Eclipsing Binary Stars from Space

We have begun a programme to obtain high-precision photometry of bright detached eclipsing binary (dEB) stars with the Wide field InfraRed Explorer (WIRE) satellite. Due to the small aperture of WIRE only stars brighter than V=6 can be observed. We are collecting data for about a dozen dEB targets and here we present preliminary results for three of them. We have chosen dEBs with primary components of B and early A type. One of our aims is to combine the information from the light curve analyses of the eclipses with asteroseismic information from the analysis of the pulsation of the primary component.Comment: 4 pages, 3 figures. To appear in conference proceedings for IAU Symposium No. 240: Binary Stars as Critical Tools & Tests in Contemporary Astrophysics, eds. W. Hartkopf, E. Guinan & P. Harmane

Accurate Fundamental Stellar Parameters

We combine results from interferometry, asteroseismology and spectroscopic analyses to determine accurate fundamental parameters (mass, radius and effective temperature) of 10 bright solar-type stars covering the H-R diagram from spectral type F5 to K1. Using ``direct'' techniques that are only weakly model-dependent we determine the mass, radius and effective temperature. We demonstrate that model-dependent or ``indirect'' methods can be reliably used even for relatively faint single stars for which direct methods are not applicable. This is important for the characterization of the targets of the CoRoT and Kepler space missions.Comment: 2 pages. To appear in the proceedings of IAU Symp. 265: Chemical Abundances in the Universe: Connecting First Stars to Planet

Asteroseismology with the WIRE satellite

I give a summary of results from the WIRE satellite, which has been used to observe bright stars from 1999-2000 and 2003-2006. The WIRE targets are monitored for up to five weeks with a duty cycle of 30-40%. The aim has been to characterize the flux variation of stars across the Hertzsprung-Russell diagram. I present an overview of the results for solar-like stars, delta Scuti stars, giant stars, and eclipsing binaries.Comment: Accepted for publication in CoAst. Proceedings of the Vienna Workshop on the Future of Asteroseismology (September 2006). 8 pages, 2 figure

'Rapid fire' spectroscopy of Kepler solar-like oscillators

The NASA Kepler mission has been continuously monitoring the same field of the sky since the successful launch in March 2009, providing high-quality stellar lightcurves that are excellent data for asteroseismology, far superior to any other observations available at the present. In order to make a meaningful analysis and interpretation of the asteroseismic data, accurate fundamental parameters for the observed stars are needed. The currently available parameters are quite uncertain as illustrated by e.g. Thygesen et al. (A&A 543, A160, 2012), who found deviations as extreme as 2.0 dex in [Fe/H] and log g, compared to catalogue values. Thus, additional follow-up observations for these targets are needed in order to put firm limits on the parameter space investigated by the asteroseismic modellers. Here, we propose a metod for deriving accurate metallicities of main sequence and subgiant solar-like oscillators from medium resolution spectra with a moderate S/N. The method takes advantage of the additional constraints on the fundamental parameters, available from asteroseismology and multi-color photometry. The approach enables us to reduce the analysis overhead significantly when doing spectral synthesis, which in turn will increases the efficiency of follow-up observations.Comment: 3 pages, 2 figures. Proceedings from Asteroseismology of Stellar Populations in the Milky Way 2013 to appear in 'Astrophysics and Space Science Proceedings

Modelling of the fast rotating delta Scuti star Altair

We present an asteroseismic study of the fast rotating star HD187642 (Altair), recently discovered to be a delta Scuti pulsator. We have computed models taking into account rotation for increasing rotational velocities. We investigate the relation between the fundamental radial mode and the first overtone in the framework of Petersen diagrams. The effects of rotation on such diagrams, which become important at rotational velocities above 150 km/s, as well as the domain of validity of our seismic tools are discussed. We also investigate the radial and non-radial modes in order to constrain models fitting the five most dominant observed oscillation modes.Comment: Accepted for publication in A&A (11 pages, 6 figures, 4 tables

Improved stellar parameters of CoRoT-7

Accurate parameters of the host stars of exoplanets are important for the interpretation of the new planet systems that continue to emerge. The CoRoT satellite recently discovered a transiting rocky planet with a density similar to the inner planets in our solar system, a so-called Super Earth. This planet is orbiting a relatively faint G9V star called CoRoT-7, and we wish to refine its physical properties, which are important for the interpretation of the properties of the planet system. We used spectra from [email protected] and [email protected]. From the analysis of Fe-1 and Fe-2 lines we determine Teff, log g and microturbulence. We use the Balmer lines to constrain Teff and pressure sensitive Mg-1b and Ca lines to constrain log g. From the analysis we find Teff=5250+-60K, log g = 4.47+-0.05, [M/H]=+0.12+-0.06, and vsini = 1.1 km/s. We compared the L/M ratio with isochrones to constrain the evolutionary status. Using the age estimate of 1.2-2.3 Gyr based on stellar activity, we determine the mass and radius 0.91+-0.03 Msun and 0.82+-0.04 Rsun. With these updated constraints we fitted the CoRoT transit light curve for CoRoT-7b. We revise the planet radius to be slightly smaller, R = 1.58+-0.10 Rearth, and the density becomes higher, rho = 7.2+-1.8 g/cm3. The host star CoRoT-7 is a slowly rotating, metal rich, unevolved type G9V star. The star is relatively faint (V=11.7) and its fundamental parameters can only be determined through indirect methods. Our methods rely on detailed spectral analyses that depend on the adopted model atmospheres. From the analysis of spectra of stars with well-known parameters with similar parameters to CoRoT-7 (the Sun and alpha Cen B) we demonstrate that our methods are robust within the claimed uncertainties. Therefore our methods can be reliably used in subsequent analyses of similar exoplanet host stars.Comment: Accepted by A&A; 10 pages; abstract abridged; resolution decreased in Fig.

Atmospheric parameters of 82 red giants in the Kepler field

Context: Accurate fundamental parameters of stars are essential for the asteroseismic analysis of data from the NASA Kepler mission. Aims: We aim at determining accurate atmospheric parameters and the abundance pattern for a sample of 82 red giants that are targets for the Kepler mission. Methods: We have used high-resolution, high signal-to-noise spectra from three different spectrographs. We used the iterative spectral synthesis method VWA to derive the fundamental parameters from carefully selected high-quality iron lines. After determination of the fundamental parameters, abundances of 13 elements were measured using equivalent widths of the spectral lines. Results: We identify discrepancies in log g and [Fe/H], compared to the parameters based on photometric indices in the Kepler Input Catalogue (larger than 2.0 dex for log g and [Fe/H] for individual stars). The Teff found from spectroscopy and photometry shows good agreement within the uncertainties. We find good agreement between the spectroscopic log g and the log g derived from asteroseismology. Also, we see indications of a potential metallicity effect on the stellar oscillations. Conclusions: We have determined the fundamental parameters and element abundances of 82 red giants. The large discrepancies between the spectroscopic log g and [Fe/H] and values in the Kepler Input Catalogue emphasize the need for further detailed spectroscopic follow-up of the Kepler targets in order to produce reliable results from the asteroseismic analysis.Comment: 16 Pages, 12 Figures, accepted for publication in A&