed for the mass gaining component in massive close binaries. Effects of stellar wind mass loss and mass loss during Roche Lobe OverFlow (RLOF) are included. Consequences for the evolutionary scenario are discussed.
Stellar mass loss and HII region morphology in Magellanic irregular galaxies
Authors: Dopita M.A. , Wilson I.R. 
Published: July 2016

AbstractThe problem of the interaction of a strong stellar wind with a massive collapsing neutral hydrogen cloud has been considered and a new class of steady flow solutions found.The detailed comparison of these models with one filamentary shell, N70 in the LMC, shows that they successfully explain all the observed properties of the HII region and enable mean mass-loss rates to be derived for the central stars.
Observation of Global 160-min Infrared (Differential) Intensity Variation of the Sun
Authors: Kotov V.A. , Koutchmy S. , Koutchmy O. 
Published: July 2016

AbstractThe method developed and the instrument designed for detecting variations of the solar limb darkening at the atmospheric transparency window of the solar opacity minimum region of λ 1.65 µ are described. This differential technique proved to be successful in rejecting undesirable low frequency noises due to the atmosphere and to the instrument. Analysis of observations made in 1977, 1978, and 1981 indicates the persistance of global fluctuations of the IR differential, center-to-limb intensity at the wellknown 160 min period with an average amplitude of about ± 2 x 10-4 in units of the ‘average Sun’ intensity near 1.65 µm.
160-min Oscillations of the Sun as the Mean of Study of its Internal Structure
Authors: Gavryuseva E. A. , Kopysov Yu. S. , Zatsepin G. T. 
Published: July 2016

AbstractThe investigation of the models of the contemporary Sun with a mixed core has shown that the amplitude of some gravity modes of oscillations of the star can be mainly concentrated in the central region. This phenomenon takes place if the node of the amplitude of radial displacement coincides with the boundary of the mixed core. In this case the core can be regarded as a driving generator of the oscillations, determining their period and phase. It is suggested as the explanation of the observational properties of the 160-min oscillation.
Adiabatic Oscillations of Solar Models with a High-Z Convective Zone
Authors: Vorontsov S.V. , Marchenkov K.I. 
Published: July 2016

AbstractNormal mode spectra and neutrino counting rates are calculated for a set of chemically-inhomogeneous solar models. Each model has a core with a high concentration of heavy elements; high opacity makes the core convective. The structure of the envelope is that of the standard model. It is shown that (1) the spectrum of g modes becomes less densely separated than that of the standard model, which simplifies the problem of interpreting 160-min oscillations; (2) low neutrino counting rates may be achieved for a low initial helium concentration in the core; (3) the models do not contradict the frequency spacing of global 5-min oscillations.
On the Influence of Nonlinearities on the Eigenfrequencies of Five-Minute Oscillations of the Sun
Authors: Belvedere Gaetano , Gough Douglas , Paternò Lucio 
Published: July 2016

AbstractFitting the results of linear normal-mode analysis of the solar five-minute oscillations to the observed κ – ω diagram selects a class of models of the Sun’s envelope. It is a property of all the models in this class that their convection zones are too deep to permit substantial transmission of internal g modes of degree 20 or more. This is in apparent conflict with Hill and Caudell’s (1979) claim to have detected such modes in the photosphere.A proposal to resolve the conflict was made by Rosenwald and Hill (1980). They pointed out that despite the impressive agreement between linearized theory and observation, nonlinear phenomena in the solar atmosphere might influence the eigenfrequencies considerably. In particular, they suggested that a correct nonlinear analysis could predict a shallow convection zone. This paper is an enquiry into whether their hypothesis is plausible.We construct κ – ω diagrams assuming that the modes suffer local nonlinear distortions in the atmosphere that are insensitive to the amplitude of oscillation over the range of amplitudes that are observed. The effect of the nonlinearities on the eigenfrequencies is parameterized in a simple way. Taking a class of simple analytical models of the Sun's envelope, we compute the linear eigenfrequencies of one model and show that no other model can be found whose nonlinear eigenfrequencies agree with them. We show also that the nonlinear eigenfrequencies of a particular solar model with a shallow eonvective zone, computed with more realistic physics, cannot be made to agree with observation. We conclude, therefore, that the hypothesis of Rosenwald and Hill is unlikely to be correct.
On the Detection of Subphotospheric Convective Velocities and Temperature Fluctuations
Authors: Gough D. O. , Toomre J. 
Published: July 2016

AbstractA procedure is outlined for estimating the influence of large-scale convective eddies on the wave patterns of five-minute oscillations of high degree. The method is applied to adiabatic oscillations, with frequency ω and wave number k, of a plane-parallel polytropic layer upon which is imposed a low-amplitude convective flow. The distortion to the k – ω relation has two constituents: one depends on the horizontal component of the convective velocity and has a sign which depends on the sign of ω/k; the other depends on temperature fluctuations and is independent of the sign of ω/k. The magnitude of the distortion is just at the limit of present observational sensitivity. Thus there is reasonable hope that it will be possible to reveal some aspects of the large-scale flow in the solar convection zone
Torsional Oscillations of the Sun
Authors: Howard Robert 
Published: July 2016

AbstractA series of digitized synoptic observations of solar magnetic and velocity fields has been carried out at the Mount Wilson Observatory since 1967. In recent studies (Howard and LaBonte, 1980; LaBonte and Howard, 1981), the existence of slow, large-scale torsional (toroidal) oscillations of the Sun has been demonstrated. Two modes have been identified. The first is a travelling wave, symmetric about the equator, with wave number 2 per hemisphere. The pattern-alternately slower and faster than the average rotation–starts at the poles and drifts to the equator in an interval of 22 years. At any one latitude on the Sun, the period of the oscillation is 11 years, and the amplitude is 3 m s-1. The magnetic flux emergence that is seen as the solar cycle occurs on average at the latitude of one shear zone of this oscillation. The amplitude of the shear is quite constant from the polar latitudes to the equator. The other mode of torsional oscillation, superposed on the first mode, is a wave number 1 per hemisphere pattern consisting of faster than average rotation at high latitudes around solar maximum and faster than average rotation at low latitudes near solar minimum. The amplitude of the effect is about 5 m s1-. For the first mode, the close relationship in latitude between the activity-related magnetic flux eruption and the torsional shear zone suggests strongly that there is a close connection between these motions and the cycle mechanism. It has been suggested (Yoshimura, 1981; Schüssler, 1981) that the effect is caused by a subsurface Lorentz force wave resulting from the dynamo action of magnetic flux ropes. But, this seems unlikely because of the high latitudes at which the shear wave is seen to originate and the constancy of the magnitude of the shear throughout the life time of the wave.