Results for "N. F. Allard"

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A collision-induced satellite in the Lyman Beta profile due to H-H collisionsJun 10 2000We present a theoretical profile of the Lyman Beta line of atomic hydrogen perturbed by collisions with neutral hydrogen atoms and protons. We use a general unified theory in which the electric dipole moment varies during a collision. A collision-induced ... More
Alkali Line Profiles in Degenerate DwarfsJul 24 2007Ultracool stellar atmospheres show absorption by alkali resonance lines severely broadened by collisions with neutral perturbers. In the coolest and densest atmospheres, such as those of T dwarfs, Na I and K I broadened by molecular hydrogen and helium ... More
Young, Jupiter-Mass Objects in OphiuchusJun 03 2005We have used 3.5 to 8 micron data from the Cores to Disks (c2d) Legacy survey and our own deep IJHKs images of a 0.5 square degree portion of the c2d fields in Ophiuchus to produce a sample of candidate young objects with probable masses between 1 and ... More
Line Profiles of the Calcium I Resonance Line in Cool Metal-polluted White DwarfsMar 20 2019Metal-polluted white dwarfs (DZ stars) are characterized by a helium-rich atmosphere contaminated by heavy elements traces originating from accreted rocky planetesimals. As a detailed spectroscopic analysis of those objects can reveal the composition ... More
Quasi-molecular Satellites of Lyman Beta in the Spectrum of the DA White Dwarf WOLF 1346Mar 20 1996We present new FUV/UV observations of the DA white dwarf Wolf 1346 obtained with the Hopkins Ultraviolet Telescope. The atmospheric parameters of this object are estimated from a fit of model atmospheres to several optical spectra to be Teff = 20000 K, ... More
Metallicity of M dwarfs IV. A high-precision [Fe/H] and Teff technique from high-resolution optical spectra for M dwarfsJun 24 2014Jul 11 2014Aims. In this work we develop a technique to obtain high precision determinations of both metallicity and effective temperature of M dwarfs in the optical. Methods. A new method is presented that makes use of the information of 4104 lines in the 530-690 ... More
Quasi-molecular lines in Lyman wings of cool DA white dwarfs; Application to FUSE observations of G231-40Aug 20 2002We present new theoretical calculations of the total line profiles of Lyman alpha and Lyman beta which include perturbations by both neutral hydrogen AND protons and all possible quasi-molecular states of H_2 and H_2^+. They are used to improve theoretical ... More
A New Generation of Cool White Dwarf Atmosphere Models. III. WD J2356$-$209: Accretion of a Planetesimal with an Unusual CompositionFeb 08 2019WD J2356$-$209 is a cool metal-polluted white dwarf whose visible spectrum is dominated by a strong and broad sodium feature. Although discovered nearly two decades ago, no detailed and realistic analysis of this star had yet been realized. In the absence ... More
FUSE observations of hot white dwarfsMay 02 2001We have analyzed FUSE observations of six hot white dwarf stars: four DA white dwarfs with T_eff >= 45000K, the DAO Feige55 (T_eff = 55000K), and the DA CD -38 10980 (T_eff = 24000K). Photospheric lines from SiIV, PV, and SVI can be observed in the majority ... More
FUSE observations of G226-29: First detection of the H_2 quasi-molecular satellite at 1150ADec 18 2003We present new FUV observations of the pulsating DA white dwarf G226-29 obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). This ZZ Ceti star is the brightest one of its class and the coolest white dwarf observed by FUSE. We report the first ... More
FUSE Observation of the Ultramassive White Dwarf PG1658+441Sep 23 2003We present an analysis of the Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum of the ultramassive (M = 1.31 solar mass), magnetic (B_s = 2.3 MG) white dwarf PG 1658+441. The far ultraviolet (FUV) spectrum exhibits very broad Lyman lines and quasi-molecular ... More
Metallicity of M dwarfs III. Planet-metallicity and planet-stellar mass correlations of the HARPS GTO M dwarf sampleDec 14 2012Aims. The aim of this work is the study of the planet-metallicity and the planet-stellar mass correlations for M dwarfs from the HARPS GTO M dwarf subsample Methods. We use a new method that takes advantage of the HARPS high-resolution spectra to increase ... More
