Publications of Michaël Gillon
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See detailWASP-5b: a dense, very hot Jupiter transiting a 12th-mag Southern-hemisphere star
Anderson, D. R.; Gillon, Michaël ULiege; Hellier, C. et al

in Monthly Notices of the Royal Astronomical Society (2008), 387

We report the discovery of WASP-5b, a Jupiter-mass planet orbiting a 12th-mag G-type star in the Southern hemisphere. The 1.6-d orbital period places WASP-5b in the class of very hot Jupiters and leads to ... [more ▼]

We report the discovery of WASP-5b, a Jupiter-mass planet orbiting a 12th-mag G-type star in the Southern hemisphere. The 1.6-d orbital period places WASP-5b in the class of very hot Jupiters and leads to a predicted equilibrium temperature of 1750K. WASP-5b is the densest of any known Jovian-mass planet, being a factor of 7 denser than TrES-4, which is subject to similar stellar insolation, and a factor of 3 denser than WASP-4b, which has a similar orbital period. We present transit photometry and radial velocity measurements of WASP-5 (= USNO-B10487-0799749), from which we derive the mass, radius and density of the planet: M[SUB]P[/SUB] = 1.58[SUP]+0.13[/SUP][SUB]-0.08[/SUB]M[SUB]J[/SUB],R[SUB]P[/SUB] = 1.090[SUP]+0.094[/SUP][SUB]-0.058[/SUB]R[SUB]J[/SUB] and rho[SUB]P[/SUB] = 1.22[SUP]+0.19[/SUP][SUB]-0.24[/SUB]rho[SUB]J[/SUB]. The orbital period is P = 1.6284296[SUP]+0.0000048[/SUP][SUB]-0.0000037[/SUB]d and the mid-transit epoch is T[SUB]C[/SUB](HJD) = 2454375.62466[SUP]+0.00026[/SUP][SUB]-0.00025[/SUB]. [less ▲]

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See detailTransiting exoplanets from the CoRoT space mission. I. CoRoT-Exo-1b: a low-density short-period planet around a G0V star
Barge, P.; Baglin, A.; Auvergne, M. et al

in Astronomy and Astrophysics (2008), 482

Context: The pioneer space mission for photometric planet searches, CoRoT, steadily monitors about 12 000 stars in each of its fields of view. Transit candidates can be detected early in the processing of ... [more ▼]

Context: The pioneer space mission for photometric planet searches, CoRoT, steadily monitors about 12 000 stars in each of its fields of view. Transit candidates can be detected early in the processing of the data and before the end of a run of observation. Aims: We report the detection of the first planet discovered by CoRoT and characterizing it with the help of follow-up observations. Methods: Raw data were filtered from outliers and residuals at the orbital period of the satellite. The orbital parameters and the radius of the planet were estimated by best fitting the phase folded light curve with 34 successive transits. Doppler measurements with the SOPHIE spectrograph permitted us to secure the detection against binaries and to estimate the mass of the planet. Results: The accuracy of the data is very high with a dispersion in the 2.17 min binned phase-folded light curve that does not exceed ~3.×10[SUP]-4[/SUP] in flux unit. The planet orbits a mildly metal-poor G0V star of magnitude V=13.6 in 1.5 days. The estimated mass and radius of the star are 0.95±0.15 M[SUB]o[/SUB] and 1.11±0.05 R[SUB]o[/SUB]. We find the planet has a radius of 1.49±0.08 R_Jup, a mass of 1.03±0.12 M_Jup, and a particularly low mean density of 0.38±0.05 g cm[SUP]-3[/SUP]. The CoRoT space mission, launched on Dec. 27th, 2006, was developed and is operated by the CNES, with participation of the Science Program of ESA, ESTEC/RSSD, Austria, Belgium, Brazil, Germany and Spain. Based in part on observations with the SOPHIE spectrograph at Obs. de Haute Provence, France. Table [see full text] is only available in electronic form at http://www.aanda.org Individual photometric measurements are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/482/L17 [less ▲]

