bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Photometric and Spectroscopic Study of Southern RV Tauri Stars
Authors: Pollard Karen , Kilmartin P.M. , Gilmore A.C. , Cottrell P.L. 
Published: June 2019

AbstractA program to obtain photometric and spectroscopic (high and medium resolution) observations of a number of southern RV Tauri stars has been undertaken over the past two years at the Mount John University Observatory (MJUO). Eleven RV Tauri stars of both RVa (constant mean magnitude) and RVb (varying mean magnitude) photometric type have been chosen as well as normal and weak metal lined RV Tauri stars.Most program stars display the alternating deep and shallow semi-regular light variations as well as the light curve - colour curve phase lag characteristic of RV Tauri stars. Fourier analyses of the light curves have revealed the dominant periodicities (see figure 1) and allowed phasing of the spectroscopic observations.High resolution échelle spectra obtained of these stars around the Hα region display the complex emission and absorption structure of the Hα line at various phases. Metallic lines show emission and line doubling or ‘splitting’ - profiles characteristic of the shock wave that propagates through the line-formation regions of these stars during a pulsational cycle. Spectra at specific phases will be used in an abundance analysis of selected RV Tauri stars.
The Bump Cepheid Mass Discrepancy Laid to Rest (?)
Authors: Moskalik P. , Buchler J. R. 
Published: June 2019

The beat and bump mass discrepancies have been a long standing, unsolved difficulty in the Cepheid modelling (Cox 1980). The new opacities of Rogers & Iglesias (1992) has provided a partial solution to the problem, bringing the beat masses into good agreement with other mass determinations (Moskalik, Buchler & Marom 1992; herafter MBM). The discrepancy for the bump masses has also been greatly reduced, nevertheless it has not been eliminated entirely.Recently, the new version of the Livermore tables has been released (Iglesias, Rogers & Wilson 1992). The new calculations take into account previously disregarded spin-orbit coupling in the iron atoms. The inclusion of this effect leeds to a further enhancement of the “metal opacity bump” around 2-5xl05K. In the following we repeat the calculations of MBM to assess the consequences of this enhancement for the bump mass calibration.
A survey of RR Lyrae models
Authors: Bono G. , Stellingwerf R.F. 
Published: June 2019

AbstractAn extensive grid of non-linear pulsating models of RR Lyrae stars have been computed. To simulate the outer regions of these variables a non-local and time-dependent treatment of convective transport has been adopted. In this poster we briefly describe some new features of the instability strip (IS).
Double-mode RR Lyrae models
Authors: Bono G. , Stellingwerf R.F. 
Published: June 2019

AbstractDouble-mode RR Lyrae stars (RRd) represent a fundamental testing ground for the theory of stellar pulsation because they play an important role in understanding the interaction between different pulsation modes. In spite of the fact that from an observational point of view the identification of the fundamental (F) and first overtone (IO) periods needs only few periods of light curve coverage (Sandage et al. 1981, Nemec 1985), the theoretical models of double-mode and mixed-mode variables dating back to the original papers of Cox et al. (1983) and Stellingwerf (1975) were not integrated for long enough times to ensure proper mode identification. Recently Kovacs and Buchler (1992) using a standard radiative hydrodynamical code investigated the theoretical properties of RRd stars in more detail. This paper represents a brief description of the results of few cases computed adopting a non-linear, non-local treatment of convective transport, and long integration times to enable positive mode identification.
New results on field and cluster RR Lyraes
Authors: Clementini G. , Merighi R. , Tosi M. , Gratton R. , Carretta E. 
Published: June 2019

AbstractRR Lyrae stars both in the field and in clusters can be used to derive the metal abundance of the regions and systems where they are found.(1) New data have been collected on a sample of field ab-type RR Lyraes with the aim of studying the composition of the halo and the disk of the galaxy, (Clementini et al. 1992a, in preparation), using the relation found by Clementini et al. (1991), (hereafter CTM91), between [Fe/H] and the equivalent width of the Ca II K-line W‘(K). (2) A quantitative chemical abundance analysis of the ab type RR Lyrae (V29) in the globular cluster M4 has been performed using high resolution, high S/N spectroscopy. We obtain [Fe/H]=–1.3 ± 0.2 and the α– elements (Mg and Ti) are overabundant by 0.6 dex. These results are in good agreement with determinations from high resolution spectra of giants and blue horizontal branch stars (Clementini et al. 1992b, in preparation).
Asymmetry of metallic spectral lines in Cepheids
Authors: Albrow Michael , Cottrel P.L. 
Published: June 2019

