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G. Hébrard

Publications and source records attributed to G. Hébrard.

At least 127 records · Page 7Linked to original sources
arXiv2012

SOPHIE+: First results of an octagonal-section fiber for high-precision radial velocity measurements

High-precision spectrographs play a key role in exoplanet searches and Doppler asteroseismology using the radial velocity technique. The 1 m/s level of precision requires very high stability and uniformity of the illumination of the spectrograph. In fiber-fed spectrographs such as SOPHIE, the fiber-link scrambling properties are one of the main conditions for high precision. To significantly improve the radial velocity precision of the SOPHIE spectrograph, which was limited to 5-6 m/s, we implemented a piece of octagonal-section fiber in the fiber link. We present here the scientific validation of the upgrade of this instrument, demonstrating a real improvement. The upgraded instrument, renamed SOPHIE+, reaches radial velocity precision in the range of 1-2 m/s. It is now fully efficient for the detection of low-mass exoplanets down to 5-10 Earth mass and for the identification of acoustic modes down to a few tens of cm/s.

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arXiv2012

The SOPHIE search for northern extrasolar planets. V. Follow-up of ELODIE candidates: Jupiter-analogs around Sun-like stars

We present radial-velocity measurements obtained in a programs underway to search for extrasolar planets with the spectrograph SOPHIE at the 1.93-m telescope of the Haute-Provence Observatory. Targets were selected from catalogs observed with ELODIE, mounted previously at the telescope, in order to detect long-period planets with an extended database close to 15 years. Two new Jupiter-analog candidates are reported to orbit the bright stars HD150706 and HD222155 in 16.1 and 10.9 yr at 6.7 (+4.0,-1.4) and 5.1(+0.6,-0.7) AU and to have minimum masses of 2.71 (+1.44,-0.66) and 1.90 (+0.67,-0.53) M_Jup, respectively. Using the measurements from ELODIE and SOPHIE, we refine the parameters of the long-period planets HD154345b and HD89307b, and publish the first reliable orbit for HD24040b. This last companion has a minimum mass of 4.01 +/- 0.49 M_Jup orbiting its star in 10.0 yr at 4.92 +/- 0.38 AU. Moreover, the data provide evidence of a third bound object in the HD24040 system. With a surrounding dust debris disk, HD150706 is an active G0 dwarf for which we partially corrected the effect of the stellar spot on the SOPHIE radial-velocities. HD222155 is an inactive G2V star. On the basis of the previous findings of Lovis and collaborators and since no significant correlation between the radial-velocity variations and the activity index are found in the SOPHIE data, these variations are not expected to be only due to stellar magnetic cycles. Finally, we discuss the main properties of this new population of long-period Jupiter-mass planets, which for the moment, consists of fewer than 20 candidates. These stars are preferential targets either for direct-imaging or astrometry follow-up to constrain the system parameters and for higher precision radial-velocity to search for lower mass planets, aiming to find a Solar System twin.

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arXiv2012

SOPHIE velocimetry of Kepler transit candidates VII. A false-positive rate of 35% for Kepler close-in giant exoplanet candidates

The false-positive probability (FPP) of Kepler transiting candidates is a key value for statistical studies of candidate properties. A previous investigation of the stellar population in the Kepler field has provided an estimate for the FPP of less than 5% for most of the candidates. We report here the results of our radial velocity observations on a sample of 46 Kepler candidates with a transit depth greater than 0.4%, orbital period less than 25 days and host star brighter than Kepler magnitude 14.7. We used the SOPHIE spectrograph mounted on the 1.93-m telescope at the Observatoire de Haute-Provence to establish the nature of the transiting candidates. In this sample, we found five undiluted eclipsing binaries, two brown dwarfs, six diluted eclipsing binaries, and nine new transiting planets that complement the 11 already published planets. The remaining 13 candidates were not followed-up or remain unsolved due to photon noise limitation or lack of observations. From these results we computed the FPP for Kepler close-in giant candidates to be 34.8% \pm 6.5%. We aimed to investigate the variation of the FPP for giant candidates with the longer orbital periods and found that it should be constant for orbital periods between 10 and 200 days. This significant disagrees with the previous estimates. We discuss the reasons for this discrepancy and the possible extension of this work toward smaller planet candidates. Finally, taking the false-positive rate into account, we refined the occurrence rate of hot jupiters from the Kepler data.

