bluuebunny/crossref_metadata_2025_split huggingface dataset:
Properties of Mira Photospheres
Authors: Scholz M. 
Published: June 2019

The first crude pictures of the structure of Mira photospheres were derived from velocity analyses of emission and absorption lines appearing shifted, doubled and doppler-broadened in Mira spectra. Positions and shapes of profiles change with phase and often do not repeat in successive cycles. Non-repeating cycles are also found in colors (e.g., TiO bands in Fig. 9 of Spinrad & Wing 1969) and in light curves and present, of course, a problem in matching specific observed and modeled cycles. The large geometric extension of Mira photospheres was demonstrated by monochromatic radius observations of o Ceti and R Leo by Labeyrie et al. (1977) and Bonneau et al. (1982) which, however, did not systematically follow the stars through different phases and cycles.The structure of a Mira photosphere is essentially determined by the propagation of shock fronts. A shock front enters the bottom of the photosphere once each cycle and travels outwards.
Convection and the Bump Cepheid Resonance
Authors: Cox Arthur N. 
Published: June 2019

AbstractBump Cepheids display a resonance between the fundamental and second overtone modes in the form of a bump on descending light for periods less than 10 days and on the ascending light curve for longer periods. A long-standing problem has been how to explain this resonance for stellar masses consistent with evolution theory, rather than significantly lower ones. New Livermore OPAL intermediate coupling opacities now produce stellar models that are less density concentrated in the outer 1/4 of the radius, and all radial mode periods are increased. The second overtone to fundamental mode period ratio is reduced. This reduction then requires larger masses for the bump resonance, much closer to those from the old Becker, Iben, and Tuggle and the new Stothers and Chin stellar evolution results with no or very little core convection overshooting and the standard (X=0.70 and Z=0.02) composition. This achievement of the OPAL opacities is not adequate, though, because the period ratios have not quite decreased enough. There is another missing ingredient suggested to me by Norman Simon. A second deep “iron line” convection zone now appears between 145,000 and 205,000 K for higher Cepheid luminosities and masses like 7 and 8 M⊙. This convection is necessary to transport the higher luminosities that cannot be carried by radiation alone. An increase in the ratio of the mixing length to the pressure scale height to about 1.5 for 7 M⊙ and 2.0 or more for 8 M⊙ can give an appropriate convection efficiency and the required deep convection zone structure. Thus OPAL opacities, when used with the full physics of convection models all across the instability strip and nonadiabatic pulsation analyses, actually do explain the bump Cepheid puzzle. Further, the unknown convection efficiency for intermediate mass yellow giants can apparently be calibrated as a function of stellar mass.
Classical Models of Cepheid Stars
Authors: Chiosi C. 
Published: June 2019

AbstractIn this paper we summarize recent work on Cepheid stars by Chiosi et al (1992a), who calculated large grids of models at varying mass, effective temperature, mass-luminosity (ML) relation or equivalently underlying evolutionary scheme for intermediate mass stars, i.e. classical models, models with mild core overshoot, and models with large core overshoot, and finally initial chemical composition. The chemical parameters bracket the abundances of the Cepheid stars in the Milky Way and Magellanic Clouds. First, we present the theoretical results limited to the analytical fits of the fundamental period-mass-radius (PMR) relation and the blue and red edges of the instability strip for the fundamental mode and first overtone. Second, we discuss the data converted to magnitudes and colours of the BVRcIc passbands with particular attention to the period-luminosity-colour (PLC) and period-luminosity (PL) relations. Finally, we briefly summarize three studies based on these models, which aimed to explain the shape and width of the observed instability strip (Chiosi et al 1992b), and the main reason for the mass discrepancy of the Cepheid stars (Chiosi et al 1992c) by means of the mass equivalency (ME) method applied to clusters of the Large Magellanic Cloud (LMC). Because the ME method turned out to be sensitive to the distance modulus, the dependence of this on the metallicity has been the subject of the last study by Bertelli et al(1992).
Stellar Structure and RR Lyrae Masses
Authors: Dorman Ben 
Published: June 2019