AbstractA program of high resolution spectroscopic observations of Cepheids has been carried out at Mt John University Observatory for several years. Radial velocities and asymmetries have been measured for selected metallic lines using the method of Wallerstein et al (1992).The line profiles show the largest asymmetry at phases of maximum inward velocity. The asymmetry at phases of maximum outward velocity is smaller and sometimes in the same direction as for the inward velocity maxima. Enhanced asymmetry is also noticed at phases where the bump appears on the radial velocity curve.To date our models are unable to predict such behaviour. It is important that a satisfactory explaination for these observations be found so that the accuracy of Baade-Wesselink radius solutions for such stars can be assessed.
Investigation of the Double-mode Cepheid TU Cas: Atmospheric Parameters and Chemical Composition
Authors: Andrievsky S. M. , Kovtyukh V. V. , Makarenko E. N. , Usenko I. A. 
Published: June 2019

AbstractAtmospheric parameters and abundances of 25 elements were determined from two spectrograms of TU Cas (with dispersion 9 Å/mm) obtained in 1977 and 1990. We find Teff= 5860 - 6000K; logg = 1.0 - 1.5; and vt = 2.9 - 5.3 km/s.The value of [Fe/H] ∼ -0.5 testifies to the fact that TU Cas is deficient in metals compared with other double-mode Cepheids. More exact values of [Fe/H] for 9 double-mode Cepheids in the Southern Hemisphere (Barrell 1982), V367 Set (a member of the open cluster NGC 6649) and our value for TU Cas all show a good correlation with P1/P0. As the atmospheric Fe abundance increases, the ratio P1/P0 decreases.Our measured values for abundances (in brackets) of various elements in the atmosphere of TU Cas are: C (8.26), Na (6.32), Mg (7.07), Si (6.85), S (6.96), Ca (5.88), Sc (2.71), Ti (4.34), V (3.35), Cr (5.29), Mn (4.92), Fe (6.94), Co (4.47), Ni (5.70), Zn (3.63), Sr (2.00), Y (2.17), Zr (2.21), Ba (1.41), La (1.08), Ce (0.96), Nd (0.82), Sm (0.42), Eu (1.04), and Gd (0.92).
The RV Variability of Yellow Giants
Authors: Larson A.M. , Irwin A.W. , Yang S.L.S. , Goodenough C. , Walker G.A.H. , Bohlender D.A. , Walker A.R. 
Published: June 2019

AbstractThe hydrogen fluoride (HF) absorption cell technique has been used at the Canada-France-Hawaii Telescope for over a decade to monitor the radial velocity variability of nearby, solar-type stars in a search for substellar companions. As a complement to this program, we have also been monitoring a select group of G and K subgiants, giants and supergiants, which have all proved variable. We present here a brief summary of our analysis.
RR Lyrae Variables in the Second-Parameter Globular Cluster NGC 7006
Authors: Wehlau Amelia , Nemec James M. 
Published: June 2019

AbstractThe distant globular cluster NGC7006 was one of the first clusters studied for which the distribution of stars along the horizontal branch of its C-M diagram showed evidence for a “second parameter” in addition to metallicity. Studies of the more than 60 known RR Lyrae stars in this cluster should yield some statistically significant trends or correlations which might help to identify the second parameter. In the first stage of this study (Wehlau, Nemec, Han-Ian $ Rich 1992, AJ, 103, 1583) photographic data from 1984 were combined with previously published data from the 1930's and 1950's and used to obtain period change rates for 46 variables. The median rate was found to fall one standard error below that predicted by the Yale evolutionary HB models. In addition, statistically significant evidence was found for a radial gradient in period change rates in the sense that rates for variables in the outer region of the cluster were more negative.In the second stage of the investigation B and V magnitudes derived from CCD frames of the cluster are being used to obtain colors and to increase the number of variables for which good periods are known, in particular variables in the inner region of this centrally concentrated cluster.
Observations of Interstellar Reddening in Cygnus and Perseus
Authors: Nandy K 
Published: June 2019