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arXiv2012

SOPHIE velocimetry of Kepler transit candidates VI. An additional companion in the KOI-13 system

We report the discovery of a new stellar companion in the KOI-13 system. KOI-13 is composed by two fast-rotating A-type stars of similar magnitude. One of these two stars hosts a transiting planet discovered by Kepler. We obtained new radial velocity measurements using the SOPHIE spectrograph at the Observatoire de Haute-Provence that revealed an additional companion in this system. This companion has a mass between 0.4 and 1 Msun and orbits one of the two main stars with a period of 65.831 \pm 0.029 days and an eccentricity of 0.52 \pm 0.02. The radial velocities of the two stars were derived using a model of two fast-rotating line profiles. From the residuals, we found a hint of the stellar variations seen in the Kepler light curve with an amplitude of about 1.41 km/s and a period close to the rotational period. This signal appears to be about three order of magnitude larger than expected for stellar activity. From the analysis of the residuals, we also put a 3-sigma upper-limit on the mass of the transiting planet KOI-13.01 of 14.8 Mjup and 9.4 Mjup, depending on which star hosts the transit. We found that this new companion has no significant impact on the photometric determination of the mass of KOI-13.01 but is expected to affect precise infrared photometry. Finally, using dynamical simulations, we infer that the new companion is orbiting around KOI-13B while the transiting planet candidate is expected to orbit KOI-13A. Thus, the transiting planet candidate KOI-13.01 is orbiting the main component of a hierarchical triple system.

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arXiv2012

Temporal variations in the evaporating atmosphere of the exoplanet HD 189733b

Atmospheric escape has been detected from the exoplanet HD 209458b through transit observations of the hydrogen Lyman-alpha line. Here we present spectrally resolved Lyman-alpha transit observations of the exoplanet HD 189733b at two different epochs. These HST/STIS observations show for the first time, that there are significant temporal variations in the physical conditions of an evaporating planetary atmosphere. While atmospheric hydrogen is not detected in the first epoch observations, it is observed at the second epoch, producing a transit absorption depth of 14.4+/-3.6% between velocities of -230 to -140 km/s. Contrary to HD 209458b, these high velocities cannot arise from radiation pressure alone and require an additional acceleration mechanism, such as interactions with stellar wind protons. The observed absorption can be explained by an atmospheric escape rate of neutral hydrogen atoms of about 10^9 g/s, a stellar wind with a velocity of 190 km/s and a temperature of ~10^5K. An X-ray flare from the active star seen with Swift/XRT 8 hours before the second-epoch observation supports the idea that the observed changes within the upper atmosphere of the planet can be caused by variations in the stellar wind properties, or by variations in the stellar energy input to the planetary escaping gas (or a mix of the two effects). These observations provide the first indication of interaction between the exoplanet's atmosphere and stellar variations.

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arXiv2011

Transiting exoplanets from the CoRoT space mission - XIX. CoRoT-23b: a dense hot Jupiter on an eccentric orbit