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See detailTransiting exoplanets from the CoRoT space mission. II. CoRoT-Exo-2b: a transiting planet around an active G star
Alonso, R.; Auvergne, M.; Baglin, A. et al

in Astronomy and Astrophysics (2008), 482

Context: The CoRoT mission, a pioneer in exoplanet searches from space, has completed its first 150 days of continuous observations of ~12 000 stars in the galactic plane. An analysis of the raw data ... [more ▼]

Context: The CoRoT mission, a pioneer in exoplanet searches from space, has completed its first 150 days of continuous observations of ~12 000 stars in the galactic plane. An analysis of the raw data identifies the most promising candidates and triggers the ground-based follow-up. Aims: We report on the discovery of the transiting planet CoRoT-Exo-2b, with a period of 1.743 days, and characterize its main parameters. Methods: We filter the CoRoT raw light curve of cosmic impacts, orbital residuals, and low frequency signals from the star. The folded light curve of 78 transits is fitted to a model to obtain the main parameters. Radial velocity data obtained with the SOPHIE, CORALIE and HARPS spectrographs are combined to characterize the system. The 2.5 min binned phase-folded light curve is affected by the effect of sucessive occultations of stellar active regions by the planet, and the dispersion in the out of transit part reaches a level of 1.09×10[SUP]-4[/SUP] in flux units. Results: We derive a radius for the planet of 1.465 ± 0.029 R_Jup and a mass of 3.31 ± 0.16 M_Jup, corresponding to a density of 1.31 ± 0.04 g/cm^3. The large radius of CoRoT-Exo-2b cannot be explained by current models of evolution of irradiated planets. Based on observations obtained with CoRoT, a space project operated by the French Space Agency, CNES, with participation of the Science Programme of ESA, ESTEC/RSSD, Austria, Belgium, Brazil, Germany and Spain; and on observations made with SOPHIE spectrograph at Observatoire de Haute Provence, France (PNP.07 A.MOUT), CORALIE, and HARPS spectrograph at ESO La Silla Observatroy (079.C-0127/F)). Table 2 is only available in electronic form at http://www.aanda.org [less ▲]

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See detailOGLE-TR-211 - a new transiting inflated hot Jupiter from the OGLE survey and ESO LP666 spectroscopic follow-up program
Udalski, A.; Pont, F.; Naef, D. et al

in Astronomy and Astrophysics (2008), 482

We present results of the photometric campaign for planetary and low-luminosity object transits conducted by the OGLE survey in the 2005 season (Campaign #5). About twenty of the most promising candidates ... [more ▼]

We present results of the photometric campaign for planetary and low-luminosity object transits conducted by the OGLE survey in the 2005 season (Campaign #5). About twenty of the most promising candidates discovered in these data were subsequently verified spectroscopically with the VLT/FLAMES spectrograph. One of the candidates, OGLE-TR-211, reveals clear changes of radial velocity with a small amplitude of 82 m/s, varying in phase with photometric transit ephemeris. Further analysis confirms the planetary nature of this system. Follow-up precise photometry of OGLE-TR-211 with VLT/FORS, together with radial velocity spectroscopy, supplemented with high-resolution, high S/N VLT/UVES spectra allowed us to derive parameters of the planet and host star. OGLE-TR-211b is a hot Jupiter orbiting an F7-8 spectral type dwarf star with a period of 3.68 days. The mass of the planet is equal to 1.03±0.20 M_Jup, while its radius 1.36[SUP]+0.18[/SUP][SUB]-0.09[/SUB] R_Jup. The radius is about 20% larger than the typical radius of hot Jupiters of similar mass. OGLE-TR-211b is, then, another example of inflated hot Jupiters - a small group of seven exoplanets with large radii and unusually low densities - objects that are a challenge to the current models of exoplanets. Based on observations made with the FORS1 camera and the FLAMES/UVES spectrograph at the VLT, ESO, Chile (program 07.C-0706, 076.C-0122, and 177.C-0666) and 1.3-m Warsaw Telescope at Las Campanas Observatory, Chile. [less ▲]

