bluuebunny/crossref_metadata_2025_split huggingface dataset:
India
Authors: Narlikar J. V. , Rana N.C. 
Published: June 2019

A summary of work related to astronomy education carried out during the last three years in India is presented here. Since India is a huge country and many educational efforts are made by individuals alone, this report cannot be regarded as complete, but a specific sampling.India has more than 200 Universities, 8000 colleges, and about 100,000 schools, 33 planetaria, more than 100 museums and about 60 well known amateur astronomers’ clubs. Scores of dedicated astronomy oriented school teachers, act as nuclei of astronomy education for the general public and school children .The astronomical almanac, used in a typical household is in some way related to the stars in the sky and the movements of the Sun, the Moon and the planets. Traditionally, a rudimentary knowledge of the celestial sphere is common. The recent developments in space technology have brought a fascination and glamour to modern astronomy for all age groups, and this is noticeably reflected in the number of media coverages of astronomy.
Mathwise Astronomy and the TLTP: aiding or degrading education?
Authors: McCabe E.M. 
Published: June 2019

The Teaching and Learning Technology Programme (TLTP) in the UK was launched in 1992 to “develop innovations in teaching and learning through the power of technology”. Increasing numbers of students with mixed abilities and backgrounds were entering into higher education. Flexible course structures and the need for remedial teaching added further motivation in the search for methods of improving productivity and efficiency.Since 1992 over 33 million of funding has been awarded to 76 projects spanning the university curriculum. When support from host institutions is taken into account, overall funding for the TLTP is estimated at 75 million. TLTP materials are now becoming available to assist institutions in maintaining and enhancing the quality of their teaching provision. The successful implementation of this new technology is requiring each institution to rethink its teaching and learning strategies (Laurillard, 1993).
Differential Rotation in B and Be Stars
Authors: Zorec J. , Divan L. , Mochkovitch R. , Garcia A. 
Published: June 2019

SummaryIn this paper we present two kinds of results which show that differential rotation is a highly probable phenomenon in B and Be stars. These results show that angular momentum is an important parameter which must be taken into account for interpreting the observed parameters of B and Be stars and for studying their structure.
An Infrared Study of Southern Be Stars: Ground-Based and Iras Observations
Authors: Persi P. , Ferrari-Toniolo M. 
Published: June 2019

Infrared observations represent a powerful tool in understanding the physical conditions of the circumstellar matter around Be stars. Previous IR studies have been reported by different authors (i.e. Gehrz et al. 1974, Persi et al. 1982, Ashok et al. 1984, and Waters, 1986).For this purpose, we have undertaken an IR study of 21 southern Be stars including JHKLM photometry, CVF spectra at resolution R=100 around the IR HI emission lines Brγ, Brα, and Pfγ and IRAS data at 12 and 25 microns taken from the Point Sources Catalogue. The IRAS flux densities were corrected following the procedure described in the IRAS Explanatory Supplement.The near-IR observations were obtained in March 1985 at the lm ESO (La Silla, Chile) telescope, equipped with the InSb Spectrophotometer. In the next section we discuss the nature of the observed IR excesses, and from the measured Brα/Brγ intensity line ratios for three Be stars, we derive the mass-loss rates.
The Relation Between Mass Loss and Luminosity For Be Stars
Authors: Waters L.B.F.M. , Lamers H.J.G.L.M. , Coté J. 
Published: June 2019

AbstractThe mass loss rates of a large sample of Be stars derived from the UV and the IR are compared. The IR rates were derived using a simple equatorial disc model, and are typically a factor 100 larger than those derived from the UV. In terms of mass fluxes, the mass flux in the polar regions (derived from the UV observations) is about a factor 103 smaller than the mass flux in the equatorial regions. The dependence of MIR and Muv on stellar luminosity is studied. It is shown that MIR depends weaker on L than Muv. This suggests that two different mechanisms are responsible for the mass flux in polar and equatorial regions.
Pole-On Cataclysmic Variables as Be Stars
Authors: Garrison R. F. 
Published: June 2019

