bluuebunny/crossref_metadata_2025_split huggingface dataset:
First Results Concerning the Capability of a TV Camera for Double Star Observations
Authors: Dommanget J. 
Published: July 2016

SummaryThe results of some first laboratory analysis of double star images recorded with a TV camera are presented.The camera – already in use since a few years for occultation-timings has been described earlier. For double star observations, the equipment has been completed by a video disc memory, a video analyser with analogic-digital converter and a small programmable calculator.Details are given about this equipment and its possibilities. The reduction method in its present state is described as well as some first results. These show a very good internal agreement leading to a high promising new observational technique.
Double Stars and Space Telescope
Authors: Fredrick Laurence W. 
Published: July 2016

With the success of the Shuttle it seems now the Space Telescope will become a reality. The author wrote a study for the Langley Research Center in the summer of 1963 on the astronomical uses of a large space telescope which formed the basic document for the National Academy of Sciences Woods Hole study in 1965. This study recommended construction of a large space telescope scaled to use a Saturn V as the launch booster.The initial study included some astrometric applications. Among these were various double star applications which is the subject of this symposium.
New theoretical developments in stellar pulsation
Authors: Christensen-Dalsgaard Jørgen 
Published: July 2016

AbstractThe basic properties of stellar oscillations are reasonably well understood, allowing measurements of their frequencies to be used as probes of stellar interiors. The detailed understanding of the processes responsible for the oscillations, in the very broad range of stars observed to pulsate, has improved substantially over the past decade, as have the techniques for asteroseismic investigations on the basis of the observations. Here I provide a brief overview of the theory of stellar oscillations, emphasizing several cases of recent progress, often inspired by new observational developments.
A Variable Star Survey of the Open Cluster NGC 2126
Authors: Derekas A. , Kiss L.L. , Bedding T.R. , Gáspár A. , Sárneczky K. , Szabó Gy.M. , Váradi M. , Kaspi S. , Kiss Cs. 
Published: July 2016

AbstractWe present the first CCD photometric observations of the northern open cluster NGC 2126. Data were taken on eight nights in 2002 February and December with a total time span of ~57 hours. We have discovered six new variable stars and have estimated the main characteristics of the cluster.
Double-radial-mode SX Phoenicis stars in the globular clusters NGC 5466 and M71
Authors: Jeon Young-Beom , Lee Myung Gyoon , Kim Seung-Lee , Lee Ho 
Published: July 2016

AbstractThrough time-series CCD photometry of the globular cluster NGC 5466, we found three double-radial-mode SX Phe stars, all of which are consistent with the theoretical period ratio of the first overtone mode to the fundamental mode (P1H/PF); their period ratios are 0.7825, 0.7826 and 0.7919, respectively. We also detected a double-radial-mode SX Phe star in M71. Its period ratio is 0.781, which is also consistent with the theoretical value.
Spectroscopy of southern δ Scuti stars
Authors: Cropp Malcolm , Pollard Karen R. , Skuljan Jovan 
Published: July 2016

AbstractFour δ Scuti stars were observed with the HERCULES fibrefed échelle spectrograph at Mount John University Observatory, New Zealand. These observations were analysed by looking at the radial velocity variations as given by a cross-correlation technique as well as spectral line moment variations. These results were compared to published photometric studies of these stars to see if the modes identified in the photometry were also present in the spectroscopic data obtained.
Metallicity effects in Mira variables: a model study
Authors: Scholz M. , Wood P.R. 
Published: July 2016

AbstractM-type Mira models with a moderate deviation from solar metallicity (2x and 0.5 x) have been computed and compared to solar-metallicity models. Selected effects of abundance changes on pulsation properties, atmospheric stratifications, spectral features (colours) and surface brightness distributions are discussed.
Time variations of IR spectra and dust properties in carbon-rich Mira variables
Authors: Sung Hyun-il , Lee Sang-gak 
Published: July 2016