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See detailLupus-TR-3b: A Low-Mass Transiting Hot Jupiter in the Galactic Plane?
Weldrake, David T F; Bayliss, Daniel D R; Sackett, Penny D et al

in Astrophysical Journal (2008), 675

We present a strong case for a transiting hot Jupiter planet identified during a single-field transit survey toward the Lupus Galactic plane. The object, Lupus-TR-3b, transits a V=17.4 K1 V host star ... [more ▼]

We present a strong case for a transiting hot Jupiter planet identified during a single-field transit survey toward the Lupus Galactic plane. The object, Lupus-TR-3b, transits a V=17.4 K1 V host star every 3.91405 days. Spectroscopy and stellar colors indicate a host star with effective temperature 5000 +/- 150 K, with a stellar mass and radius of 0.87 +/- 0.04 M[SUB]solar[/SUB] and 0.82 +/- 0.05 R[SUB]solar[/SUB], respectively. Limb-darkened transit fitting yields a companion radius of 0.89+/-0.07 R[SUB]J[/SUB] and an orbital inclination of 88.3[SUP]+1.3[/SUP][SUB]-0.8[/SUB] deg. Magellan 6.5 m MIKE radial velocity measurements reveal a 2.4 sigma K = 114 +/- 25 m s[SUP]-1[/SUP] sinusoidal variation in phase with the transit ephemeris. The resulting mass is 0.81 +/- 0.18 M[SUB]J[/SUB] and density 1.4 +/- 0.4 g cm[SUP]-3[/SUP]. Y-band PANIC image deconvolution reveals a V>=21 red neighbor 0.4[SUP]''[/SUP] away which, although highly unlikely, we cannot conclusively rule out as a blended binary with current data. However, blend simulations show that only the most unusual binary system can reproduce our observations. This object is very likely a planet, detected from a highly efficient observational strategy. Lupus-TR-3b constitutes the faintest ground-based detection to date, and one of the lowest mass hot Jupiters known. [less ▲]

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See detailWASP-4b: A 12th Magnitude Transiting Hot Jupiter in the Southern Hemisphere
Wilson, D. M.; Gillon, Michaël ULiege; Hellier, C. et al

in Astrophysical Journal (2008), 675

We report the discovery of WASP-4b, a large transiting gas-giant planet with an orbital period of 1.34 days. This is the first planet to be discovered by the SuperWASP-South observatory and CORALIE ... [more ▼]

We report the discovery of WASP-4b, a large transiting gas-giant planet with an orbital period of 1.34 days. This is the first planet to be discovered by the SuperWASP-South observatory and CORALIE collaboration and the first planet orbiting a star brighter than 16th magnitude to be discovered in the southern hemisphere. A simultaneous fit to high-quality light curves and precision radial velocity measurements leads to a planetary mass of 1.22[SUP]+0.09[/SUP][SUB]-0.08[/SUB] M[SUB]Jup[/SUB] and a planetary radius of 1.42[SUP]+0.07[/SUP][SUB]-0.04[/SUB] R[SUB]Jup[/SUB]. The host star is USNO-B1.0 0479-0948995, a G7 V star of visual magnitude 12.5. As a result of the short orbital period, the predicted surface temperature of the planet is 1761 K, making it an ideal candidate for detections of the secondary eclipse at infrared wavelengths. [less ▲]

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See detailCharacterization of the hot Neptune GJ 436 b with Spitzer and ground-based observations
Demory, B*-O; Gillon, Michaël ULiege; Barman, T. et al

in Astronomy and Astrophysics (2007), 475

We present Spitzer Space Telescope infrared photometry of a secondary eclipse of the hot Neptune GJ 436 b. The observations were obtained using the 8-mum band of the InfraRed Array Camera (IRAC). The data ... [more ▼]

