bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetic-Loop Model For Be Stars (Review Paper)
Authors: Underhill Anne B. 
Published: June 2019

AbstractThe magnetic-loop model for a stellar mantle is described and it is shown how this model may be used to understand the differences in spectrum and change of spectrum which are observed for main-sequence stars haying effective.temperatures in the range from 2.5 x 104 to 3.0 x 104 K.It is suggested that the difference in spectrum between a shell star such as Gamma Cas when it is in an active state and a Wolf-Rayet star may be due to a difference in environment.
Consistent Spherical NLTE-Models for BE-Stars
Authors: Peter Höflich  
Published: June 2019

AbstractSpherical NLTE-model photospheres surrounded by envelopes are calculated in order to interpret classical Be-stars. The existence of the Hll-region can be understood by such models. The dependence of the calculated spectra on parameters corresponds to the observations. Applications to special objects show good agreement between the predicted and observed spectra in the visual and infrared wavelengh range.
Effect of Compact Objects Near Be Stars
Authors: Apparao Krishna M.V. , Tarafdar S.P. 
Published: June 2019

Several Be stars are identified with bright X-ray sources. (Rappaport and Van den Heuvel, 1982). The bright X-ray emission and observed periodicities indicate the existence of compact objects (white dwarfs, neutron stars or black holes) near the Be stars. A prime example is the brightest X-ray source A0538-66 in LMC, which contains a neutron star with a rotation period of 59 ms. Apparao (1985) explained the X-ray emission, which occurs in periodic flares, by considering an inclined eccentric orbit for the neutron star around the assumed Be-star. The neutron star when it enters a gas ring (around the Be-star) accreting matter giving out X-rays.The X-ray emission from the compact objects, when the gas ring from the Be-star envelopes the objects, has interesting consequences. The X-ray emission produces an ionized region (compact object Stromgren sphere or COSS) in the gas surrounding the compact object (CO).
Infrared Period-Luminosity Relations of RR Lyraes in M5 and Ml5
Authors: Liu T. , Janes K. A. 
Published: June 2019

AbstractWe have carried out K band photometric observations of RR Lyrae stars in two globular clusters which both have large populations of RR Lyraes but different characteristics: the moderately metal-rich cluster M5 ([Fe/H] = –1.40) and the metal-poor one M15 ([Fe/H] = –2.15). The purpose is to accurately calibrate the linear relationship between RR Lyrae infrared (K) absolute magnitudes and their periods that has been confirmed by recent Baade-Wesselink type studies of RR Lyraes and IR photometry of cluster variables. A total of 47 RR Lyraes in M15 was observed and each has more than 8 measures on the average, which allows the accurate determination of a mean K magnitude for each star. In M5 44 stars have been observed with each RR Lyrae having 4 measurements. Our preliminary results show that the RR Lyrae infrared period-luminosity relations for the two clusters have roughly the same slope, despite the fact that they have a large metallicity difference. This suggests that the metallicity effect on the (MK)-log P relation is indeed small as one would expect. The M5 and M15 RR Lyrae IR photometry gives a reliable determination for the slope of the infrared period-luminosity relation because of the large number of stars measured. A well-calibrated (MK)-log P relation will be very useful in distance determinations to heavily reddened star regions such as the Galactic center and globular clusters in the Galactic bulge.
Search for a Secondary Frequency in the Large-Amplitude δ Scuti Star CY Aqr
Authors: Coates D. , Fernley J. , Sekiguchi K. , Barnes T. G. , Frueh M. 
Published: June 2019

AbstractThe large-amplitude δ Scuti star CY Aqr was observed from sites in the U.S.A., South Africa and Australia during August 1988. Coates et al. (1991) published 48 new times of maximum light derived from these observations and assembled, from the literature, previous times of maximum light. It is clear that the period of the star is changing with the balance of evidence favouring discrete changes in 1951 and 1966, rather than a continuous change.It has been suggested by Fitch (1973) and Else (1972), from an analysis of the observations of Zissell (1968), that there is a secondary frequency present in CY Aqr. Coates et al. (1992) have analysed both the 1988 observations and those of Zissell. After subtracting the primary frequency and its harmonics, they find no stable secondary frequency above the noise level of two millimagnitudes.
Hydrodynamical Models of Radially Pulsating Hot Extreme Helium Stars
Authors: Fadeyev Yu. A. 
Published: June 2019

