Papers by Christophe Jean
Astronomy & Astrophysics, 2012
Context. Fomalhaut is a young (2 ± 1 × 10 8 years), nearby (7.7 pc), 2 M star that is suspected t... more Context. Fomalhaut is a young (2 ± 1 × 10 8 years), nearby (7.7 pc), 2 M star that is suspected to harbor an infant planetary system, interspersed with one or more belts of dusty debris. Aims. We present far-infrared images obtained with the Herschel Space Observatory with an angular resolution between 5.7 and 36.7 at wavelengths between 70 μm and 500 μm. The images show the main debris belt in great detail. Even at high spatial resolution, the belt appears smooth. The region in between the belt and the central star is not devoid of material; thermal emission is observed here as well. Also at the location of the star, excess emission is detected. We aim to construct a consistent image of the Fomalhaut system. Methods. We use a dynamical model together with radiative-transfer tools to derive the parameters of the debris disk. We include detailed models of the interaction of the dust grains with radiation, for both the radiation pressure and the temperature determination. Comparing these models to the spatially resolved temperature information contained in the images allows us to place strong constraints on the presence of grains that will be blown out of the system by radiation pressure. We use this to derive the dynamical parameters of the system. Results. The appearance of the belt points toward a remarkably active system in which dust grains are produced at a very high rate by a collisional cascade in a narrow region filled with dynamically excited planetesimals. Dust particles with sizes below the blow-out size are abundantly present. The equivalent of 2000 one-km-sized comets are destroyed every day, out of a cometary reservoir amounting to 110 Earth masses. From comparison of their scattering and thermal properties, we find evidence that the dust grains are fluffy aggregates, which indicates a cometary origin. The excess emission at the location of the star may be produced by hot dust with a range of temperatures, but may also be due to gaseous free-free emission from a stellar wind.
Journal of Cosmology and Astroparticle Physics, 2004
The XMM Large Scale Structure survey (XMM-LSS) is a medium deep large area X-ray survey. Its goal... more The XMM Large Scale Structure survey (XMM-LSS) is a medium deep large area X-ray survey. Its goal is to extend large scale structure investigations attempted using ROSAT cluster samples to two redshift bins between 0 < z < 1 while maintaining the precision of earlier studies. Two main goals have constrained the survey design: the evolutionary study of the cluster-cluster correlation function and of the cluster number density. The adopted observing configuration consists of an equatorial mosaic of 10 ks pointings, separated by 20 ′ and covering 8 • × 8 • , giving a point source sensitivity of ∼ 5 10 −15 erg cm −2 s −1 in the [0.5-2] keV band. This will yield more than 800 clusters of galaxies and a sample of X-ray AGN with a space density of about 300 deg −2. We present the expected cosmological implications of the survey in the context of ΛCDM models and cluster evolution. We give an overview of the first observational results. The XMM-LSS survey is associated with several other major surveys, ranging from the UV to the radio wavebands which will provide the necessary resources for Xray source identification and further statistical studies. In particular, the associated CFHTLS weak lensing and AMiBA Sunyaev-Zel'dovich surveys over the entire XMM-LSS area will provide for the first time a comprehensive study of the mass distribution and of cluster physics in the universe on scales of a few hundred Mpc. We describe the main characteristics of our wavelet-based X-ray pipeline and source identification procedures, including the classification of the cluster candidates by means of a photometric redshift analysis. This permits the selection of suitable targets for spectroscopic follow-up. We present preliminary results from the first 25 XMM-LSS pointings : X-ray source properties, optical counterparts,highlights from the first Magellan and VLT/FORS2 spectroscopic runs as well as preliminary results from the NIR search for z > 1 clusters. The results are promising and, so far, in accordance with our predictions. In particular: (1) we reproduce the LogN-LogS distribution for point sources obtained from deeper surveys at our sensitivity; (2) we find a cluster number density of 15-20 per deg 2 ; (3) for the first time, we statistically sample the group mass regime at a redshift out to ∼ 0.5.