We present Spitzer Space Telescope infrared photometry of a secondary eclipse of the hot Neptune GJ 436 b. The observations were obtained using the 8-mum band of the InfraRed Array Camera (IRAC). The data spanning the predicted time of secondary eclipse show a clear flux decrement with the expected shape and duration. The observed eclipse depth of 0.58 mmag allows us to estimate a blackbody brightness temperature of T[SUB]p[/SUB] = 717 ± 35 K at 8 mum. We compare this infrared flux measurement to a model of the planetary thermal emission, and show that this model reproduces properly the observed flux decrement. The timing of the secondary eclipse confirms the non-zero orbital eccentricity of the planet, while also increasing its precision (e = 0.14 ± 0.01). Additional new spectroscopic and photometric observations allow us to estimate the rotational period of the star and to assess the potential presence of another planet. Our final secondary eclipse, photometric and Ca II H+K index time series are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/475/1125 [less ▲]

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See detailThe Transit Light Curve Project. VII. The Not-So-Bloated Exoplanet HAT-P-1b
Winn, Joshua N; Holman, Matthew J; Bakos, Gaspar Á et al

in Astronomical Journal (2007), 134

We present photometry of the G0 star HAT-P-1 during six transits of its close-in giant planet, and we refine the estimates of the system parameters. Relative to Jupiter's properties, HAT-P-1b is 1.20 ± 0 ... [more ▼]

We present photometry of the G0 star HAT-P-1 during six transits of its close-in giant planet, and we refine the estimates of the system parameters. Relative to Jupiter's properties, HAT-P-1b is 1.20 ± 0.05 times larger, and its surface gravity is 2.7 ± 0.2 times weaker. Although it remains the case that HAT-P-1b is among the least dense of the known sample of transiting exoplanets, its properties are in accord with previously published models of strongly irradiated, coreless, solar-composition giant planets. The times of the transits have a typical accuracy of 1 minute and do not depart significantly from a constant period. [less ▲]

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See detailThe HARPS search for southern extra-solar planets. X. A m sin i = 11 M_â planet around the nearby spotted M dwarf <ASTROBJ>GJ 674</ASTROBJ>
Bonfils, X.; Mayor, M.; Delfosse, X. et al

in Astronomy and Astrophysics (2007), 474

Context: How planet properties depend on stellar mass is a key diagnostic of planetary formation mechanisms. Aims: This motivates planet searches around stars that are significantly more massive or less ... [more ▼]

Context: How planet properties depend on stellar mass is a key diagnostic of planetary formation mechanisms. Aims: This motivates planet searches around stars that are significantly more massive or less massive than the Sun, and in particular our radial velocity search for planets around very low-mass stars. Methods: As part of that program, we obtained measurements of <ASTROBJ>GJ 674</ASTROBJ>, an M 2.5 dwarf at d = 4.5 pc. These measurements have dispersion much in excess of their internal errors. An intensive observing campaign demonstrates that the excess dispersion is due to two superimposed coherent signals, with periods of 4.69 and 35 days. Results: These data are described well by a 2-planet Keplerian model where each planet has a ~11 M_â minimum mass. A careful analysis of the (low-level) magnetic activity of <ASTROBJ>GJ 674</ASTROBJ>, however, demonstrates that the 35-day period coincides with the stellar rotation period. This signal therefore originates in a spot inhomogeneity modulated by stellar rotation. The 4.69-day signal, on the other hand, is caused by a bona-fide planet, <ASTROBJ>GJ 674b</ASTROBJ>. Conclusions: Its detection adds to the growing number of Neptune-mass planets around M-dwarfs and reinforces the emerging conclusion that this mass domain is much more populated than the Jovian mass range. We discuss the metallicity distributions of M dwarf with and without planets and find a low 11% probability that they are drawn from the same parent distribution. Moreover, we find tentative evidence that the host star metallicity correlates with the total mass of their planetary system. Based on observations made with the HARPS instrument on the ESO 3.6 m telescope under the GTO program ID 072.C-0488 at Cerro La Silla (Chile). Radial-velocity, photometric and Ca II H+K index time series are only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strabg.fr/cgi-bin/qcat?J/A+A/474/293 [less ▲]

