bluuebunny/crossref_metadata_2025_split huggingface dataset:
Two-Dimensional Hydrodynamic and Evolution Sequences of Rotating Stars
Authors: Deupree R.G. , Guzik J.A. , Neuforge-Verheecke C. 
Published: July 2016

Two-dimensional hydrodynamic simulations were calculated for ZAMS models with Z=0.02, and masses of 3, 5, 8, 12, and 20 M⊙. For each mass five models were calculated - one nonrotating and four with progressively higher rotation rates. The rotating models were categorized by the ratio of the polar to the equatorial radius, with values of 0.985, 0.92, 0.84, and 0.72. The simulations were performed with the fully two-dimensional implicit code ROTORC (actually what is known as 2.5 dimensions, with azimuthal symmetry, but with a conservation law for the rotational velocity in the azimuthal direction).All models showed considerable core overshooting. To first order, the value is about 0.5 Hp, but with a fairly large variation of about 0.2 Hp. It is not clear why the variation is so large, but comparison with other turbulence models shows that overshooting/is one of the more sensitive features of the model (Deupree, 1998). However, there are some trends that may be significant. For the two highest masses there was apparently no dependence on the rotation rate, but the three smaller masses showed a linear decrease in the extent of overshooting with increasing rotation. There is a hint that the 20 M⊙ model has slightly larger overshooting than models of the other masses. With the random variations, it is difficult to assign a level of significance to these trends.
Qualitative Explanation of Phase Shifts Observed in Line Profile Variations
Authors: Montgomery M.H. 
Published: July 2016

AbstractIn a series of papers, Telting & Schrijvers (1997) have demonstrated the correlation between the phase shift across a line, ∆Ψ0 and the l-value of a mode. In addition, they found that the phase shift of the harmonic (i.e., at frequency 2ω) was an indicator of m. In this poster, we present a heuristic derivation of these results under a set of idealized assumptions. Within this framework, exact analytical formulae for the Ilrn(x) were calculated, which are available upon request.
The Slowly Pulsating B Star HD 147394
Authors: Briquet M. , Noels A. , Aerts C. , Mathias P. 
Published: July 2016

AbstractHD 147394 is a Slowly Pulsating B star for which we found three periods in the moments of the Si II 4128-4130 lines: f1 = 0.8008 c/d, f2 = 0.7813 c/d and f3 = 0.6710 c/d. A mode identification is perform ed by using the moment method.
Fundamental Parameters of Be Stars Seen Equator-On
Authors: Zorec J. , Frémat Y. , Hubert A.M. , Floquet M. 
Published: July 2016

AbstractThe geometric deformation, as well as the non-uniform surface gravity and temperature distributions induced by the fast rotation, are taken into account to determine the fundamental parameters of 10 Be stars seen nearly equator-on. The stars occur in the first half of the main sequence evolutionary span, which suggests that their fast rotation is related to initial formation conditions, rather than to evolutionary effects.
Applications of Non-Adiabatic Radial Pulsation Equations to roAp Stars
Authors: Medupe R. , Christensen-Dalsgaard J. , Kurtz D.W. 
Published: July 2016

AbstractWe apply a code that solves grey radial non-adiabatic pulsation equations with consistent treatment of radiative transfer to the roAp frequency regime. We find evidence for the existence of chromospheric modes at frequencies 2.5 mHz, 3.7 mHz, 4.6 mHz and 5.7 mHz in the equilibrium model we used. We also find that, since the oscillations are not adiabatic at the surfaces of roAp stars, better surface boundary conditions need to be considered in future studies.
Unusual Mode Changes in the δ Scuti Type Variable Star FL Cancri
Authors: Goranskij V.P. , Kusakin A.V. 
Published: July 2016

AbstractOn the base of 105 hour photoelectric monitoring, we show that FL Cnc is a multiperiodic δ Set type variable with rapid night-tonight changes of the amplitudes of the periodic components in the Fourier spectra. We observed an event of pulsating frequency doubling on a time scale of a week, which was treated as an azimuthal mode change.
An Attempt at Mode Identification for V480 Tau
Authors: Di Mauro M.P. , Christensen-Dalsgaard J. , Pijpers F. , Hao J. 
Published: July 2016