AbstractWe have studied variations of physical parameters in the circumstellar envelopes of carbon-rich Mira variables at different pulsation phases. After comparing the ISO/SWS spectra of these stars with spectral energy distributions calculated from models, we could find the best-fitted parameters for the physical state of the dust envelope at each phase. The variations of the parameters effective temperature, fraction of SiC grains, mass-loss rates, and inner radius of shell, are found to have nearly the same trend as that of the light curve. The other parameters grain size, optical depth, radius of central star and dust temperature at the inner boundary of envelope, are inversely varying to the light curve.
Pulsating white dwarfs in cataclysmic variables: The marriage of ZZ Cet and dwarf nova
Authors: Warner Brian , Woudt Patrick A. 
Published: July 2016

AbstractThere are now four dwarf novae known with white dwarf primaries that show large amplitude non-radial oscillations of the kind seen in ZZ Cet stars. We compare the properties of these stars and point out that by the end of the Sloan Digital Sky Survey more than 30 should be known.
Precessing accretion discs in binary systems
Authors: Retter Alon , Liu Alexander , Bos Marc 
Published: July 2016

AbstractSuperhumps – quasi-periodic oscillations at periods a few percent different than the orbital periods – have been observed in several dozen binary systems of various types. It is well-accepted now that they are caused by the precession of the accretion disc. New findings on TV Col, TX Col and V4742 Sgr are presented. These cataclysmic variables (CVs) have exceptional precessing periods that cast strong doubt on the predictions of the Tidal Disc Instability model.
Non-adiabatic Asteroseismology of Near-Main Sequence Variable Stars
Authors: Dupret M.-A. 
Published: July 2016

AbstractWe present in this talk a new linear non-adiabatic pulsation code: MAD. We detail all the possible applications of it in the frame of asteroseismology. By using it, photospheric observables such as multi-color photometric amplitude ratios, phase differences and line profile variations can be determined accurately and confronted with observations. Moreover, MAD enables the precisely analysis of the excitation mechanisms of pulsating stars. Applications to different kinds of variable stars (δ Sct, β Cephei, Slowly Pulsating B and γ Dor stars) are presented by Dupret et al. (these proceedings), Handler & Aerts (these proceedings), De Cat et al. (these proceedings) and De Ridder et al. (these proceedings).
Analysis of Long-Term Single-Site Observations of The Pulsating DB White Dwarf GD 358
Authors: Bradley P.A. 
Published: July 2016

AbstractWe briefly describe the analysis of single-site data collected from 1982 to 1992 for the pulsating DB white dwarf GD 358. We show that the amplitudes of almost all of the l = 1 modes change over time, and some of the l = 1 modes disappear for months at a time. We also find a new mode at k = 19, with a frequency of ~1173μHz.
The Evolution of Stars of Medium Mass
Authors: Chiosi Cesare 
Published: July 2016

AbstractThe main properties of the evolution of low, intermediate, and high mass stars are reviewed focusing on a few issues tightly related to the interpretation of Pop I Cepheid stars. After a summary discussion of the physical mechanism responsible for the Cepheid pulsation, the classical results of stellar evolution theory for the main evolutionary phases (main sequence, core He-burning, and later) all over the HR diagram are presented, putting into evidence the various points of disagreement with current observational data. We then review the models incorporating the effect of convective overshoot, and present in some detail a study on the rich, young cluster NGC 1866 in the Large Magellanic Cloud, in which they are compared with the observational data. Arguments are given to favour the adoption of models with convective overshoot instead of the classical ones. The topics of the mass discrepancy and frequency-period distribution of Cepheid stars are then discussed in the light of models with convective overshoot, showing how they can better account for the observational data. Finally, we address the question of the enhancement in the radiative opacity of heavy elements in the middle temperature region (approximately where the ultimate ionization of the CNO group of elements occurs), which has been suggested to explain the mass anomalies and period ratios encountered in double-mode and bump Cepheids. Evolutionary models for intermediate mass stars incorporating the above modification in the radiative opacity are then presented and discussed in some detail.
Stellar Mass Loss and Pulsation
Authors: Willson L.A. 
Published: July 2016

AbstractMass loss at rates sufficient to alter the evolution of stars is known to occur during the pre-main sequence evolution of most stars, on the main sequence for massive stars, and during advanced evolutionary phases when the luminosity is high and the effective temperature is low. While most investigations of the effects of mass loss on stellar evolution have assumed continuous (parametrized) mass loss laws apply, there is increasing evidence that mass loss rates are substantially higher for stars that are pulsating with large amplitude and/or in selected modes. Some new insights into the mass loss that terminates the AGB evolution of intermediate mass stars, and leads to the formation of planetary nebulae, come from recent detailed studies of the mass loss process from the Mira variables.
Anomalous Cepheids and Population II Blue Stragglers
Authors: Nemec James M. 
Published: July 2016

