bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies of Mira and Semiregular Variables Using Visual Databases
Authors: Bedding T. R. , Conn B. C. , Zijlstra A. A. 
Published: June 2019

AbstractWe used wavelets to investigate period and amplitude changes in Mira and semiregular variables and found a variety of behaviours. Period and amplitude changes often go together, perhaps because changes in amplitude are causing period changes via nonlinear effects.
On the Pulsation Properties of Red Supergiant Variables
Authors: Bono Giuseppe , Panagia Nino 
Published: June 2019

AbstractWe present the preliminary results of a detailed theoretical investigation on the pulsation properties and modal stability of red supergiant (RSG) stars at solar chemical composition and for stellar masses ranging from 10 to 20 M⊙. We find that the main parameter governing their pulsation behavior is the effective temperature, and indeed when moving from the blue edge toward lower effective temperatures the models show an increase in the pulsation amplitudes. For temperatures cooler than 3800 K the pulsation amplitudes are still large but the radial displacements become aperiodic.
New R Coronae Borealis Stars in the LMC Discovered in the MACHO Photometry Database
Authors: Clayton Geoffrey C. , Kilkenny D. , Welch D. L. ,   The MACHO Collaboration
Published: June 2019

AbstractAn extensive search has been made in the MACHO photometry database for new R Coronae Borealis (RCB) stars in the LMC. Only three such stars were known previously. Nine new LMC RCB stars have been spectroscopically confirmed so far.
Cepheids from the EROS-2 Microlensing Survey
Authors: Beaulieu Jean-Philippe , Marquette Jean-Baptiste 
Published: June 2019

AbstractUsing observations obtained in the pilot campaign of the EROS-2 microlensing survey we observed 290 Cepheids towards the LMC and 590 Cepheids towards the SMC. We present the constraints they give to stellar pulsation theory. We detect a statistically significant break in the slope of the period–luminosity relation for SMC fundamental mode Cepheids with periods shorter than 2 d and discuss its origin.
An Analysis of Cepheid Distances Using Bayesian Statistics
Authors: Barnes Thomas G. , Jefferys William H. 
Published: June 2019

We have applied an approximately Bayesian and a fully Bayesian analysis to the calculation of Cepheid distances, radii and absolute magnitudes using the surface brightness (Baade–Wesselink) method. Both methods successfully account for errors in the data, provide unbiased distance estimates, and provide objective model selection for the radial velocity curve. In addition, the fully Bayesian analysis objectively selects a model for the magnitude curve; averages over models of various Fourier orders, properly weighted by the posterior probabilities of the individual models; and includes a Lutz–Kelker correction.The approximately Bayesian method is that described by Jefferys & Barnes (1999) and Barnes & Jefferys (1999). It is a maximum likelihood approach with objective selection of the order of the Fourier series model of the radial velocities.
The Cepheid Distance to NGC 4414
Authors: Thim Frank 
Published: June 2019

AbstractA search for Cepheids in NGC 4414 has been performed using HST archive data. Accurate photometry for this galaxy is challenging due to its high surface brightness background with steep gradients and the rather low S/N of stellar point sources. The photometry package ROMAFOT has been used, and the results compare favorably with published photometry reported by Turner et al. (1998). All eleven Cepheids were recovered and nine additional candidates were discovered. The resulting distance modulus of 31ṃ50±0ṃ27 is only 0ṃ1 larger than previously reported.
Critical Complements: Progress on the Orbit of T Mon
Authors: Evans N. R. , Carpenter K. , Robinson R. , Massa D. , Wahlgren G. M. , Vinkó J. , Szabados L. 
Published: June 2019

AbstractA preliminary orbit has been derived for the high luminosity, 27-d classical Cepheid T Mon. Velocities for the hot companion have been measured from an HST GHRS spectrum and 3 IUE spectra. The companion velocities are inconsistent with binary orbital motion and it is likely that the companion is itself a short period binary. The HST spectrum also shows that the companion is a chemically peculiar star, probably magnetic.
ω Centauri – a Laboratory for Critical Tests of Stellar Structure and Evolution
Authors: Freyhammer L. M. , Petersen J. O. , Andersen M. I. 
Published: June 2019