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See detailDetection of transits of the nearby hot Neptune GJ 436 b
Gillon, Michaël ULiege; Pont, F.; Demory, B*-O et al

in Astronomy and Astrophysics (2007), 472

This Letter reports on the photometric detection of transits of the Neptune-mass planet orbiting the nearby M-dwarf star GJ 436. It is by far the closest, smallest, and least massive transiting planet ... [more ▼]

This Letter reports on the photometric detection of transits of the Neptune-mass planet orbiting the nearby M-dwarf star GJ 436. It is by far the closest, smallest, and least massive transiting planet detected so far. Its mass is slightly larger than Neptune's at M = 22.6 ± 1.9 M_â . The shape and depth of the transit lightcurves show that it is crossing the host star disc near its limb (impact parameter 0.84 ± 0.03) and that the planet size is comparable to that of Uranus and Neptune, R = 25 200 ± 2200 km = 3.95 ± 0.35 R_â . Its main constituant is therefore very likely to be water ice. If the current planet structure models are correct, an outer layer of H/He constituting up to ten percent in mass is probably needed on top of the ice to account for the observed radius. [less ▲]

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See detailAccurate Spitzer infrared radius measurement for the hot Neptune GJ 436b
Gillon, Michaël ULiege; Demory, B*-O; Barman, T. et al

in Astronomy and Astrophysics (2007), 471

We present Spitzer Space Telescope infrared photometry of a primary transit of the hot Neptune GJ 436b. The observations were obtained using the 8 mum band of the InfraRed Array Camera (IRAC). The high ... [more ▼]

We present Spitzer Space Telescope infrared photometry of a primary transit of the hot Neptune GJ 436b. The observations were obtained using the 8 mum band of the InfraRed Array Camera (IRAC). The high accuracy of the transit data and the weak limb-darkening in the 8 mum IRAC band allow us to derive (assuming M = 0.44 ± 0.04 M_o for the primary) a precise value for the planetary radius (4.19[SUP]+0.21[/SUP][SUB]-0.16[/SUB] R_â ), the stellar radius (0.463[SUP]+0.022[/SUP][SUB]-0.017[/SUB] R_o), the orbital inclination (85.90°[SUP]+0.19°[/SUP][SUB]-0.18°[/SUB]) and transit timing (2454280.78186[SUP]+0.00015[/SUP][SUB]-0.00008[/SUB] HJD). Assuming current planet models, an internal structure similar to that of Neptune with a small H/He envelope is necessary to account for the measured radius of GJ 436b. The photometric data are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/471/L51 [less ▲]

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See detailDECPHOT: An Optimal Deconvolution-based Photometric Reduction Method
Gillon, Michaël ULiege; Magain, Pierre ULiege; Chantry, Virginie ULiege et al

in Transiting Extrapolar Planets Workshop (2007, July 01)

A high accuracy photometric reduction method is needed to take full advantage of the potential of the transit method for the detection and characterization of exoplanets, especially in deep crowded fields ... [more ▼]

A high accuracy photometric reduction method is needed to take full advantage of the potential of the transit method for the detection and characterization of exoplanets, especially in deep crowded fields. In this context, we present DECPHOT, a new deconvolution-based photometry algorithm able to deal with a very high level of crowding and large variations of seeing. It also increases the resolution of astronomical images, an important advantage for the discrimination of false positives in transit photometry. [less ▲]

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See detailFirst Results from SuperWASP
Street, R. A.; Collier Cameron, A.; Maxted, P. et al

in Transiting Extrapolar Planets Workshop (2007, July 01)

We present a summary of the first results from the SuperWASP survey, including the detection of two new transiting exoplanets. We summarize our candidate selection procedure and the process by which we ... [more ▼]

