bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rotational Instabilities and Stellar Evolution
Authors: Zahn Jean-Paul 
Published: June 2019

This review deals with the local instabilities arising when the effects of rotation are taken into account in the evolution of a non-magnetic star.The Rayleigh and shear instabilities will be examined under the conditions prevailing in radiative zones where the effect of density stratification, thermal diffusion, viscosity and varying chemical composition must be taken into account. The possible consequences on the evolution of a star are finally outlined.
Are Solar P Modes Correlated?
Authors: Foglizzo T. , Garcí R.A. ,   The GOLF Team
Published: June 2019

We have studied the statistical properties of the energy of individual p modes, extracted from 310 days of GOLF data near the solar minimum. The exponential distribution of the energy of each mode is clearly seen. The modes are found to be uncorrelated with a ±0.6% accuracy, thus supporting the hypothesis of stochastic excitation by the solar convection.The same analysis performed on the same modes just before the solar maximum, using IPHIR data, rejects the hypothesis of no correlation at a 99.3% confidence level. A simple model suggests that 31.3 ± 9.4% of the energy of each mode is coherent among the modes studied in IPHIR data, corresponding to a mean correlation of 10.7 ± 5.9%.
Velocity dispersion and the stability of galactic disks
Authors: Kormendy John 
Published: June 2019

This paper estimates the effect of the stellar velocity dispersion on local and global instabilities in galaxy disks. Measurements of rotation velocities and velocity dispersions are illustrated for the disks of NGC 488 (Illingworth and Kormendy, in preparation), NGC 936 and NGC 1553. These are used to derive the Toomre stability parameter Q, i.e. the ratio of the observed dispersion to that needed for marginal stability against local modes. In both NGC 488 and 1553, Q = 2.5 − 4, depending on the assumed mass-to-light ratio. These values larger than 2 imply that the stellar disks are stable, although the gas in NGC 488 may remain unstable. This is consistent with the observation that both galaxies largely lack coherent spiral structure: NGC 1553 is an SO and NGC 488 a flocculent spiral. The SBO galaxy NGC 936 is more extreme: Q = 5 (estimated error is a factor of two). This is consistent with Sellwood's suggestion that a bar heats the disk until it is too hot to support spiral structure. In contrast to the above galaxies, Toomre has shown that our Galaxy has Q = 1.6 ± 0.5 near the Sun. It is therefore responsive enough to make spiral structure, as observed.We also explore the stellar kinematics of the disk of NGC 1553 as a function of radius. The exceptionally strong lens component in this galaxy is very hot. At half of the radius of the lens the velocity dispersion appears to be large enough to have an effect even on global stability.
IV / Village Pattern and Architecture
Authors: Wheat Joe Ben 
Published: June 2019

Having briefly considered the location, environment, and layout of the various Mogollon villages, we may now analyze them to determine whether or not they follow a pattern.In their choice of village sites, it is clear that, with few exceptions, the Mogollon chose places of some elevation and isolation. Twelve of 2I4. villages were located on a mesa, a bluff, or a ridge; 10 others occupied terraces well above valley bottoms; and one was situated on the outwash fan of nearby mountains. Only one was located in a valley bottom. Furthermore, Danson. (1952) found in his survey that the early people built their villages on mesas or isolated ridges well back from the main stream of travel. Without exception, sites were located in mountainous country or near to mountains. Whether by preference or for some other reason, it was in the mountain country that the Mogollon people had their ecological niche. Many sites lie in secluded valleys on tributary streams; but except, perhaps, in the northernmost sites, the availability of agricultural land seems to have been one of the deciding factors in selecting a village site.
Material Culture
Authors: Jennings Jesse D. 
Published: June 2019

