Antonio Claret

A new non-linear limb-darkening law for LTE stellar atmosphere models III - Sloan filters: Calculations for –5.0 ≤ log [M/H] ≤ +1, 2000 K ≤ T

Continuing our studies on stellar atmospheres (Claret [CITE], [CITE]), we present in this paper the limb-darkening coefficients for the Sloan photometric system. The calculations cover a wide range of values of log  g , T eff , metallicities and microturbulent velocities. The atmosphere models used are ATLAS and PHOENIX. In addition to the traditional applications of the limb-darkening coefficients, the present ones will be useful since the Sloan filters are now being used in the interpretation of light curves of extrasolar transiting planets, for example. The present calculations may also be useful, as a complement, for the Kepler mission, dedicated to the search for terrestrial planets.

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We present radial-velocity sequences acquired during three transits of the exoplanet HD 189733b and one transit of CoRoT-3b. We applied a combined Markov-chain Monte-Carlo analysis of spectroscopic and photometric data on these stars, to determine a full set of system parameters including the projected spin-orbit misalignment angle of HD 189733b to an unprecedented precision via the Rossiter-McLaughlin effect: β = 0.85 ◦ +0.32 −0.28 . This small but non-zero inclination of the planetary orbit is important to understand the origin of the system. On CoRoT-3b, results seem to point towards a non-zero inclination as well with β = 37.6 ◦ +10.0 −22.3 , but this remains marginal. Systematic effects due to non-Gaussian cross-correlation functions appear to be the main cause of significant residuals that prevent an accurate determination of the projected stellar rotation velocity V sin(I) for both stars.

≤ 50 000 K at several surface gravities

We revised the current status of the apsidal-motion test to stellar structure and evolution. The obser- vational sample was increased by about 50% in comparison to previous studies. Classical and relativistic systems were analyzed simultaneously and only systems with accurate absolute dimensions were considered. New interior models incorporating recent opacity tables, stellar rotation, mass loss, and moderate core overshooting were used as theoretical tools to compare the predicted with the observed shifts of the position of the periastron. The stellar models were computed for the precise observed masses and the adopted chemical compositions are consistent with the corresponding tables of opacities to avoid the inherent problems of interpolation in mass and in (X, Z). The derived chemical composition for each individual system was used to infer the primordial helium content as well as a law of enrichment. The values found are in good agreement with those obtained from various independent sources. For the rst time, the eects of dynamic tides are taken into account systematically to determine the con- tribution of the tidal distortion to the predicted apsidal-motion rate. The deviations between the apsidal-motion rates resulting from the classical formula and those determined by taking into account the eects of dynamic tides are presented as a function of the level of synchronism. For systems close to synchronisation, dynamic tides cause deviations with respect to the classical apsidal-motion formula due to the eects of the compressibility of the stel- lar fluid. For systems with higher rotational angular velocities, additional deviations due to resonances arise when the forcing frequencies of the dynamic tides come into the range of the free oscillation modes of the component stars. The resulting comparison shows a good agreement between the observed and theoretical apsidal-motion rates. No systematic eects in the sense that models are less mass concentrated than real stars and no correlations with the evolutionary status of the systems were detected.

The Rossiter-McLaughlin effect of CoRoT-3b and HD 189733b

CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs) is a next-generation instrument to be built for the 3.5m telescope at the Calar Alto Observatory by a consortium of Spanish and German institutions. Conducting a five-year exoplanet survey targeting ~ 300 M stars with the completed instrument is an integral part of the project. The CARMENES instrument consists of two separate spectrographs covering the wavelength range from 0.52 to 1.7 μm at a spectral resolution of R = 85, 000, fed by fibers from the Cassegrain focus of the telescope. The spectrographs are housed in a temperature-stabilized environment in vacuum tanks, to enable a 1m/s radial velocity precision employing a simultaneous ThAr calibration.

New results on the apsidal-motion test to stellar structure and evolution including the effects of dynamic tides

We present 3004 differential observations in the V bandpass measured by a robotic telescope, as well as 36 pairs of radial velocities from high-resolution spectroscopic observations, of the detached, eccentric, EA-type, 10.37 day period, double-lined eclipsing binary star RW Lac. Absolute dimensions of the components are determined with excellent precision (better than 0.7% in the masses and 0.5% in the radii) for the purpose of testing various aspects of theoretical modeling. We obtain 0.928 ± 0.006 M⊙ and 1.186 ± 0.004 R⊙ for the hotter, larger, more massive, and more luminous photometric primary (star A) and 0.870 ± 0.004 M⊙ and 0.964 ± 0.004 R⊙ for the cooler, smaller, less massive, and less luminous photometric secondary (star B). A faint, third component contributes 2.6% of the light in V but is not detected in our spectrograms. The effective temperatures and interstellar reddening of the stars are accurately determined from UBV and uvbyβ photometry and from analysis of the spectrograms: 5760 ± 100 K for the primary and 5560 ± 150 K for the secondary, corresponding to spectral types of G5 and G7, and 0.050 mag for interstellar reddening Eb-y. The orbits are slightly eccentric, and spectral line widths give observed rotational velocities that are not significantly different from synchronous for both components. The components of RW Lac are old, somewhat metal-deficient, low-mass, main-sequence stars with an age of about 11 Gyr, according to models.

