bluuebunny/crossref_metadata_2025_split huggingface dataset:
CCD Photometry of Variable Stars in the Galactic Open Cluster NGC 7419
Authors: Kołaczkowski Z. , Pigulski A. , Kopacki G. 
Published: July 2016

AbstractWe present results of a CCD variability search in the field of the young open cluster NGC 7419. This cluster contains a large number of Be stars and almost all of them turned out to be variable. They show mostly irregular variations on different time-scales with ranges up to 0.4 mag in the IC band. The most interesting result is the discovery of short-period variability in some of the Be stars.
Automated Classification of Variable Stars for ASAS Data
Authors: Eyer Laurent , Blake Cullen 
Published: July 2016

AbstractWith the advent of surveys generating multi-epoch photometry and their discoveries of large numbers of variable stars, the classification of the obtained time series has to be automated. We have developed a classification algorithm for the periodic variable stars using a Bayesian classifier on a Fourier decomposition of the light curve. This algorithm is applied to ASAS (AII Sky Automated Survey, Pojmanski, 2000). In ASAS 85% of the variables are red giants. A remarkable relation between their period and amplitude is found for a large fraction of those stars.
Tuning Pulsation Modes with Stellar Interferometry
Authors: Domiciano de Souza A. , Vakili F. , Jankov S. , Janot-Pacheco E. 
Published: July 2016

AbstractStellar interferometry represents a qualitative jump toward stellar surface imaging. We propose a method that tunes and filters out high degree non-radial pulsation (NRP) modes from the Fourier plane associated to the stellar brightness distribution. The proposed method can be applied to continuum flux, slow stellar rotation and high degree multi mode NRP stars.
Cycle to Cycle Irregularities in the Monoperiodic β Cephei Star BW Vulpeculae
Authors: Garnier D. , Nardetto N. , Mathias P. , Gillet D. , Fokin A.B. 
Published: July 2016

AbstractHigh spectral and time resolution observations show that the monoperiodic β Cephei star BW Vul presents differences in both line profiles and velocities from one cycle to another, which may be due to the consequence of the passage of two strong shock waves.
Search for a Magnetic Field in the B2IV Star V 2052 Oph
Authors: Neiner C. , Henrichs H.F. , Tijani A. , Geers V. , Nichols J.S. 
Published: July 2016

AbstractWe have searched for magnetic signatures in the B2IV star V 2052 Oph, a β Cep star with stellar wind behavior typical for an oblique magnetic rotator, as β Cep itself. From UV spectroscopy we determined an accurate rotational period and v sin i and present the magnetic measurements as a function of rotational phase. The (small) class of magnetic pulsating early B stars are of great asteroseismological interest.
Photometric Modeling of Slowly Pulsating B Stars
Authors: Townsend R.H.D. 
Published: July 2016

AbstractHighlights are presented from a theoretical study of the photometric characteristics of slowly pulsating B stars. One outstanding result is the discovery, for l ≥ 2 modes, of cancellation between the flux variations originating from surface temperature perturbations, and those arising from radius perturbations. In addition to reducing greatly the variability generated by such modes, the cancellation introduces significant phase differences between the flux changes in each passband. On the grounds that similarly-large phase differences are not seen in observational data, it is suggested that the light variations of slowly pulsating B stars might be due primarily to l = 1 modes.
Activity as the Main Explanation of Light Variations of o And — Towards a Rotational Modulation Model
Authors: Sareyan J.P. , Chauville J. , Alvarez M. , Guerrero G. , Ferro A. Arellano , Mathias P. , Peña J. 
Published: July 2016

