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Asteroseismology offers an opportunity for examination and detailed understanding of the internal structure of stars by probing their pulsating modes. To obtain reliable results by asteroseismology, accurate atmospheric parameters and metallicities of pulsating stars are required. Hence, in this study we carried out a spectroscopic survey of 8 single δ Scuti stars in detail. The accurate atmospheric parameters (effective temperature, surface gravity), projected rotational velocities and the metallicities of these stars were derived. [ABSTRACT FROM AUTHOR]

Pulsations in subdwarf B (sdB) stars are an important tool to constrain the evolutionary status of these evolved objects. Interestingly, the same data used for this asteroseismological approach can also be used to search for substellar companions around these objects by analyzing the timing of the pulsations by means of a so-called O-C diagram. Substellar objects around sdB stars are important for two different reasons: they are suspected to be able to influence the evolution of their host-star and they are an ideal test case to examine the properties of exoplanets which have survived the red giant expansion of their host stars. [ABSTRACT FROM AUTHOR]

We present our new grids of NLTE model atmospheres for hot subdwarf O (sdO) stars computed with the public codes TLUSTY and SYNSPEC and including the effects of metal line blanketing. Until recently, large grids of NLTE models could not be practically computed over reasonable timescales, and have remained unavailable for quantitative spectroscopic analyses of this category of hot stars. We solved the problem by adapting TLUSTY and SYNSPEC to run in parallel mode on a small dedicated cluster of 80 fast processors. We present a comparison of three different NLTE grids including different elements. By fitting synthetic spectra from a given grid with another one, we obtain 'maps' showing the line blanketing effects of metals, i.e., the differences between the real atmospheric parameters (Teff and log g) and the ones inferred by the fitting procedure. Finally, we present the results of the spectral analysis of SDSS J1600+0748, this unique pulsating sdO star, using our different grids of NLTE model atmospheres. [ABSTRACT FROM AUTHOR]

KUV 08368+4026 was considered a member of ZZ Ceti stars with large amplitudes and frequencies around a narrow range of 1.6 mHz and 2.0 mHz. As the first effort of asteroseismological study for KUV 08368+4026 since the discovery of its variability in 1996, a single-site run in February of 2009 and a 3-site observation campaign from December of 2009 to January of 2010 for KUV 08368+4026 were carried out in China and Mexico. More than 15,000 frames on 32 nights were obtained. 19 frequencies were distinguished in the datasets with 8 frequencies identified as independent modes. These results are helpful in determining stellar parameters including mass, rotation period, hydrogen mass fraction, and in constructing practical stellar and oscillation models, which will bring new knowledge about the internal structures of ZZ Ceti stars. [ABSTRACT FROM AUTHOR]

We present our preliminary results on the asteroseismological investigations of the ZZ Ceti star GD 244. We used literature values of the effective temperature and surface gravity and utilized the White Dwarf Evolution Code of Bischoff-Kim, Montgomery and Winget (2008, ApJ, 675, 1512) to build our model grid for the seismological analysis. Five observed pulsational modes published up to now were used to find acceptable model solutions. We found that the best model fits have masses between 0.61 and 0.74 M⊙ and constitute two groups with hydrogen layer masses of either ∼10-5 or 10-6 M⊙. Based on a statistical analysis of a larger sample of possible model solutions, we assume that the mass of the star is below ∼0.68 M⊙ and the oxygen content in the centre is less than 60 percent. [ABSTRACT FROM AUTHOR]

We present color-amplitue, time dependent photometry of FEIGE 48 FUSE data. [ABSTRACT FROM AUTHOR]

Stellar rotation breaks the spherical symmetry of a star, and in the case of a pulsating star, it removes the intrinsic mode degeneracy of a nonradial g-mode characterized by an harmonic degree ℓ and a radial order κ. As a result, each pulsation frequency is split into multiplets of frequencies specified by different values of the azimuthal index m. Here, we explore the potential of asteroseismology to place constraints on the internal rotation of pulsating PG1159 stars, also known as GW Vir variables. We employ dedicated seismological models for the pulsating PG1159 stars PG 0122+200, PG 1159-035, and RX J2117+3412 in order to accurately assess the expected frequency splittings induced by rotation, and compare them with the observed ones. To this end, we assume different types of very simplified internal rotation profiles. We found that while PG 1159-035 definitely rotates as a rigid body, PG 0122+200 and RX J2117+3412 appear to be spinning with a rotation rate that depends on the depth. [ABSTRACT FROM AUTHOR]