Cataclysmic-variable stars (CVs) are technically Be stars, since Balmer emission lines appear in their spectra. In general, CV spectra are so unusual that they are easily recognized. The main features are extremely broad, shallow hydrogen lines with broad, faint emission cores. The Balmer emission decrement is very slow, more like that of an H II region than that of a normal Be star. The Balmer decrement in cataclysmic variable stars has been discussed by Elitzur, et al.If a CV were viewed pole-on, the spectrum might be quite different. It could exhibit a smooth continuum or may even resemble a normal Be star, except for the Balmer decrement. In this case, there may be a bright cataclysmic variable lurking in the Be star class. A possible example is the star NS 274-67, an 03e star described by Conti et al. (1986), which has Balmer emission from H-beta to H-ep-silon, but no nebular emission at [0 II] or [0 III].
The Evolution of Rapidly Rotating B Stars (Review Paper)
Authors: Smith Robert Connon 
Published: June 2019

AbstractBe stars are located in or near the main-sequence band for non-rotating stars. Although this stage of evolution is relatively well understood, there are two main effects that make it impossible to say whether all Be stars are in the same stage of evolution and, if so, what that stage is. One effect is the spread in observed magnitude and colour as a result of rotation. Correction for rotation is not possible because of the unknown inclination of any particular star's rotation axis to the line of sight and because it is not clear what the internal angular momentum distribution is or how it changes as a result of evolution. The other effect is that there are uncertainties in the theoretical evolutionary tracks because the amount of convective overshooting is unclear. Other mixing mechanisms that might in principle also confuse the tracks seem to be small near the main sequence. If Be stars are related to theβCephei and 53 Persei stars in the same part of the HR diagram, then the non-radial pulsation properties of Be stars may give a clue to their evolutionary state. The existence of a circumstellar disc or ring, however, tells us very little about the evolutionary stage of the underlying star. A useful way forward may be to try to understand individual stars in as much detail as possible.
Be Stars as Members of Open Clusters
Authors: Feinstein A. 
Published: June 2019

A list of 124 Be-type stars belonging to 52 open clusters has been compiled. All of them have photometric UBV data, and many of them spectral classification in the MK system. Besides, the cluster's distance modulus and the mean color excess from the member stars are known. Then, we have computed the absolute magnitude and the intrinsic colors of each Be star.The observed color-color diagram (Figure 1) shows clearly that nearly all Be stars appear to be reddened. In Figure 2 is given the color-magnitude diagram, (B-V)o versus Mv, in whicn the ZAMS (Blaauw, 1963) is also included. A few stars to the left of the main sequence belong to the young open clusters: NGC 869, 6167, 6530 and 6611. This effect may be due to wrong correction of the color indices because of abnormal values of the reddening law.
The Oosterhoff Period Effect and the Age of the Galactic Globular Cluster System
Authors: Sandage Allan 
Published: June 2019

AbstractThe Oosterhoff division of globular clusters into two dichotomous mean period groups is a result of the variation with metallicity of the combined effects of (1) a mean increase in period with decreasing metallicity, and (2) the change of globular cluster horizontal branch (HB) morphology from the M3 to the M13 HB type within the instability strip in the metallicity range of [Fe/H] between -1.7 and -1.9. A new representation of the Oosterhoff period effect showing this property is made from the individual cluster data in Figure 1. The relation between period and metallicity for cluster and for field RR Lyraes at the blue fundamental edge of the instability strip in the HR diagram as read from this figure islog Pab = -0.122(±0.02)([Fe/H]) - 0.500(±0.01)using the metallicity scale of Butler.The high slope coefficient is consistent with the extant models of the HB when they are read at the varing temperature of the fundamental blue edge given by equation (3) of the text. Most of the current literature treats only the constant temperature condition, which is manifestly incorrect. It is this temperature effect that reconciles the observations and the models.A new calibration of the absolute magnitudes of RR Lyrae stars as a function of metallicity, combined with new oxygen enhanced isochrones for globular clusters (Bergbusch & VandenBerg 1992) reduces the age of the Galactic globular cluster system to 14.1 ± 0.3 Gyr (internal error). The resulting lower age of the universe which, when combined with a Hubble constant near 50 km s-1 Mpc-1 determined from type I supernovae, shows that the cosmological expansion has been decelerated by an amount consistent with the closure density, permitting Ω ∼ 1 now from the timing test.
Recent improvements to the Cepheid distance scale
Authors: Freedman Wendy L. , Madore Barry F. 
Published: June 2019