AbstractThe blue edge of the instability region of radially pulsating helium stars is located on the H-R diagram nearly vertically at luminosities less than 104L⊙ and corresponds to Teff = 7400K and 1.1 · 104K for stars with mass of 1M⊙ and 0.7M⊙, respectively. The pulsation instability of the stars located along the vertical part of the instability edge is characterised by the increasing order of the pulsation mode with decreasing luminosity. For example, for stars with M = 0.7M⊙ and Tteff = 104K the principal pulsation mode is nearly second overtone for Mbol = –5 mag and is nearly fourth overtone for Mbol = –4 mag. For stars brighter than Mbol = –5 mag the blue edge turns blueward so that the models with Teff as high as 3 · 104K are pulsationally unstable. The sequences of the hydrodynamic models characterized by constant luminosity Mbol < – 5 mag) reveal the decrease of the light amplitude with increasing Teff, whereas the amplitude of the radial velocities of the outer layers is almost independent of Teff. For example, for stars with Teff > 2·104K the light amplitude is less than 0.01 mag, whereas the radial velocity amplitude is in the range from 20 to 50 km/s. The pulsation instability of these stars is driven mainly due to the γ-mechanism. Fourier analysis of the hydrodynamic solution shows that the pulsation motions of the hot helium stars can be represented as a superposition of the running waves (in contrast to Classical cepheids where the pulsation motions are described in the terms of superposition of standing waves). The pulsation constant gradually decreases with increasing Teff, down to Q ≈ 0.012 day at Teff ≈ 3 · 104K.
A Photometric and Spectrographic Study of SX Phœnicis
Authors: Kim Chulhee , McNamara D.H. , Feltz Kent A. , Christensen C.G. 
Published: June 2019

AbstractNew simultaneous photometric (uvbyβ) and spectrographic observations of SX Phe are described. Analysis of the light variation frequency spectrum is performed and the oscillation modes are investigated. After separating the light curves and radial velocity curve, atmospheric and physical parameters corresponding to each different oscillation mode were determined. Intrinsic (b – y), m1, and c1 values used in conjunction with a model-atmosphere grid yield a mean effective temperature < Teff > = 7590K, a mean surface gravity, < logg > = 4.02, and [Fe/H]= -0.47 for the first period. The pulsation theory and stellar model sequences yield bolometric magnitude of mass of 1.4 M⊙ and age of 2.0 Gyrs. It was found that these atmospheric parameters are almost independent upon different oscillation mode. The radial-velocity data indicates a mean radial velocity of -37km/s and a total velocity amplitude range of 38km/s.
New Radial Velocities and the Barnes-Evans Method
Authors: Hindsley Robert , Bell R.A. 
Published: June 2019

AbstractNew radial velocities by Butler are used to recalculate the absolute magnitudes of Eta Aquilae and X Cygni using the Barnes-Evans method. The new velocities have little effect on the result for Eta Aquilae, but the absolute magnitude of X Cygni is found to be 0.40 mag fainter than that obtained earlier.
Moving Through The Instability Strip
Authors: Belserene Emilia Pisani 
Published: June 2019

The purpose: To look at period changes in pulsating variables from the point of view of stellar evolution. Is there evidence of systematic, slow changes that might be caused by the changes in mean density during passage across the Instability Strip?The data: O – C diagrams for 67 RR Lyrae stars and Cepheids by student assistants at the Maria Mitchell Observatory, and for 88 northern Cepheids by L. SzabadosThe method: Least-squares lines and parabolae (unless the O – C diagram shows that the period has changed in both directions). The rate of change of period comes from the coefficient of the square term in the parabola. The principal feature of these analyses is that the rate is taken to be non-zero only if the parabola is significantly better than the linear fit, at the 2-sigma level.
Observed Interstellar Extinction in the Ultraviolet
Authors: Stecher T. P. 
Published: June 2019