Modeling of the Lyman gamma satellites in FUSE spectra of DA white dwarfsMay 20 2003We present new theoretical calculations of the line profile of Lyman gamma that include transitions in which a photon is absorbed by a neutral hydrogen atom while it interacts with a proton. Models show that two absorption features located near 992 A ... More
A New Generation of Cool White Dwarf Atmosphere Models. I. Theoretical Framework and Applications to DZ StarsJul 17 2018The photospheres of the coolest helium-atmosphere white dwarfs are characterized by fluid-like densities. Under those conditions, standard approximations used in model atmosphere codes are no longer appropriate. Unfortunately, the majority of cool He-rich ... More
Metallicity of M dwarfs II. A comparative study of photometric metallicity scalesOct 12 2011Nov 16 2011Stellar parameters are not easily derived from M dwarf spectra, which are dominated by complex bands of diatomic and triatomic molecules and not well described at the line by line level by atmospheric models. M dwarf metallicities are therefore most commonly ... More
Steady-state MreB helices inside bacteria: dynamics without motorsAug 03 2007Within individual bacteria, we combine force-dependent polymerization dynamics of individual MreB protofilaments with an elastic model of protofilament bundles buckled into helical configurations. We use variational techniques and stochastic simulations ... More
Methane Opacities in T Dwarf AtmospheresSep 09 2002Sep 09 2002We present the current status of PHOENIX model atmospheres for dwarfs of the spectral type T, typical for older field brown dwarfs and low-mass brown dwarfs. The results are based on new predictions of the CH_4 line opacities from theoretical calculations ... More
Cosmogenic Neutrinos from the propagation of Ultra High Energy NucleiMay 12 2006May 22 2006We calculate the flux of neutrinos generated by the propagation of ultra-high energy nuclei over cosmological distances. The propagation takes into account the interactions with cosmic background radiations including the CMB and the most recent estimates ... More
Primeval very low-mass stars and brown dwarfs - II. The most metal-poor substellar objectFeb 07 2017Feb 22 2017SDSS J010448.46+153501.8 has previously been classified as an sdM9.5 subdwarf. However, its very blue $J-K$ colour ($-0.15 \pm 0.17$) suggests a much lower metallicity compared to normal sdM9.5 subdwarfs. Here, we re-classify this object as a usdL1.5 ... More
Propagation of high-energy cosmic rays in extragalactic turbulent magnetic fields: resulting energy spectrum and compositionSep 11 2007We extend previous studies of mixed-composition extragalactic cosmic-ray source models, by investigating the influence of a non-negligible extragalactic magnetic field on the propagated cosmic-ray spectrum and composition. We study the transport of charged ... More
Evolutionary models for low-mass stars and brown dwarfs: uncertainties and limits at very young agesNov 20 2001We analyse pre-Main Sequence evolutionary tracks for low mass stars with masses $m \le 1.4 \msol$ based on the Baraffe et al. (1998) input physics. We also extend the recent Chabrier et al. (2000) evolutionary models based on dusty atmosphere to young ... More
Model Atmospheres From Very Low Mass Stars to Brown DwarfsNov 24 2010Since the discovery of brown dwarfs in 1994, and the discovery of dust cloud formation in the latest Very Low Mass Stars (VLMs) and Brown Dwarfs (BDs) in 1996, the most important challenge in modeling their atmospheres as become the understanding of cloud ... More
Alkali Line Profiles in Ultracool White DwarfsJul 27 2007Jul 28 2007We present PHOENIX atmosphere models for metal-rich cool white dwarfs using improved line shapes for the Na I and K I resonance doublets. Profiles for collisional broadening due to H2 and He based on the adiabatic representation show strong deviations ... More
K-H_2 Quasi-molecular absorption detected in the T-dwarf epsilon Indi BaSep 10 2007T-type dwarfs present a broad and shallow absorption feature centred around 6950 A in the blue wing of the K doublet at 0.77 micron which resembles in depth and shape the satellite absorption predicted by detailed collisional broadening profiles. In our ... More
