119199263
Evidence against the young hot-Jupiter around BD +20 1790
Context. The young active star BD +201790 has been inferred to host a substellar companion from radial-velocity measurements that detected the reflex motion induced on the parent star. Aims. We attempt to completely characterize the radial-velocity signal in order to assess its nature. Methods. We used the CORALIE spectrograph to obtain precise (∼10 m s −1 ) radial-velocity measurements of this active star, while characterizing the bisector span variations. We took particular care to correctly sample both the proposed planetary orbital period, of 7.8 days, and the stellar rotation period, of 2.4 days. Results. We measure a smaller radial-velocity signal (with peak-to-peak variations <500 m s −1 ) than reported previously, and of different amplitude for two different campaigns. A periodicity similar to the rotational period is found in the data, as well as a clear correlation between radial velocities and bisector span. These results imply that the radial-velocity variations of the star are photospheric in origin and not caused by a barycentric movement movement of the star, and contradict the previous detection of a hot-Jupiter.
73585455
Observation of the full 12-hour-long transit of the exoplanet HD 80606b - Warm-Spitzer photometry and SOPHIE spectroscopy
We present new observations of a transit of the 111.4-day-period exoplanet HD 80606b. Due to this long orbital period and to the orientation of the eccentric orbit (e = 0.9), HD 80606b's transits last for about 12 hours. This makes the observation of a full transit practically impossible from a given ground-based observatory. With the Spitzer Space Telescope and its IRAC camera on the post-cryogenic mission, we performed a 19-h photometric observation of HD 80606 that covers the full 2010 January 13-14 transit as well as off-transit references immediately before and after the event. We complement these photometric data by new spectroscopic observations that we simultaneously performed with SOPHIE at the Haute-Provence Observatory. This provides radial velocity measurements of the first half of the transit that was previously uncovered with spectroscopy. This new dataset allows the parameters of this singular planetary system to be significantly refined. We obtained a planet-to-star radius ratio R p /R * = 0.1001 ± 0.0006 that is more accurate but slightly lower than the one measured from previous ground observations in the optical. We found no astrophysical interpretations able to explain this difference between optical and infrared radii; we rather favor underestimated systematic uncertainties, maybe in the ground-based composite light curve. We detected a feature in the Spitzer light curve that could be due to a stellar spot. We also found a transit timing about 20 minutes earlier than the ephemeris prediction; this could be caused by actual transit-timing variations due to an additional body in the system, or again by underestimated systematic uncertainties. The actual angle between the spin-axis of HD 80606 and the normal to the planetary orbital plane is found to be near 40° thanks to the fit of the Rossiter-McLaughlin anomaly, with a sky-projected value λ = 42° ± 8°. This allows scenarios with aligned spin-orbit to be definitively rejected. Over the twenty planetary systems with measured spin-orbit angles, a few are misaligned; this is probably the signature of two different evolution scenarios for misaligned and aligned systems, depending whether or not they experienced gravitational interaction with a third body. As in the case of HD 80606, most of the planetary systems including a massive planet are tilted; this could be the signature of a separate evolution scenario for massive planets compared with Jupiter-mass planets.
119158686
A survey of M stars in the field of view of Kepler space telescope
M dwarfs constitute more than 70% of the stars in the solar neighborhood. They are cooler and smaller than Sun-like stars and have less-massive disks which suggests that planets around these stars are more likely to be Neptune-size or smaller. The transit depths and transit times of planets around M stars are large and well-matched to the Kepler temporal resolution. As a result, M stars have been of particular interest for searching for planets in both radial velocity and transit photometry surveys. We have recently started a project on searching for possible planet-hosting M stars in the publicly available data from Kepler space telescope. We have used four criteria, namely, the magnitude, proper motion, H-Ks and J-H colors, and searched for M stars in Q0 and Q1 data sets. We have been able to find 108 M stars among which 54 had not been previously identified among Kepler's targets. We discuss the details of our selection process and present the results.
118750676
New and updated stellar parameters for 90 transit hosts - The effect of the surface gravity
Context. Precise stellar parameters are crucial in exoplanet research for correctly determining the planetary parameters. For stars hosting a transiting planet, determining the planetary mass and radius depends on the stellar mass and radius, which in turn depend on the atmospheric stellar parameters. Different methods can provide different results, which leads to different planet characteristics. Aims. In this paper, we use a uniform method to spectroscopically derive stellar atmospheric parameters, chemical abundances, stellar masses, and stellar radii for a sample of 90 transit hosts. Surface gravities are also derived photometrically using the stellar density as derived from the light curve. We study the effect of using these different surface gravities on the determination of the chemical abundances and the stellar mass and radius. Methods. A spectroscopic analysis based on Kurucz models in local thermodynamical equilibrium was performed through the MOOG code to derive the atmospheric parameters and the chemical abundances. The photometric surface gravity was determined through isochrone fitting and the use of the stellar density, directly determined from the light curve. Stellar masses and radii are determined through calibration formulae. Results. Spectroscopic and photometric surface gravities differ, but this has very little effect on the precise determination of the stellar mass in our spectroscopic analysis. The stellar radius, and hence the planetary radius, is most affected by the surface gravity discrepancies. For the chemical abundances, the difference is, as expected, only noticable for the abundances derived from analyzing lines of ionized species.
119247043
Volatiles and refratories in solar analogs: no terrestial planet connection
We have analysed very high-quality HARPS and UVES spectra of 95 solar analogs, 24 hosting planets and 71 without detected planets, to search for any possible signature of terrestial planets in the chemical abundances of volatile and refractory elements with respect to the solar abundances. We demonstrate that stars with and without planets in this sample show similar mean abundance ratios, in particular, a sub-sample of 14 planet-host and 14 "single" solar analogs in the metallicity range 0.14<[Fe/H]<0.36. In addition, two of the planetary systems in this sub-sample, containing each of them a super-Earth-like planet with masses in the range ~ 7-11 Earth masses, have different volatile-to-refratory abundance ratios to what would be expected from the presence of a terrestial planets. Finally, we check that after removing the Galactic chemical evolution effects any possible difference in mean abundances, with respect to solar values, of refratory and volatile elements practically dissappears.
118449365
LOW Mg/Si PLANETARY HOST STARS AND THEIR Mg-DEPLETED TERRESTRIAL PLANETS
Simulations have shown that a diverse range of extrasolar terrestrial planet bulk compositions are likely to exist based on the observed variations in host star elemental abundances. Based on recent studies, it is expected that a significant proportion of host stars may have Mg/Si ratios below 1. Here we examine this previously neglected group of systems. Planets simulated as forming within these systems are found to be Mg-depleted (compared to Earth), consisting of silicate species such as pyroxene and various feldspars. Planetary carbon abundances also vary in accordance with the host star C/O ratio. The predicted abundances are in keeping with observations of polluted white dwarfs, lending validity to this approach. Further studies are required to determine the full planetary impacts of the bulk compositions predicted here.
14252204
Metadata services on the Grid
We present an interface for metadata access on the Grid, designed to support flexible schema management, efficient retrieval of large result sets and to allow a broad range of implementations. We also describe an implementation of this interface, which supports a wide range of storage back-ends and two access protocols: SOAP and a TCP-streaming-based protocol. This interface and implementation have been selected as the official metadata components of the gLite-EGEE middleware. Finally, we present the results of extensive performance studies, where the two front-ends are compared to evaluate the cost of using SOAP as metadata access protocol.