Astronomy and Astrophysics, 2010
Detached circumstellar dust shells are detected around three carbon variables using Herschel-PACS... more Detached circumstellar dust shells are detected around three carbon variables using Herschel-PACS. Two of them are already known on the basis of their thermal CO emission and two are visible as extensions in IRAS imaging data. By model fits to the new data sets, physical sizes, expansion timescales, dust temperatures, and more are deduced. A comparison with existing molecular CO material shows a high degree of correlation for TT Cyg and U Ant but a few distinct differences with other observables are also found.
Monthly Notices of the Royal Astronomical Society, 2007
We present a sample of 29 galaxy clusters from the XMM-LSS survey over an area of some 5 deg2 out... more We present a sample of 29 galaxy clusters from the XMM-LSS survey over an area of some 5 deg2 out to a redshift of z= 1.05. The sample clusters, which represent about half of the X-ray clusters identified in the region, follow well-defined X-ray selection criteria and are all spectroscopically confirmed. For all clusters, we provide X-ray luminosities and temperatures as well as masses, obtained from dedicated spatial and spectral fitting. The cluster distribution peaks around z= 0.3 and T= 1.5 keV, half of the objects being groups with a temperature below 2 keV. Our LX–T(z) relation points towards self-similar evolution, but does not exclude other physically plausible models. Assuming that cluster scaling laws follow self-similar evolution, our number density estimates up to z= 1 are compatible with the predictions of the concordance cosmology and with the findings of previous ROSAT surveys. Our well-monitored selection function allowed us to demonstrate that the inclusion of selec...
Astronomy and Astrophysics, 2010
With a luminosity >10 5 L and a mass-loss rate of ∼2 × 10 -4 M yr -1 , the red supergiant VY CMa ... more With a luminosity >10 5 L and a mass-loss rate of ∼2 × 10 -4 M yr -1 , the red supergiant VY CMa truly is a spectacular object. Because of its extreme evolutionary state, it could explode as supernova any time. Studying its circumstellar material, into which the supernova blast will run, provides interesting constraints on supernova explosions and on the rich chemistry taking place in such complex circumstellar envelopes. We have obtained spectroscopy of VY CMa over the full wavelength range offered by the PACS and SPIRE instruments of Herschel, i.e. 55-672 micron. The observations show the spectral fingerprints of more than 900 spectral lines, of which more than half belong to water. In total, we have identified 13 different molecules and some of their isotopologues. A first analysis shows that water is abundantly present, with an ortho-to-para ratio as low as ∼1.3:1, and that chemical non-equilibrium processes determine the abundance fractions in the inner envelope.
Detached circumstellar dust shells are detected around three carbon variables using Herschel-PACS... more Detached circumstellar dust shells are detected around three carbon variables using Herschel-PACS. Two of them are already known on the basis of their thermal CO emission and two are visible as extensions in IRAS imaging data. By model fits to the new data sets, physical sizes, expansion timescales, dust temperatures, and more are deduced. A comparison with existing molecular CO
Après avoir rappelé quelques définitions et résultats concernant l'atténuation du flux lumineux d... more Après avoir rappelé quelques définitions et résultats concernant l'atténuation du flux lumineux d'une source éloignée due à la poussière dans notre Galaxie et dans des galaxies proches (phénomène physique appelé extinction), nous décrivons brièvement le phénomène de mirage gravitationnel ainsi que les processus physiques pouvant affecter la photométrie observée des images multiples d'un quasar distant.
Nous présentons ensuite une méthode originale pour estimer le décalage vers le rouge (le redshift) du déflecteur (la galaxie lentille) d'un mirage gravitationnel. Cette méthode se base sur les effets causés par l'extinction de la lumière par la poussière interstellaire au sein de la lentille.
Après une présentation de la méthode et quelques considérations préalables, des simulations numériques sont effectuées pour tester la méthode et calculer sa précision. La méthode est ensuite appliquée à des données réelles.