New constraints on the formation and settling of dust in the atmospheres of young M and L dwarfsFeb 07 2014We obtained medium-resolution near-infrared spectra of seven young M9.5-L3 dwarfs classified in the optical. We aim to confirm the low surface gravity of the objects in the NIR. We also test whether atmospheric models correctly represent the formation ... More
The very low mass multiple system LHS\,1070 -- a testbed for model atmospheres for the lower end of the main sequenceAug 02 2012LHS1070 is a nearby multiple system of low mass stars. It is an important source of information for probing the low mass end of the main sequence, down to the hydrogen-burning limit. The primary of the system is a mid-M dwarf and two components are late-M ... More
A global cloud map of the nearest known brown dwarfJan 31 2014Brown dwarfs -- substellar bodies more massive than planets but not massive enough to initiate the sustained hydrogen fusion that powers self-luminous stars -- are born hot and slowly cool as they age. As they cool below about 2,300 K, liquid or crystalline ... More
Primeval very low-mass stars and brown dwarfs - VI. Population properties of metal-poor degenerate brown dwarfsMar 13 2019We presented 15 new T dwarfs that selected from UKIDSS, VISTA and WISE surveys, and confirmed with optical to near infrared spectra obtained with VLT/X-shooter and GTC/OSIRIS. One of these new T dwarfs is mildly metal-poor with slightly suppressed K-band ... More
Kinematics in the starbursting circumnuclear region of M100Nov 23 2004We have obtained integral-field spectroscopic data, using the SAURON instrument, of the bar and starbursting circumnuclear region in the barred spiral galaxy M100. From our data we have derived kinematic maps of the mean velocity and velocity dispersion ... More
A high resolution spectral atlas of brown dwarfsJul 18 2007We present a UVES/VLT high resolution atlas of three L dwarfs and one T dwarf system, spectral classes at which most of the objects are brown dwarfs. Our atlas covers the optical region from H$\alpha$ up to the near infrared at 1 $\mu$m. We present spectral ... More
A New Generation of Cool White Dwarf Atmosphere Models. II. A DZ Star with Collision-Induced AbsorptionSep 28 2018In the first paper of this series (Blouin et al. 2018), we presented our upgraded cool white dwarf atmosphere code. In this second paper, we use our new models to analyze SDSS J080440.63+223948.6 (J0804+2239), the first DZ star to show collision-induced ... More
High Resolution Spectroscopy of M subdwarfsSep 18 2013M subdwarfs are metal poor and cool stars. They are important probes of the old galactic populations. However, they remain elusive due to their low luminosity. Observational and modeling efforts are required to fully understand the physics and to investigate ... More
Numerical simulations of surface convection in a late M-dwarfAug 30 2002Based on detailed 2D and 3D numerical radiation-hydrodynamics (RHD) simulations of time-dependent compressible convection, we have studied the dynamics and thermal structure of the convective surface layers of a prototypical late-type M-dwarf (Teff~2800K ... More
Period - luminosity - color - radius relationships of Cepheids as a function of metallicity: evolutionary effectsJan 21 1999Based on consistent evolutionary and pulsation calculations, we analyse the effect of metallicity and of different convection treatments in the stellar models on period - magnitude, - color and - radius relationships. In order to perform an accurate comparison ... More
Review on low-mass stars and brown dwarfsSep 27 2005In this review, we examine the successes and weaknesses of modern low-mass star and brown dwarf theory.(1) We first focus on the mechanical (equation of state) and thermal (atmosphere) properties and on the evolution. We then examine the current shortcomings ... More
Optical Spectroscopy of DENIS Mini-survey Brown Dwarf CandidatesMay 25 1998Aug 26 1998We present optical (6500-9200A) spectroscopy of eight cool dwarfs detected in a 231 square degree ``Mini-survey'' of the Deep NEar Infrared Survey (DENIS) data. We are able to confirm that the spectral types derived from the Mini-survey infrared spectroscopy ... More
Cool Gas and Massive Stars - the Nuclear Ring in M100Sep 26 2005The SAURON integral field spectrograph was used to observe the central area of the barred spiral galaxy M100 (NGC 4321). M100 contains a nuclear ring of star formation, fueled by gas channeled inward by the galaxy's bar. We present maps of emission line ... More
