180 research outputs found
A method for spatial deconvolution of spectra
A method for spatial deconvolution of spectra is presented. It follows the
same fundamental principles as the ``MCS image deconvolution algorithm''
(Magain, Courbin, Sohy, 1998) and uses information contained in the spectrum of
a reference Point Spread Function (PSF) 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 artefacts''. 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 magnitudes
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 10m class telescopes.Comment: 18 pages, 6 postscript figures, in press in Ap
A deconvolution-based algorithm for crowded field photometry with unknown Point Spread Function
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 (Magain, Courbin, Sohy, 1998) 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 to construct an accurate PSF. The
possibility to simultaneously consider several exposures makes it very 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 NGC5128 (Cen A).Comment: Institutes: (1) Institut d'Astrophysique et de Geophysique,
Universite de Liege, allee du 6 Aout 17, B-4000 Liege, Belgium; (2) Ecole
Polytechnique Federale de Lausanne (EPFL), Laboratoire d'Astrophysique,
Observatoire, CH-1290 Sauverny, Switzerland; (3) Observatoire de Geneve, 51
Chemin des Maillettes, CH-1290 Sauverny, Switzerland. 8 pages, 8 figures.
Accepted for publication in A&
Deconvolution with correct sampling
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 not be deconvolved 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 which are, in
at least some cases, superior to those of other commonly used techniques: in
particular, it does not produce ringing around point sources superimposed on a
smooth background. Moreover, it allows 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.Comment: 22 pages, LaTex file + 10 color jpg and postscript figures. To be
published in ApJ, Vol 484 (1997 Feb.
High precision photometry in crowded stellar fields
peer reviewedA 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
High accuracy transit photometry of the planet OGLE-TR-113b with a new deconvolution-based method
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 in order 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.Comment: 8 pages, 4 figure
A novel approach for extracting time-delays from lightcurves of lensed quasar images
We present a new method to estimate time delays from light curves of lensed
quasars. The method is based on chi^2 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 Q0957+561 yields results in agreement with other published
estimates.Comment: 6 pages, accepted for publication in A&
Dysregulation of Chemokine/Chemokine Receptor Axes and NK Cell Tissue Localization during Diseases.
Chemokines are small chemotactic molecules that play key roles in physiological and pathological conditions. Upon signaling via their specific receptors, chemokines regulate tissue mobilization and trafficking of a wide array of immune cells, including natural killer (NK) cells. Current research is focused on analyzing changes in chemokine/chemokine receptor expression during various diseases to interfere with pathological trafficking of cells or to recruit selected cell types to specific tissues. NK cells are a heterogeneous lymphocyte population comprising several subsets endowed with distinct functional properties and mainly representing distinct stages of a linear development process. Because of their different functional potential, the type of subset that accumulates in a tissue drives the final outcome of NK cell-regulated immune response, leading to either protection or pathology. Correspondingly, chemokine receptors, including CXCR4, CXCR3, and CX3CR1, are differentially expressed by NK cell subsets, and their expression levels can be modulated during NK cell activation. At first, this review will summarize the current knowledge on the contribution of chemokines to the localization and generation of NK cell subsets in homeostasis. How an inappropriate chemotactic response can lead to pathology and how chemokine targeting can therapeutically affect tissue recruitment/localization of distinct NK cell subsets will also be discussed
Development of the SPECULOOS exoplanet search project
SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) aims to
perform a transit search on the nearest (pc) ultracool (K) dwarf
stars. The project's main motivation is to discover potentially habitable
planets well-suited for detailed atmospheric characterisation with upcoming
giant telescopes, like the James Webb Space Telescope (JWST) and European Large
Telescope (ELT). The project is based on a network of 1m robotic telescopes,
namely the four ones of the SPECULOOS-Southern Observatory (SSO) in Cerro
Paranal, Chile, one telescope of the SPECULOOS-Northern Observatory (SNO) in
Tenerife, and the SAINT-Ex telescope in San Pedro M\'artir, Mexico. The
prototype survey of the SPECULOOS project on the 60~cm TRAPPIST telescope
(Chile) discovered the TRAPPIST-1 system, composed of seven temperate
Earth-sized planets orbiting a nearby (12~pc) Jupiter-sized star. In this
paper, we review the current status of SPECULOOS, its first results, the plans
for its development, and its connection to the Transiting Exoplanet Survey
Satellite (TESS) and JWST
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