AbstractRecent studies of anomalous Cepheids (ACs) and Pop II blue stragglers (BSs), including photometrically variable BSs (VBSs), are reviewed. The VBSs represent about 25% of the BSs, the majority of which are SX Phe short-period variables in the Cepheid instability strip. Mass estimates derived using various techniques suggest that both ACs and BSs are relatively massive (about 1.0–1.6 Me). The recent discovery that two BSs in the globular cluster NGC 5466 are contact binaries, and the earlier discovery that one of the BSs in ω Cen is an eclipsing binary, provide direct evidence that at least some BSs are binary systems. If all BSs are binaries, and the time scale for coalescence is a few Gyr, then the majority are likely to be coalesced. Because ACs and BSs are found in the same stellar systems, and are probably related through their evolution, it is highly likely that most ACs are also coalesced binary systems. The fact that ACs and BSs are found only in low density environments, suggests that they were primordial binaries.
Cepheid Evolution with Pulsationally-Driven Mass Loss
Authors: Brunish Wendee M. , Willson Lee Anne 
Published: July 2016

AbstractWe have studied the effects of a pulsationally-driven wind on Cepheid evolution. Mass loss due to the wind, which occurs only when the star is crossing the Cepheid instability strip, is a function of luminosity and radius. We have investigated the evolution of 4, 5, 6, 7 and 8 M⊙ stars using the updated 12C(α,γ) 16O rates.
Discontinuity Modes in Polytropes
Authors: Carroll Bradley W. 
Published: July 2016

AbstractIn the calculation of linear nonradial oscillation modes in composite polytropes with a small density discontinuity, a discontinuity mode may occur. This mode consists of a wave propagating along the discontinuity interface with a large amplitude that declines exponentially away from the interface. The period P of this mode is well-estimated (to within 10%) bywhere Δρ/<ρ> is the fractional density discontinuity and k is the horizontal wavenumber (c.f. Gabriel and Scuflaire 1980, in Nonradial and Nonlinear Stellar Pulsation, eds. H. Hill and W. Dziembowski, Springer-Verlag). For a 12 solar-mass polytrope with a radius of 4.27 R⊙, a 3% density discontinuity at fractional radius 0.15 produces a discontinuity mode with a period of 7.329 hours. As the density discontinuity increases the period P decreases, resulting in avoided crossings with the normal g-mode spectrum. Between these avoided crossings, the discontinuity mode has an unusually large amplitude at the location of the discontinuity.
S Sge: A Cepheid Triple System
Authors: Evans Nancy Remage , Slovak Mark H. , Welch Douglas L. 
Published: July 2016

AbstractIUE spectra have been used to investigate the companion of the classical Cepheid S Sge. At the phase of the IUE observations, 45 Dra (F7Ib) is a good match to S Sge, both in (B–V)o and from 2200 to 3200 Å. However, from 1700 to 1900 Å, the S Sge spectrum has excess flux, as compared to 45 Dra. The flux remaining after subtracting 45 Dra from S Sge is a good match to an A5V to A7V star. The magnitude difference between the Cepheid and the companion is consistent with the absolute magnitude and colors of an A5V star. This corresponds to a mass of 1.9 solar masses (Popper, 1981, Ann. Rev. Astr. Ap., 18, 115). A spectral type range from A3V to A7V corresponds to an uncertainty in the mass of ±0.2 solar masses. However, the mass function from the orbit and an evolutionary mass for the Cepheid require a companion mass of 2.7 solar masses or greater. We infer that the companion is itself a binary.
The Blue Edge of the Helium Star Instability Strip
Authors: Fadeyev Yu. A. 
Published: July 2016