CARMENES: Calar Alto high-resolution search for M dwarfs with exo-earths with a near-infrared Echelle spectrograph

We present photometric observations in B and V, as well as spectroscopic observations of the detached, eccentric 6.6 day double-lined eclipsing binary GG Ori, a member of the Orion OB1 association. Absolute dimensions of the components, which are virtually identical, are determined to high accuracy (better than 1% in the masses and better than 2% in the radii) for the purpose of testing various aspects of theoretical modeling. We obtain MA = 2.342 ± 0.016 M⊙ and RA = 1.852 ± 0.025 R⊙ for the primary, and MB = 2.338 ± 0.017 M⊙ and RB = 1.830 ± 0.025 R⊙ for the secondary. The effective temperature of both stars is 9950 ± 200 K, corresponding to a spectral type of B9.5. GG Ori is very close to the zero-age main sequence, and comparison with current stellar evolution models gives ages of 65–82 Myr or 7.7 Myr, depending on whether the system is considered to be burning hydrogen on the main sequence or still in the final stages of pre–main-sequence contraction. Good agreement is found in both scenarios for a composition close to solar. We have detected apsidal motion in the binary at a rate of = 000061 ± 000025 cycle-1, corresponding to an apsidal period of U = 10,700 ± 4500 yr. A substantial fraction of this (~70%) is due to the contribution from general relativity, and our measurement is entirely consistent with theory. The eccentric orbit of GG Ori is well explained by tidal evolution models, but both theory and our measurements of the rotational velocity of the components are as yet inconclusive as to whether the stars are synchronized with the orbital motion.

ABSOLUTE PROPERTIES OF THE ECLIPSING BINARY STAR RW LACERTAE

The star λ Virginis is a well-known double-lined spectroscopic Am binary with the interesting property that both stars are very similar in abundance but one is sharp-lined and the other is broad-lined. We present combined interferometric and spectroscopic studies of λ Vir. The small scale of the λ Vir orbit (~20 mas) is well resolved by the Infrared Optical Telescope Array (IOTA), allowing us to determine its elements, as well as the physical properties of the components, to high accuracy. The masses of the two stars are determined to be 1.897 and 1.721 M_☉, with 0.7% and 1.5% errors, respectively, and the two stars are found to have the same temperature of 8280 ± 200 K. The accurately determined properties of λ Vir allow comparisons between observations and current stellar evolution models, and reasonable matches are found. The best-fit stellar model gives λ Vir a subsolar metallicity of Z = 0.0097 and an age of 935 Myr. The orbital and physical parameters of λ Vir also allow us to study its tidal evolution timescales and status. Although atomic diffusion is currently considered to be the most plausible cause of the Am phenomenon, the issue is still being actively debated in the literature. With the present study of the properties and evolutionary status of λ Vir, this system is an ideal candidate for further detailed abundance analyses that might shed more light on the source of the chemical anomalies in these A stars.

Absolute Dimensions of the Unevolved B-Type Eclipsing Binary GG Orionis

As an extension of our previous investigations on stellar atmospheres (Claret 2000), the limb-darkening coefficients for the Geneva and Walraven photometric systems are presented for the first time using the ATLAS and PHOENIX models. They cover a wide range of values of log y, T e f f , metallicities and microturbuient velocities. In addition to the traditional applications of limb-darkening coefficients, the present ones are now being used in the interpretation of phase shift of B and A-F type pulsating stars.

Physical Orbit for λ Virginis and a Test of Stellar Evolution Models

The Spanish MEC (AYA2015-71718-R) is gratefully acknowledged for its support during the development of this work. G.T. acknowledges partial support from the NSF through grant AST-1509375

A new non-linear limb-darkening law for LTE stellar atmosphere models II - Geneva and Walraven systems: Calculations for

We present absolute photometric observations in uvby? and 5759 differential observations in the V filter (the most complete light curve ever obtained) measured by a robotic telescope, as well as radial velocities from spectroscopic observations of the detached, eccentric, 2.3 day, double-lined, eclipsing binary star WW Camelopardalis. Absolute dimensions of the components are determined with high precision (better than 1% in the masses and radii) for the purpose of testing various aspects of theoretical modeling. We obtain 1.920 ? 0.013 M? and 1.911 ? 0.016 R? for the primary, and 1.873 ? 0.018 M? and 1.808 ? 0.014 R? for the secondary. The effective temperatures and interstellar reddening of the stars are accurately determined from new uvby? photometry: 8350 ? 135 K for the primary and 8240 ? 135 K for the secondary, corresponding to a spectral type of A4m for both, and 0.294 mag for Eb-y. The metallic-lined character of the stars is revealed by high-resolution spectroscopy and uvby? photometry. Spectral line widths give rotational velocities that are synchronous with the orbital motion in a slightly eccentric orbit (e = 0.0098). The components of WW Cam are main-sequence stars with an age of about 490 Myr according to models.