AbstractI describe qualitatively the constraints on RR Lyrae masses that arise from consideration of the interior structure of Horizontal Branch (HB) stars. Briefly, the stellar models lying within the temperature range of the instability strip are slightly less massive than those with deep exterior convection zones. I discuss therefore what brings about the existence of these zones in the models.
Period Shifts in RR Lyrae Stars
Authors: Fernley J. 
Published: June 2019

Using recently published infrared photometry of RR Lyrae stars from both the field (Fernley et al. 1992) and globular clusters (Longmore et al. 1990), period shifts have been calculated using the mean (V – K) colour rather than the mean (B – V) colour employed in most previous analyses (e.g., Sandage 1990 and references therein). The advantage of using (V – K) rather than (B – V) is the reduced sensitivity to, firstly, metallicity and, secondly, non-LTE radiation. This latter occurs in many RR Lyrae stars near maximum light and clearly should not be included when calculating the mean colour and hence, mean temperature. This, and all other aspects of the present paper, are discussed more fully in Fernley (1992a).The mean (V – K) colour of both the field and cluster stars were de-reddened using the maps of Burstein and Heiles (1982) and converted to effective temperature using the calibration of Fernley (1989).
A Spectroscopic Abundance Study of Dwarf Cepheid V1719 Cygni
Authors: Kim Chulhee , Sadakane Kozo 
Published: June 2019

AbstractSpectroscopic CCD observations were carried out for V1719 Cygni and the spectrum in the visual region is analysed relative to the Sun with a line-blanketed convective model atmosphere. Adopted atmospheric parameters are : an effective temperature < Teff > = 7000 K, a surface gravity logg = 3.4. Although our result is dependent on microturbulent velocity and damping constant, it was found that Mg in V1719 Cygni is nearly solar, or underabundent by 0.2 to 0.3 dex according to the analysis of 5172.684 Å MgI line which is relatively free from blending. This is inconsistent with the previous photometric result where VI719 Cygni was known as an abnormally metal rich variable. Because the analysis was given to the single magnesium line which is not a good metallicity indicator and S/N ratio was low due to poor seeing condition, the investigation for iron lines in blue region is undertaken.
RR Lyrae: Shock waves and atmospheric motions.
Authors: Lebre Agnès 
Published: June 2019

AbstractNew high resolution spectroscopic observations of the star RR Lyrae are reported (resolution between 15,000 and 20,000). The spectra were taken in July 1990 with the 1.52m telescope of the Observatoire de Haute Provence, using the AURELIE spectrograph, and were centered around Hβ and NaD. They were distributed in time through almost an entire composite cycle (P = 13.6 hours). Photospheric FeI lines were analysed and their FWHM variations over one luminosity cycle are interpreted in the framework of the propagation of shock waves running through the low atmospheric layers.
Alinement of Solid Interstellar Particles by a Magnetic Field
Authors: Spitzer Lyman , Jones R. V. 
Published: June 2019

For a Long Time the Davis-Greenstein Theory (ref. 1) has been generally considered an adequate explanation of the mechanism responsible for the alinement of interstellar grains and thus for the observed interstellar polarization. The magnetic field required to orient paramagnetic grains is apparently somewhat greater than 10-5 gauss, a relatively large field, but according to reference 2 ferromagnetic grains, proposed by the authors of reference 3, can be oriented by a field of only 10-7 gauss. These results indicate that orientation of interstellar grains is easily explained, even if the magnetic field in interstellar space is relatively weak.Unfortunately, this relatively satisfactory state of affairs has been upset by two developments. Firstly, the basic mechanism of magnetic relaxation proposed by Davis and Greenstein has been questioned by Dr. C. Kittel of the University of California, who has pointed out that the disorienting effect associated with thermal fluctuations of magnetization within the solid particles is ignored in the formulation of this mechanism.
Models of Reflection Nebulae
Authors: Roark T. P. , Mayo Greenberg J. 
Published: June 2019

A Feasibility Study For an Observational Program was made to investigate models of reflection nebulae. Specifically, for a relatively simple model of an interstellar dust cloud with a source of illumination nearby, predictions of the color of the nebula, relative to the source color, at points along any radial direction from the source are sought. Furthermore, from these color differences, the possibility is studied of discriminating between the effects produced by the cloud-source-observer geometry and those due to the assumed optical properties of the scattering particles. If such discrimination is feasible, the types of observations that would be most useful in separating the effects must be known to the investigator.Plane-parallel slab models similar to those of reference 1 in which the scattering particles are distributed isotropically and homogeneously were used. The scattering properties of the particles were assumed to be those obtained by using the Mie theory of electromagnetic scattering.
Diffuse Interstellar Lines and Chemical Characterization of Interstellar Dust
Authors: Johnson Fred M. 
Published: June 2019