Observations carried out for 5 years on o And show that 65 to 85% of its light variations can be described by a double wave: A sin (2πt/P1 + ϕ1) + B sin (2πt/P2 + ϕ2) + C with P1 ≈ 1.6 d = 2P2. When determined independently, P1 and P2 are always found in a 2:1 ratio (within 1%), while they can vary together by as much as 4%. The peak to peak amplitudes of this double-wave fit lay between 40 and 140 mmag (and can even be reduced to less than 10 mmag - our 1987 observations). The rest of the light variations do not show any permanent period or behavior, although a ∼ 2.3 d. (i.e. ≈ 3P1/2) period is frequently detected. Sometimes a marginal ∼ 6 d. period or time constant has been detected.In spite of the quality of our photometric data, the precision on the periods and amplitudes obtained over a few nights is never increased by longer observations: our phase diagrams show significant irregular displacements around the average double-wave analytical solution if we include longer data strings (Fig. 1). This phenomenon was already apparent in our 1992 study (Sareyan et al., 1998): the star shows real irregular behaviour superimposed onto its double-wave “mean” light curve; these changes may show up as a progressive, or sometimes abrupt, modification of the shape of the double-wave light curve (Fig. 1).
Unified NRP-Modelling of Be Stars
Authors: Rivinius Th. , Baade D. , Štefl S. , Maintz M. 
Published: July 2016

AbstractRecently, the line profile variability (lpv) of two low-v sin i Be stars, μ Cen and ω (28) CMa was successfully modelled as nonradial pulsation (nrp) of rapidly rotating stars seen pole-on. In this work, it is shown that the lpv of low-v sin i early-type Be stars in general closely resembles these two cases, and is therefore explainable by the same mechanism. The lpv of intermediate to high-v sin i Be stars can be explained by the same model if the inclination angle of the model alone is increased. Consequently, early-type Be stars form a distinct, fairly homogeneous class of non-radial low-order g-mode pulsators.
Detailed Line-Profile Modeling of B Stars with Chemical Inhomogeneities
Authors: Briquet M. , Scuflaire R. , Aerts C. , De Cat P. 
Published: July 2016

AbstractWe report monoperiodic variability for the four B-type stars HD 131120, HD 105382, HD 138769 and HD 55522, which we explain by rotational modulation rather than by pulsation. Consequently these variables are removed from the list of candidate Slowly Pulsating B stars.
On the Combined Effects of a Magnetic Field and Rotation on Acoustic Modes
Authors: Bigot L. , Dziembowski W.A. 
Published: July 2016

AbstractWe present new results on the effects of a strong dipole magnetic field and rotation on p-mode oscillations. We take into account both Coriolis and centrifugal distortion as manifestations of rotation. We apply these improvements to the case of dipole (l = 1) modes. We show that these modes, during the pulsation cycle, move the stellar surface in a plane, which is inclined from both magnetic and rotation axes. In general, the displacement vector describes an ellipse in that plane. This work is devoted to the study of the roAp star pulsations.
δ Scuti Variables in the HR Diagram
Authors: Rodríguez E. , Breger M. 
Published: July 2016

The location of the δ Scuti variables in the HR diagram is discussed on the basis of HIPPARCOS parallaxes and uvbyβ photometry together with the R00 catalogue (Rodríguez et al., 2000). In particular, the properties of the α Scuti-type pulsators with nonsolar surface abundances (SX Phe, λ Boo, ρ Pup, δ Del and classical Am stars subgroups) are examined.The latter four classes of stars are spectroscopically defined subclasses with surface abundance anomalies. Although the stars ρ Pup and δ Del are also pulsators, the groups named after these stars should not be regarded as pulsation subclasses of δ Scuti stars. The abundance anomalies in these stars affect the pulsation properties, e.g., the classical Am stars are constant in light or show only small pulsation amplitudes (e.g., HD 1097). These four groups are only a small selection from the bewildering zoo of stars with unusual surface abundances in this temperature region and represent the groups with δ Scuti pulsation.
Close Frequency Pairs in Delta Scuti Stars
Authors: Bischof K.M. , Breger M. 
Published: July 2016

AbstractThe power spectra of several δ Scuti stars show close peaks with similar frequencies and amplitudes. Apart from possible observational problems, this can be interpreted in terms of two separate pulsation modes with similar, close frequencies or an artifact of amplitude variability of a single pulsation mode. If sufficient data are available, it is possible to distinguish between the two hypotheses on the basis of expected systematic phase changes associated with the amplitude variations of an assumed single frequency. This phase-shift test has been applied to modes found for BI CMi. In this paper we present the evidence for one of the close frequency pairs found in this star.
Oscillations in Young Stellar Objects
Authors: Pinheiro F.J.G. , Folha D.F.M. , Monteiro M.J.P.F.G. , Marconi M. , Ripepi V. , Palla F. 
Published: July 2016