AbstractSpectroscopic observations of the δ Scuti star V480 Tau, obtained during the MUSICOS 1996 campaign (Hao et al., 2001), detected a large number of modes. In order to assess the information available from such data, we compare the observed spectrum of frequencies with the theoretical predictions obtained for models computed by including the effect of fast rotation on global oscillations.
New Observations of the Pulsating PMS Star V351 Ori
Authors: Marconi M. , Ripepi V. , Bernabei S. , Palla F. 
Published: July 2016

AbstractWe present new photoelectric observations of the Pre–Main-Sequence δ Scuti star, V351 Ori. These new data suggest that V351 Ori could be a multiperiodic variable. The comparison between observations and detailed pulsational models allows us to put independent constraints on the mass and luminosity of the star. The predicted distance is 210 pc, indicating that V351 Ori is much closer than the Orion star forming region. With an inferred mass of ∼1.8 M⊙ and an uncertain evolutionary stage, V351 Ori represents an excellent candidate for future asteroseismological studies that will assess whether it is a young PMS star (∼6 Myr) or an evolved object (∼1 Gyr) leaving the main-sequence.
Frequency Analysis of δ Scuti and RR Lyrae Stars in the OGLE-1 Database
Authors: Moskalik P. , Poretti E. 
Published: July 2016

AbstractWe discuss the results of a systematic search for multi-periodic pulsations in Galactic Bulge δ Scuti and RR Lyrae stars. Six “normal” double-mode variables pulsating in two radial modes have been identified (5 δ Scuti-type and 1 RR Lyrae-type). In 37 RR Lyrae stars secondary periodicities very close to the primary pulsation frequency have been detected. These periodicities correspond to nonradial modes of oscillation. They are found in ∼ 23% of RRab and in ∼ 3% of RRc variables of our sample.
Combined Modeling of Stellar Evolution and Pulsation
Authors: Csubry Z. , Szabó R. , Kolláth Z. , Buchler J.R. 
Published: July 2016

AbstractThe radial pulsations of variable stars at specified points along their evolution are accurately described with numerical hydrodynamics. The behavior of the pulsations along evolutionary tracks can then be modeled with amplitude equations, whose coefficients are obtained from fits to these hydrodynamical models. To simulate stellar evolution we make the stellar core’s properties time-dependent and can investigate directly the effects on pulsation despite the very different time-scales (dynamical, thermal, evolutionary).
Observation of γ Doradus Stars in the Space Asteroseismology Era
Authors: Zerbi F.M. , Kaye A.B. 
Published: July 2016

AbstractAlmost 10 years have passed since the first claims of the existence of a new class of slowly pulsating variables near the cool border of δ Scuti instability strip. The consolidated class of γ Doradus variables faces now the challenge of space. In this paper, we review the most recent theoretical and observational results of these stars and we discuss how our knowledge of their nature will benefit from data collected in the forthcoming space-borne asteroseismological missions.
Complex Pulsation-Like Variability of the LBV Star v532 in M33
Authors: Sholukhova O. , Zharova A. , Fabrika S. , Malinovskii D. 
Published: July 2016

AbstractWe present an analysis of a light curve of LBV star v532 (Romano’s star) in M33. The data consist of 881 individual photographic observations from 1960 to 2000. The star shows extremely rich periodic variations. We find that the amplitudes of the periods depend on brightness, as they rise when the star becomes brighter. We suggest that the 13.08-day period corresponds to the star’s rotation, other short periods (∼ 20 – 30 days) represent the star’s pulsations, and the longer periods are instability driven wind pulsations. The spectral variability of v532 is also strong, with the spectrum excitation depending on the stellar brightness.
Dynamical Atmospheres and Mass Loss of Pulsating AGB Stars
Authors: Höfner Susanne , Loidl Rita , Aringer Bernhard , Jørgensen Uffe G. 
Published: July 2016

AbstractWe present a new generation of dynamic model atmospheres for pulsating AGB stars based on a combined solution of hydrodynamics, frequency-dependent radiative transfer, and time-dependent dust formation. At present, we are performing a systematic study of the dependence of atmospheric structure, observable properties and mass loss on stellar parameters and pulsation properties. Preliminary results show a good agreement with observations and a considerable improvement compared to existing grey dynamical models.
The Influence of Dust Properties on the Mass Loss in Pulsating AGB Stars
Authors: Andersen Anja C. , Höfner Susanne , Loidl Rita 
Published: July 2016