AbstractHydrodynamic calculations of nonlinear pulsations were done for models of helium stars with mass 1 M⊙, luminosity from 3220 L⊙ to 12820 L⊙ and effective temperature from 6000K to 8000K. The models with L > 8000L⊙ were found to pulsate in the fundamental mode with large amplitude (ΔR/R ~ 1), whereas less luminous models (L < 8000L⊙) revealed small amplitude oscillations (ΔR/R ~ 0.2) in the first overtone. In the luminosity range considered the blue edge of the instability strip corresponds to an effective temperature of 7500K, that is to the upper limit of the effective temperatures of R CrB stars. Application of the period-luminosity relation to the variables R CrB and RY Sgr gives their luminosities to be of 9000L⊙.
Envelope Distention and Mass Loss IN W VIR Pulsating Variables
Authors: Fadeyev Yu. A. , Muthsam H. 
Published: July 2016

AbstractThe hydrodynamic calculations of nonlinear self-excited radial pulsations were done for the models of W Vir stars with mass 0.6 M⊙ and luminosities from 794L⊙ to 3981L⊙. The periods of the models are longer than 10 days. The pulsations are shown to be accompanied by periodic shocks that change the density distribution in the pulsating stellar atmosphere. At radii less than 5 Rph, where Rph is the radius of the photosphere, the mean dynamic scale height is nearly five times the static scale height. In this region of the atmosphere the mean radii of outer mass zones do not change perceptably. On the other hand, at radii larger than 5 Rph the scale height is of the order of Rph so that the outermost layers ultimately expand with a velocity exceeding the local escape velocity. The mass flux in the atmosphere increases with decreasing mass to radius ratio and mass loss rate in W Vir type variables is in the range from 2 X 10−6M⊙·yr−1 to 10−5M⊙·yr−1.
Forthcoming Cepheid Database
Authors: Fernie J. Donald , Evans Nancy Remage 
Published: July 2016

AbstractA summary of basic parameters of classical Cepheid variable stars is being prepared. It will contain stars from the fourth edition of the General Catalogue of Variable Stars in the categories CEP, CEP(B), DCEP, and DCEPS, excluding those which belong to Population II according to the criteria of Harris (1985, A.J.,90, 756). V and B intensity means, as well as velocity means are derived from Fourier fits using the N. Simon program MINFIT. In addition to the data contained in the catalogue by Fernie and Hube (1968, A.J., 73, 492), it will provide a comparison of reddenings from a number of sources, binary status, and period change information. We anticipate a hardcopy version, and also a version on floppy disks. The computer version uses dBaselll, and will include programs, for instance, to calculate phases using changing periods.
CCD Observations of Variable Stars in Globular Clusters
Authors: Smith H.A. , Kuhn J.R. , Curtis J. 
Published: July 2016

AbstractBVR observations of the relatively metal-rich globular cluster NGC 6388 have been obtained with a CCD on the CTIO 0.9 m telescope. Eighteen possible short period variable stars have been discovered in or near the cluster. At least 10 of these are probable RR Lyrae members of NGC 6388. We confirm the finding of Hazen and Hesser that this cluster is one of the most metal-rich to contain a significant number of RR Lyraes. A program of CCD photometry of field and cluster variable stars has been initiated on the 0.6m telescope of the Michigan State University Observatory.
X-ray Line Formation in Astrophysical Environments: The L-shell Spectra of Ionized Iron
Authors: Liedahl Duane A. , Kahn Steven M. , Osterheld Albert L. , Goldstein William H. 
Published: July 2016

AbstractWe have initiated an extensive atomic modeling effort applicable to X-ray line emission in high-temperature astrophysical plasmas. The emphasis of our program is on the detailed accounting of the mechanisms which populate excited states of highly ionized atoms over a wide range of electron temperatures and densities. As a first demonstration we have calculated spectra for the important L -shell ions Fe XVI-XIX in a complete collisional-radiative model under conditions appropriate to solar coronal plasmas. Using methods presented here, we have synthesized the X-ray spectra of solar flares and active regions over the wavelength interval 13 – 18 Ǡ. The atomic model, which includes 705 atomic energy levels, is the largest and most detailed of its kind. In this introductory paper, we discuss the effects of dielectronic recombination on the spectrum of Fe XVII and present a new technique whereby the 3s lines can be used as a diagnostic of the electron temperature. Also included are new values for the rate of resonance excitation of the n=3 Fe XVII excited states. These rates are lower than those previously obtained and suggest that resonance excitation does not contribute significantly to the population kinetics. Finally, we present a direct comparison of our a calculated model spectrum with data from a solar flare.
Role of Magnetospheric Plasma Physics for Understanding Cosmic Phenomena
Authors: Das Indra Mohan Lal 
Published: July 2016