We present a summary of the first results from the SuperWASP survey, including the detection of two new transiting exoplanets. We summarize our candidate selection procedure and the process by which we eliminated many false positives prior to radial velocity observations carried out with the Sophie spectrograph at the Observatoire de Haute-Provence. These data confirmed the discovery of two new transiting hot Jupiters, while rejecting 23 other targets. The two confirmed planets, WASP-1b & WASP-2b, respectively orbit F7V and K1V host stars with periods of 2.52 days and 2.15 days. The mass of WASP-1b is constrained to the range 0.80-0.98 M_{Jup} and the planet appears to be `bloated' with a radius of at least 1.33 R_{Jup}. WASP-2b has a mass between 0.81-0.95 M_{Jup} and a radius in the range 0.65-1.26 R_{Jup}. [less ▲]

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See detailThe transiting planet OGLE-TR-132b revisited with new spectroscopy and deconvolution photometry[SUP], [/SUP]
Gillon, Michaël ULiege; Pont, F.; Moutou, C. et al

in Astronomy and Astrophysics (2007), 466

OGLE-TR-132b transits a very metal-rich F dwarf about 2000 pc from the Sun, in the Galactic disc towards Carina. It orbits very close to its host star (a = 0.03 AU) and has an equilibrium temperature of ... [more ▼]

OGLE-TR-132b transits a very metal-rich F dwarf about 2000 pc from the Sun, in the Galactic disc towards Carina. It orbits very close to its host star (a = 0.03 AU) and has an equilibrium temperature of nearly 2000 K. Using rapid-cadence transit photometry from the FORS2 camera on the VLT and SUSI2 on the NTT, and high-resolution spectroscopy with UVES on the VLT, we refine the shape of the transit light curve and the parameters of the system. In particular, we improve the planetary radius estimate, R = 1.18 ± 0.07 R[SUB]J[/SUB] and provide very precise ephemeris, T_tr = 2 453 142.59123 ± 0.0003 BJD and P = 1.689868 ± 0.000003 days. The obtained planetary mass is 1.14 ± 0.12 M_J. Our results give a slightly smaller and lighter star, and bigger planet, than previous values. As the VLT/FORS2 light curve obtained in this analysis with the deconvolution photometry algorithm DECPHOT shows a transit depth in disagreement with the one obtained by a previous study using the same data, we analyze them with two other reduction methods (aperture and image subtraction). The light curves obtained with the three methods are in good agreement, though deconvolution-based photometry is significantly more precise. It appears from these results that the smaller transit depth obtained in the previous study was due to a normalisation problem inherent to the reduction procedure used. Based on data collected with the FORS2 imager at the VLT-UT4 telescope (Paranal Observatory, ESO, Chile) in the programme 273.C-5017A, with the SUSI2 imager at the NTT telescope (La Silla Observatory, ESO, Chile) in the programme 075.C-0462A, and with the UVES spectrograph at the VLT-UT2 telescope (Paranal Observatory, ESO, Chile) in the programme 076.C-0131. The reduced photometric data used in this work are available only in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/466/743 [less ▲]

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See detailThe "666" collaboration on OGLE transits. I. Accurate radius of the planets OGLE-TR-10b and OGLE-TR-56b with VLT deconvolution photometry
Pont, F.; Moutou, C.; Gillon, Michaël ULiege et al

in Astronomy and Astrophysics (2007), 465

Transiting planets are essential to study the structure and evolution of extra-solar planets. For that purpose, it is important to measure precisely the radius of these planets. Here we report new high ... [more ▼]