AbstractPreliminary results are reported for a monitoring program on ω Cen. We search for multi-mode SX Phe stars and changes in pulsation parameters of the cluster variables in order to test models of stellar evolution. With a periodogram for 10,000 light curves, we estimate that ω Cen hosts several hundred SX Phe stars.
Variable Stars in the Metal-Rich Globular Clusters NGC 6388 and NGC 6441
Authors: Pritzl Barton , Smith Horace A. , Catelan Márcio , Sweigart Allen V. 
Published: June 2019

AbstractNew observations show that RR Lyrae stars in the metal-rich globular clusters NGC 6388 and NGC 6441 have unusually long periods, which indicate that the horizontal branches of these clusters are unusually bright for their metallicities, as predicted by Sweigart & Catelan (1998).
The Oblique Pulsator Model for the Blazhko Effect in RR Lyrae Stars. Theory of Amplitude Modulation I
Authors: Shibahashi Hiromoto 
Published: June 2019

AbstractBy assuming that RR Lyrae stars have fairly strong dipole magnetic fields with symmetry axis oblique to the rotation axis of the star, I show that the oscillation mode which would be a pure radial oscillation in absence of the magnetic field has a quadrupole component, whose symmetry axis coincides with the magnetic axis. The aspect angle of the quadrupole component changes due to the stellar rotation, and this apparent amplitude variation is interpreted as the Blazhko effect in RR Lyrae stars. It is shown that, in the case of off-axis magnetic field, phase modulation is expected. I list up some theoretical predictions based on this model, which would observationally examine this hypothesis.
Long-Term Photometric and Spectroscopic Monitoring of Slowly Pulsating B Stars
Authors: Aerts C. , De Cat P. , De Ridder J. , Kolenberg K. , Waelkens C. , Mathias P. , Briquet M. 
Published: June 2019

AbstractWe review the current status of our long-term monitoring project on slowly pulsating B stars that we started in the course of 1996 and that was recently completed as far as the first part of our plan is concerned. In total, we have selected 17 southern and 8 northern stars. The idea is to fully exploit our current data in the near future and to select the most interesting targets for further very-long-term follow-up monitoring. A first conclusion is that half of the southern targets turn out to be spectroscopic binaries. Some of these have circular orbits and periods of the same order of magnitude as the intrinsic pulsation period(s) of the primary. The eccentric binaries have periods ranging from 12 to 460 d. For most stars the photometric behaviour is dominated by the same frequency as the intrinsic spectroscopic variability. Multiperiodicity in the expected frequency range is found for almost all stars. Two objects, however, turn out to have only one dominant pulsation mode.
Binary Slowly Pulsating B Stars
Authors: De Cat P. , Aerts C. 
Published: June 2019

AbstractThe satellite Hipparcos led to the discovery of 267 new variable B-type stars. Some 100 of them were classified as candidate slowly pulsating B stars (SPBs) by Waelkens et al. (1998). Twelve of the brightest southern candidate SPBs were selected together with 5 confirmed SPBs to start a long-term follow-up study (Aerts et al. 1999). From 1996 up to 1998, numerous high-resolution, high signal-to-noise spectra were taken with the CAT/CES combination at La Silla in order to study the line profile variations of the Si II-doublet centered at 4130 Å.We report our finding that at least 8 of 17 targets turn out to be spectroscopic binaries. We have found a large variety in the obtained orbits. HD 123515 and HD 140873 were known as single-lined spectroscopic binaries, but both turn out to be double-lined. All the others binaries are single-lined. For HD 140873 and HD 177863, we find orbits with large eccentricities of respectively e = 0.731 α 0.006 and e = 0.603 α 0.007. HD 69144, HD 92287 and HD 169978 are three binaries with circular orbits and very short orbital periods (a few days). Since their photometric measurements are dominated by (close to) sinusoidal variations with twice the orbital frequency, these stars are ellipsoidal variables. Their orbital periods are of the same order of magnitude as the expected periods of pulsation.After removing the orbit, we find the same first frequency in the residual radial velocities as in the gathered photometric measurements for 6 stars. For HD 69144 and HD 169978 we did not yet succeed in deriving an intrinsic period, although HD 69144 has prominent line profile variations. For HD 169978, we have serious doubts about the SPB nature.For a detailed description, we refer to De Cat et al. (1999).
Z-bump Pulsations in Helium Stars
Authors: Jeffery C. Simon , Saio Hideyuki 
Published: June 2019