Before outlining this section concerned with material culture I should perhaps try to be explicit about the philosophy which guides me in archeological matters. It is my conviction that archeological work does not transcend antiquarianism (a legitimate and justifiable occupation) unless the specimens and the observational data are regarded as reflecting some cultural situation. For me a continuing circular preoccupation with artifacts is sterile. The only excuse for excavation, it seems, is that ever-present hope that by means of archeological search we can catch a meaningful glimpse of, or a series of moments in, a once dynamic living culture. In this interest, of course, I am not alone.It seems to me we are interested in archeological specimens because we are in reality, and at some distance, and often obscurely, working with a way of life, for which the observed relationships and the artifacts are the meager documentation. One freely admits that the archeological record is very incomplete; it is, moreover, heavily weighted towards the material things.
Variable Star Research by the PLANET Collaboration
Authors: Albrow Michael D. , Pollard K. R. , Beaulieu J.-P. , Caldwell J. A. R. , Menzies J. , Vermaak P. , DePoy D. L. , Gaudi B. S. , Gould A. , Pogge R. W. , Dominik M. , Naber R. M. , Sackett P. D. , Greenhill J. , Hill K. , Kane S. , Watson R. , Martin R. , Williams A. , Sahu K. C. ,   The PLANET collaboration
Published: June 2019

AbstractWe review the current status and future prospects of the PLANET collaboration, an international team of astronomers performing high-precision photometric monitoring of microlensing events. Our photometric precision and sampling is characterised and the suitability of the database for variable star studies is discussed. Preliminary results on K-giant stability are presented.
Prospects of Variable Star Research by Future Space Missions
Authors: Eyer Laurent 
Published: June 2019

AbstractESA and NASA are studying projects having a tremendous return on variable star research. Other national space agencies are also studying or developing projects of smaller costs but with impressive returns. The projects range from global Galactic surveys like the ESA mission GAIA which will give photometric time series for about 1 billion stars, to detailed pulsation-mode studies like the CNES mission COROT which could reach a photometric precision lower than 1 ppm. The presentation will emphasize the future astrometric, asteroseismological and planet detection missions.
COROT – A Unique Database for Low Amplitude Variability Between 1 Minute and 150 Days
Authors: Michel E. , Baglin A. , Barge P. , Catala C. , Auvergne M. , Weiss W. W. , Appourchaux T. , Garrido R. ,   the COROT Team
Published: June 2019

AbstractCOROT is a high precision wide field photometry experiment from space, funded in the framework of the CNES “Petites Missions” program (the PI is A. Baglin). It will observe approximately 30000 objects with mV between 4.5 and 15.5 over long observational periods (up to 150 d), with a time sampling between 1 s and 16 min, a precision of the order of 10−4 per measurement. The scientific objectives are stellar seismology and the search for telluric planets. The instrument and the core program have already been presented in several places. We here focus on a description of the characteristics of the data to be obtained with COROT. The large amount of high quality data collected by COROT will constitute rich material for several research programs beyond the core program as already defined (http://www.astrsp-mrs.fr/www/corot.html). A call for proposal of additional programs will be made during Northern Spring 2000.
Nonlinear Pulsations of Luminous Blue Variables
Authors: Dorfl Ernst A. , Feuchtinger Michael U. , Gautschy Alfred 
Published: June 2019

AbstractWe present the results of various nonlinear radial pulsation calculations of LBVs with different luminosity to mass ratios. Depending on the stellar parameters, most of these objects undergo strongly non-adiabatic pulsations which can also modify their stellar atmospheres. In some cases part of the kinetic energy of the motions is transferred by shock waves into the atmospheric layers leading to an overall decrease or increase of the stellar radius. This results in different mean density accompanied by a change of the pulsational behavior which can be compared to the results of a linear stability analysis. We also find that regular pulsations can occur around a different equilibrium than the initial configuration which has been determined by stellar evolution calculations. In cases of even higher luminosity to mass ratios the linear stability analysis predicts several unstable modes and the nonlinear computations can exhibit rather irregular light curves. Due to the large non-adiabaticity of the pulsation the corresponding velocity curves still remain more regular, but show increasing amplitudes until the energy stored is released. The pulsations are far from equilibrium conditions and may also lead to a pulsationally driven mass loss for certain stellar parameters.
Photometry of R Coronae Borealis Stars during the Recovery Phases of Their Declines
Authors: Skuljan Ljiljana , Cottrell Peter L. 
Published: June 2019