We report the detection of CoRoT-23b, a hot Jupiter transiting in front of its host star with a period of 3.6314 \pm 0.0001 days. This planet was discovered thanks to photometric data secured with the CoRoT satellite, combined with spectroscopic radial velocity (RV) measurements. A photometric search for possible background eclipsing binaries conducted at CFHT and OGS concluded with a very low risk of false positives. The usual techniques of combining RV and transit data simultaneously were used to derive stellar and planetary parameters. The planet has a mass of Mp = 2.8 \pm 0.3 MJup, a radius of Rpl = 1.05 \pm 0.13 RJup, a density of \approx 3 g cm-3. RV data also clearly reveal a non zero eccentricity of e = 0.16 \pm 0.02. The planet orbits a mature G0 main sequence star of V =15.5 mag, with a mass M\star = 1.14 \pm 0.08 M\odot, a radius R\star = 1. 61 \pm 0.18 R\odot and quasi-solar abundances. The age of the system is evaluated to be 7 Gyr, not far from the transition to subgiant, in agreement with the rather large stellar radius. The two features of a significant eccentricity of the orbit and of a fairly high density are fairly uncommon for a hot Jupiter. The high density is, however, consistent with a model of contraction of a planet at this mass, given the age of the system. On the other hand, at such an age, circularization is expected to be completed. In fact, we show that for this planetary mass and orbital distance, any initial eccentricity should not totally vanish after 7 Gyr, as long as the tidal quality factor Qp is more than a few 105, a value that is the lower bound of the usually expected range. Even if Corot-23b features a density and an eccentricity that are atypical of a hot Jupiter, it is thus not an enigmatic object.

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arXiv2011

The SOPHIE search for northern extrasolar planets. IV. Massive companions in the planet-brown dwarf boundary

The mass domain where massive extrasolar planets and brown dwarfs lay is still poorly understood. Indeed, not even a clear dividing line between massive planets and brown dwarfs has been established yet. This is partly due to the paucity of this kind of objects orbiting close to solar-type stars, the so-called brown dwarf desert, that hinders setting up a strong observational base to compare to models and theories of formation and evolution. We search to increase the current sample of massive sub-stellar objects with precise orbital parameters, and to constrain the true mass of detected sub-stellar candidates. The initial identification of sub-stellar candidates is done using precise radial velocity measurements obtained with the SOPHIE spectrograph at the 1.93-m telescope of the Haute-Provence Observatory. Subsequent characterisation of these candidates, with the principal aim of identifying stellar companions in low-inclination orbits, is done by means of different spectroscopic diagnostics, as the measurement of the bisector velocity span and the study of the correlation mask effect. With this objective, we also employed astrometric data from the Hipparcos mission and a novel method of simulating stellar cross-correlation functions. Seven new objects with minimum masses between ~ 10 Mjup and ~90 Mjup are detected. Out of these, two are identified as low-mass stars in low-inclination orbits, and two others have masses below the theoretical deuterium-burning limit, and are therefore planetary candidates. The remaining three are brown dwarf candidates; the current upper limits for their the masses do not allow us to conclude on their nature. Additionally, we have improved on the parameters of an already-known brown dwarf (HD137510b), confirmed by astrometry.

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arXiv2011

SOPHIE velocimetry of Kepler transit candidates. V. The three hot Jupiters KOI-135b, KOI-204b and KOI-203b (alias Kepler-17b)

We report the discovery of two new transiting hot Jupiters, KOI-135b and KOI-204b, that were previously identified as planetary candidates by Borucki et al. 2011, and, independently of the Kepler team, confirm the planetary nature of Kepler-17b, recently announced by Desert et al. 2011. Radial-velocity measurements, taken with the SOPHIE spectrograph at the OHP, and Kepler photometry (Q1 and Q2 data) were used to derive the orbital, stellar and planetary parameters. KOI-135b and KOI-204b orbit their parent stars in 3.02 and 3.25 days, respectively. They have approximately the same radius, Rp=1.20+/-0.06 R_jup and 1.24+/-0.07 R_jup, but different masses Mp=3.23+/-0.19 M_jup and 1.02+/-0.07 M_jup. As a consequence, their bulk densities differ by a factor of four, rho_p=2.33+/-0.36 g.cm^-3 (KOI-135b) and 0.65+/-0.12 g.cm-3 (KOI-204b). Our SOPHIE spectra of Kepler-17b, used both to measure the radial-velocity variations and determine the atmospheric parameters of the host star, allow us to refine the characterisation of the planetary system. In particular we found the radial-velocity semi-amplitude and the stellar mass to be respectively slightly smaller and larger than Desert et al. These two quantities, however, compensate and lead to a planetary mass fully consistent with Desert et al.: our analysis gives Mp=2.47+/-0.10 M_jup and Rp=1.33+/-0.04 R_jup. We found evidence for a younger age of this planetary system, t<1.8 Gyr, which is supported by both evolutionary tracks and gyrochronology. Finally, we confirm the detection of the optical secondary eclipse and found also the brightness phase variation with the Q1 and Q2 Kepler data. The latter indicates a low redistribution of stellar heat to the night side (<16% at 1-sigma), if the optical planetary occultation comes entirely from thermal flux. The geometric albedo is A_g<0.12 (1-sigma).