AbstractWe report the discovery of periodicities in the light curve of the Herbig Ae star V346 Ori. We interpret these variations as the superposition of at least two signals with periods P1=42±6 min and P2=68±12 min resulting from stellar oscillations. The computation of linear non-adiabatic pulsation models for Pre-Main Sequence (PMS) stars reproduces these periods for a 1.5 M⊙ star with Teff= 7300 K and log L/L⊙= 0.74, pulsating in the fundamental and second overtones.
Resonant Excitation of Nonradial Modes in RR Lyrae Stars
Authors: Nowakowski R. 
Published: July 2016

AbstractA nonlinear development of radial pulsation instability to a resonant excitation of nonradial modes is studied. The theory covers the cases of axisymmetric (m = 0) modes as well as (m, −m) pairs. Adopting a simplified treatment of the mode coupling, it is found that multimode pulsation with constant amplitudes is a highly probable solution. An observable consequence of the m = 0 mode excitation is randomness of pulsation amplitude. The case of an l = 1 mode is the most important because of a small averaging effect and a large excitation probability. A significant amplitude and phase modulation is predicted in the case of excitation of an l = 1, m= ±1 pair. This may explain Blazhko-type modulation in RR Lyrae stars. If this model is correct, the modulation period is determined by the rotation rate and the Brunt-Väisälä frequency in the deepest part of the radiative envelope.
The Changing Blazhko Effect of XZ Cygni
Authors: LaCluyzé A. , Smith H.A. , Gill E.-M. , Hedden A. , Kinemuchi K. , Rosas A.M. , Pritzl B.J. , Sharpee B. , Robinson K.W. , Baldwin M. , Samolyk G. 
Published: July 2016

AbstractAn analysis of new and old photometry of the RR Lyrae star XZ Cyg indicates that both its primary period and its Blazhko period have undergone significant changes.
Interrelation of Modal Amplitudes of Double-Mode Pulsators
Authors: Szabados L. 
Published: July 2016

AbstractDuring the study of the factors governing the modal amplitudes of the double-mode radial pulsators, it has been found that the R21 Fourier parameter deduced from the light curves is in a relationship with the ratio of the modal amplitudes, for beat Cepheids and RR Lyrae variables, as well. The form of this relation gives a natural explanation for the fact that double-mode pulsators with slightly excited second modes do not exist.
Tomography of the Atmosphere of the Mira Variable Z Oph
Authors: Jorissen A. , Dedecker M. , Plez B. , Alvarez R. , Gillet D. , Fokin A.B. 
Published: July 2016

AbstractThe new tomographic technique devised by Alvarez et al. (2000) to explore the velocity field across the atmosphere of long-period variable stars (LPVs) is applied to the Mira variable Z Oph. The method cross-correlates the optical spectrum with numerical masks constructed from synthetic spectra and probing layers of increasing depths. This technique reveals that the line doubling often observed in LPVs around maximum light is the signature of the shock wave propagating in the atmosphere of these pulsating stars.
Hydrodynamic Simulations of Convection
Authors: Asida S.M. 
Published: July 2016

Convection is one of the most problematic components of almost every model of a pulsating star. RR Lyrae stars, in particular, have a narrow convection zone at the outer layers, and a model without convection cannot get the red edge of the instability strip (see for example Kollath et al., 2000).In recent years, the common approach is to use non-local time-dependent extensions to the Mixing Length Theory of convection (Bono et al., 1997; Feuchtinger, 1999). These models have many free parameters that need to be calibrated. In this paper we report on a preliminary work in which a different approach is used: 2D hydro simulations similar to the red giant model in Asida (2000). This approach was used by Deupree (1975, 1977) but we used a much better numerical resolution and focused on comparison with MLT results.
The Link between Radiation-Driven Winds and Pulsation in Massive Stars
Authors: Owocki S.P. , Cranmer S.R. 
Published: July 2016