Transiting planets are essential to study the structure and evolution of extra-solar planets. For that purpose, it is important to measure precisely the radius of these planets. Here we report new high-accuracy photometry of the transits of OGLE-TR-10 and OGLE-TR-56 with VLT/FORS1. One transit of each object was covered in Bessel V and R filters, and treated with the deconvolution-based photometry algorithm DECPHOT, to ensure accurate millimagnitude light curves. Together with earlier spectroscopic measurements, the data imply a radius of 1.22{[SUP]+0.12[/SUP][SUB]-0.07[/SUB]} R[SUB]J[/SUB] for OGLE-TR-10b and 1.30 ± 0.05 R[SUB]J[/SUB] for OGLE-TR-56b. A re-analysis of the original OGLE photometry resolves an earlier discrepancy about the radius of OGLE-TR-10. The transit of OGLE-TR-56 is almost grazing, so that small systematics in the photometry can cause large changes in the derived radius. Our study confirms both planets as inflated hot Jupiters, with large radii comparable to that of HD 209458b and at least two other recently discovered transiting gas giants. Based on data collected with the FORS1 imager at the VLT-Kueyen telescope (Paranal Observatory, ESO, Chile) in the programme 177.C-0666E. [less ▲]

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See detailA deconvolution-based algorithm for crowded field photometry with unknown point spread function
Magain, Pierre ULiege; Courbin, F.; Gillon, Michaël ULiege et al

in Astronomy and Astrophysics (2007), 461

A new method is presented for determining the point spread function (PSF) of images that lack bright and isolated stars. It is based on the same principles as the MCS image deconvolution algorithm. It ... [more ▼]

A new method is presented for determining the point spread function (PSF) of images that lack bright and isolated stars. It is based on the same principles as the MCS image deconvolution algorithm. It uses the information contained in all stellar images to achieve the double task of reconstructing the PSFs for single or multiple exposures of the same field and to extract the photometry of all point sources in the field of view. The use of the full information available allows us to construct an accurate PSF. The possibility to simultaneously consider several exposures makes it well suited to the measurement of the light curves of blended point sources from data that would be very difficult or even impossible to analyse with traditional PSF fitting techniques. The potential of the method for the analysis of ground-based and space-based data is tested on artificial images and illustrated by several examples, including HST/NICMOS images of a lensed quasar and VLT/ISAAC images of a faint blended Mira star in the halo of the giant elliptical galaxy NGC 5128 (Cen A). [less ▲]

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See detailHigh accuracy transit photometry of the planet OGLE-TR-113b with a new deconvolution-based method
Gillon, Michaël ULiege; Pont, F.; Moutou, C. et al

in Astronomy and Astrophysics (2006), 459

A high accuracy photometry algorithm is needed to take full advantage of the potential of the transit method for the characterization of exoplanets, especially in deep crowded fields. It has to reduce to ... [more ▼]

A high accuracy photometry algorithm is needed to take full advantage of the potential of the transit method for the characterization of exoplanets, especially in deep crowded fields. It has to reduce to the lowest possible level the negative influence of systematic effects on the photometric accuracy. It should also be able to cope with a high level of crowding and with large-scale variations of the spatial resolution from one image to another. A recent deconvolution-based photometry algorithm fulfills all these requirements, and it also increases the resolution of astronomical images, which is an important advantage for the detection of blends and the discrimination of false positives in transit photometry. We made some changes to this algorithm to optimize it for transit photometry and used it to reduce NTT/SUSI2 observations of two transits of OGLE-TR-113b. This reduction has led to two very high precision transit light curves with a low level of systematic residuals, used together with former photometric and spectroscopic measurements to derive new stellar and planetary parameters in excellent agreement with previous ones, but significantly more precise. [less ▲]

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See detailHigh precision determination of the atmospheric parameters and abundances of the COROT main targets
Gillon, Michaël ULiege; Magain, Pierre ULiege

in Astronomy and Astrophysics (2006), 448

Context: .One of the main goals of the COROT mission is to get precise photometric observations of selected bright stars in order to allow the modelling of their interior through asteroseismology. However ... [more ▼]