The Problem of Chemical Identification of the interstellar dust grains has vexed astronomers for over three decades. The earliest evidence for the mere presence of interstellar dust was deduced from the observation of stars (via star counts) in the Milky Way. The best presently available clues for possible chemical identification are spectroscope data, particularly the diffuse (hitherto unidentified) interstellar absorption lines. This paper is concerned primarily with a discussion of new theoretical interpretations of the spectroscopic data.Much related information on the dust grains was obtained from observations of space reddening, its wavelength dependence, and from interstellar polarization. Furthermore, correlation of space reddening and the strength of some of the diffuse lines is important to the discussion of possible chemical identification of the dust.
Interferometric Techniques Applied to High Resolution Observation of the Solar Granulation
Authors: Aime Claude 
Published: June 2019

AbstractMichelson,one-dimensional, and two-dimensional apertures are used to obtain the statistical properties of the solar granulation. The calibration of the power spectrum is performed via Michelson stellar interferometry as well as by the use of changes in seeing conditions during speckle-interferometric measurements. The correction of 40 analyses, determined with Fried's parameter ro ranging between 2.5 cm and 11.5 cm, provides satisfactory convergence for frequencies up to 3 cycles per arc second
4d → 4f Excitation in Lanthanide Vapours
Authors: Radtke E. R. 
Published: June 2019

Since the last VUV conference in Hamburg, there has been speculation on the possible occurrence of collective effects in the 4d-f excitation channels of the lanthanide sequence. However, the data available so far has been restricted to solids, with the exceptions of Barium and Europium, due to the need for a high temperature absorption cell.In the present paper we report the first observation of the 4d-f ‘Giant Resonance’ for the atomic vapours of Lanthanum, Samarium and Cerium using a 42 cm long induction furnace working up to 2700 K. The spectra were calibrated by superposing the emission lines from a Garton flash tube.
Theoretical Ultraviolet Spectra of B Type Stars : Uncertainties in gf Values
Authors: Burger Marijke 
Published: June 2019

Theoretical spectra have been computed (in LTE) for B type stars, in the wavelength range 2000-3000 Å. The results show a good agreement with observations (S59 and Copernicus).It will be shown that the most important factor that influences the resulting computed spectrum - at a resolution of 1.8 Å or lower - is the completeness of the list of spectral lines used in the computations, owing to the large (number) density of lines in the ultraviolet.At a resolution of 1.8 Å a large error is tolerated on gf values, while identification of observed line features from the theoretical spectra remains possible.The accuracy of the gf values becomes increasingly more important if one goes to higher spectral resolution, as will be shown by comparison of theoretical spectra with observations.Our present knowledge of oscillator strengths is sufficient for. identification of a large number of spectral lines in high resolution spectra; for a detailed analysis more accurate data are preferable in many cases.
X-Ray Spectra of Tokamak Plasma
Authors: Fraenkel B.S. 
Published: June 2019

A spectrum covering Fe XXV to Fe XXII x ray lines from a tokamak (PLT) plasma has been obtained. Results indicate similarity with the flare spectrum in this region - the forbidden lines also appear in the PLT spectrum.Te was about 1.8 keV- a value confirmed by intensity of dielectronic recombination lines. Ti was found to be not more than 0.7 keV, by Doppler width of the He like singlet 1s2 –ls2p 1S0 -1P0. A Johansson crystal was used, with the spectrograph adapted for an extended X-ray source.
An Observational Evidence of the Common Envelope Phase
Authors: Sarna Marek J. , Drake Jeremy J. 
Published: June 2019