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arXiv2011

Planetary transit candidates in the CoRoT LRa01 field

Context: CoRoT is a pioneering space mission whose primary goals are stellar seismology and extrasolar planets search. Its surveys of large stellar fields generate numerous planetary candidates whose lightcurves have transit-like features. An extensive analytical and observational follow-up effort is undertaken to classify these candidates. Aims: The list of planetary transit candidates from the CoRoT LRa01 star field in the Monoceros constellation towards the Galactic anti-center is presented. The CoRoT observations of LRa01 lasted from 24 October 2007 to 3 March 2008. Methods: 7470 chromatic and 3938 monochromatic lightcurves were acquired and analysed. Instrumental noise and stellar variability were treated with several filtering tools by different teams from the CoRoT community. Different transit search algorithms were applied to the lightcurves. Results: Fifty-one stars were classified as planetary transit candidates in LRa01. Thirty-seven (i.e., 73 % of all candidates) are "good" planetary candidates based on photometric analysis only. Thirty-two (i.e., 87 % of the "good" candidates) have been followed-up. At the time of this writing twenty-two cases have been solved and five planets have been discovered: three transiting hot-Jupiters (CoRoT-5b, CoRoT-12b, and CoRoT-21b), the first terrestrial transiting planet (CoRoT-7b), and another planet in the same system (CoRoT-7c, detected by radial velocity survey only). Evidences of another non-transiting planet in the CoRoT-7 system, namely CoRoT-7d, have been recently found.

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arXiv2011

Higher-precision radial velocity measurements with the SOPHIE spectrograph using octagonal-section fibers

High-precision spectrographs play a key role in exoplanet searches using the radial velocity technique. But at the accuracy level of 1 m.s-1, required for super-Earth characterization, stability of fiber-fed spectrograph performance is crucial considering variable observing conditions such as seeing, guiding and centering errors and, telescope vignetting. In fiber-fed spectrographs such as HARPS or SOPHIE, the fiber link scrambling properties are one of the main issues. Both the stability of the fiber near-field uniformity at the spectrograph entrance and of the far-field illumination on the echelle grating (pupil) are critical for high-precision radial velocity measurements due to the spectrograph geometrical field and aperture aberrations. We conducted tests on the SOPHIE spectrograph at the 1.93-m OHP telescope to measure the instrument sensitivity to the fiber link light feeding conditions: star decentering, telescope vignetting by the dome,and defocussing. To significantly improve on current precision, we designed a fiber link modification considering the spectrograph operational constraints. We have developed a new link which includes a piece of octagonal-section fiber, having good scrambling properties, lying inside the former circular-section fiber, and we tested the concept on a bench to characterize near-field and far-field scrambling properties. This modification has been implemented in spring 2011 on the SOPHIE spectrograph fibers and tested for the first time directly on the sky to demonstrate the gain compared to the previous fiber link. Scientific validation for exoplanet search and characterization has been conducted by observing standard stars.