AbstractIn the course of the last decade significant advances have been made in the observations of Cepheid variables and in their successful application to the extragalactic distance scale. Much of this progress has come about as a result of new CCD and near-infrared photometry. These recent improvements are discussed, and a comparison is given of Population I Cepheids and Population II distances. The correspondence is good, with the zero points agreeing at a level of better than 15% in distance. At this same level of significance, a systematic difference between these distances scales may exist, in the sense that the RR Lyrae distances appear to be smaller than the Cepheid distances (if it is assumed, as has generally been done for extragalactic studies of RR Lyraes, that Mv(RR) = 0.77 mag, independent of [Fe/H]). However, several recently-published calibrations of Mv(RR) significantly reduce this discrepancy. Finally, new Cepheid data for the nearby galaxy M81 are presented based on recent Hubble Space Telescope observations.
Cepheid and Long – Period Variables in Virgo Cluster Galaxies
Authors: Pierce M.J. , McClure R.D. , Welch D.L. , Racine R. , van den Bergh S. 
Published: June 2019

AbstractWe are currently undertaking a ground-based imaging survey which attempts to discover and determine periods for variable stars in Virgo Cluster galaxies. Such a survey is now feasible thanks to the high resolution imaging (FWHM ≤ 0.50 arcsec) routinely obtained with the High Resolution Camera on the Canada-France-Hawaii Telescope. The Virgo Cluster has long been considered a crucial “stepping-stone” in the extragalactic distance scale problem given that the cluster is at a “cosmologically interesting” distance and that there is little controversy in the relative distance between Virgo and more distant clusters, such as Coma. Consequently, much of the controversy regarding the extragalactic distance scale and the Hubble Constant can be eliminated with a determination of the Virgo Cluster distance. Some preliminary results and the prospects for establishing the distance to the Virgo Cluster using Cepheids and LPVs are discussed.
An Adjustment to Cepheid Distances Calculated Using Model Atmospheres
Authors: Hindsley Robert , Bell R.A. 
Published: June 2019

Hindsley and Bell (1989, Ap. J., 341, 1004) determined distances for 23 Cepheids using the surface brightness method. The color V – IC on the Cousins system or V – RJ on the Johnson system was used to measure visual surface brightness. Combined with the observed visual magnitudes, angular diameters were then calculated. Comparison of angular diameters with radius differences in linear units, obtained by integrating the radial velocity curve, yielded each Cepheid's distance.Hindsley and Bell calibrated the relationship between color and surface brightness using model atmospheres. The zero point of the relationship was found using observations of Vega and an appropriate model. More recently the spectral scans of Gunn and Strycker (1983, Ap. J. Suppl., 52, 121) and the Cousins filter response curves of Hindsley and Bell were used to calculate colors and these were compared to the corresponding observed colors.
The Effect of a Vertical Magnetic Field on the Periods of Trapped g-modes in White Dwarfs
Authors: Carroll Bradley W. 
Published: June 2019

AbstractA white dwarf model with cylindrical symmetry is used to investigate the effect of a uniform vertical magnetic field on the periods of g-modes trapped in the compositionally stratified surface layers. For those modes for which trapping is most effective, the periods wander by approximately 10% about their zero-field values as B0 increases. As the field strength increases further, the period may abruptly increase by some 25% to a new, more stable value; see Figure 1. The periods of less efficiently trapped modes do not show this sensitivity for field strengths up to 1 MG, the upper limit examined.
Fourier Analysis of Line-Profile Variations: Toward Stellar m – v Diagrams?
Authors: Merryfield W.J. , Kennelly E.J. 
Published: June 2019