AbstractCosmic phenomena occur in the remote regions of space where in-situ observations are not possible. For proper understanding of these phenomena laboratory experiments are essential, but the in-situ observations of magnetospheric plasma provides even a better background to test various hypothesis of cosmic interest. This is because the ionospheric-magnetospheric plasma and the solar wind are the only cosmic plasmas accessible to extensive in-situ observations and experiments.
X-ray Spectroscopy across the HR Diagram
Authors: Schmitt J.H.M.M. 
Published: July 2016

AbstractX-ray spectra of stellar X-ray sources taken with high, moderate and low spectral resolution are discussed. Only low resolution spectra are available for a sufficiently large number of late-type stars. It is shown that high temperature plasmas (log T > 7) produce the dominant emission component in the coronae of red dwarfs as well as yellow giants, while the coronae of F stars – usually – have X-ray temperatures similar to those found in the quiet Sun. The need for density diagnostics of stellar coronae is stressed and it is argued that the waveband region between 90 – 140 Å is particularly well suited for this purpose.
The ROSAT Mission
Authors: Trümper J. 
Published: July 2016

AbstractThe scientific payload of ROSAT consists of a 83 cm X-ray telescope (6 – 100 Å) and a 60 cm XUV-telescope (60 – 300 Å) which are looking parallel. An important objective of the mission is to perform the first all-sky survey with imaging X-ray telescopes providing an improvement in sensitivity by several orders of magnitude compared with previous surveys. A large number of new X-ray sources (~ 105) is expected to be discovered and located with an accuracy of 1 arcmin or better, depending on source strength. The sources discovered will represent almost all types of astronomical objects, ranging from nearby normal stars to distant quasars.After completion of the sky survey which will take half a year, the instruments will be used for detailed investigations of selected sources with respect to spatial structures, spectra and time variability. In this pointing mode, which will be open for guest observers, ROSAT is expected to provide substantial improvements over the imaging instruments of the Einstein observatory.
XSPECT: A Telescope/Spectrometer System on SPECTRUM RÖNTGEN GAMMA
Authors: Schnopper Herbert W. 
Published: July 2016

AbstractThe SPECTRUM RÖNTGEN-GAMMA mission is being developed by the Babakin Center (BC) together with the Space Research Institute (IKI) of the Academy of Sciences, USSR and is scheduled for launch in 1993. Mission objectives include broad and narrow band imaging spectroscopy over a wide range of energies from the EUV through gamma rays with particular emphasis on the study of extragalactic objects. The Danish Space Research Institute (DSRI) BC and IKI share the responsibility for the preparation of the XSPECT system. Two thin foil telescopes which are conical shell approximations to Wolter 1 geometry, each with an aperture of 60 cm and a focal length of 8 m, are designed to have a half-power width of less than 2 arcmin and will have collecting areas of 1700 and 1200 cm at 2 and 8 keV, respectively. Images and spectra will be recorded with position sensitive proportional counters with good spectral resolution. An objective Bragg crystal panel, placed in front of one of the telescopes, will make high resolution spectroscopic studies (E/ΔE ~103) of point- and extended sources. Other instruments are under consideration.
Expected Scientific Performance of the Three Spectrometers on the Extreme Ultraviolet Explorer
Authors: Vallerga J. V. , Jelinsky P. , Vedder P. W. , Malina R. F. 
Published: July 2016

AbstractThe expected in-orbit performance of the three spectrometers included on the Extreme Ultraviolet Explorer (EUVE) astronomical satellite is presented. Recent calibrations of the gratings, mirrors and detectors using monochromatic and continuum EUV light sources allow the calculation of the spectral resolution and throughput of the instrument. An effective area range of 0.2 to 2.8 cm2 is achieved over the wavelength range 70-600Å with a peak spectral resolution λ/Δλ (FWHM) of ~ 360 assuming a spacecraft pointing knowledge of 10 arc seconds (FWHM). For a 40,000 sec observation, the average 3σ sensitivity to a monochromatic line source is 3 × 103 photons cm-2 sec-1. Simulated observations of known classes of EUV sources such as hot white dwarfs and cataclysmic variables are also presented.