AbstractRadial and nonradial pulsations are excited in low-mass helium stars with effective temperatures between 7000 and 35000 K. In the case of the most luminous stars, these are driven by strange-mode instabilities (Saio & Jeffery 1988). Less luminous helium stars are mostly non-variable, except around 25000 K. V652Her is the prototype radially pulsating helium star, with Teff ~ 25000 K and a pulsation period of 0ḍ08 (Hill et al. 1981). The pulsation was only understood to be driven by the K-mechanism with the introduction of Z-bump opacity (Saio 1993).The importance of Z-bump instability in low-mass helium stars has been investigated further through a series of pulsation models (Jeffery & Saio 1999a). It is shown that Z-bump pulsations can persist to surprisingly high hydrogen abundances in low-mass stars, and may consequently be excited in several helium-rich hot subdwarfs with Teff ~ 25000 K. Within the Z-bump instability region, both radial and nonradial pulsations are excited, and multi-periodic variability is expected.Pulsation properties are closely linked to the global dimensions of a pulsating star by the period – mean density relation. When spectroscopic measurements are also available, the twin constraints of period and surface gravity can place very tight limits on the stellar radius (Jeffery & Saio 1999b). These are in excellent agreement with independent measurements for V652 Her and place a lower limit on the mass of the recently discovered Z-bump pulsator BXCir (Kilkenny et al. 1999).
Do Herbig Ae Stars Pulsate?
Authors: Marconi M. , Ripepi V. , Alcalá J. , Covino E. , Terranegra L. , Palla F. 
Published: June 2019

AbstractWe present some preliminary results of a Strömgren photometric survey searching for radially pulsating variables among Herbig Ae stars. These young objects are expected to show a characteristic δ Scuti variability when entering the instability strip along their pre-main sequence evolutionary tracks, according to the theoretical predictions by Marconi & Palla (1998). We identified at least five pulsating Herbig Ae stars with periods in the expected range. On the basis of these encouraging first results, we foresee both new more detailed observations and accurate comparisons with theoretical models.
Spectroscopic Survey of Rapidly Oscillating Ap Stars
Authors: Weiss W. W. , Ryabchikova T. A. , Kupka F. , Lueftinger T. R. , Savanov I. S. , Malanushenko V. P. 
Published: June 2019

AbstractA spectroscopic survey of roAp stars has been initiated in Vienna in order to determine their fundamental astrophysical parameters and abundances. We report here on our attempt to confirm and elaborate an atmospheric peculiarity recently discovered (Ryabchikova et al. 1999) which should allow to identify roAp stars with a single spectrum.
Pulsation among Λ Bootis Stars
Authors: Weiss Werner W. , Paunzen Ernst , Pamyatnykh A. , Mkrtichian D. 
Published: June 2019

AbstractWe report on the pulsation characteristics of λ Bootis stars as a result of a survey initiated to increase the number of known λ Bootis stars and to improve the definition of this group of peculiar stars.
1995-1998 Large-Scale Campaigns on Λ Boo Star 29 Cygni
Authors: Mkrtichian D. E. , Kusakin A. V. , Koval V. A. , Akan M. C. , Ibanoglu C. , Paunzen E. , Weiss W. W. , de Coca P. Lopez , Rolland A. , Costa V. , Olivares J. I. , Hobart M. A. , Hatzes A. P. , Malanushenko V. P. , Devlen A. , Ozturk A. , Paparó M. , Krisciunas K. , Percy J. , Thompson S. , Handle G. , Burnashev V. I. , Movchan A. I. 
Published: June 2019

AbstractWe present the main results of a photometric and spectroscopic study of the Λ Boo star 29 Cyg carried out from 1995 – 1998.
Frequency Stability of the Cooler Pulsating White Dwarfs
Authors: Sullivan D. J. 
Published: June 2019

AbstractAlthough the frequencies of the pulsating white dwarfs are extremely stable, the evolutionary cooling of these geometrically constrained objects should lead to an observable period change over a sufficiently long time base. Direct measurement of a period change rate for the cooler white dwarfs should provide fundamental data on the core composition of these stellar remnants, and hence their cooling time scales. Progress on attempts to measure the period change rates of two white dwarfs is reported.
Some Remarks on Stellar Pulsation
Authors: Gough Douglas 
Published: June 2019