An Observational Program to measure stellar energy distributions - in the ultraviolet between 3000 Å and 1200 Å has recently been completed. The instrumentation used was similar to that reported in reference 1. A necessary preliminary for discussion of this material is some knowledge of the extinction due to interstellar absorption. The trend of this extinction was first reported in 1964. (See ref. 2.) Additional observational material has since been obtained and is presented herein.Five pairs of stars with similar Morgan-Keenan (MK) spectral classifications have been observed that are suitable for obtaining extinction: ζ Per and ρ Leo; ξ Per and ζ Pup; o Per and β Can Maj; σ Sco and π SCO; and δ Sco and τ SCO. The telemetry records were hand reduced by the author, each star was multiplied by the absolute calibration curve for the appropriate instrument, and the resulting flux curve was placed on a magnitude scale.
Graphite and Interstellar Extinction
Authors: Stecher T. P. , Donn Bertram 
Published: June 2019

The Theory That Graphite Particles could be responsible for interstellar extinction is presented in references 1 and 2, and this paper will present evidence that further supports this contention. The complex dielectric constant (m = n(l — ik) for graphite has been measured as a function of energy by the authors of reference 3, and the optical constants as function of wavelength λ have been obtained from this measurement. A large variation occurs in both n and k at wavelengths below 3000 Å.The results reported in the preceding paper indicated the desirability of performing Mie scattering calculations on graphite. The measured values of the complex index of refraction corresponding to 17 wavelengths were used in the calculation for spherical particles. The IBM 7094 computer program for Mie scattering follows that of van de Hulst. (See ref. 4.) The Oort-van de Hulst size distribution (ref. 5), which may not be applicable to the type of particle discussed herein, has been used to obtain an integrated cross section for extinction.
A Prototype 11 Metre Modern Michelson Stellar Interferometer
Authors: Davis John 
Published: June 2019

AbstractThe Astronomy Department of the University of Sydney is currently exploring the feasibility of building a Micheson stellar interferometer using modern techniques and detectors to surmount the atmospheric and stability problems that limited the development of the original Michelson interferometers. The main part of this programme is the design and construction of an 11 m fixed baseline prototype instrument to establish whether fringe visibility can be measured with an accuracy better than ±2% over a range of atmospheric seeing conditions and instrumental parameters. The design of the prototype instrument, its status and prospects are discussed.
A Direct Measurement of the Collisional Population and Depopulation Rates for the N = 2 State of Atomic Hydrogen
Authors: Burgess D.D. , Kolbe G. , Ward J.M. 
Published: June 2019

A technique is described in which a plasma is prepared using a tunable laser such that the population of only a single atomic bound state differs significantly from its equilibrium value. Subsequent observation of the relaxation of this single state in the absence of laser irradiation and with all other levels close to their equilibrium populations then yields unambiguous values for the collisional depopulation and re-population rates for the level, free from uncertainties present e.g. in laser-induced fluorescence experiments.Results will be presented for the n = 2 state of hydrogen, but the technique is applicable to many first excited states in plasmas which need not be in either LTE or pure coronal equilibrium.
Hydrodynamic Modelling of Accretion Flows
Authors: Murray J. R. , Truss M. R. , Foulkes S. B. , Haswell C. A. , Manson K. J. 
Published: June 2019

AbstractIn the proceedings of this, and of several recent close binary conferences, there have been several contributions describing smoothed particle hydrodynamics simulations of accretion disks. It is opposite therefore to review the numerical scheme itself with emphasis on its advantages for disk modelling, and the methods used for modelling viscous processes.
X-Ray Spectroscopy of the High-Mass X-Ray Binary 4U 1700-37
Authors: van der Meer A. , Kaper L. , Di Salvo T. , Méndez M. , van der Klis M. 
Published: June 2019