AbstractChandra Low Energy Transmission Grating Spectrograph observations of the pre-cataclysmic binary V471 Tau have been used to estimate the C/N abundance ratio of the K dwarf component for the first time. While the white dwarf component dominates the spectrum longward of 50 Å, at shorter wavelengths the observed X-ray emission is entirely due to coronal emission from the K dwarf. The H-like 2p 2Р3/2, 1/2 → 1s 2S1/2 resonance lines of С and N yield an estimate of their logarithmic abundance ratio relative to the Sun of [C/N]= –0.38 ± 0.15—half of the currently accepted solar value. We interpret this result as the first clear observational evidence for the presumed common envelope phase of this system, during which the surface of the K dwarf was contaminated by CN-cycle processed material dredged up into the red giant envelope
Testing Common Envelope Theories with White Dwarf Binaries
Authors: Nelemans G. , Tout C.A. 
Published: June 2019

AbstractWe determine the possible masses and radii of the progenitors of white dwarfs in binaries from fits to detailed stellar evolution models and use these to reconstruct the mass-transfer phase in which the white dwarf was formed. We confirm the earlier finding that in the first phase of mass transfer in the binary evolution leading to a close pair of white dwarfs, the standard common-envelope formalism based on energy balance in the system, does not work. A formalism based on angular momentum balance can explain the observations. We extend our analysis to all close binaries with at least one white dwarf component. Comparing the two, we show that the formalism based on angular momentum balance can explain all observations at least as well as the energy formalism.
Substellar Secondaries in Zero-Age Cataclysmic Variables
Authors: Politano M. 
Published: June 2019

AbstractThe present-day formation of cataclysmic variables (CVs) with brown dwarf (BD) secondaries is investigated using a population synthesis technique. Results from the latest, detailed models for BDs have been incorporated into the population synthesis code. We find that zero-age CVs (ZACVs) with BD secondaries have orbital periods in the range 46 min to 2.5 hrs, and that they comprise 18% of the total, present-day ZACV population. Consequently, we find that 15% of the present-day ZACV population should have orbital periods shorter than the observed orbital period minimum for CVs. We also investigate the dependence of the present-day formation rate of CVs with BD secondaries on the assumed value of the common envelope efficiency parameter, αCE, for three different assumed mass ratio distributions in ZAMS binaries. We find that the common envelope process must be extremely inefficient (αCE < 0.1) in order for CVs with BD secondaries not to be formed. Finally, we find that the progenitor binaries of ZACVs with BD secondaries have ZAMS orbital separations < 3 AU and ZAMS primary masses between ~1-10 M⊙ , with ~75% of the primary masses less than ~ 1.6 M⊙. Interestingly, these ranges in orbital separation and primary mass place the majority of the progenitor binaries within the so-called “brown dwarf desert.”
Realistic Models for Donors in Ultracompact Binaries
Authors: Deloye C. J. , Bildsten L. 
Published: June 2019

AbstractWe present the first realistic set of arbitrarily degenerate stellar models appropriate for donors in ultracompact binaries. The mass-radius M-R relations for these objects are parameterized by the donor's entropy and composition. We highlight how this fact can affect our understanding on the current configuration of ultracompact binaries today and their potential evolutionary tracks.
A Disk Instability Interpretation for the 2001 Outburst of WZ SGE
Authors: Osaki Y. 
Published: June 2019

AbstractThe 2001 outburst of WZ SGE is discussed based on the thermal-tidal instability model (TTI model). It is demonstrated that the overall development of the outburst can be understood by the disk instability model (TTI model) and that no enhanced mass transfer is needed to explain observations.
Possible Density Determination of the Nebular Component of Cataclysmic Variables with the N III 4641/4635 Line Ratio
Authors: Bohigas Joaquín , Pérez-Tijerina Eduardo , Machorro Roberto 
Published: June 2019

The dependence of the N III 4641/4635 line ratio on the electron density is presented. It is shown that this ratio may be an important diagnostic tool in cataclysmic variables.Pérez-Tijerina, Bohigas & Machorro (2001) used the Chianti code and database developed by the U.S. Nautical Observatory (Landi, 200) in order to find density and temperature sensitive line ratios in the conditions occuring in plasmas produced in pulsed laser deposition experiments for thin film deposition, i.e., around 1018 cm 3 and 104 K. Level populations are determined considering only radiative decay and collisional excitation and de-excitation.
Detection of Possible Interstellar Particles by the HITEN Spacecraft
Authors: Svedhem H. , Münzenmayer R. , Iglseder H. 
Published: June 2019