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arXiv2011

XX. CoRoT-20b: A very high density, high eccentricity transiting giant planet

We report the discovery by the CoRoT space mission of a new giant planet, CoRoT-20b. The planet has a mass of 4.24 +/- 0.23 MJ and a radius of 0.84 +/- 0.04 RJ. With a mean density of 8.87 +/- 1.10 g/cm^3, it is among the most compact planets known so far. Evolution models for the planet suggest a mass of heavy elements of the order of 800 ME if embedded in a central core, requiring a revision either of the planet formation models or of planet evolution and structure models. We note however that smaller amounts of heavy elements are expected from more realistic models in which they are mixed throughout the envelope. The planet orbits a G-type star with an orbital period of 9.24 days and an eccentricity of 0.56. The star's projected rotational velocity is vsini = 4.5 +/- 1.0 km/s, corresponding to a spin period of 11.5 +/- 3.1 days if its axis of rotation is perpendicular to the orbital plane. In the framework of Darwinian theories and neglecting stellar magnetic breaking, we calculate the tidal evolution of the system and show that CoRoT-20b is presently one of the very few Darwin-stable planets that is evolving towards a triple synchronous state with equality of the orbital, planetary and stellar spin periods.

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arXiv2011

SOPHIE velocimetry of Kepler transit candidates IV. KOI-196b: a non-inflated hot-Jupiter with a high albedo

We report the discovery of a new hot-Jupiter, KOI-196b, transiting a solar-type star with an orbital period of 1.855558 days\pm0.6s thanks to public photometric data from the Kepler space mission and new radial velocity observations obtained by the SOPHIE spectrograph mounted on the 1.93-m telescope at the Observatoire de Haute-Provence, France. The planet KOI-196b, with a radius of 0.841\pm0.032 Rjup and a mass of 0.49\pm0.09 Mjup, orbits a G2V star with R* = 0.996\pm0.032 Rsun, M*= 0.94\pm0.09 Msun, [Fe/H] = -0.10\pm0.16 dex, Teff= 5660\pm100 K and an age of 7.7\pm3.4 Gy. KOI-196b is one the rare close-in hot-Jupiters with a radius smaller than Jupiter suggesting a non-inflated planet. The high precision of the Kepler photometry permits us to detect the secondary transit with a depth of 64 +10/-12 ppm as well as the optical phase variation. We find a geometric albedo of Ag = 0.30\pm0.08 which is higher than most of the transiting hot-Jupiters with a measured Ag. Assuming no heat recirculation, we find a day-side temperature of Tday = 1930\pm80 K. KOI-196b seems to be one of the rare hot-Jupiters located in the short-period hot-Jupiter desert.

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arXiv2011

WASP-35b, WASP-48b and WASP-51b: Two new planets and an independent discovery of HAT-P-30b

We report the detection of WASP-35b, a planet transiting a metal-poor ([Fe/H] = -0.15) star in the Southern hemisphere, WASP-48b, an inflated planet which may have spun-up its slightly evolved host star of 1.75 R_sun in the Northern hemisphere, and the independent discovery of HAT-P-30b / WASP-51b, a new planet in the Northern hemisphere. Using WASP, RISE, FTS and TRAPPIST photometry, with CORALIE, SOPHIE and NOT spectroscopy, we determine that WASP-35b has a mass of 0.72 +/- 0.06 M_J and radius of 1.32 +/- 0.03 R_J, and orbits with a period of 3.16 days, WASP-48b has a mass of 0.98 +/- 0.09 M_J, radius of 1.67 +/- 0.08 R_J and orbits in 2.14 days, while WASP-51b, with an orbital period of 2.81 days, is found to have a mass of 0.76 +/- 0.05 M_J and radius of 1.42 +/- 0.04 R_J, agreeing with values of 0.71 +/- 0.03 M_J and 1.34 +/- 0.07 R_J reported for HAT-P-30b.

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arXiv2011

Transiting exoplanets from the CoRoT space mission: XIII. CoRoT-14b: an unusually dense very hot Jupiter

In this paper, the CoRoT Exoplanet Science Team announces its 14th discovery. Herein, we discuss the observations and analyses that allowed us to derive the parameters of this system: a hot Jupiter with a mass of $7.6 \pm 0.6$ Jupiter masses orbiting a solar-type star (F9V) with a period of only 1.5 d, less than 5 stellar radii from its parent star. It is unusual for such a massive planet to have such a small orbit: only one other known exoplanet with a higher mass orbits with a shorter period.