Par la suite, nous tentons d'extraire la loi d'extinction de la galaxie lentille à partir des spectres des images multiples de la source d'arrière-plan.
Enfin, nous utilisons la technique de l'analyse en composantes principales pour classifier une loi d'extinction parmi une collection de lois d'extinction connues. À nouveau, après une rapide présentation de l'analyse en composantes principales et de son application aux lois d'extinction, des simulations numériques sont utilisées pour évaluer la fiabilité de
la méthode, laquelle est également appliquée à un cas réel.
Surveys with the 4-m International Liquid Mirror Telescope
ESO ASTROPHYSICS SYMPOSIA, 2001
Page 1. Surveys with the 4-m International Liquid Mirror Telescope J. Poels, O. Moreau, J. Manfro... more Page 1. Surveys with the 4-m International Liquid Mirror Telescope J. Poels, O. Moreau, J. Manfroid, J. Surdej, E. Borra, JF Claeskens, C. Jean, F. Montfort, JP Swings, B. Vangeyte, E. van Dessel, Th. Nakos 1 Institute of Astrophysics ...
The à Pictoris disk imaged by Herschel PACS and SPIRE
We obtained Herschel PACS and SPIRE images of the thermal emission of the debris disk around the ... more We obtained Herschel PACS and SPIRE images of the thermal emission of the debris disk around the A5V star ò Pic. The disk is well resolved in the PACS filters at 70, 100, and 160 üm. The surface brightness profiles between 70 and 160 üm show no significant asymmetries along the disk, and are compatible with 90% of the emission between 70 and 160 üm originating in a region closer than 200 AU to the star. Although only marginally resolving the debris disk, the maps obtained in the SPIRE 250-500 üm filters provide full-disk photometry, completing the SED over a few octaves in wavelength that had been previously inaccessible. The small far-infrared spectral index (ò = 0.34) indicates that the grain size distribution in the inner disk (<200 AU) is inconsistent with a local collisional equilibrium. The size distribution is either modified by non-equilibrium effects, or exhibits a wavy pattern, caused by an under-abundance of impactors which have been removed by radiat...
A 4-m International Liquid Mirror Telescope (ILMT) is being built in the north of Chile by an int... more A 4-m International Liquid Mirror Telescope (ILMT) is being built in the north of Chile by an international consortium and will become operational in two years from now. We present here a short description of the telescope as well as estimates of the microlensing, macrolensing and weak lensing effects expected from a deep, multicolor imaging survey made with such a telescope.
Astronomy and Astrophysics
Light rays from a multiply imaged quasar usually sample different path lengths across the deflect... more Light rays from a multiply imaged quasar usually sample different path lengths across the deflector. Extinction in the lensing galaxy may thus lead to a differential obscuration and reddening between the observed macro-lensed QSO images. These effects naturally depend on the precise shape of the extinction law and on the redshift of the lens. By means of numerical Monte-Carlo simulations, using a least-squares fitting method and assuming an extinction law similar to that observed in the Galaxy, we show how accurate photometric observations of multiply imaged quasars obtained in several spectral bands could lead to the estimate of the lens redshift, irrespective of the visibility of the deflector. Observational requirements necessary to apply this method to real cases are thoroughly discussed. If extinction laws turn out to be too different from galaxy to galaxy, we find out that more promising observations should consist in getting high signal-to-noise low resolution spectra of at l...