The Object of the Edinburgh Spectrophotometry Survey is to determine the interstellar extinction law as precisely as possible and to search for intrinsic variations in it. The observations have been extended to early type stars up to a limiting magnitude of 11ṃ0 in regions extending from lII = 50° to lII = 200°. The 16/24/60-inch Schmidt telescope of the Royal Observatory has been used in conjunction with an objective prism and grating. Spectra extend from λ = 3300 Å to λ = 9000 Å with a dispersion of 1000 Å/mm at Hγ. Since few stars fainter than 9m have been measured in earlier investigations, the present survey extends considerably the amount of information available.In determining the extinction from a comparison of pairs of stars, one reddened and the other unreddened, one is faced by the problem of having to find two intrinsically similar stars in the same galactic region.
Dispersion of Polarization in Reflection Nebulae
Authors: Gehrels Thomas 
Published: June 2019

A Few Observations Were Made in NGC 7023 with filters at 0.36, 0.56, and 0.74 μ The wavelength dependence of polarization fitted with a straight line shows an appreciable rise with longer wavelengths. (See refs. 1 and 2.) The observations at the three filters were compared with Mie calculations obtained from Dr. B. M. Herman and General S. R. Browning of the University of Arizona for various refractive indices and particle sizes. Only single particle sizes have been considered, and therefore the results are preliminary. The present work represents a first reconnaissance to learn the techniques and some of the geometrical conditions.A firm conclusion, however, is reached in ruling out purely graphitic and purely metallic interstellar grains. The reasoning is as follows: The polarizations in various reflection nebulae (observed by Elvius and Hall) are “positive” and strong, and the color dependence is strong, with a fairly steep rise toward longer wavelengths; this behavior occurs for scattering angles from 20° to 70°. Such behavior is found in the Mie calculations at 2<a/λ ≅ 1.5. (See ref. 3.)
Formation of Molecular Hydrogen in Interstellar Space
Authors: Knaap H. F. P. , Van Den Meijdenberg C. J. N. , Beenakker J. J. M. , Van De Hulst H. C. 
Published: June 2019

Although Several Attempts at observing the interstellar hydrogen molecules in the ultraviolet or infrared are in preparation (ref. 1), these molecules are still undetected. They may form the most abundant unobserved constituent of the interstellar gas. The strongest indirect argument for the presence of these molecules lies in the fact that the density of atomic hydrogen observed by the 21-cm line goes down in some dark clouds, where the dust density and, presumably, the total gas density goes up by a large factor.Inasmuch as the density in the interstellar clouds is of the order of 10 atoms/cm3 and the temperature is only of the order of 100° K, any formation of molecules by atom-atom collisions is too slow to be of importance. The most eligible process for H2 formation is recombination on the surface of an interstellar dust grain. Rate estimates of this process have been made in various degrees of detail, as reported in references 2 to 4.
Near Infrared Interferometry of the Galilean Satellites
Authors: Howell R 
Published: June 2019

AbstractSome of the Galilean satellites show evidence of two distinct surface types, a high albedo frost and a dark, presumably silicate material. We are beginning a program to map the spatial distribution of these components with a Michel son spatial interferometer. This will be done both in and next to the 2.0µm frost absorption band. While the mapping program is just beginning, this investigation has already yielded new information on the wavelength dependence of seeing in the infrared.
UV Absorption Spectra of Molecules and the Connection with Pumping Mechanisms for Astrophysical Masers
Authors: Viney J.C. 
Published: June 2019

Since interstellar masers were first discovered in 1965, various attempts have been made to account for the variety of behaviour observed. In particular a number of theoretical models have been advanced to account for the pumping mechanisms but none have gained a wide acceptance.Over forty molecules have now been identified in the interstellar medium, of these five exhibit maser action; they are detected by virtue of their small angular diameter and very large brightness temperatures > 1013°K. The molecules in question are H20, OH, SiO, CH3OH and CH, of these the Hydroxyl maser presents the widest range of behaviour and therefore if the physical mechanisms involved could be understood these masers could be used to probe the interstellar environment and obtain more information about this important region where new stars are formed
Possibility of a White Dwarf as the Accreting Compact Star in CI Cam (XTE J0421+560)
Authors: Ishida Manabu , Morio Kazuyuki , Ueda Yoshihiro 
Published: June 2019