AbstractI wondered at first why I had been asked to perform the task of commenting on the scientific discussion of this meeting, until a member of the Scientific Organising Committee pointed out to me that I have not published a serious paper on the subject of the colloquium in his memory (I am not sure whether this is more a statement of the seriousness of my publications, of my publication frequency or of the duration of Jørgen’s memory); however, I am presumably considered to be unbiased by recent advances. Nevertheless, the time allotted (for the oral address) and the corresponding space (in these published proceedings) are inadequate for a complete and balanced review – in any case, that is hardly either desirable or necessary, since the discussions are all still fresh in our minds – and therefore I have been freed to comment personally on some selected issues that have captured my interest.
Active Control for Michelson Stellar Interferometers
Authors: Hardy John W. , Wallner Edward P. 
Published: June 2019

AbstractThe effects of atmospheric turbulence on the image structure in a ground based Michelson Stellar Interferometer are analyzed. A complete system requires compensation both for the wavefront distortions over the collecting apertures and for path length differences between them. Wavefront sensing and compensation have been previously described and analyzed. In this paper, a method of path length compensation and estimation of the mutual coherence function of the source is developed using matched filters in multiple spectral bands. A practical implementation of the resulting system is described and estimates of its performance given.
The Limiting Sensitivity and Visibility Loss in a Small Aperture Amplitude Interferometer
Authors: Tango William J. 
Published: June 2019

AbstractWe analyze the behaviour of an amplitude interferometer with aperture diameters of the order of r0. A simple optical correlator can be used to measure the source coherence function, and the limiting magnitude is found to depend principally on the optical bandwidth. The basic instrument appears to have a limiting magnitude m = +8, but this can be improved by more elaborate correlators. The effects of atmospheric turbulence on such an interferometer can be substantially reduced by an active optical system which compensates for the wavefront tilts in the incident light, and it appears that the limiting magnitude of the interferometer, when atmospheric effects are taken into account, is around m = 7 - 8.
Observational Speckle Interferometry
Authors: Koechlin L. 
Published: June 2019

AbstractSpeckle interferometry techniques have improved appreciably during the past few years. Current progress to be reviewed includes: steps towards a fully digital analysis in the photon counting mode allowing for high resolution on faint astrophysical objects (i.e. quasars), practical prospects for phase recovery procedure, and the design of compact, self-contained interferometers for on-line results at remote sites.
Restoration Of Turbulence Degraded Images - A Review
Authors: Nisenson P , Stachnik R. V. 
Published: June 2019

AbstractThe success of speckle interferometry in recovering high resolution information from atmospheric turbulence degraded images has renewed interest in the restoration of images recorded through a turbulent medium. There are a number of different approaches to image restoration which have been proposed. The effectiveness of each of these techniques is strongly dependent on the brightness and the angular extent of the object being observed. This paper will attempt to summarize the areas of application of such techniques, the current state-of-the-art in this field, and the expected performance range of the various techniques.
Studies of the Ultraviolet Spectra of Wolf-Rayet Stars
Authors: Willis A. J. , Wilson R. 
Published: June 2019

New ultraviolet observations of nine Wolf-Rayet stars have been obtained with the S2/68 experiment of the ESRO satellite TD-1. These low resolution (Δλ ∼35Å) spectra have been studied yielding line identifications and strengths of the numerous emission lines observed in both WN and WC stars. The ultraviolet data are combined with complementary ground based photoelectric measurements to yield new estimates of the interstellar reddening corrections required. The combined ultraviolet and visible WR energy distributions, corrected for interstellar extinction, yield colour temperatures ∽30000 K for all nine stars. these temperatures are close to those derived from a Zanstra analysis of the He II 1640 Å line observed in emission in single WN and WC stars.the observed helium, carbon and nitrogen lines in the ultraviolet and visible spectra of four WR stars have been analysed using a non-LTE treatment and Escape Probability methods to determine the abundances of these species in the WR atmospheres. The analysis of low excitation carbon and nitrogen lines in the ultraviolet allows for the first time accurate abundances for these species to be determined. It is found that in the WC star studied the C/He and N/He ratios are close to the normal cosmic values. In the WN stars the N/He ratio is slightly higher than normal but the C/He ratio is much reduced. In both sequences the H/He ratio is very low. Thus it appears that the carbon abundance is the controlling factor in determining the spectral characteristics of both sequences. It is clear that the WR stars are in the helium burning phase, with the WN sequence being less evolved than the WC sequence. These results in many ways support the recent suggestion of Conti (1976) that the of stars are the progenitors of the WR class.
An Emission Line in the Hard X-Ray Spectrum of Hercules X-1: Quantized Cyclotron Emission from the Neutron Star
Authors: Pietsch W. , Reppin C. , Staubert R. , Truemper J. , Voges W. , Kendziorra E. 
Published: June 2019