New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limitMar 13 2015We present new models for low-mass stars down to the hydrogen-burning limit that consistently couple atmosphere and interior structures, thereby superseding the widely used BCAH98 models. The new models include updated molecular linelists and solar abundances, ... More
Rejuvenation of the Controls for the CERN PS/Isolde Facilty Using Industrial ComponentsNov 26 2001In the context of the general consolidation of the CERN ISOLDE facility, a project has been started to upgrade the ISOLDE control system. We describe the new ISOLDE control system, emphasizing the systematic use of industrial components such as PLCs and ... More
The evolution of irradiated planets. Application to transitsJan 23 2004Extending the theory we derived recently for HD209458b to different cases of strongly irradiated gaseous exoplanets, we have calculated the consistent evolution of the new transiting planet, OGLE-TR-56b, for its recently revised mass determination. The ... More
Deuterium-burning in substellar objectsSep 12 2000We consider the depletion of primordial deuterium in the interior of substellar objects as a function of mass, age and absolute magnitude in several photometric passbands. We characterize potential spectroscopic signatures of deuterium in the lines of ... More
Energy transport, overshoot, and mixing in the atmospheres of M-type main- and pre-main-sequence objectsAug 12 2006We constructed hydrodynamical model atmospheres for mid M-type main-, as well as pre-main-sequence (PMS) objects. Despite the complex chemistry encountered in these cool atmospheres a reasonably accurate representation of the radiative transfer is possible, ... More
Infrared Colors at the Stellar/Substellar BoundaryJul 24 1998We present new infrared photometry for 61 halo and disk stars around the stellar/substellar boundary. These data are combined with available optical photometry and astrometric data to produce color--color and absolute magnitude--color diagrams. The disk ... More
Pre-Main Sequence models for low-mass stars and brown dwarfsJul 12 2000We present evolutionary models for low mass stars and brown dwarfs ($m \le 1.2 \msol$) based on recent improvement of the theory: equation of state, atmosphere models, ... We concentrate on early evolutionary phases from the initial deuterium burning ... More
Evolutionary models for very-low-mass stars and brown dwarfs with dusty atmospheresMay 29 2000We present evolutionary calculations for very-low-mass stars and brown dwarfs based on synthetic spectra and non-grey atmosphere models which include dust formation and opacity, i.e. objects with $\te\simle 2800$ K. The interior of the most massive brown ... More
Evolution of low-mass stars and substellar objects. Contribution to the Galactic mass budgetMay 17 1999We briefly summarize our present knowledge of the theory of low-mass stars and substellar objects and their contribution to the Galactic population.
The Effective temperature scale of M dwarfs from spectral synthesisFeb 07 2011Feb 08 2011We present a comparison of low-resolution spectra of 60 stars covering the whole M-dwarf sequence. Using the most recent PHOENIX BT-Settl stellar model atmospheres (see paper by F. Allard, in this book) we do a first quantitative compari- son to our observed ... More
Physical parameter determinations of young Ms. Taking advantage of the Virtual Observatory to compare methodologiesJul 02 2014One of the very first steps astronomers working in stellar physics perform to advance in their studies, is to determine the most common/relevant physical parameters of the objects of study (effective temperature, bolometric luminosity, surface gravity, ... More
Modelling Alkali Line Absorption and Molecular Bands in Cool DAZsJan 05 2005Two peculiar stars showing an apparent extremely broadened and strong NaI D absorption have been discovered in surveys for cool white dwarfs by Oppenheimer et al. (2001) and Harris et al. (SDSS, 2003). We discuss the nature of these objects using PHOENIX ... More
Primeval very low-mass stars and brown dwarfs. I. Six new L subdwarfs, classification and atmospheric propertiesSep 22 2016We have conducted a search for L subdwarf candidates within the photometric catalogues of the UKIRT Infrared Deep Sky Survey and Sloan Digital Sky Survey. Six of our candidates are confirmed as L subdwarfs spectroscopically at optical and/or near infrared ... More
