References of "Sohy, Sandrine"
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See detailSPECULOOS: Search for habitable Planets EClipsing ULtra-cOOl Stars
Gillon, Michaël ULg; Jehin, Emmanuel ULg; Delrez, Laetitia ULg et al

Poster (2013, July 01)

The 1000 nearest ultra-cool stars (spectral type M6 and latter) represent a unique opportunity for the search for life outside our solar system. Due to their small luminosity, their habitable zone is 30 ... [more ▼]

The 1000 nearest ultra-cool stars (spectral type M6 and latter) represent a unique opportunity for the search for life outside our solar system. Due to their small luminosity, their habitable zone is 30-100 times closer than for the Sun, the corresponding orbital periods ranging from one to a few days. Thanks to this proximity, the transits of a habitable planet are much more probable and frequent than for an Earth-Sun analog, while their tiny size (about 1 Jupiter radius) leads to transits deep enough for a ground-based detection, even for sub-Earth size planets. Furthermore, a habitable planet transiting one of these nearby ultra-cool stars would be amenable for a thorough atmospheric characterization, including the detection of possible biosignatures, notably with the near-to-come JWST. Motivated by these reasons, we have set up the concept of a ground-based survey optimized for detecting planets of Earth-size and below transiting the nearest Southern ultra-cool stars. We present here this concept and its status. [less ▲]

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See detailTime Delays in Gravitationally Lensed Quasars
Eulaers, Eva ULg; Magain, Pierre ULg; Sohy, Sandrine ULg

Poster (2013, June 25)

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See detailMeasuring Time Delays in Gravitational Lenses
Eulaers, Eva ULg; Magain, Pierre ULg; Sohy, Sandrine ULg et al

Poster (2008, September)

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See detailDECPHOT: An Optimal Deconvolution-based Photometric Reduction Method
Gillon, Michaël ULg; Magain, Pierre ULg; Chantry, Virginie ULg 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 detailA deconvolution-based algorithm for crowded field photometry with unknown point spread function
Magain, Pierre ULg; Courbin, F.; Gillon, Michaël ULg 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 ULg; 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 photometry in crowded stellar fields
Magain, Pierre ULg; Courbin, Frédéric; Gillon, Michaël ULg 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 detailA novel approach for extracting time-delays from lightcurves of lensed quasar images
Burud, I.; Magain, Pierre ULg; Sohy, Sandrine ULg et al

in Astronomy and Astrophysics (2001), 380

We present a new method to estimate time delays from light curves of lensed quasars. The method is based on chi [SUP]2[/SUP] minimization between the data and a numerical model light curve. A linear ... [more ▼]

We present a new method to estimate time delays from light curves of lensed quasars. The method is based on chi [SUP]2[/SUP] minimization between the data and a numerical model light curve. A linear variation can be included in order to correct for slow long-term microlensing effects in one of the lensed images. An iterative version of the method can be applied in order to correct for higher-order microlensing effects. The method is tested on simulated light curves. When higher-order microlensing effects are present, the time delay is best constrained with the iterative method. Analysis of a published data set for the lensed double Q 0957+561 yields results in agreement with other published estimates. [less ▲]

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See detailA Method for Spatial Deconvolution of Spectra
Courbin, F.; Magain, Pierre ULg; Kirkove, Murielle ULg et al

in Astrophysical Journal (2000), 529

A method for spatial deconvolution of spectra is presented. It follows the same fundamental principles as the ``MCS image deconvolution algorithm'' recently developed by Magain, Courbin, & Sohy and uses ... [more ▼]

A method for spatial deconvolution of spectra is presented. It follows the same fundamental principles as the ``MCS image deconvolution algorithm'' recently developed by Magain, Courbin, & Sohy and uses information contained in the spectrum of a reference point-spread function to spatially deconvolve spectra of very blended sources. An improved resolution rather than an infinite one is aimed at, overcoming the well-known problem of ``deconvolution artifacts.'' As in the MCS algorithm, the data are decomposed into a sum of analytical point sources and a numerically deconvolved background so that the spectrum of extended sources in the immediate vicinity of bright point sources may be accurately extracted and sharpened. The algorithm has been tested on simulated data including seeing variation as a function of wavelength and atmospheric refraction. It is shown that the spectra of severely blended point sources can be resolved while fully preserving the spectrophotometric properties of the data. Extended objects ``hidden'' by bright point sources (up to 4-5 mag brighter) can be accurately recovered as well, provided the data have a sufficiently high total signal-to-noise ratio (200-300 per spectral resolution element). Such spectra are relatively easy to obtain, even down to faint magnitudes, within a few hours of integration time with 10 m class telescopes. [less ▲]

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See detailDeconvolving spectra of lensing galaxies, QSO hosts, and more ...
Courbin, F.; Magain, Pierre ULg; Sohy, Sandrine ULg et al

in The Messenger (1999), 97

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See detailDeconvolution with Correct Sampling
Magain, Pierre ULg; Courbin, F.; Sohy, Sandrine ULg

in Astrophysical Journal (1998), 494

A new method for improving the resolution of astronomical images is presented. It is based on the principle that sampled data cannot be fully deconvolved without violating the sampling theorem. Thus, the ... [more ▼]

A new method for improving the resolution of astronomical images is presented. It is based on the principle that sampled data cannot be fully deconvolved without violating the sampling theorem. Thus, the sampled image should be deconvolved not by the total point-spread function but by a narrower function chosen so that the resolution of the deconvolved image is compatible with the adopted sampling. Our deconvolution method gives results that are, in at least some cases, superior to those of other commonly used techniques: in particular, it does not produce ringing around point sources superposed on a smooth background. Moreover, it allows researchers to perform accurate astrometry and photometry of crowded fields. These improvements are a consequence of both the correct treatment of sampling and the recognition that the most probable astronomical image is not a flat one. The method is also well adapted to the optimal combination of different images of the same object, as can be obtained, e.g., from infrared observations or via adaptive optics techniques. [less ▲]

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See detailDeconvolution with correct sampling.
Magain, Pierre ULg; Courbin, F.; Sohy, Sandrine ULg

in The Messenger (1997), 88

The authors briefly describe the basic ideas behind a new deconvolution technique which overcomes some of the drawbacks of the traditional methods and which gives results of high photometric and ... [more ▼]

The authors briefly describe the basic ideas behind a new deconvolution technique which overcomes some of the drawbacks of the traditional methods and which gives results of high photometric and astrometric accuracy. The authors also show how it can be combined with other techniques (e.g. adaptive optics) to give even better results. [less ▲]

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