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arXiv2010

The Doppler Shadow of WASP-3b: A tomographic analysis of Rossiter-McLaughlin observations

Hot-Jupiter planets must form at large separations from their host stars where the temperatures are cool enough for their cores to condense. They then migrate inwards to their current observed orbital separations. Different theories of how this migration occurs lead to varying distributions of orbital eccentricity and the alignment between the rotation axis of the star and the orbital axis of the planet. The spin-orbit alignment of a transiting system is revealed via the Rossiter-McLaughlin effect, which is the anomaly present in the radial velocity measurements of the rotating star during transit due to the planet blocking some of the starlight. In this paper we aim to measure the spin-orbit alignment of the WASP-3 system via a new way of analysing the Rossiter-McLaughlin observations. We apply a new tomographic method for analysing the time variable asymmetry of stellar line profiles caused by the Rossiter-McLaughlin effect. This new method eliminates the systematic error inherent in previous methods used to analyse the effect. We find a value for the projected stellar spin rate of v sin i = 13.9 \pm 0.03 km/s which is in agreement with previous measurements but has a much higher precision. The system is found to be well aligned which favours an evolutionary history for WASP-3b involving migration through tidal interactions with a protoplanetary disc. Using gyrochronology we estimate the age of the star to be ~300 Myr with an upper limit of 2 Gyr from comparison with isochrones.

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arXiv2010

Transiting exoplanets from the CoRoT space mission XIV. CoRoT-11b: a transiting massive "hot-Jupiter" in a prograde orbit around a rapidly rotating F-type star

The CoRoT exoplanet science team announces the discovery of CoRoT-11b, a fairly massive hot-Jupiter transiting a V=12.9 mag F6 dwarf star (M*=1.27 +/- 0.05 Msun, R*=1.37 +/- 0.03 Rsun, Teff=6440 +/- 120 K), with an orbital period of P=2.994329 +/- 0.000011 days and semi-major axis a=0.0436 +/- 0.005 AU. The detection of part of the radial velocity anomaly caused by the Rossiter-McLaughlin effect shows that the transit-like events detected by CoRoT are caused by a planet-sized transiting object in a prograde orbit. The relatively high projected rotational velocity of the star (vsini=40+/-5 km/s) places CoRoT-11 among the most rapidly rotating planet host stars discovered so far. With a planetary mass of mp=2.33+/-0.34 Mjup and radius rp=1.43+/-0.03 Rjup, the resulting mean density of CoRoT-11b (rho=0.99+/-0.15 g/cm^3) can be explained with a model for an inflated hydrogen-planet with a solar composition and a high level of energy dissipation in its interior.

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arXiv2010

Transiting exoplanets from the CoRoT space mission. XI. CoRoT-8b: a hot and dense sub-Saturn around a K1 dwarf

We report the discovery of CoRoT-8b, a dense small Saturn-class exoplanet that orbits a K1 dwarf in 6.2 days, and we derive its orbital parameters, mass, and radius. We analyzed two complementary data sets: the photometric transit curve of CoRoT-8b as measured by CoRoT and the radial velocity curve of CoRoT-8 as measured by the HARPS spectrometer. We find that CoRoT-8b is on a circular orbit with a semi-major axis of 0.063 +/- 0.001 AU. It has a radius of 0.57 +/- 0.02 RJ, a mass of 0.22 +/- 0.03 MJ, and therefore a mean density 1.6 +/- 0.1 g/cm^3. With 67 % of the size of Saturn and 72 % of its mass, CoRoT-8b has a density comparable to that of Neptune (1.76 g/cm^3). We estimate its content in heavy elements to be 47-63 Earth masses, and the mass of its hydrogen-helium envelope to be 7-23 Earth masses. At 0.063 AU, the thermal loss of hydrogen of CoRoT-8b should be no more than about 0.1 % over an assumed integrated lifetime of 3~Ga.

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