AbstractWe are currently studying carbon based dust types of relevance for carbon-rich AGB stars, to obtain a better understanding of the influence of the optical and chemical properties of the grains on the mass loss of the star. An investigation of the complex interplay between hydrodynamics, radiative transfer and chemistry has to be based on a better knowledge of the micro-physics of the relevant dust species.
The Effects of a Weak Magnetic Field in the Line Profiles of A-type Supergiant Winds
Authors: Verdugo E. , de Castro  Gómez A. , Ferro-Fontán C. , Talavera A. 
Published: July 2016

Solutions for the stellar winds of hot luminous stars are obtained by solving the magnetohydrodynamic (MHD) equations, combined with the theory of radiation-driven winds. The formalism is basically the same as developed by Rotstein & Giménez de Castro (1996). We have considered the interaction of radiation pressure with an open magnetic field . The magnetic field lines are pushed by the intense radiation field and adopt a purely radial configuration:and the polar magnetic flux at the photosphere:Rotstein & Giménez de Castro (1996) assume all the lines contributing to the radiation pressure are optically thick (α = 1) in order to decouple the MHD equations. Here the model has been improved to adopt a value of α = 0.6 which is a better approach for A-supergiants.
The Controversial Sun
Authors: Ulrich Roger K. 
Published: July 2016

AbstractThe sun serves as an important test case for a variety of problems related to stellar structure and evolution as well as fundamental physics. The sun also influences the terrestrial environment through its varied outputs. These two aspects of the solar interior combine to generate a surprising level of controversy for such an inherently simple star. I review three topics each of which is the subject of some degree of controversy: 1) the solar neutrino problem, 2) the status of modeling and observational efforts to understand the solar cycle of activity and 3) observational efforts to detect and identify solar g–modes.
CESAM Solar Models
Authors: Morel P. , Berthomieu G. , Provost J. , Lebreton Y. 
Published: July 2016

AbstractSolar models have been computed using the code CESAM constructed at Nice (Morel, 1992), and the new opacities of Livermore for different mixtures. Their global characteristics, predicted capture rates of neutrinos for the chlorine and gallium experiments and their seismological properties are given.
Restoration of the Atmosphere in Solar Models
Authors: Morel P. , Van’t Veer C. , Berthomieu G. , Cayrel R. , Castelli F. , Goupil M.J. , Lebreton Y. , Provost J. 
Published: July 2016

AbstractFrom models of the Sun atmosphere obtained with ATLAS 9 (Kurucz 1992) it appears that the diffusion limit of the transfer equation becomes valid only at depths larger than TR ~ 10. Even with physics as consistent as possible one restores the atmosphere with an accuracy not better than ~ 40%, but with small consequences on solar calibrated models. Despite the eigenmodes have turning points located in the atmosphere, the study of the oscillations reveals differences less than 2μHz when the atmosphere is restored with various assumptions.
The Infrared Excess of Early-Type Stars: Modelling the Iras Observations
Authors: Runacres M. , Blomme R. 
Published: July 2016

AbstractThe IRAS satellite has observed some early-type stars in the infrared part of the spectrum. Most of this infrared radiation is due to free-free scattering in the dense stellar wind of these stars. We modelled this phenemenon by solving the equations of hydrodynamics as well as the radiative transfer equation (for a H and He mixture). This yields continuum fluxes at visible and infrared wavelengths which have been compared with the observations.
A Search for Lithium in Brown Dwarf Candidates
Authors: Rebolo Rafael , Martin Eduardo L. , Magazzu Antonio 
Published: July 2016

AbstractWe are conducting a search for lithium in very low mass objects with the aim of discriminating between stellar and substellar objects. Lithium is expected to be preserved in brown dwarfs with M/M⊙ ≤0.06, while it is known to be efficiently destroyed in low mass stars. In this paper we present high resolution observations in the region of the λ 6708 Li I resonance line of 5 very low mass dwarfs. In none of them lithium is detected, implying a Li destruction in their atmospheres of about four orders of magnitude. Our results suggest that these objects are probably very low mass stars rather than brown dwarfs.
A Multiline Method to Determine Stellar Magnetic Fields
Authors: Rípodas Pilar , Collados Manuel , Almeida Jorge Sánchez , López Ramón J. García 
Published: July 2016