AbstractHot, luminous, massive stars have strong stellar winds driven by line-scattering of the star’s continuum radiation. They are also often observed to exhibit radial or non-radial pulsations. Such pulsations are possible candidates for providing the base perturbations that induce large-scale structure in the overlying wind, and as such they could help explain various observational manifestions of wind variability, e.g., absorption enhancemens or modulations in UV P-Cygni lines of OB stars, and perhaps even moving bumps in optical emission lines of Wolf-Rayet (WR) stars. Here we review the physics of line driving, with emphasis on how perturbations induce variations in a wind outflow. In particular, we present results of a time-dependent dynamical simulation of wind variations induced by the radial pulsation of the β Cep variable BW Vulpeculae, and show that observed variability in UV wind lines can be quite well reproduced by synthetic line profiles for this model. We conclude with a discussion of recent evidence that resonances among multiple modes of non-radial pulsation in Be stars play a role in inducing mass ejections that contribute to formation of a circumstellar disk.
Velocity Observations of Multiple Mode AGB Variable Stars
Authors: Lebzelter T. , Hinkle K.H. , Joyce R.R. , Fekel F.C. 
Published: July 2016

AbstractNumerous infrared Spectroscopic observations were obtained of eight AGB field M giants that have multiple periods of light variability. For six of the eight giants we found radial-velocity periods that confirm the long-period light variability. Although we consider the possibility that the velocity variations result from orbital motion, we conclude that the long-period velocity changes in most, if not all of our sample stars, likely result from pulsation rather than duplicity.
The COROT Mission and its Seismology Programme
Authors: Baglin A. , Auvergne M. , Catala C. , Michel E. , Goupil M.J. , Samadi R. , Popielsky B. ,   the COROT Team
Published: July 2016

AbstractThe COROT project, developed in the framework of the CNES small satellite programme with a wide European cooperation, will be launched in 2004. It is dedicated to seismology and the detection of telluric planets. It will perform relative broad-band photometry in visible light, during very long (150 days) observing runs in the same direction. Both programmes are working simultaneously on the same region of the sky. The seismology programme aims at mapping the HR diagram and study in detail 50 targets brighter than 9th magnitude. Another 50 will also be observed with a lower accuracy. The exoplanet programme will search for telluric planets slightly larger than the Earth, in the habitable zone and closer. Its data will also address many seismology problems.
Preliminary Results from Observations with the Fourier Tachometer
Authors: Schou J. , Brown T.M. , Bachmann K.T. 
Published: July 2016

Recently several interesting results concerning the time dependence of solar p-mode frequencies have appeared. In particular it has been shown that the mode frequencies change with solar activity (Libbrecht and Woodard 1991).We present preliminary results from an analysis of two ≈ 3 month observation runs with the Fourier Tachometer (which was operated by HAO and NSO) from 1987 and 1989. The analysis was done with two different methods in order to test for systematic errors. We show that the mode frequencies change in a manner similar to that reported by Libbrecht and Woodard. We also present results for the frequency splittings caused by the solar rotation.
Progress in High S/N Spectroscopy and its Importance for Stellar Modelling
Authors: Nissen P.E. 
Published: July 2016

AbstractRecent advances in high S/N spectroscopy are reviewed with particular emphasis on new data for the abundances of chemical elements of importance for the modelling of stellar interiors.It seems well established that young, nearby B-type stars have abundances of CNO elements that are about a factor of two lower than in the Sun except for a small fraction of nitrogen-rich stars. The existence of such stars among main sequence stars remains to be explained.Among normal A-type stars (excluding Am and Ap stars) large deviations from solar abundance ratios occur with interesting anticorrelations of the abundances of C and Si. This suggests that diffusion processes and/or gas-dust separation of the chemical elements in the protostellar cloud play an important rôle.
Effective Temperatures and Angular Diameters of A–G Main Sequence Stars
Authors: Glushneva I.N. , Voloshina I.B. , Knyazeva L.N. 
Published: July 2016

AbstractFor 9 stars of A5–G2 spectral type interval IV and V luminosity classes effective temperatures, bolometric corrections, radii, angular diameters and luminosities were obtained by means of the infrared flux method in the modification by Blackwell et al. (1980).
High S/N Na I D Line Profiles in Late-Type MS Stars and their Importance for Stellar Modelling
Authors: Covino E. , Gomez M.T. , Severino G. , Franchini M. 
Published: July 2016