Context: .One of the main goals of the COROT mission is to get precise photometric observations of selected bright stars in order to allow the modelling of their interior through asteroseismology. However, in order to interpret the asteroseismological data, the effective temperature, surface gravity, and chemical composition of the stars must be known with sufficient accuracy.Aims.To carry out this task, we have developed a spectroscopic method called APASS (Atmospheric Parameters and Abundances from Synthetic Spectra) which allows precise analysis of stars with a moderate to high rotational velocity, which is the case for most primary COROT targets.Methods.Our method is based on synthetic spectra in which individual lines are replaced by analysis units (isolated lines or line blends, depending on the crowding of the spectral region and on the rotational broadening). It works differentially with respect to the Sun and allows the atmospheric parameters and chemical abundances to be determined by considering analysis units with different sensitivities to these various parameters.Results.Using high signal-to-noise spectra and the APASS method, we determined the atmospheric parameters and chemical abundances of 13 primary COROT targets. Our results agree well with those obtained by Bruntt using his software VWA and with those obtained with the software TEMPLOGG. However, in both cases, our error bars are significantly smaller than those of other methods. Our effective temperatures are also in excellent agreement with those obtained with the IR photometry method. For five stars with relatively low rotational velocity, we also performed an analysis with a classical equivalent-width method to test agreement with APASS results. We show that equivalent-width measurements by Gaussian or Voigt profile-fitting are sensitive to the rotational broadening, leading to systematic errors whenever the projected rotation velocity is non-negligible. The APASS method appears superior in all cases and should thus be preferred. [less ▲]

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See detailContribution à la mission CoRoT et à la recherche d'exoplanètes par la méthode des transits photométriques
Gillon, Michaël ULiege

Doctoral thesis (2006)

In this thesis, we present our contributions to the CoRoT mission and to the search for exoplanets with the photometric transit method. We developped a spectroscopic analysis method, APASS, which allows ... [more ▼]

In this thesis, we present our contributions to the CoRoT mission and to the search for exoplanets with the photometric transit method. We developped a spectroscopic analysis method, APASS, which allows to obtain a precise determination of atmospheric physical parameters and abundances for stars with an unnegligeable rotational speed. We present APASS and the high-precision results we obtained for main target stars of the asteroseismological part of the CoRoT mission. Our results are in agreement with those obtained by other authors using different analysis methods, while beeing more precise. Furthermore, they show that the use of a spectroscopic analysis method based on equivalent widths measurements by gaussian or Voigt profiles fitting should be avoided for stars whose rotational velocity is significantly higher then the Sun’s, and that a method using synthetic spectra fitting for which the convolution is a free parameter should be prefered. Next, we investigate the potential of extrasolar planet transit surveys. We show that CoRoT has a very high potential for the detection of close-in giant planets, better than the one of the KEPLER mission. This latter reveals to be better for the detection of terrestrial planets. Nevertheless, CoRoT could detect a few giant telluric planets of short orbital period, provided that this kind of object is frequent in our galaxy. For ground-based surveys, our results based on the use of large telescopes and wide-field cameras seem to indicate that an important potential is also available from the ground. These results are nevertheless less reliable, mainly because of the lack of knowledge about the influence of systematic effects, and additional investigations using actual data will be necessary. We present then the deconvolution method MCS and the way we adapted it to planetary transit photometry. We present the results we obtained after analysis of actual data for OGLE-TR-123 (VLT/FORS2 data) and OGLE-TR-132 (VLT/FORS2 and NTT/SUSI2 data). These results are very encouraging and demonstrate the high potential of MCS for this kind of high-precision analysis. Finally, we present the future improvements we intend to install to obtain a still higher level of precision and to increase the speed of analysis. [less ▲]

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See detailHigh precision photometry in crowded stellar fields
Magain, Pierre ULiege; Courbin, Frédéric; Gillon, Michaël ULiege et al

in SPIE Newsroom (2006)

A deconvolution-based method which allows to derive high-precision photometry of stars in crowded fields, proves very useful for a variety of astronomical projects, including transit searches for ... [more ▼]

A deconvolution-based method which allows to derive high-precision photometry of stars in crowded fields, proves very useful for a variety of astronomical projects, including transit searches for extrasolar planets. [less ▲]

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