AbstractR Coronae Borealis (RCB) stars are a rare class of variable stars, well-known by their declines, but still posing two fundamental questions: what is the origin and what is the nature of their unpredictable minima? Possible contributions to the answering of these questions could use large-scale surveys, by discovering new RCB stars. In addition, photometric databases from these surveys and other long-term photometric programs of targeted stars can be used to compile information about these decline phases.The photometric observations (UBVRI) of nine cool RCB stars have been collected at Mt John University Observatory, New Zealand, for the last ten years. Analysis of the magnitude–color diagrams for the recovery phase of a number of declines of these stars has been made in order to determine the extinction properties of the dust. The photometric magnitudes and colors show significant changes during the RCB declines. The asymptotic approach to the normal brightness can be seen on the magnitude–color diagrams from the recovery phase. This is observed for all RCB declines, and without exception is independent of their decline amplitude. According to the most acceptable theory, the distribution of the dust matter in the cloud which causes the light fading can be considered uniform as the stars recover to the maximum brightness. The slopes of the magnitude–color and color–color diagrams from the recovery phase of 26 observed RCB declines have been used in order to define the normalized extinction quantity Aλ/AV. Although the extinction curve in the UBVRI region is not a good indicator of the type and size of the particles, our data show that the material causing the RCB declines has extinction properties similar to that for the interstellar medium. The reddening parameter (RBV = AV/E(B – V)) for the RCB stars in our sample is in the range 2.5 to 4.6, similar to the interstellar dust. Observations have been compared with the theoretical extinction curves for different sorts of grains. The extinction properties in the U region follow the trend of the UV data from other RCB observations as well as laboratory data for amorphous carbon.
Changes of the Physical State in Semiregular Variables
Authors: Kiss L. L. , Szabó Gy. , Szatmáry K. , Mattei J. A. 
Published: June 2019

AbstractWe present a progress report on a detailed analysis of long-term (70–90 years) visual observations for seven semiregular variables. Fundamental changes of the physical state (amplitude and/or frequency modulations, mode change and switching) are studied with conventional Fourier- and wavelet analyses. Besides two examples of repetitive mode changes we report a simple geometric model of a rotationally induced amplitude modulation in RY Ursae Majoris.
Unusual Secondary Variations in the Mira Star T Cep
Authors: Marsakova Vladislava I. , Andronov Ivan L. 
Published: June 2019

AbstractCyclic period variations (P ≈ 19400d) in T Cep were investigated. As the result of cross-correlation analysis, relations between individual cycle parameters were found. Relations between period–amplitude, hump–amplitude, hump–minimum magnitude, and others have been obtained.
Baade–Wesselink Analysis of Magellanic Cloud Cepheids
Authors: Storm Jesper , Carney Bruce W. , Gieren Wolfgang P. , Fouqué Pascal , Fry Anne M. 
Published: June 2019

AbstractWe apply the Barnes–Evans variant of the Baade–Wesselink method to Cepheids in the LMC and SMC in an attempt to determine the distance directly to individual stars in these galaxies and to determine the metallicity effect on the Cepheid period–luminosity relation. We now haveK-band light curves for a sample of SMC stars as well as for many Cepheids in young clusters in the LMC. Using theFV, (V–K) calibration of Fouqué & Gieren (1997) we find preliminary evidence for a metallicity effect which makes metal poor Cepheids brighter. This is at odds with earlier results based on optical photometry and the reason is not entirely understood yet.
A Synoptic Variability Survey of M3
Authors: Szentgyorgyi Andrew , Stanek Krzysztof Z. , Sasselov Dimitar , Kaluzny Janusz , Schwarzenberg-Czerny Aleksander 
Published: June 2019

AbstractWe present preliminary results from a synoptic photometric variability survey of the galactic globular cluster M3. These data consist of between 9 and 13 nights of data, the sampling allows a minimum detectable period of 10 minutes and is complete to MV ~ 21.
Numerical Simulations of the Cepheid Population in the Hipparcos Catalogue
Authors: Groenewegen M. A. T. 
Published: June 2019

