Publications of Michaël Gillon
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See detailOn the Influence of Blends on the Potential of Ground-based Transit Surveys
Gillon, Michaël ULiege; Magain, Pierre ULiege

in Afonso, C.; Weldrake, D.; Henning, T. (Eds.) Transiting Extrapolar Planets Workshop (2007, July 01)

Transit surveys have to observe many stars all at once in order to compensate for the rarity of the searched events. Such surveys, especially the ones observing a deep field of view and/or broadening ... [more ▼]

Transit surveys have to observe many stars all at once in order to compensate for the rarity of the searched events. Such surveys, especially the ones observing a deep field of view and/or broadening their stellar images, have to deal with a relatively high level of crowding. This crowding could lead to a reduction of the number of detectable transits, and the estimation of the potential of such surveys without taking into account the influence of blends could give overoptimistic results. We have developed a code which allows to estimate the extent by which such a survey is affected by the crowding of the field of view. Our results show that the influence of blends is important only for severe levels of crowding and is in general much less crucial than the influence of red noise. [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 detailWASP-1b and WASP-2b: two new transiting exoplanets detected with SuperWASP and SOPHIE
Cameron, A Collier; Bouchy, F.; Hébrard, G. et al

in Monthly Notices of the Royal Astronomical Society (2007), 375

We have detected low-amplitude radial-velocity variations in two stars, USNO-B1.0 1219-0005465 (GSC 02265-00107 = WASP-1) and USNO-B1.0 0964-0543604 (GSC 00522-01199 = WASP-2). Both stars were identified ... [more ▼]

We have detected low-amplitude radial-velocity variations in two stars, USNO-B1.0 1219-0005465 (GSC 02265-00107 = WASP-1) and USNO-B1.0 0964-0543604 (GSC 00522-01199 = WASP-2). Both stars were identified as being likely host stars of transiting exoplanets in the 2004 SuperWASP wide-field transit survey. Using the newly commissioned radial-velocity spectrograph SOPHIE at the Observatoire de Haute-Provence, we found that both objects exhibit reflex orbital radial-velocity variations with amplitudes characteristic of planetary-mass companions and in-phase with the photometric orbits. Line-bisector studies rule out faint blended binaries as the cause of either the radial-velocity variations or the transits. We perform preliminary spectral analyses of the host stars, which together with their radial-velocity variations and fits to the transit light curves yield estimates of the planetary masses and radii. WASP-1b and WASP-2b have orbital periods of 2.52 and 2.15 d, respectively. Given mass estimates for their F7V and K1V primaries, we derive planet masses 0.80-0.98 and 0.81-0.95 times that of Jupiter, respectively. WASP-1b appears to have an inflated radius of at least 1.33 R[SUB]Jup[/SUB], whereas WASP-2b has a radius in the range 0.65-1.26 R[SUB]Jup[/SUB]. [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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See detailOn the potential of extrasolar planet transit surveys
Gillon, Michaël ULiege; Courbin, F.; Magain, Pierre ULiege et al

in Astronomy and Astrophysics (2005), 442

We analyse the respective benefits and drawbacks of ground-based and space-based transit surveys for extrasolar planets. Based on simple but realistic assumptions about the fraction of lower main sequence ... [more ▼]

We analyse the respective benefits and drawbacks of ground-based and space-based transit surveys for extrasolar planets. Based on simple but realistic assumptions about the fraction of lower main sequence stars harboring telluric and giant planets within the outer limit of the habitable zone, we predict the harvests of fictitious surveys with three existing wide field optical and near-IR cameras: the CFHT-Megacam, SUBARU-Suprime and VISTA-IR. An additional promising instrument is considered, VISTA-Vis, currently under development. The results are compared with the harvests predicted under exactly the same assumptions, for the space missions COROT and KEPLER. We show that ground-based wide field surveys may discover more giant planets than space missions. However, space surveys seem to constitute the best strategy to search for telluric planets. In this respect, the KEPLER mission appears 50 times more efficient than any of the ground-based surveys considered here. KEPLER might even discover telluric planets in the habitable zone of their host star. [less ▲]

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See detailThe Influence of Blends on the Potential of Extrasolar Planets Transit Surveys
Gillon, Michaël ULiege; Magain, Pierre ULiege; Guillot, T. et al

in Protostars and Planets V (2005)

Due to their low geometric probability, planetary transits are rare, and photometric surveys searching for such events have to observe many stars at once and, thus, deal with rather crowded fields. This ... [more ▼]

Due to their low geometric probability, planetary transits are rare, and photometric surveys searching for such events have to observe many stars at once and, thus, deal with rather crowded fields. This crowding has two negative effects on the final results of the survey: it decreases the number of detectable transits and increases the number of false positives. We have studied the influence of crowding on different surveys (existing ones as well as planned or even fictitious ones). On the basis of simple but realistic assumptions about the fraction of lower main sequence stars harboring telluric and giant planets within the outer limit of their habitable zone, we predict the harvests of several surveys with and without taking into account the losses due to blends. Our results show that deep surveys such as OGLE-III are much more affected by blends than wide field surveys. Space missions such as Corot and Kepler, although they use very broad PSFs in order to increase the S/N, loose a much lower fraction of transits than deep ground-based surveys. We have also estimated the proportion of false positives in the harvest of the surveys. Thus, our results provide a reliable comparison between the considered surveys. [less ▲]

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See detailA STEP: An Antarctica Search for Transiting Extrasolar Planets
Fressin, F.; Guillot, T.; Bouchy, F. et al

in Protostars and Planets V (2005)

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See detailAbundance analysis of targets for the COROT/MONS asteroseismology missions. II. Abundance analysis of the COROT main targets
Bruntt, H.; Bikmaev, I. F.; Catala, C. et al

in Astronomy and Astrophysics (2004), 425

One of the goals of the ground-based support program for the COROT and MONS/RÖMER satellite missions is to characterize suitable target stars for the part of the missions dedicated to asteroseismology. We ... [more ▼]

One of the goals of the ground-based support program for the COROT and MONS/RÖMER satellite missions is to characterize suitable target stars for the part of the missions dedicated to asteroseismology. We present the detailed abundance analysis of nine of the potential COROT main targets using the semi-automatic software VWA. For two additional COROT targets we could not perform the analysis due to the high rotational velocity of these stars. For five stars with low rotational velocity we have also performed abundance analysis by a classical equivalent width method in order to test the reliability of the VWA software. The agreement between the different methods is good. We find that it is necessary to measure abundances extracted from each line relative to the abundances found from a spectrum of the Sun in order to remove systematic errors. We have constrained the global atmospheric parameters T[SUB]eff[/SUB], log g, and [Fe/H] to within 70-100 K, 0.1-0.2 dex, and 0.1 dex for five stars which are slow rotators (v sin i < 15 km s[SUP]-1[/SUP]). For most of the stars we find good agreement with the parameters found from line depth ratios, H alpha lines, Strömgren indices, previous spectroscopic studies, and also log g determined from the HIPPARCOS parallaxes. For the fast rotators (v sin i > 60 km s[SUP]-1[/SUP]) it is not possible to constrain the atmospheric parameters. Based on observations obtained with the 193 cm telescope at Observatoire de Haute Provence, France. [less ▲]

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