The current observational status of β Cep, SPB and Be stars is presented and confronted with theory. In the low-metallicity environments of the LMC and SMC recent observations of β Cep and SPB stars are posing a challenge to theory. We also do not understand why low-degree β Cep pulsations do not occur among the O stars and why SPB stars have substantially smaller rotational velocities than stars in the same spectral type and luminosity class. The well-known opacity problem and the limitations of asteroseismic investigations for these stars is discussed. An understanding of pulsation in Be stars requires models of pulsation in rapidly rotating stars. Attempts in this regard are discussed and compared. The idea that Be stars rotate at critical velocity is not supported by an analysis of photometric rotational periods. We highlight problems with the idea that Be star variations are explained entirely by pulsation with reference to recent MOST and COROT results. An oblique magnetic field seems to account for the major observational characteristics of Be stars. [ABSTRACT FROM AUTHOR]

We review recent research on Delta Scuti stars from an observer’s viewpoint. First, some signposts helping to find the way through the Delta Scuti jungle are placed. Then, some problems in studying individual pulsators in the framework of asteroseismology are given before a view on how the study of these variables has benefited (or not) from past and present high-precision asteroseismic space missions is presented. Some possible pitfalls in the analysis of data with a large dynamical range in pulsational amplitudes are pointed out, and a strategy to optimize the outcome of asteroseismic studies of Delta Scuti stars is suggested. We continue with some views on “hybrid” pulsators and interesting individual High Amplitude Delta Scuti stars, and then take a look on Delta Scuti stars in stellar systems of several different kinds. Recent results on pre-main sequence Delta Scuti stars are discussed as are questions related to the instability strip of these variables. Finally, some remarkable new theoretical results are highlighted before, instead of a set of classical conclusions, questions to be solved in the future, are raised. [ABSTRACT FROM AUTHOR]

γ Doradus variables are a relatively recently defined class of multi-periodic pulsating variable star that have a tremendous asteroseismic potential. The high-order, low-degree gravity modes present in these stars allow us to probe as deep as the core in the deep stellar interiors. In addition, several γ Doradus stars also have simultaneously excited p-modes pulsation in their outer envelopes allowing us to simultaneous examine their outer layer. Finally the region of the HR diagram where solar-like variability is present is very close, which may give us an additional final tool to probe the internal structure of these stars. In this paper I review the photometric and spectroscopic observations of the class, the techniques used for mode identification in these stars and give a brief review of some theoretical considerations. [ABSTRACT FROM AUTHOR]

We summarize our ground-based program of spectroscopic and photometric observations of the asteroseismic targets of the Kepler space telescope. We have already determined atmospheric parameters, projected velocity of rotation, and radial velocity of 62 Kepler asteroseismic targets and 33 other stars in the Kepler field of view. We discovered six single-lined and two double-lined spectroscopic binaries, we determined the interstellar reddening for 29 stars in the Kepler field of view, and discovered three δ Sct, two γ Dor and 14 other variable stars in the field of NGC 6866. [ABSTRACT FROM AUTHOR]

The rich acoustic oscillation spectrum in solar-type variables make these stars particularly interesting for studying fluid-dynamical aspects of the stellar interior. I present a summary of the properties of solar-like oscillations, how they are excited and damped and discuss some of the recent progress in using asteroseismic diagnostic techniques for analysing low-degree acoustic modes. Also the effects of stellar-cycle variations in low-mass main-sequence stars are addressed. [ABSTRACT FROM AUTHOR]

Over the past two decades, helioseismology has revolutionized our understanding of the interior structure and dynamics of the Sun. Asteroseismology will soon place this knowledge into a broader context by providing structural data for hundreds of Sun-like stars. Solar-like oscillations have already been detected from the ground in several stars, and NASA’s Kepler mission is poised to unleash a flood of stellar pulsation data. Deriving reliable asteroseismic information from these observations demands a significant improvement in our analysis methods. We report the initial results of our efforts to develop an objective stellar model-fitting pipeline for asteroseismic data. The cornerstone of our automated approach is an optimization method using a parallel genetic algorithm. We describe the details of the pipeline and we present the initial application to Sun-as-a-star data, yielding an optimal model that accurately reproduces the known solar properties. [ABSTRACT FROM AUTHOR]

The best known Solar oscillation-like star is the Sun. During the last 14 years, the ESA/NASA Solar and Heliospheric Observatory (SoHO) has been continuously observing this star from the Lagrange point L1 with enormous success. Among the 11 instruments placed onboard, 3 of them are dedicated to helioseismology: GOLF, VIRGO and MDI. The first two observe the Sun as a star by integrating the velocity or intensity signal of the visible solar disk into a single point. They are thus similar to any other observation done in asteroseismology. During this review I will present the most important results obtained during the mission concerning the Sun seen as a star and how these results have evolved our thoughts of the inside of our star. [ABSTRACT FROM AUTHOR]