Primeval very low-mass stars and brown dwarfs. I. Six new L subdwarfs, classification and atmospheric propertiesSep 22 2016Nov 09 2016We have conducted a search for L subdwarf candidates within the photometric catalogues of the UKIRT Infrared Deep Sky Survey and Sloan Digital Sky Survey. Six of our candidates are confirmed as L subdwarfs spectroscopically at optical and/or near infrared ... More
Physical and orbital properties of Beta Pictoris bJul 15 2014The intermediate-mass star Beta Pictoris is known to be surrounded by a structured edge-on debris disk within which a gas giant planet was discovered orbiting at 8-10 AU. The physical properties of Beta Pic b were previously inferred from broad and narrow-band ... More
Primeval very low-mass stars and brown dwarfs - III. The halo transitional brown dwarfsMay 21 2018Jun 21 2018We report the discovery of an esdL3 subdwarf, ULAS J020858.62+020657.0, and a usdL4.5 subdwarf, ULAS J230711.01+014447.1. They were identified as L subdwarfs by optical spectra obtained with the Gran Telescopio Canarias, and followed up by optical-to-near-infrared ... More
Temperature constraints on the coldest brown dwarf known WISE 0855-0714Aug 22 2014Oct 06 2014Context. Nearby isolated planetary mass objects are beginning to be discovered, but their individual properties are poorly constrained because their low surface temperatures and strong molecular self-absorption make them extremely faint. Aims. We aimed ... More
Manual Encryption RevisitedFeb 21 2019This document brings together several articles devoted to manual encryption and introduces new algorithms and ciphers: a permutation algorithm, Spirale (a one-time-pad cipher), a solution to the problem of the ordered route of a table, Diagonales (a cipher ... More
Hot-Jupiters and hot-Neptunes: a common origin?May 03 2005We compare evolutionary models for close-in exoplanets coupling irradiation and evaporation due respectively to the thermal and high energy flux of the parent star with observations of recently discovered new transiting planets. The models provide an ... More
The effect of evaporation on the evolution of close-in giant planetsApr 05 2004We include the effect of evaporation in our evolutionary calculations of close-in giant planets, based on a recent model for thermal evaporation taking into account the XUV flux of the parent star (Lammer et al. 2003). Our analysis leads to the existence ... More
Extragalactic propagation of ultrahigh energy cosmic-raysNov 14 2011In this paper we review the extragalactic propagation of ultrahigh energy cosmic-rays (UHECR). We present the different energy loss processes of protons and nuclei, and their expected influence on energy evolution of the UHECR spectrum and composition. ... More
Propagation of extragalactic ultra-high energy cosmic-ray nuclei : implications for the observed spectrum and compositionJun 17 2009In this paper, we study the propagation of cosmic-ray nuclei and protons. We emphasize the influence of the source composition on the expected spectrum and composition on Earth as well as on the phenomenology of the transition from Galactic to extragalactic ... More
Progress in Modeling Very Low Mass Stars, Brown Dwarfs, and Planetary Mass ObjectsFeb 26 2013Feb 28 2013We review recent advancements in modeling the stellar to substellar transition. The revised molecular opacities, solar oxygen abundances and cloud models allow to reproduce the photometric and spectroscopic properties of this transition to a degree never ... More
The physics of extrasolar gaseous planets : from theory to observable signaturesJan 29 2004We review our present understanding of the physical properties of substellar objects, brown dwarfs and irradiated or non-irradiated gaseous exoplanets. This includes a description of their internal properties, mechanical structure and heat content, their ... More
Infrared Spectroscopy of Substellar Objects in OrionMay 09 2001May 14 2001We present broad band spectra of a sample of 21 low luminosity sources in the Trapezium Cluster, with masses in the range 0.008 - 0.10 Msun (assuming an age of 1 Myr). These were selected for low extinction in most cases and are located west of the brighter ... More
Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 20945Feb 14 2003We present evolutionary models for cool brown dwarfs and extra-solar giant planets. The models reproduce the main trends of observed methane dwarfs in near-IR color-magnitude diagrams. We also present evolutionary models for irradiated planets, coupling ... More
Broad-band photometric colors and effective temperature calibrations for late-type giants. II. Z<0.02Mar 16 2006(Abridged) We investigate the effects of metallicity on the broad-band photometric colors of late-type giants, and make a comparison of synthetic colors with observed photometric properties of late-type giants over a wide range of effective temperatures ... More
Spectral Energy Distributions for Disk and Halo M--DwarfsJan 07 2000We have obtained infrared (1 to 2.5 micron) spectroscopy for 42 halo and disk dwarfs with spectral type M1 to M6.5. These data are compared to synthetic spectra generated by the latest model atmospheres of Allard & Hauschildt. Photospheric parameters ... More
High-contrast imaging of Sirius~A with VLT/SPHERE: Looking for giant planets down to one astronomical unitAug 31 2015Sirius has always attracted a lot of scientific interest, especially after the discovery of a companion white dwarf at the end of the 19th century. Very early on, the existence of a potential third body was put forward to explain some of the observed ... More
Star formation in the central regions of galaxiesNov 02 2006Massive star formation in the central regions of spiral galaxies plays an important role in the dynamical and secular evolution of their hosts. Here, we summarise a number of recent investigations of the star formation history and the physical conditions ... More
The Star Formation History and Evolution of the Circumnuclear Region of M100Jun 20 2006Jul 12 2006(Abridged) Star-forming nuclear rings in barred galaxies are common in nearby spirals, and their detailed study can lead to important insights into the evolution of galaxies, their bars, and their central regions. We present integral field spectroscopic ... More
Revisiting Spitzer transit observations with Independent Component Analysis: new results for the GJ436 systemJan 23 2015We analyzed four Spitzer/IRAC observations at 3.6 and 4.5 {\mu}m of the primary transit of the exoplanet GJ436b, by using blind source separation techniques. These observations are important to investigate the atmospheric composition of the planet GJ436b. ... More
Implications of the cosmic ray spectrum for the mass composition at the highest energiesMay 30 2008The significant attenuation of the cosmic-ray flux above $\sim 5 10^{19}$ eV suggests that the observed high-energy spectrum is shaped by the so-called GZK effect. This interaction of ultra-high-energy cosmic rays (UHECRs) with the ambient radiation fields ... More
Atmospheric Analysis of the M/L- and M/T-Dwarf Binary Systems LHS 102 and Gliese 229Dec 14 2001We present 0.9-2.5um spectroscopy with R~800 and 1.12-1.22um spectroscopy with R~5800 for the M dwarfs Gl 229A and LHS 102A, and for the L dwarf LHS 102B. We also report IZJHKL' photometry for both components of the LHS 102 system, and L' photometry for ... More
Infrared Spectra and Spectral Energy Distributions of Late-M- and L-DwarfsOct 10 2000We have obtained 1.0-2.5um spectra at R~600 of 14 disk dwarfs with spectral types M6 to L7. For four of the dwarfs we have also obtained infrared spectra at R~3000 in narrow intervals. In addition, we present new L' photometry for four of the dwarfs in ... More
Highlights of Stellar Modeling with PHOENIXSep 03 2002We briefly describe the current version of the PHOENIX code. We then present some illustrative results from the modeling of Type Ia and Type II supernovae, hot stars, and irradiated giant planets. Good fits to observations can be obtained, when account ... More
A high resolution spectroscopic atlas of M subdwarfs - Effective temperature and metallicityJan 13 2014Jan 30 2014Context. M subdwarfs are metal poor and cool stars. They are important probes of the old galactic populations. However, they remain elusive due to their low luminosity. Observational and modeling efforts are required to fully understand their physics ... More
A very cool brown dwarf in UKIDSS DR1Aug 05 2007(abridged) We report the discovery of a very cool brown dwarf, ULAS J003402.77-005206.7 (ULAS J0034-00), identified in UKIDSS DR1. We provide optical, near-infrared, and mid-infrared photometry of the source, and two near-infrared spectra. Comparing the ... More