AbstractNumerous rapidly rotating δ Scuti stars exhibit variable line profiles containing traveling subfeatures [l]-[2], which may be signatures of nonradial pulsations having relatively high azimuthal order |m| We describe a procedure whereby a time series of spectral line profiles is Fourier analysed both in time and in a wavelength variable that is presumed to correspond to azimuthal position Φ on the star. What such an analysis can tell us is examined by analysing artificially-generated data. For an ideal example in which sin i = 1 and a single mode having is present, the two-dimensional Fourier transform yields a power spectrum in frequency and an apparent azimuthal order that provides a good indication of the actual and m. Such a straightforward interpretation is also possible when sin i < 1, and when multiple sectoral modes are present. For tesseral modes may correspond more closely to than to m.
Interpretations of Solar Oscillations
Authors: Cox Arthur N. 
Published: June 2019

AbstractThe current theoretical status of understanding solar oscillations is reviewed. Interpretation of the thousands of well-determined frequencies refines our knowledge of the composition and convection structure of the Sun, since its mass, radius, luminosity, and age are better known from other sources. Recent issues that have been discussed are the solar center structure, bearing on the missing solar neutrino problem, the convection zone helium content, validating helium settling by diffusion, the variations of the oscillation frequencies over the solar cycle, indicating cyclical structure changes in the very outer magnetic layers, and the fine structure splittings of mode frequencies, revealing the internal rotation. Our ability to match observed frequencies to now within only a few microhertz has been enhanced by the recently improved MHD equation of state and the new Livermore OPAL opacities. Thus solar oscillations not only reveal solar structure data, but also they guide improvements for stellar astrophysics material properties. A new discussion of current investigations of the convection zone helium abundance and its depth is presented.
New Opacities and the Beta Cephei Stars
Authors: Balona L.A. 
Published: June 2019

AbstractThe recent revision of metal opacities has opened up the possibility that the long-sought mechanism for driving pulsations in these stars has at last, been found. This hypothesis makes a testable prediction — that noβCep variables should exist among metal-poor B-type stars. We report on the results of an intensive CCD monitoring campaign to test this prediction. The question of the pulsation mode ofβCep stars and the consequence of a revision of the absolute magnitudes to accommodate the fundamental radial mode among these stars is also discussed. Pulsational instability due to driving by ionization of metals has many other repercussions for the incidence of pulsation among the B-type stars. A classification scheme for other intrinsically variable B-type stars is suggested. It is shown that if, as generally supposed, pulsation is common among B-type stars then at least two different mechanisms must be in operation.
Did Beta Canis Majoris Quit Pulsating?
Authors: Odell Andrew P. , Watson Robert D. 
Published: June 2019

AbstractThe star β CMa, prototype of the β CMa variables, is known to have been a double mode pulsator since the beginning of the century, with amplitudes of 12 and 7 km/sec for the 6.00 and 6.03 hour oscillations (Shobbrook, 1973). Recently, Dziembowski, Moskalik, and Pamyatnykh (1992) have produced models of B stars using OPAL opacities which have many radial and non-radial modes unstable. As only a few modes are observed in these stars, these authors suggest that modes might change amplitude in such a way that modes can appear, disappear, or be replaced by other modes. Based on unsubstantiated rumour that β CMa had, like α Vir, quit pulsating (Pesnell, priv. comm.), we undertook observations with the Mt. John University Observatory (New Zealand) echelle spectrograph and CCD camera on the 1-m McLelland telescope. We found that β CMa is still pulsating, but with reduced amplitude and substantial period change compared with earlier data.In particular, quadratic ephemerides fit to all known times of spectroscopic maxima agree with our times of maxima [P1: HJD 2448611.8436; P2: HJD 2448611.8278] to better than two minutes, but an earlier linear ephemeris by Chappelier (1985) disagrees by over two hours. Our data is best fit with amplitudes of about 7 km/sec for both modes-this gives a nominal beat amplitude of nearly zero at the 49-day beat minimum (at a time when the linear ephemeris would have predicted a maximum amplitude). This may be the cause of the rumour mentioned above. Additional support for our conclusion of continuing pulsation comes from the fact that obvious line profile changes occur on the pulsation time scale.
An Extraordinary Early-Type Eclipsing Binary
Authors: Balona L.A. , Cuypers J. 
Published: June 2019