We present the first results of a monitoring campaign of the high-mass X-ray binary system 4U 1700-37/HD 153919, carried out with XMM-Newton.We have observed the high-mass X-ray binary (HMXB) 4U 1700-37 with XMM-Newton at four orbital phases in February 2001. 4U 1700-37 is powered by the dense stellar wind of the O supergiant HD 153919. Numerous X-ray flares are observed with a typical duration, of the order of half an hour. We focus on three intervals in which the data are not affected by pile up: the eclipse, the eclipse egress and a low-flux part around orbital phase ϕ ~ 0.28.
Long-Term Photometric and Spectroscopic Behaviour of Symbiotic System AG Dra
Authors: Gális R. , Hric L. , Petrík K. 
Published: June 2019

The general behaviour of AG DRA was studied in the context of the long-term photometry and radial velocity analysis.AG DRA is a symbiotic binary with quiescent and active stages; the latter may be explainable by increased thermonuclear burning of a white dwarf accreting from the wind of the cool component.In our previous studies a second period in addition to the orbital period of 549.7 days has been found for AG DRA. Such a period of about 350 days was indicated in our study using photometry (Friedjung et al. 1998, Petrík et al. 1998)as well as radial velocities (Gális et al. 1999 Friedjung et al. 2003).
Martian Self-Sustaining Dust Torus
Authors: Sasaki Sho 
Published: June 2019

AbstractRecent theoretical studies show that orbits of circummartian dust particles are controlled by solar radiation pressure and the Martian oblateness. Smaller dust particles (< 22μm) with enhanced orbital eccentricity are quickly captured by Mars. We find that the collisions of ring particles with Phobos and Deimos are the most important dust sources. Erosion of Phobos should set the upper limit on the dust production efficiency controlling this self-sustaining mechanism, and then the ring dust abundance.
A Collector for Interplanetary Dust Particles and Space Debris
Authors: Yin-Lin Xu , He-Qi Zhang , Nan Zhang , Min Yu , Ping Xie , Fan C. Y. 
Published: June 2019

AbstractWe are constructing a collector for capturing Interplanetary Dust Particles (IDPs) and space debris on space shuttle. The unit consists of three pieces of thin polyester film, equally spaced 7 cm apart, and an aerogel disk of 3 cm thickness. For each particle captured in the aerogel disk, we determine its direction of impact and its speed, from which we can trace its trajectory. The purpose of the experiment is to study the compositions of IDPs from different origins.
Optical Properties of Dust from Laboratory Scattering Measurements
Authors: Gustafson Bo Å. S. 
Published: June 2019

AbstractThis is a description of the beginning of a systematic investigation into the optical properties of dust structures that are likely to be representative of interplanetary dust. I delineate the development of a physical dust model to parameterize the optically important characteristics of the dust. The result is a system with two refractive indexes in an aggregate structure of varying porosity - a challenging model for most current light scattering theories. Experimental data is needed to investigate the scattering by these structures and to test new theoretical solutions (e.g., Xu 1995) as they develop. I give a brief description of the new microwave analog scattering laboratory that has been developed for this purpose at the Laboratory for Astrophysics of the University of Florida's Astronomy Department. Finally, laboratory data is shown in support of dense aggregate models for interplanetary dust.
Scattering Properties of Dust Particles in Weightlessness
Authors: Worms J. C. , Levasseur-Regourd A.C. , Hadamcik E. , Bourras D. 
Published: June 2019

AbstractPolarimetric measurements of the light scattered by irregular dust particles are essential to interpret observations of solar system dust in terms of its physical properties. We developed a iight scattering unit to retrieve polarimetric phase curves of dust samples in microgravity conditions. Preliminary results suggest that the values for the maximum polarization are higher under 1 “ g ” than under 0 “ g ” This can be compared to ground-based measurements which exhibit higher values for packed dust than for sifted dust. The unit is operational and is used to help design a related orbital experiment.
Free Molecular Gas Drag on Fluffy Aggregates
Authors: Nakamura R. 
Published: June 2019

AbstractComputer simulations of the collisions of gas molecules with fluffy aggregates have been carried out to estimate gas drag forces in the free molecular flow limit. It is found that the gas drag force on fluffy aggregates can be approximated by that on an area-equivalent sphere in a wide range of relative velocities of the aggregate through ambient gas. The deviation from this approximation is weakly dependent on the relative velocity. This result leads to a significant increase of gas drag forces on fluffy aggregates compared to that on a mass-equivalent sphere.
From research-as-practice to exploratory practice-as-research in language teaching and beyond
Authors: Hanks Judith 
Published: June 2019