The discovery of the T8.5 dwarf UGPS J0521+3640Apr 08 2011Apr 12 2011We have carried out a search for late-type T dwarfs in the UKIDSS Galactic Plane Survey 6th Data Release. The search yielded two persuasive candidates, both of which have been confirmed as T dwarfs. The brightest, UGPS J0521+3640 has been assigned the ... More
Primeval very low-mass stars and brown dwarfs - IV. New L subdwarfs, Gaia astrometry, population properties, and a blue brown dwarf binaryJul 27 2018Aug 28 2018We present 27 new L subdwarfs and classify five of them as esdL and 22 as sdL. Our L subdwarf candidates were selected with the UKIRT Infrared Deep Sky Survey and Sloan Digital Sky Survey. Spectroscopic follow-up was carried out primarily with the OSIRIS ... More
The Effective Temperature Scale of M dwarfsApr 15 2013Despite their large number in the Galaxy, M dwarfs remain elusive objects and the modeling of their photospheres has long remained a challenge (molecular opacities, dust cloud formation). Our objectives are to validate the BT-Settl model atmospheres, ... More
CFBDSIR2149-0403: a 4-7 Jupiter-mass free-floating planet in the young moving group AB Doradus ?Oct 01 2012Using the CFBDSIR wide field survey for brown dwarfs, we identified CFBDSIRJ214947.2-040308.9, a late T dwarf with atypically red J-Ks colour. We obtained an X-Shooter spectra, with signal detectable from 0.8 to 2.3 micron, which confirmed a T7 spectral ... More
A young binary Brown Dwarf in the R-CrA star formation regionApr 29 2004We present imaging and spectroscopic observations with HST (WFPC2, ACS/HRC and STIS), VLT (FORS2) and Keck (HIRES) of the dM8 ultra-cool dwarf DENIS-P J185950.9-370632, located in the R-CrA region. The presence of lithium absorption at 670.8 nm and the ... More
Photometric colors of late-type giants: theory versus observationsDec 14 2005To assess the current status in the theoretical modeling of the spectral properties of late-type giants, we provide a comparison of synthetic photometric colors of late-type giants (calculated with PHOENIX, MARCS and ATLAS model atmospheres) with observations, ... More
Broad-band photometric colors and effective temperature calibrations for late-type giants. I. Z=0.02Oct 14 2005We present new synthetic broad-band photometric colors for late-type giants based on synthetic spectra calculated with the PHOENIX model atmosphere code. The grid covers effective temperatures T_eff=3000...5000K, gravities log g=-0.5...+3.5, and metallicities ... More
Deep near-IR observations of the Globular Cluster M4: Hunting for Brown DwarfsJun 03 2015Nov 16 2015We present an analysis of deep HST/WFC3 near-IR (NIR) imaging data of the globular cluster M4. The best-photometry NIR colour-magnitude diagram (CMD) clearly shows the main sequence extending towards the expected end of the Hydrogen-burning limit and ... More
A Hubble Space Telescope ACS Search for Brown Dwarf Binaries in the Pleiades Open ClusterSep 27 2005We present the results of a high-resolution imaging survey for brown dwarf binaries in the Pleiades open cluster. The observations were carried out with the Advance Camera for Surveys onboard the Hubble Space Telescope. Our sample consists of 15 bona-fide ... More
Atmospheres from very low-mass stars to extrasolar planetsJun 05 2012Within the next few years, several instruments aiming at imaging extrasolar planets will see first light. In parallel, low mass planets are being searched around red dwarfs which offer more favorable conditions, both for radial velocity detection and ... More
Atmosphere Models for Very Low Mass Stars, Brown Dwarfs and ExoplanetsMay 12 1997Over the past decade considerable effort, both observational and theoretical, has been directed towards a more accurate determination of the stellar lower main sequence and of the sub-stellar domain covered by Brown Dwarfs and Planets. A review of the ... More
Half-tapering strategy for conditional simulation with large datasetsJul 28 2016Gaussian conditional realizations are routinely used for risk assessment and planning in a variety of Earth sciences applications. Conditional realizations can be obtained by first creating unconditional realizations that are then post-conditioned by ... More