HR 2680 (B5V) was used as a comparison star in a multi-site (ESO & SAAO) campaign organised in 1988 to observe Be stars. We found that the star is an eclipsing binary with a period of 8.1 days. The eclipse is partial with a depth of 0.18 mag. Radial velocity observations confirmed the period.A light variation with an amplitude of as much as 0.03 mag was seen outside the eclipse (Fig. 1). This variation can be interpreted as two oscillations with approximate periods of 1.19 and 1.28 days. Further photometric observations were obtained in 1989, 1990 and 1991 at SAAO. The multiperiodicity was confirmed, but the periods were not constant from season to season.We suspect that the star is a pulsator of the 53 Per class of line-profile variables. Being an eclipsing binary, this unique system is of potentially great importance as a test bed for stellar dynamics and nonradial pulsations.
Pulsation Properties of Hydrodynamic Models with Dimensional Analysis
Authors: Aikawa Toshiki 
Published: June 2019

AbstractWe demonstrate that the dimension deduced from time series data of hydro-dynamic models for chaotic pulsation is a function of luminosity. The dimension is proposed as a good quantity to guess stellar parameters and the physics of stellar envelopes like as the pulsation periods and light curve shapes used for regular variables.
The Evolution of Hα Profiles in S-type Mira Stars
Authors: Woodsworth A.W. 
Published: June 2019

Past attempts to model the Hα emission profiles from Mira stars have been hampered by the strong absorption bands produced by TiO (M-type Miras) or carbon-based molecules (C-type Miras). The S-type Miras, however, exhibit relatively clean emission lines. As part of a larger study of Mira variables, I have obtained a series of high-dispersion Hα profiles of S-type Miras at different phases, using the DAO 48” coudé spectrograph. Although most profiles were obtained from different stars, their shapes develop in a regular way with advancing phase, so it appears that the observations can be used together to provide a good data base for the fitting of evolutionary (rather than static) models for the shock waves in S-type Miras.Initial experiments with fitting simple models to the profiles have been extremely encouraging. The profiles can be represented very well by three Gaussian components.
OPAL Opacities
Authors: Rogers F. J. , Iglesias C. A. 
Published: June 2019

AbstractWe have continued to improve and update the OPAL opacity code. Addition of intermediate coupling has further increased the opacity over earlier LS coupling results. A ‘corresponding states’ method has been used to extend the tables in both X and Z. This has allowed the calculation and distribution of extensive opacity tables for several different sets of metal abundance.
Convection in RR Lyrae Stars
Authors: Stellingwerf R. F. , Bono G. 
Published: June 2019

AbstractConvection undoubtedly plays a strong role in defining the RR Lyrae instability strip, but its effects on amplitude, mode of pulsation, and light curve have always been problematical. One reason is simply that convective models are difficult to compute, and their accuracy is difficult to ascertain. We present results of a new convective survey of RR Lyrae stars that constitute the best models available at this time, with better boundary conditions, physics, zoning, and length of computational run than previous results.
Modelling Cepheids and RR Lyrae Stars
Authors: Kovács G. 
Published: June 2019

AbstractWe review the recent nonlinear hydrodynamical results and the numerical problems to be solved by the next generation of codes. The behavior of the Fourier parameters and double-mode RR Lyrae pulsation will be discussed in detail. We emphasize the importance of the implementation of the various adaptive-mesh schemes for stellar pulsations. A further goal is the substitution of the artificial viscosity with modern shock capturing methods and a better treatment of radiative transfer. Convection however, must ultimately be included in order to supply the necessary physical mechanism for dissipation.
Theoretical Implications of Triple-Mode RR Lyrae Pulsations
Authors: Kovács G. , Buchler J. R. 
Published: June 2019

AbstractWe argue that triple-mode RR Lyrae pulsation with low amplitudes might be quite common. It is shown that until very accurate abundance data become available, triple-mode RR Lyrae stars are the only hope to estimate reliable stellar parameters from the periods alone.