Progress in observational techniques (i.e. high S/N spectroscopy) and modelling (e.g. RE models including convection, nonLTE codes, accurate atomic data) make significant to carry to extremes the numerical fit of a portion of the stellar spectrum and try to interpret the residual differences between calculations and observations in terms of stellar characteristics new respect to the employed model.We have started to apply this synthesis method to a set of high resolution, high S/N spectra of late-type dwarfs in the region of the Na I D lines, obtained at ESO with the 1.4m CAT on May 1989 (Franchini et al. 1992). The dwarf stars are modelled in radiative equilibrium (RE), and the Na I D line synthesis accounts for nonLTE and blend effects.
Modelling Time-Dependent Diffusion in Am Star Envelopes
Authors: Alecian G. 
Published: July 2016

AbstractWe study the diffusion process occurring just below the superficial convection zone of Am stars, improving the methods used sofar. We are now able to compute, in a more realistic way, the evolution of the concentrations during the stay of the stars on the main sequence for a large number of elements. This allows to better constrain the different properties (mass loss, depth of the superficial convection zone, transition between convection and radiative zone) entering the modelling of Am stars in the framework of a diffusion-dominant description.
Stellar Masses and Radii as Constraints on Stellar Models
Authors: Andersen Johannes 
Published: July 2016

AbstractThe current status of empirical data on stellar masses and radii of sufficient accuracy to give constraints on stellar models is reviewed. Results from the best-studied eclipsing binaries can already trace the main-sequence evolution of 1-10 M⊙ stars in considerable detail and will be even more useful when supplemented by chemical abundance data.Taking the deceptively simple question of the observed width of the main sequence as an example, it is shown how careful attention to the details of the data is required to reach robust conclusions about such features of modern stellar evolution models as opacity tables or convective overshooting. Only detailed modelling of specific systems with known masses, radii, and metal abundance constrain the theory strongly enough that a truly critical test is achieved. The same is true when using tidal interactions in binaries (apsidal motion, rotational synchronization, and orbital circularization) as another probe into stellar interiors.
Time-Resolved Spectroscopy of Short Period RS CVn Systems
Authors: Lázaro C. , Arévalo M.J. 
Published: July 2016

AbstractWe have initiated a programme of spectroscopic observations of RS CVn short-period group, with orbital phase resolution. The systems of this group are all eclipsing binaries with both components at the Main Sequence, and most of them have similar spectral type components. The high rotational velocities and their short orbital periods (less than 1 day) hinder the spectroscopic study of these stars. We presents the first results yielded by Hα line observations of the systems XY UMa and WY Cnc. Both systems were observed during 1991 with reasonably wide orbital phase coverage. The analysis of the spectra is made by comparison with a binary model, constructed from the observed spectra of normal stars of the same spectral type as the RS CVn system components. The model accounts for the partial contribution of each component at any orbital phase within eclipses.
The Properties of Accretion Disks of Herbig AE/BE Stars and Their Influence on the Surface and the Inside
Authors: Thé P.S. 
Published: July 2016

AbstractIn this paper we review the observations which lead to the believe that intermediate mass pre-main sequence Herbig Ae/Be stars are surrounded by accretion disks. A discussion is given of their properties and their contributions to surface and inside phenomena of the central stars.
The Evolutionary Code Cesam: Numerical Techniques
Authors: Morel P. 
Published: July 2016

AbstractCESAM is a consistent set of programs and routines designed for the calculations of stellar evolution. Untill now it allows the computation of the evolution from PMS or ZAMS to helium flash for stellar masses of some solar mass. It is constructed in such a way that all the physics works as external routines. The numerical techniques are based on the B-spline formalism. This formalism used both for the integration of the differential equations and for 1D and 2D interpolation schemes of various tables of physical data.
A Peculiar Effect of Core Overshooting on the Internal Structure of Low-Mass Stars
Authors: Mowlavi Nami 
Published: July 2016

AbstractWith the aid of detailed stellar model computations, we analyse the consequences of applying a mild overshooting to 1.0 M⊙ to 1.2 M⊙ stars with solar metallicity. It is shown that solar models with a small convective core can be constructed, resulting in a decrease in the 8B neutrino flux that can amount to 30% relative to the value obtained in models without convective core.