Near-infrared integral-field spectra of the planet/brown dwarf companion AB Pic bJan 04 2010Chauvin et al. 2005 imaged a co-moving companion at ~260 AU from the young star AB Pic A. Evolutionary models predictions based on J H K photometry of AB Pic b suggested a mass of ~13 - 14 MJup, placing the object at the deuterium-burning boundary. We ... More
Spectral energy distribution of M-subdwarfs: A study of their atmospheric propertiesSep 22 2016Sep 27 2016Context. M-type subdwarfs are metal-poor low-mass stars and probe for the old populations in our Galaxy. Accurate knowledge of their atmospheric parameters and especially the composition is essential for understanding the chemical history of our Galaxy. ... More
A library of near-infrared integral field spectra of young M-L dwarfsJun 16 2013We present a library of near-infrared (1.1-2.45 microns) medium-resolution (R~1500-2000) integral field spectra of 15 young M6-L0 dwarfs, composed of companions with known ages and of isolated objects. We use it to (re)derive the NIR spectral types, luminosities ... More
Spectral Classification Beyond MSep 16 2004Significant populations of field L and T dwarfs are now known, and we anticipate the discovery of even cooler dwarfs by Spitzer and ground-based infrared surveys. However, as the number of known L and T dwarfs increases so does the range in their observational ... More
A physicist's view of DNANov 11 2013Nucleic acids, like DNA and RNA, are molecules that are present in any life form. Their most notable function is to encode biological information. Why then would a physicist be interested in these molecules? As we will see, DNA is an interesting molecular ... More
Constraints on the origin of ultra-high-energy cosmic rays from cosmogenic neutrinos and photonsJul 19 2011Nov 15 2011We study the production of cosmogenic neutrinos and photons during the extragalactic propagation of ultra-high-energy cosmic rays (UHECRs). For a wide range of models in cosmological evolution of source luminosity, composition and maximum energy we calculate ... More
First-passage time to clear the way for receptor-ligand binding in a crowded environmentMar 06 2016Certain biological reactions, such as receptor-ligand binding at cell-cell interfaces and macromolecules binding to biopolymers, require many smaller molecules crowding a reaction site to be cleared. Examples include the T cell interface, a key player ... More
VOSA: Virtual Observatory SED Analyzer. An application to the Collinder 69 open clusterAug 02 2008The physical properties of almost any kind of astronomical object can be derived by fitting synthetic spectra or photometry extracted from theoretical models to observational data. We want to develop an automatic procedure to perform this kind of fittings ... More
Cool objects: From SED fitting to age estimationApr 20 2007The physical properties of almost any kind of astronomical object can be derived by fitting synthetic spectra or photometry extracted from theoretical models to observational data. This process usually involves working with multiwavelength data, which ... More
Exploring the stellar properties of M dwarfs with high-resolution spectroscopy from the optical to the near-infraredOct 31 2018Dec 28 2018Context. Being the most numerous and oldest stars in the galaxy, M dwarfs are objects of great interest for exoplanet searches. The presence of molecules in their atmosphere complicates our understanding of their atmospheric properties. But great advances ... More
Means and covariance functions for geostatistical compositional data: an axiomatic approachDec 16 2015Oct 23 2017This work focuses on the characterization of the central tendency of a sample of compositional data. It provides new results about theoretical properties of means and covariance functions for compositional data, with an axiomatic perspective. Original ... More
The properties of the T8.5p dwarf Ross 458CMar 08 2011Apr 13 2011We present near-infrared photometry and spectroscopy, and warm-Spitzer IRAC photometry of the young very cool T dwarf Ross 458C, which we have typed as T8.5p. By applying the fiducial age constraints (< 1Gyr) imposed by the properties of the active M ... More
Means and covariance functions for spatial compositional data: an axiomatic approachDec 16 2015This work focuses on the characterization of the central tendency of a sample of compositional data.It provides new results about theoretical properties of means and covariance functions for compositional data, with an axiomatic perspective. Original ... More