Hot subdwarf stars, including helium core burning subdwarf B (sdB) stars and more evolved subdwarf O (sdO) stars, host three classes of nonradial pulsators. Two of them show rapid acoustic mode oscillations (with periods in the 60–600 s range), while the third class features slow gravity mode vibrations of period typically 1h. All three classes provide a strong potential for sounding the internal properties of stars in these evolved phases of stellar evolution through asteroseismology. This has so far been exploited mainly for the rapid p-mode sdB pulsators, but the long period g-mode sdB pulsators, with the advent of space observations, carry good promises for sounding even deeper regions inside these stars. In this review paper, we summarize the properties of pulsating hot subdwarf stars and we outline progress that have recently occured in the asteroseismic exploitation of the pulsations observed in sdB stars. [ABSTRACT FROM AUTHOR]

We present the results of the asteroseismological analysis of two rich DAVs, G38-29 and R808, recent targets of the Whole Earth Telescope. 20 periods between 413 s and 1089 s were found in G38-29’s pulsation spectrum, while R808 is an even richer pulsator, with 24 periods between 404 s and 1144 s. Traditionally, DAVs that have been analyzed asteroseismologically have had less than half a dozen modes. Such a large number of modes presents a special challenge to white dwarf asteroseismology, but at the same time has the potential to yield a detailed picture of the interior chemical make-up of DAVs. We explore this possibility by varying the core profiles as well as the layer masses. We use an iterative grid search approach to find best fit models for G38-29 and R808 and comment on some of the intricacies of fine grid searches in white dwarf asteroseismology. [ABSTRACT FROM AUTHOR]

The ZZ Ceti star KUV 02464+3239 was observed over a whole season at the mountain station of Konkoly Observatory. A rigorous frequency analysis revealed 6 certain periods between 619 and 1250 seconds, with no shorter period modes present. We use the observed periods, published effective temperature and surface gravity, along with the model grid code of Bischoff-Kim, Montgomery and Winget [1] to perform a seismological analysis. We find acceptable model fits with masses between 0.60 and 0.70 M⊙. The hydrogen layer mass of the acceptable models are almost always between 10- and 10-6 M*. In addition to our seismological results, we also show our analysis of individual light curve segments. Considering the non-sinusoidal shape of the light curve and the Fourier spectra of segments showing large amplitude variations, the importance of non-linear effects in the pulsation is clearly seen. [ABSTRACT FROM AUTHOR]

Since 1995, the extrasolar planet search has driven the high resolution spectroscopy community to build more and more sensible spectrograph in order to reach the photon statistics limit in radial velocity measurements. This situation opened the possibility of asteroseismic observations of stellar p-mode pulsations in solar—like stars. In this contribution we summarize the high precision radial velocity measurements on the two Solar type stars, α CMi and μ Her, using the SARG spectrograph at TNG equipped, with an iodine cell. The analyzed spectra show individual measurement errors of about 1.0 m/s (very close to the theoretical photon noise limit). Further we discuss the synergy between astersoseismology high precision radial velocity campaigns and the search for Super Earths. [ABSTRACT FROM AUTHOR]

Oscillations occur in stars of most masses and essentially all stages of evolution. We discuss briefly the potential of asteroseismology, i.e., the study of the frequencies and other properties of stellar oscillations with the aim of extracting fundamental parameters such as density, mass, radius, age and rotation period. We also describe the Kepler Asteroseismic Investigation—the use of asteroseismology on the NASA Kepler mission to study stellar structure and evolution and provide information on the accuracy of the frequency measurements that can be obtained by the NASA Kepler mission. The Kepler mission will provide a comprehensive overview of stellar properties across a large part of the HR diagram, including information about the excitation and damping of the modes, and detailed information about the internal structure of a substantial number of stars. [ABSTRACT FROM AUTHOR]

This is a presentation of the asteroseismological method (ROMOSC) implemented in the Bucharest Observatory to be used in the CoRoT mission. We will also present a calibration of this method with the similar one implemented in the MOST mission in the case of the star η Boo. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

I first argue that, so far as macroscopic dynamical processes are concerned, to a high degree of accuracy the solar plasma, at least beneath the photosphere, may be regarded as being electrically neutral. I then turn to discuss, elaborating on Christensen-Dalsgaard’s excellent but brief introduction in these proceedings, some of those aspects of helioseismology that are pertinent to determining those properties of the Sun that are pertinent to studies of the equation of state. I discuss one of the ways in which one can establish a representation of the structure of the Sun that is consistent with the helioseismic constraints, and I present some properties of the outcome. Finally, I describe some minor conclusions concerning opacity and the equation of state that can be drawn, mindful that in the not-too-distant future more penetrating insight will be gained. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

We present different aspects of the ground-based observational counterpart of the CoRoT satellite mission. We give an overview of the selected asteroseismic targets, the numerous instruments and observatories involved, and the first scientific results. [ABSTRACT FROM AUTHOR]