AbstractThe population of Cepheids in the Hipparcos catalogue is retrieved. Some observational properties of the sample are modelled using a. Monte Carlo code. This code is then used to verify that the bias introduced by the method of “reduced parallax” in deriving the zero point of the P–L relation is of order 0.01 mag, confirming earlier results. This bias is likely due to Malmquist bias.
Theoretical Distribution of Cepheid Periods in the SMC and LMC
Authors: Alibert Yann , Baraffe Isabelle 
Published: June 2019

AbstractWe have computed stellar evolutionary models for stars in a mass range characteristic of Cepheid variables for metallicities representative of the Magellanic Clouds populations. These calculations are coupled to a linear non-adiabatic stability analysis in order to get self-consistent mass-period-luminosity relationships. We construct period histograms taking into account a mass function and evolutionary time scales, and we compare them to those given by the microlensing surveys EROSl and OGLE.
Revised Empirical Formulae for the Absolute Magnitudes and Intrinsic Colors of RRab Stars
Authors: Walker A. R. , Kovács G. 
Published: June 2019

AbstractThe relations between the physical parameters of the RRab stars and the Fourier parameters of their light curves have been reanalyzed on the basis of new CCD data. We show that the absolute magnitude MV and the dereddened color indices (B − V)0, (V − I)0 are linear functions of the period and of the A1 Fourier amplitude of the V light curve. Due to the large datasets, we are able to test the consistency of the formulae on independent sets. The present results are in good or fair agreement with our previous studies, despite the fewer number of significant parameters entering in the revised formulae.
Fourier Coefficients of OGLE Variables
Authors: Morgan Siobahn , Simet Melanie , Bargenquast Stephanie , Dickerson Chris 
Published: June 2019

AbstractFourier coefficients for the variable stars in the OGLE survey of the Galactic Center and several globular clusters are presented. The characteristics of the RR Lyrae, δ Scuti and SX Phe stars are presented and a comparison to those observed in other studies is made. In some cases the coefficients of the stars can be used to determine distances and the physical characteristics of the variables.
AH Cam: An RR Lyr (Double Mode?) Star with Blazhko Effect
Authors: Garrido Rafael , Kim Seung-Lee , Yi Jonghyuk , Lee Bo-Won , Bossi Michele 
Published: June 2019

AbstractWe report here the discovery of a new frequency not belonging to the Blazhko series and suggest an interpretation based on coupling between a radial and a nonradial mode from multicolor observations.
Any Recent Progress in the Theory of Pulsating Stars?
Authors: Gautschy Alfred 
Published: June 2019

AbstractTo answer the topical question we survey synoptically the recent literature in pulsation theory. We restrict the topics to those which are not dealt with otherwise in this volume. We address research on roAp stars, EC 14026 variables, strange modes, luminous blue variables, pulsation-rotation coupling, and pulsations in compact objects seen from the classical, as well as the relativistic, viewpoint.
Nonlinear Survey of RRd Models
Authors: Szabó R. , Kolláth Z. , Csubry Z. , Buchler J. R. 
Published: June 2019

AbstractWe used our nonlinear hydrodynamical code with turbulent convection to model RR Lyrae stars. In some regime this approach produces double-mode solutions. We investigated series of models with different parameters (metallicity, luminosity, etc.). Our goal was to estimate the width of the double-mode region. The resulting tendencies can be directly compared with observational properties.
Influence of a Close Companion on the Variability of a Mira-Type Star
Authors: Rudnitskij G. M. 
Published: June 2019

AbstractThe effects of a low-mass companion (a planet?) revolving around a red giant at a short distance (inside its circumstellar envelope) are discussed. Calculations are given for a conical shock wave, induced by the orbital motion of the companion. Consequences for the stellar spectrum and light curve are derived, and predictions for the evolution of such a system are made.
Magnetic Oscillations in Radiative Stars
Authors: Zita E. J. 
Published: June 2019

AbstractWhat drives acoustic modes in magnetic, radiative stars, such as the rapidly oscillating Ap (roAp) stars? We propose that oscillations in the shape of the magnetic field can drive magnetosonic waves, which are observed as p modes. The force-free atmosphere minimizes magnetic energy. If the field is strong enough, the magnetic configuration can oscillate about its equilibrium state. Initial calculations showed that the wavenumbers, frequencies, and available energy are consistent with observations of roAp stars (Zita 1997). We present the results of new calculations and proposed tests of our model. We also discuss the resultant <υ×b> dynamo, which may shed light on observations in B stars.
New γ Doradus Stars from the Hipparcos Mission and Geneva Photometry
Authors: Eyer Laurent , Aerts Conny 
Published: June 2019