Microlensing observations with the 4-m International Liquid Mirror Telescope
The XMM-LSS survey
We present five newly found galaxy clusters at $z>0.6$ from the XMM Large-Scale Structure Surv... more We present five newly found galaxy clusters at $z>0.6$ from the XMM Large-Scale Structure Survey (XMM-LSS). All five objects are extended X-ray sources in the XMM images. For three of them we have sufficient spectroscopically confirmed member galaxies that an estimate of the velocity dispersion is possible: XLSSC 001 at $z=0.613$ and $\sigma_V=867^{+80}_{-60}$ km s$^{-1}$, XLSSC 002 at $z=0.772$ and $\sigma_V=524^{+267}_{-116}$ km s$^{-1}$ and XLSSC 003 at $z=0.839$ and $\sigma_V=780^{+137}_{-75}$ km s$^{-1}$. These three clusters have X-ray bolometric luminosities $L_{\rm X} \sim 1{-}3 \times 10^{44}$ erg s$^{-1}$ and temperatures $2{-}4$ keV, and consequently are less massive than previously known clusters at similar redshifts, but nevertheless they follow the low redshift scaling relations between $L_{\rm X}, T$ and $\sigma_v$, within the limits of the measurement errors. One of the clusters, XLSSC 004, is detected independently as an overdensity of galaxies of a colour $R-z&#...
Ground-based and Airborne Telescopes, 2006
The entire funding has recently been obtained in Belgium for the construction of a 4m Liquid Mirr... more The entire funding has recently been obtained in Belgium for the construction of a 4m Liquid Mirror Telescope. Its prime focus will be equipped with a semi-conventional glass corrector allowing to correct for the TDI effect and a thinned, high quantum efficiency, 4K x 4K pixel equivalent CCD camera. It will be capable of subarcsecond imaging in the i'(760 nm) and possibly r', g' band(s) over a field of ∼ 30' in diameter. This facility will be entirely dedicated to a deep photometric and astrometric variability survey over a period of ∼ 5 years. In this paper, the working principle of liquid mirror telescopes is first recalled, along with the advantages and disadvantages of the latter over classical telescopes. Several science cases are described. For a good access to one of the galactic poles, the best image quality sites for the ILMT are located either in Northern Chile (latitude near −29 • 30) or in NorthEast India (Nainital Hills, latitude near +29 • 30). At those geographic latitudes, a deep (i' = 22.5 mag.) survey will approximately cover 90 square degrees at high galactic latitude, which is very useful for gravitational lensing studies as well as for the identification of various classes of interesting galactic and extragalactic objects (cf. microlensed stars, supernovae, clusters, etc.). A description of the telescope, its instrumentation and the handling of the data is also presented.
ESO Astrophysics Symposia, 1999
… and Systems XVIII, 2009
ESA's Herschel Space Observatory, to be launched in 2009, is the first space observatory cov... more ESA's Herschel Space Observatory, to be launched in 2009, is the first space observatory covering the full far-infrared and sub-millimeter wavelength range (60-670 micron). The Photodetector Array Camera & Spectrometer (PACS) is one of the three ...
XMM -LSS discovery of a galaxy cluster
Monthly Notices of the Royal Astronomical Society, 2006
ABSTRACT We present details of the discovery of XLSS J022303.0−043622, a z= 1.2 cluster of galaxi... more ABSTRACT We present details of the discovery of XLSS J022303.0−043622, a z= 1.2 cluster of galaxies. This cluster was identified from its X-ray properties and selected as a z &amp;gt; 1 candidate from its optical/near-infrared (IR) characteristics in the XMM Large-Scale Structure Survey (XMM-LSS). It is the most distant system discovered in the survey to date. We present ground-based optical and near-IR observations of the system carried out as part of the XMM-LSS survey. The cluster has a bolometric X-ray luminosity of 1.1 ± 0.7 × 1044 erg s−1, fainter than most other known z &amp;gt; 1 X-ray selected clusters. In the optical it has a remarkably compact core, with at least a dozen galaxies inside a 125 kpc radius circle centred on the X-ray position. Most of the galaxies within the core, and those spectroscopically confirmed to be cluster members, have stellar masses similar to those of massive cluster galaxies at low redshift. They have colours comparable to those of galaxies in other z &amp;gt; 1 clusters, consistent with showing little sign of strong ongoing star formation. The bulk of the star formation within the galaxies appears to have ceased at least 1.5 Gyr before the observed epoch. Our results are consistent with massive cluster galaxies forming at z &amp;gt; 1 and passively evolving thereafter. We also show that the system is straightforwardly identified in Spitzer/IRAC 3.6- and 4.5-μm data obtained by the Spitzer Wide-area Infrared Extragalactic (SWIRE) survey emphasizing the power and utility of joint XMM and Spitzer searches for the most distant clusters.