The β Cephei star HD 180642 was observed by the CoRoT satellite during a run of 156 days in 2007. The space white light photometry revealed the rich frequency spectrum of the star (Degroote et al. 2009). In the present study, we provide additional information on the target, based on both ground-based multi-colour photometry and high-resolution spectroscopy. We place our object in the (Teff, log g) diagram. In addition, we derive the chemical abundances of several elements as well as the metallicity of HD 180642. Finally, we put constraints on the identification of some modes. All these observational constraints will be used to compute stellar models of the target. [ABSTRACT FROM AUTHOR]

We present the first results of determing the δ Scuti population observed with CoRoT during the Initial Run (IRa01). From more than 10000 stars observed continuously in the exoplanet-channel during 58 days, 397 stars show pulsation in the δ Scuti domain. For 39 of the 397 stars low resolution classification spectra and Strömgren uvby photometry were available; thus fundamental parameters like effective temperature and surface gravity could be derived. Classical Fourier techniques and least squares multi-sine fits were applied to identify the pulsation frequencies. For additional 90 stars a pair of radial modes were found and by comparing with pulsation models it was possible to estimate the corresponding fundamental parameters. [ABSTRACT FROM AUTHOR]

The evolutionary stage of the δ Scuti star 44 Tau has been unclear. Recent pulsation studies have claimed both main sequence and post-main sequence expansion models. A new photometric study increased the number of detected frequencies in 44 Tau to 49, of which 15 are independent modes. We now find that a previously ignored third possibility, the post-main sequence contraction phase, is in excellent agreement with the observed frequency range, as well as the frequency values of all individual radial and nonradial modes. These results resolve the previous disagreements in the literature and exemplify that asteroseismology can determine the evolutionary status of a star. [ABSTRACT FROM AUTHOR]

The present work focuses on the discussion of the λ Bootis nature of the multiperiodic δ Scuti star HD 192640 (29 Cyg), through a comprehensive asteroseismic modelling. Some of the most recent asteroseismic tools are used to check whether the observed low metallicity is internal, i.e., intrinsic, present throughout the star, or due to superficial processes as accretion, diffusive settling, radiative levitation, mass loss, etc. The modelling method includes: 1) effects of rotation on equilibrium models, on the adiabatic oscillation spectrum, and its influence in multicolour observables, 2) non-adiabatic stability of radial and non-radial modes, 3) inclusion of the atmosphere-pulsation interaction for a more accurate multicolour mode identification. The analysis performed reveals that the models fulfilling all the constraints are those in the middle of the Main Sequence, with sub-solar metallicity, except for some other unlikely possibilities. Therefore this study does not support the idea of the λ Bootis stars being ZAMS or Pre-MS stars interacting with their primordial cloud of gas and dust, but suggests the explanation of their nature as sub-metallic MS objects. Nevertheless, more accurate multicolour photometric observations are required for a more conclusive study using the procedure presented here, since the observational errors are too large for a definitive rejection of any of the possible explanations. [ABSTRACT FROM AUTHOR]

We introduce the spectroscopic multi-site campaigns that are organised for a sample of slowly pulsating B and γ Doradus stars to make a big step forward in the asteroseismic studies of these main-sequence g-mode pulsators. [ABSTRACT FROM AUTHOR]

With the rapid advances in sophisticated solar modeling and the abundance of high-quality solar pulsation data, efficient and robust inversion techniques are crucial for seismic studies. We present some aspects of an efficient Fourier Optimally Localized Averaging (OLA) inversion method with an example applied to time-distance helioseismology. [ABSTRACT FROM AUTHOR]

The Kepler mission will provide a huge amount of asteroseismic data during the next few years, among which hundreds of solar-like stars will be targeted. The amount of stars and their observation length represent a step forward in the comprehension of the stellar evolution that has already been initiated by CoRoT and MOST missions. Up to now, the slow cadence of observed targets allowed an individual and personalized analysis of each star. During the survey phase of Kepler, this will be impossible. This is the reason why, within the AsteroFLAG team, we have been developing automatic pipelines for the Kepler solar-like oscillation stars. Our code starts by finding the frequency-range where p-mode power is present and, after fitting the background, it looks for the mode amplitudes as well as the central frequency of the p-mode hump. A good estimation of the large separation can thus be inferred in this region. If the signal to noise is high enough, the code obtains the characteristics of the p modes by doing a global fitting on the power spectrum. Here, we will first describe a few features of this pipeline and its application to AsteroFLAG synthetic data to check the validity of the code. [ABSTRACT FROM AUTHOR]

We present a first analysis of our asteroseismology campaign on the planet host star γ Cep A. We used seven consecutive nights at the Harlan J. Smith 2.7 m telescope at McDonald Observatory to obtain 1200 highly precise radial velocity measurements. We find the star to be a multi-periodic pulsator with a frequency spacing of 15 μHz. [ABSTRACT FROM AUTHOR]