AbstractThe Cosmic Dust experiment on the Hiten spacecraft detected more than 500 events likely to be associated with particle impacts during its three years life in space. An excess of approximately 40% was observed in the direction of 220° ecliptic longitude. This direction corresponds well with the direction of the reported interstellar Helium and interstellar dust seen by other experimenters. In absolute number this is about 20 particles. Since this data was taken during three full years and thus most other effects should be averaged out we believe that these particles are of interstellar origin.
Electromagnetic Escape of Dust from the Solar System
Authors: Hamilton Douglas P. , Grün Eberhard , Baguhl Michael 
Published: June 2019

AbstractCollisions of asteroids and among Zodiacal cloud particles produce large amounts of submicron-sized debris, much of which is immediately ejected from our solar system by electromagnetic forces. We investigate the trajectories of tiny grains started on circular uninclined orbits within the Zodiacal cloud and find that they reach high ecliptic latitudes during the current configuration of the solar magnetic.field, perhaps accounting for particles detected by the Ulysses spacecraft at latitudes up to 80°. When the solar magnetic field is reversed, particles are more strongly confined to the ecliptic plane and escape the solar system less readily. Both fluxes and spatial densities of sub-micron sized Zodiacal dust particles vary with time through the dependence of orbital dynamics on the 22-year solar cycle.
Dynamical Evolution of Interplanetary Dust due to Gravitational Scattering by Jupiter and the Inner Planets
Authors: Gor'kavyi Nikolai N. , Ozernoy Leonid M. , Mather John C. 
Published: June 2019

AbstractWe introduce the continuity equation written in the coordinate space of the orbital elements (e.g. large semi-axis a vs. eccentricity e, etc.) to explore the density evolution of the zodiacal cloud. Emphasis is on those terms of the continuity equation which describe ‘jumps’ of particles in the (a, e)-space due to gravitational scattering of the interplanetary dust particles by planets, which represents one of the leading factors in the dynamical evolution of the zodiacal cloud. In the remainder (div-terms of the continuity equation), one can incorporate the known analytical expressions for the rates of gradual change of orbital elements due to the Poynting-Robertson and solar wind drags (Liou et al. 1995).
Dynamics of the Leonid Meteoroid Stream: a Numerical Approach
Authors: Brown P. , Jones J. 
Published: June 2019

AbstractWe have simulated the evolution of the Leonid stream via numerical integration of 3 million test particles ejected from 55P/Tempel-Tuttle during five perihelion passages of that comet. Using the Whipple ejection velocity formula and a random ejection spread in true anomaly about the parent comet orbit inside 2.3 AU, we have followed the subsequent evolution of Leonid meteoroids differing by over 5 orders of magnitude in mass under the influence of radiation pressure and planetary perturbations. By comparing the model predictions of Leonid activity on a year by year basis with the available observations we have attempted to determine roughly the time of ejection associated with each Leonid storm occurrence and model the observed mass distribution. On the basis of the demonstrated accuracy of the model we make predictions regarding times of peak activity and relative strengths for the Leonid returns for each year during the latter part of the 1990s.
The First in a New Series of Leonid Outbursts
Authors: Jenniskens P. 
Published: June 2019

AbstractThe Leonids returned with higher than usual rates in November 1994. From an analysis of the available visual and radio forward m teor scatter observations, it is found that the meteor stream activity curve and the magnitude distribution index are similar to those of the outbursts in 1961 and 1965 during the previous return of the parent comet. It is possible that the outburst was due to the same dust component or dust with a similar stream evolution history.
Regular and Stochastic Motion of Meteoroid Streams in Halley-type Orbits
Authors: Emel'yanenko V.V. , Bailey M.E. 
Published: June 2019

AbstractDespite the complicated structure of old meteoroid streams in Halley-type orbits, the positions of their ecliptic-plane crossings are insensitive to the initial conditions of ejection and have a form determined by resonances due to planetary perturbations. This allows the main observational features of meteor showers such as the η-Aquarids, Orionids, Lyrids and Perseids to be understood. A proportion of the particles ejected into such orbits librate about the centres of mean-motion resonances and produce compact streams which may lead to meteor storms.