AbstractAlthough CI Cam, which showed an outburst in April 1998, has been regarded as a soft X-ray transient (SXT) harboring a, black hole, it has some characteristics that can hardly be reconciled with the SXT picture. In this paper, we propose a white dwarf as the central accreting star in CI Cam.
1RXS J232953.9+062814: A Possible Progenitor of AM CVn Stars
Authors: Uemura M. 
Published: June 2019

AbstractWe revealed that the hydrogen-rich cataclysmic variable lRXS J232953.9+062814 is an SU UMa-type dwarf nova with a superbump period of 66.774±0.010 min. A photometric orbital period is determined to be 64.184± 0.003 min, which is below the period minimum. Although the standard evolutionary scenario of cataclysmic variables predicts lower mass-transfer rates in systems with shorter orbital periods, its short recurrence time of outbursts and bright apparent magnitude indicate that this object has a relatively high mass-transfer rate. With the analogous system V485 Cen, these objects establish the first subpopulation in hydrogen-rich cataclysmic variables below the period minimum. Concerning the evolutionary status of them, we propose that they are progenitors of AM CVn stars on evolutionary courses in which systems have an evolved secondary star with a hydrogen-exhausted core.
Spectroscopic Diagnostics of Precessing Discs: The Stream-Disc Impact in XTE J1118+480 (= KV UMA) in Outburst
Authors: Haswell С. A. , Foulkes S. B. , Rolfe D. J. , Murray J. R. , Tovmassian G. H. , Zharikov S. V. , Maxted P. F. L. , North R. , Charles P. A. , Hynes R. I. 
Published: June 2019

AbstractWe present orbital trailed spectrograms of XTE J1118+480 taken at the rise to outburst maximum in 2000. These show an evolving S-wave feature arising from the stream impact on the edge of the eccentric precessing disc. By comparing the observed S-waves with those generated in an SPH simulation, we deduce the disc precession phases corresponding to our observations. Hence we infer changes in the disc precession period around the outburst maximum: taken at face value our spectroscopy suggests a precession period temporarily as short as 20 days.
Dynamic Populations of Dust in Interplanetary Space
Authors: Grün E. , Staubach P. 
Published: June 2019

AbstractInformation on the dynamics of interplanetary dust is obtained by observations of radio-meteors, zodiacal light, thermal infrared emission, and by measurements with in-situ detectors on board Earth satellites and deep spaceprobes. These methods are sensitive to different meteoroid sizes (mm- to sub-micron sized) and refer to different regions of space. Bigger particles (> 10-9 g) move on bound Keplerian orbits and are dynamically dominated by solar gravity, while the trajectories of particles smaller than 10-10 g are strongly influenced by radiation pressure and electromagnetic interactions. Modelling interplanetary dust is done by dividing the whole meteoritic complex into dynamically distinct populations. Divine's (1993) model identifies five dynamically different populations of interplanetary meteoroids: bigger particles are described by the “core”, and “asteroidal”-populations, intermediate sizes by the “halo”-population, and small particles are included in the “eccentric” and the “inclined”-populations. The intermediate and the small particle populations, in particular, have to be redefined for several reasons: new data are available which require the consideration of hyperbolic orbits and the inclusion of radiation pressure and electromagnetic forces. New small particle populations are interstellar dust and beta-meteoroids.
Orbital Evolution of the Lunar Ejecta
Authors: Yamamoto S. , Mukai T. 
Published: June 2019

AbstractWe have estimated the flux of lunar ejecta near the Earth, e.g., the cumulative flux of ejecta larger than 10-13g is 10-10particles cm-2s-1. In addition, our numerical simulations for the orbital evolution of lunar ejecta lead to the orbital characterization of these ejecta. Since our calculations suggest that the incident direction of lunar ejecta onto the Earth is nearly isotropic, it is expected that the dynamical properties of lunar ejecta make it possible to distinguish them from other IDPs.
Fragmenting Particles During 1989-1994 Perseid Radar Observations
Authors: Šimek M. 
Published: June 2019

AbstractThe occurrence of fragmenting particles was investigated from radar observations of the Perseids at Ondřejov Observatory. Diurnal patterns of fragmenting meteoroids are presented. Their minimum occurrence coincides with the culmination of the Perseid radiant while the maximum appears at the time of sunset at meteor heights. Solar longitude of the main contribution of fragmenting meteoroids at L⊙ = 138°86±0°04 (equinox 1950.0) fits with the peak activity of the new filament in the stream. This supports the concept of the low age of the filament. The maximum proportion of fragmenting particles occurred in 1991.
Modelling the Orbital Evolution of the Perseid Meteoroids
Authors: Jones J. , Brown P. 
Published: June 2019