AbstractPractitioner research is a flourishing area with a significant body of theoretical and empirical research, but often researchers remain isolated, unaware of impactful work by colleagues in related fields. Exploratory Practice (EP) is one innovative form, uniting creative pedagogy and research methods. The potential contributions have hitherto been neglected. EP's emphasis on puzzling and understanding is a means of demystifying occluded practices which place learners, teachers and researchers as co-investigators at the heart of the research-practice nexus. EP's radical positioning of learners as co-researchers, alongside teachers, teacher educators and others, means crossing boundaries – (re-)negotiating identities, in language learning/teaching/researching – thus raising epistemological challenges for the field. The contribution of this state-of-the-art article is to provide a meta-analysis of these themes and challenges, critically analysing the complexities involved as the paradigms of research, practice and practitioner research shift from research-as-practice towards practice-as-research.
Developments in methods for breeding value and parameter estimation in livestock
Authors: Hill William G. , Meyer Karin 
Published: June 2019

In an effective animal breeding programme the objectives are appropriate, the population structure is good, suitable records are collected, and these records are used in an optimal way so that animals likely to have the best offspring are chosen.Estimates of genetic parameters such as heritabilities and correlations influence the design of the programme: for example, the optimal number of daughters to progeny test per dairy sire or, more fundamentally, whether to adopt performance or progeny testing, whether to record food conversion efficiency or simply growth rate, and whether or not to collect records on some indicator trait such as blood urea nitrogen level. The estimates of parameters also influence the weightings given to different traits and to individuals and relatives' performance in breeding value estimation and selection. Methods for estimating parameters have become much more sophisticated as a result of advances in theory, particularly, restricted maximum likelihood (REML), in computer power, and in development of special computer programs.
Genetic components of potential and actual growth
Authors: Emmans G C 
Published: June 2019

1. It is shown how the growth of an animal in non-limiting conditions can be predicted from the values of a small set of animal variables. The functions used are derived from a small set of simple, and reasonable, assumptions.2. Growth may be limited by intakes of nutrients and energy which are less than those needed. The prediction of growth where such limitation occurs calls for the prediction of the intakes. There may be genetic variation in the abilities of animals to deal with the relevant constraints which are, commonly, feed bulk or hot environments.3. Breeders need to pay more attention to giving sufficient descriptions of their stocks.
Feeding the young ruminant
Authors: Williams P. E. V. , Frost A. I. 
Published: June 2019

AbstractYoung calves and lambs are weaned early to reduce the amount of milk products consumed and potentially improve the profitability of rearing enterprises. At weaning the pre-ruminant must make a number of adjustments to cope with the change in dietary substrate. The microbial population in the rumen must develop and metabolic changes are required in order for the young ruminant to metabolize the end products of microbial digestion. It is recognized that early weaning poses a stress to the calf but it is generally considered that the calf rapidly adjusts to the change in diet composition. A number of factors indicate that considerable advantage would be gained from delaying the weaning of calves and indeed that the calf is not physiologically capable of adapting to an early-weaning regime. Work has indicated that a diverse anaerobic microbial population can be identified in the developing rumen of the calf. More recent results show that the presence of a faculative anaerobic population, which exists for a considerable period of time, has an adverse effect on the development of a mature anaerobic population. Low rumen pH is a problem in the young calf. The level of rumen pH verges on that which would be described as acidosis in the adult ruminant. The young calf is unable to stabilize rumen pH and increasing the level of dry food intake at weaning may further depress rumen pH if the salivary buffering capacity of the calf is not adequately developed. Results indicate that the ability to utilize volatile fatty acids is not fully developed in the young calf and that early weaning can result in high levels of VFAs in the circulation.The composition of the dry diet has a major effect on the response of the calf to weaning. Choice of the ingredients can affect the buffering capacity of the rumen and the physiological development of the digestive tract. Strategies to limit the nutrient intake from dry food to levels commensurate with the developing physiology of the calf may result in a more uniform transition to full ruminant status with consequent benefits in growth rate and health.