In the past, much effort has been devoted to determine stellar magnetic fields by means of the analysis of two spectral lines with different magnetic sensitivities (see, e.g., Robinson, 1980; Saar, 1988; Basri and Marcy, 1988). However, these methods are largely influenced by the uncertainties caused by, for instance, the presence of blends, uncertainties of atomic parameters, etc. Gray (1984) and, more recently, Basri et al. (1992) used a multiline analysis to measure stellar magnetic fields, reducing the importance of those uncertainties, thus increasing, in a statistical sense, the confidence of the results.Here we present a new method based on the analysis of the equivalent widths of many Fe I spectral lines. The central idea is to obtain information on the magnetic field from the magnetic strengthening of the equivalent width of spectral lines. This technique has been applied to a weak-emission-line T Tauri star (TAP35) and a main sequence star (ξ Boo A), using data published by Basri et al., (1992).
The Equation of State
Authors: Däppen Werner 
Published: July 2016

AbstractThere are two basic approaches to the equation of state for stellar envelopes and interiors. The traditional method chooses the so-called “chemical picture”, in which the notion of atoms is maintained despite the plasma environment. A mixture of atoms, molecules, ions, electrons and nuclei is considered, and the occurring ionization and dissociation reactions (thus the name chemical picture) are treated according to the entropy-maximum (or free-energy-minimum) principle. The alternative method is based on the so-called “physical picture”, where only fundamental particles (electrons, nuclei) explicitly enter. Through the means of activity expansions, the problems of plasma physics and statistical mechanics are treated simultaneously and on the same footing. For helio- and asteroseismology, an accurate and precise equation of state is essential. Progress towards a better equation of state can be made in several ways: purely theoretical efforts, checks with experiments, including astrophysical data, and comparisons between different theoretical formalisms. Comparisons are useful to assess the domain of temperature and density where the theoretical complications matter, and to determine the diagnostic potential of astrophysical observables for equation of state issues.
V 3903 Sagitarii: A Main-Sequence (07V+09V) Detached Eclipsing Binary
Authors: Vaz L.P.R. , Cunha N.C.S. , Vieira E.F. , Myrrha M.L.M. 
Published: July 2016

AbstractPhotometric and spectroscopic observations of V3903 Sgr are analyzed, and absolute dimensions (masses and radii) are determined to a precision better then 3%.
Coulomb Corrections and Globular Cluster Stellar Evolution
Authors: Proffitt Charles R. 
Published: July 2016

AbstractThe effects of Coulomb corrections on the evolution of globular clusters stars are discussed. Coulomb corrections alter the equation of state by about 1% in most of the stellar interior, and for stars of fixed initial parameters, this results in an 8% increase in the ZAMS luminosity and an 8% decrease in the age at the main sequence turnoff. Ages for globular clusters measured by comparing to the turnoff luminosity of theoretical isochrones are lowered by ≈ 4% when Coulomb effects are included.
Spin-Down of Solar-Type Stars with Internal Magnetic Fields
Authors: Charbonneau Paul , Macgregor Keith B. 
Published: July 2016

AbstractWe present a selection of results from a large set of numerical simulations of the spin-down of a solar-type star containing a large scale magnetic field in its radiative interior. Our computations are dynamical, in that they take into account both the generation of the toroidal component by the wind-induced shear endits back-reaction on the azimuthal flow. Our results demonstrate the existence of classes of internal magnetic fields that can accomodate rapid spin-down near the ZAMS, and yield weak internal differential rotation by the solar age.
Asymptotic Theory of Low-Degree Stellar Acoustic Oscillations
Authors: Roxburgh I.W. , Vorontsov S.V. 
Published: July 2016

AbstractWe extend the second-order asymptotic description developed by Tassoul (1980, 1990) to the forth order, taking into account both gravity perturbations and realistic (non-polytropic) structure of the stellar envelope. We examine the accuracy of the asymptotic description by the direct computations for a solar model.
Detecting Convective Overshoot In Solar-Type Stars
Authors: Monteiro M.J. P. F. G. , Christensen-Dalsgaard J. , Thompson M.J. 
Published: July 2016

It is important for understanding stellar evolution to constrain observationally how overshoot occurs for stellar conditions. Simplified models of the dynamics (eg. Zahn 1991) indicate that overshoot results in a slightly subadiabatic region beyond the convectively unstable layers, followed by an almost discontinuous transition to radiative stratification. Abrupt changes such as this contribute with a characteristic periodic signal to the frequencies ωn,l, of modes of low degree l (Gough 1990). This signature may therefore be detectable for distant stars. Here we show that the signal is sensitive to the “severity” of the overshoot and, of practical importance for the solar case, how it may be extracted from modes of higher degree. Finally we apply our method to solar data.To analyze the applicability of the method, we consider four stellar models, Z1 — Z4, with solar mass, radius (R) and luminosity; of these, Z2 and Z4 have overshoot. The bases of the nearly adiabatically stratified region in the models are at radii rd/R = .729, .713, .713 and .700 respectively.
Theory of The Oblique Pulsator Model For The Rapidly Oscillating Ap Stars
Authors: Shibahashi Hiromoto , Takata Masao 
Published: July 2016