AbstractWe have modelled the evolution in the distribution of orbits of 1.5 x 106 particles released at the 1862, 1737 and 1610 apparitions of 109P/Swift-Tuttle for a range of particle masses and for a range of ejection angles about the comet-solar line. The evolution of the stream is dominated by the influence of planetary perturbations, most notably those due to Jupiter. A periodicity of approximately 12 years in Perseid activity is noted in the material ejected during the 1862 apparition. Without Jovian perturbations, the nodes of these recently released Perseid particles would not cross the Earth's orbit. Activity from 1862 is notable in the simulations for 1991-1994 and also for the early 1980's. Ejections in 1737 and to a lesser extent in 1610 contribute material seen at the Earth in the late 1980's.
Sources of Interplanetary Dust
Authors: Dermott S.F. , Grogan K. , Gustafson B.Å.S. , Jayaraman S. , Kortenkamp S.J. , Xu Y.L. 
Published: June 2019

AbstractAsteroids, comets and interstellar dust are possible sources of the particles that constitute the dust in the inner solar system. Each of these components gives rise to particular, characteristic features, the amplitudes of which can be used to estimate the size of the associated source. The asteroidal component feeds the dust bands and the Earth's resonant ring, while the cometary component may account for the large scale height of the zodiacal cloud observed at 1 AU Previous discussions of the observed strengths of these various features indicated that the source of about one third of the thermal flux observed, for example, in the IRAS 25μm waveband is asteroidal, while two thirds is cometary. However, a variety of assumptions go into this calculation (the size-frequency distribution of the particles is particularly significant) and we now know that the result is highly dependent on these assumptions. The zodiacal cloud is also the source of the IDPs collected on Earth. Because of strong gravitational focusing by the Earth of particles in low e and I orbits, it is probable that the majority of IDPs originate from asteroids, particularly those asteroids in the Themis and Koronis families.
The Contribution of Kuiper Belt Dust Grains to the Inner Solar System
Authors: Liou Jer-Chyi , Zook Herbert A. , Dermott Stanley F. 
Published: June 2019

AbstractThe recent discovery of the so-called Kuiper belt objects has prompted the idea that these objects produce dust grains that may contribute significantly to the interplanetary dust population at 1 AU. We have completed a numerical study of the orbital evolution of dust grains, of diameters 1 to 9 μm, that originate in the region of the Kuiper belt. Our results show that about 80% of the grains are ejected from the Solar System by the giant planets while the remaining 20% of the grains evolve all the way to the Sun. Surprisingly, these dust grains have small orbital eccentricities and inclinations when they cross the orbit of the Earth. This makes them behave more like asteroidal than cometary-type dust particles. This also enhances their chances to be captured by the Earth and makes them a possible source of the collected interplanetary dust particles (IDPs); in particular, they represent a possible source that brings primitive/organic materials from the outer Solar System to the Earth.When collisions with interstellar dust grains are considered, however, Kuiper belt dust grains larger than about 9 μm appear likely to be collisionally shattered before they can evolve to the inner part of the Solar System. Therefore, Kuiper belt dust grains may not, as they are expected to be small, contribute significantly to the zodiacal light.
The COSMIC DUST ANALYZER for the CASSINI Mission to Saturn
Authors: Srama R. , Grün E. ,   The CASSINI-Dust-Science Team
Published: June 2019

AbstractIn October 1997 a unique mission to the Saturnian system will be launched by NASA, the CASSINI mission. One goal of this mission is to study the Saturnian dust environment, and for this task, the COSMIC DUST ANALYZER (CDA) has been developed and is currently being tested. Impact ionization is used to determine the speed (1 - 100 km/s) and the mass (1•10–15 – 1•10–9 g) of impinging particles. Furthermore, the electric charge (1•10–15 – 1•10–12 C) of the particles can be measured via the induction principle, and an integrated time-of-flight mass spectrometer will analyze the chemical composition of individual dust particles. In order to achieve sufficient sensitivity for dust fluxes as low as 10 particles/(month-m2), the sensor has a large sensitive area of 0.1 m2. This paper will describe the function of the experiment.