Monthly Notices of the Royal Astronomical Society, 2006
We present the XMM-LSS cluster catalogue corresponding to the CFHTLS D1 area. The list contains 1... more We present the XMM-LSS cluster catalogue corresponding to the CFHTLS D1 area. The list contains 13 spectroscopically confirmed, X-ray selected galaxy clusters over 0.8 deg 2 to a redshift of unity and so constitutes the highest density sample of clusters to date. Cluster Xray bolometric luminosities range from 0.03 to 5 × 10 44 erg s −1. In this study, we describe our catalogue construction procedure: from the detection of X-ray cluster candidates to the compilation of a spectroscopically confirmed cluster sample with an explicit selection function. The procedure further provides basic X-ray products such as cluster temperature, flux and luminosity. We detected slightly more clusters with a (0.5-2.0 keV) X-ray fluxes of > 2 × 10 −14 erg s −1 cm −2 than we expected based on expectations from deep ROSAT surveys. We also present the Luminosity-Temperature relation for our 9 brightest objects possessing a reliable temperature determination. The slope is in good agreement with the local relation, yet compatible with a luminosity enhancement for the 0.15 < z < 0.35 objects having 1 < T < 2 keV, a population that the XMM-LSS is identifying systematically for the first time. The present study permits the compilation of cluster samples from XMM images whose selection biases are understood. This allows, in addition to studies of large-scale structure, the systematic investigation of cluster scaling law evolution, especially for low mass X-ray groups which constitute the bulk of our observed cluster population. All cluster ancillary data (images, profiles, spectra) are made available in electronic form via the XMM-LSS cluster database.
… Analysis Software & …, 2001
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Papers by Christophe Jean
Nous présentons ensuite une méthode originale pour estimer le décalage vers le rouge (le redshift) du déflecteur (la galaxie lentille) d'un mirage gravitationnel. Cette méthode se base sur les effets causés par l'extinction de la lumière par la poussière interstellaire au sein de la lentille.
Après une présentation de la méthode et quelques considérations préalables, des simulations numériques sont effectuées pour tester la méthode et calculer sa précision. La méthode est ensuite appliquée à des données réelles.
Par la suite, nous tentons d'extraire la loi d'extinction de la galaxie lentille à partir des spectres des images multiples de la source d'arrière-plan.
Enfin, nous utilisons la technique de l'analyse en composantes principales pour classifier une loi d'extinction parmi une collection de lois d'extinction connues. À nouveau, après une rapide présentation de l'analyse en composantes principales et de son application aux lois d'extinction, des simulations numériques sont utilisées pour évaluer la fiabilité de
la méthode, laquelle est également appliquée à un cas réel.
Nous présentons ensuite une méthode originale pour estimer le décalage vers le rouge (le redshift) du déflecteur (la galaxie lentille) d'un mirage gravitationnel. Cette méthode se base sur les effets causés par l'extinction de la lumière par la poussière interstellaire au sein de la lentille.
Après une présentation de la méthode et quelques considérations préalables, des simulations numériques sont effectuées pour tester la méthode et calculer sa précision. La méthode est ensuite appliquée à des données réelles.
Par la suite, nous tentons d'extraire la loi d'extinction de la galaxie lentille à partir des spectres des images multiples de la source d'arrière-plan.
Enfin, nous utilisons la technique de l'analyse en composantes principales pour classifier une loi d'extinction parmi une collection de lois d'extinction connues. À nouveau, après une rapide présentation de l'analyse en composantes principales et de son application aux lois d'extinction, des simulations numériques sont utilisées pour évaluer la fiabilité de
la méthode, laquelle est également appliquée à un cas réel.