A four hour balloon observation of HERC X-l during the 'On-state' in the 35 day cycle was performed on May 3rd, 1976. The 1.24 second pulsations show a pulsed fraction of 58 ± 8% in the 18-31 KeV interval. A pulsed flux (1.24 sec) was discovered in the 31-88 KeV interval with a pulsed fraction of 51 ± 14%. The spectrum of the pulsed flux can be represented up to 50 KeV by an exponential distribution with KT approximately 8 KeV. At approximately 58 KeV a strong and narrow line feature occurs which we interpret as electron cyclotron emission (ΔN = 1 Landau transition) from the polar cap plasma of the rotating neutron star. The corresponding magnetic field strength is approximately 5 x 1012 Gauss, neglecting gravitational red shift. There is evidence for a second harmonic at approximately 110 KeV (ΔN = 2 ).The astrophysical application of this discovery will be discussed in some detail.
Simultaneous Multi-Wavelength Observations of Microquasars (The Mine Collaboration)
Authors: Fuchs Y. , Rodriguez J. , Mirabel I. F. , Shaw S. E. , Kretschmar P. , Ribó M. , Chaty S. , Dhawan V. , Brown I. , Spencer R. , Pooley G. G. , Hannikainen D. C. 
Published: June 2019

AbstractWe present the international collaboration MINE (Multi-λ INTEGRAL NEtwork) aimed at conducting multi wavelength observations of microquasars simultaneously with the INTEGRAL satellite. The first results of GRS 1915+105 are encouraging and those to come should help us to understand the physics of the accretion and ejection phenomena around a compact object.
Energy and Angular Momentum Deposition During Common Envelope Evolution
Authors: Soker Noam 
Published: June 2019

AbstractI consider three processes which enhance mass loss rate from a common envelope of a giant star with a main sequence or a white dwarf companion spiraling-in inside its envelope. I consider deposition of orbital energy and orbital angular momentum to the giant's envelope, and the formation of jets by an accreting companion and their propagation in the envelope. I find that in many cases the deposition of orbital angular momentum to the envelope may be more important to the mass loss process than the deposition of orbital energy. Jets blown by an accreting companion, in particular a white dwarf, orbiting inside the outer regions of the giant's envelope may also dominate over orbital energy deposition at early stage of the common envelope evolution. These imply that, studies which ignore the deposition of angular momentum to the envelope and the effects of the accreting companion may reach wrong conclusions.
Cyclic Period Changes in the Algol WW Cygni
Authors: Zavala R. T. , McNamara B. J. , Harrison T. E. , Bogue H. , Maness H. L. 
Published: June 2019

AbstractYear to decade-long cyclic period changes have been observed in many classes of close binaries. The Algol binary WW Cygni shows a cyclic change in its orbital period with an amplitude of slightly more than 0.02 days and a period of 56 years. A hypothetical third or fourth body does not satisfactorily explain the observed variation in the orbital period. The change in luminosity and color of the system at primary eclipse minimum are in agreement with the model proposed by Applegate for a magnetic cycle induced period change in WW Cygni. We have commenced monitoring 9 close binaries for evidence of the luminosity and color changes consistent with the magnetic cycle hypothesis. δ Librae is suggested as a case suitable for observation with an optical interferometer to test the third body proposed for this Algol system.
AM CVn Systems as Optical, X-Ray and GWR Sources
Authors: Yungelson L. , Nelemans G. , Portegies Zwart S. F. 
Published: June 2019

AbstractWe discuss the model for the Galactic sample of the AM CVn systems with Porb, ≤ 1500 s that can be detected in the optical and/or X-ray bands and may be resolved by the gravitational waves detector LISA. At 3 ≲ P ≲ 10 min all detectable systems are X-ray sources. At P ≳ 10 min most systems are only detectable in the V-band. About 30% of the X-ray sources is also detectable in the V-band. About 10,000 AM CVn systems might be resolved by LISA: this is comparable to the number of detached double white dwarfs that can be resolved. Several hundreds of AM CVn LISA sources might be also detectable in the V- and/or X-ray bands.