AbstractRecently, one of the rapidly oscillating Ap stars, HR 3831, has been found to have an equally split frequency septuplet, though its oscillation seems to be essentially an axisymmetric dipole mode with respect to the magnetic axis which is oblique to the rotation axis (Kurtz et al. 1992; Kurtz 1992). In order to explain this fine structure, we investigate oscillations of rotating magnetic stars by taking account of the perturbations due to the magnetic fields and the rotation. We show that the magnetic field on axisymmetric dipole modes distorts the dipole oscillation pattern to have axisymmetric octapole components so that the frequency pattern becomes a septuplet rather than a triplet, and that the additional effect of the rotation leads the frequency pattern to be asymmetric. The formula allows us to get information about the magnetic fields, the rotation, and the geometrical configuration of the star from the oscillation data.
Winds
Authors: MacGregor K.B. 
Published: July 2016

AbstractIt is by now well known that most main sequence stars continuously lose mass as a consequence of the winds they emit. In addition to affecting the thermal and dynamical state of the stellar atmosphere, such mass loss can also induce changes in the interiors of stars. In the present review, we consider a few of the ways in which sustained, wind-like mass loss can alter the physical state of main sequence stellar interiors by examining the differences in internal structure, composition, and rotation between mass-losing and conservatively evolving stars.
Stellar Activity: Constraints Expected From Space Experiments
Authors: Catala Claude 
Published: July 2016

AbstractDynamo theory needs to be guided and tested by observations. However, solar observations alone cannot provide sufficient tests of the dynamo models, and constraints obtained from stellar observations are still few, indirect, and poorly related to the properties of dynamos.This review discusses which parameters must be observed on stars other than the Sun to usefully guide the theoretical efforts and test the resulting models. We show that most of these observables, which characterize the stellar activity phenomena, are accessible only from space, and that space-based experiments are one of the best took to trigger progress in the field of solar and stellar activity in the next few decades.
Lithium Abundance and Activity for 57 Rs Cvn Systems
Authors: Xuefu Liu , Gang Zhao , Huisong Tan , Fangjun Lu 
Published: July 2016

AbstractHigh-resolution (0.145A/diode, high signal-to-noise (> 100) Reticon spectra of 57 RS CVn systems, which were observed with the coudé spectrographs of the McDonald 2.1m telescope and Yunnan lm telescope, were used to analyse a correlation between Li abundance and chromospere activity. Li abundances of 57 RS CVn stars, which include 76 detected components have been determined through the determination of equivalent widths of Li doublet (6707.761A + 6707.912A) and Kuruz’s model atmosphere. The model metal abundance and line analysis of 10 RS CVn stars were determined from the present spectral lines data. The main results are the following: 1, Lithium abunances of 76 RS CVn components for 57 RS CVn systems are obviously reduced with the the effective temperatures gradually decreasing. 2, Li abundance has staistically decreasing trend in RS CVn stars with the rotational velocities vsini increasing. 2, The position of 168 RS CVn stars in the (U-B, B-V) Figure show that they can be devided into two groups. The most of them seem to be not poor-metal stars. Li abundances of these stars seem to have no obious correlations with their stellar chromosphery activity levels, but 7 RS CVn systems, in which cool component is more active show that the more active component has a lower Li abundance.
Observational Constraints on Mode Excitation in δ-Scuti Stars In Open Clusters
Authors: Frandsen S. , Kjeldsen H. 
Published: July 2016

The special opportunities offered by δ-Scuti stars are the following:
-They regularly oscillate in several modes, and with high precision observations one has measured of the order 5 modes (Michel and Baglin 1991-The excitation is a very delicate and therefore a very sensitive measure of the internal structure.-They are found in open clusters which constitute a very rich scenario for tests of the theory of stellar structure and evolution. This makes it feasible to observe several stars simultaneously and gain more results than for single stars.-The brightness is moderately high and still they live long enough to be present in a variety of clusters and in the field as well.