AbstractA search for new γ Dor stars was undertaken using the Hipparcos periodic variable star catalogue and the Geneva photometric database, leading to a list of 40 new candidates. We started a monitoring of the candidates which suited the observational window with the CORALIE spectrograph at the Swiss Euler Telescope for establishing a robust list of new γ Dor stars and studying line profile variations. We present here our long-term program.
The STACC 1998 Campaign on Praesepe: The Spectroscopy
Authors: Dall Thomas H. 
Published: June 2019

AbstractThe STACC campaign of 1998 on BN Cnc was an extensive international photometric campaign aimed at obtaining accurate frequencies of the pulsations in this star. To facilitate identification of the modes, parallel spectroscopic observations were made from six observatories around the world. I here present preliminary results from the spectroscopy made from the Nordic Optical Telescope. The accurate frequencies from the photometric campaign are used to obtain accurate amplitudes of the equivalent width variations. These results are to be used in an attempt to identify the pulsation modes in this star.
Period Variations and Binary Hypotheses of Three δ Scuti stars: CY Aqr, BS Aqr, AD CMi
Authors: Fu Jian Ning 
Published: June 2019

AbstractSome new times of light maxima for three δ Scuti stars – CY Aqr, BS Aqr and AD CMi – have been determined based on new photoelectric photometry. Incorporated with the times presented in the literature, the O–C method is used to study the period variations of these stars with a newly-developed program OMC. The results reveal that for these three stars, the binary hypothesis concerning a low mass companion is reasonable in explaining the O–C diagrams.
Radial Velocity Studies of Pulsations in roAp Stars: γ Equ Revisited
Authors: Kanaan A. , Hatzes A. P. , Mkrtichian D. 
Published: June 2019

We have used the 2D-Coudé spectrograph of the 2.7-m telescope at McDonald Observatory at a resolution of 60,000. We use an iodine cell which provides us with permanent wavelength reference.γ Equ was observed for a period of approximately 6 hours. The signal to noise ratio was variable due to the presence of clouds. A typical value for the “good” spectra is 80.The use of a large detector provides us with complete spectral coverage from 5,000 to 6,000 Å (the region where I2 lines are most visible and useful as a wavelength reference). This allowed us to expand over our previous work analyzing the pulsations of γ Equulei through the use of spectroscopy.
Time-Series Spectroscopy of EC 14026 Stars: Preliminary Results
Authors: O’Toole Simon J. , Teixeira Teresa C. , Bedding Timothy R. , Kjeldsen Hans 
Published: June 2019

AbstractWe have obtained time-series spectra for the pulsating hot subdwarf (sdB) PG1605+072. Previous time-series photometry of this star has shown maximum amplitude variations of ∼0.1 mag and at least 50 periods. The pulsator has the largest amplitude and longest periods of all the pulsating sdBs (or EC 14026 stars) discovered so far, and appears to be unusual in its class. Preliminary results of a search for velocity variations are presented here. With these variations, along with equivalent width measurements, oscillation mode identification should be possible.
Search For Cool White Dwarf Pulsators
Authors: Nitta Atsuko , Mukadam A. , Winget D. E. , Kanaan A. , Kleinman S. J. , Kepler S. O. , Montgomery M. H. 
Published: June 2019

AbstractWe are searching for pulsations in cool (< 6000 K) white dwarfs (WDs), hoping to apply asteroseismological techniques to improve our understanding of their structure and the physical processes inside them. This information is important as we use cool WDs to estimate the lower limit of the age of the Galactic disk. Within a spectroscopic and photometric survey of 110 cool WDs by Bergeron, Ruiz, & Legget, we find 28 candidates with appropriate effective temperatures, masses, and chemical compositions for possible pulsations in nonradial g modes with periods similar to those we observe in DAVs. So far, we have observed 4 candidates, but have found no evidence of large variation.