Results for "P. Bergeron"

total 121895took 0.11s
The Halo White Dwarf WD 0346+246 RevisitedMay 18 2001The extreme helium-rich atmospheric composition determined for the halo white dwarf WD 0346+246 is reexamined. This solution is shown to be improbable from an astrophysical point of view when accretion of hydrogen and metals from the interstellar medium ... More
A Critical Examination of Halo White Dwarf CandidatesNov 26 2002A detailed analysis of halo white dwarf candidates is presented, which is based on model atmosphere fits to observed energy distributions built from photoelectric or photographic magnitudes. Most of the candidates identified in reduced proper motion diagrams ... More
Bounded Height Interlaced Pairs of Parking FunctionsApr 27 2015We enumerate interlaced pairs of parking functions whose underlying Dyck path has a bounded height. We obtain an explicit formula for this enumeration in the form of a quotient of analogs of Chebicheff polynomials having coefficients in the ring of symmetric ... More
Analysis of Helium-Rich White Dwarfs Polluted by Heavy Elements in the Gaia EraJul 12 2019We present a homogeneous analysis of 1023 DBZ/DZ(A) and 319 DQ white dwarf stars taken from the Montreal White Dwarf Database. This represents a significant increase over the previous comprehensive studies on these types of objects. We use new trigonometric ... More
STM Studies of Synthetic Peptide MonolayersApr 24 1998We have used scanning probe microscopy to investigate self-assembled monolayers of chemically synthesized peptides. We find that the peptides form a dense uniform monolayer, above which is found a sparse additional layer. Using scanning tunneling microscopy, ... More
Spectroscopic Analysis of the DAB White Dwarf PG 1115+166: An Unresolved DA + DB Degenerate BinaryOct 25 2001A spectroscopic analysis of the DAB white dwarf PG 1115+166 is presented. The observed hydrogen and helium line profiles are shown to be incompatible with model spectra calculated under the assumption of homogeneous or stratified chemical compositions. ... More
A note about combinatorial sequences and Incomplete Gamma functionSep 10 2013In this short note we present a set of interesting and useful properties of a one-parameter family of sequences including factorial and subfactorial, and their relations to the Gamma function and the incomplete Gamma function.
Comparison of White Dwarf Mass DeterminationsMar 04 2005White dwarf masses can be determined in several ways. Here we compare masses obtained from Balmer line spectroscopy with those derived from trigonometric parallax measurements for an ensemble of cool hydrogen-atmosphere white dwarfs.
The Ratio of Helium- to Hydrogen-Atmosphere White Dwarfs: Direct Evidence for Convective MixingOct 04 2007We determine the ratio of helium- to hydrogen-atmosphere white dwarf stars as a function of effective temperature from a model atmosphere analysis of the infrared photometric data from the Two Micron All Sky Survey combined with available visual magnitudes. ... More
A Comparative Study of Optical and Ultraviolet Effective Temperatures for DA White Dwarfs from the IUE ArchiveJun 20 2007We present a comparative study of effective temperatures determined from the hydrogen Balmer lines and from the UV energy distribution for 140 DA white dwarfs drawn from the IUE archive. Our results indicate that the optical and UV temperatures of the ... More
Near-Infrared Photometric Analyses of White Dwarf StarsNov 29 2006We review the available near- and mid- infrared photometry data sets for white dwarfs from the Two Micron All-Sky Survey (2MASS) Point Source Catalog and the Spitzer Space Telescope. These data sets have been widely used to search for white dwarfs with ... More
Lattice Diagram polynomials in one set of variablesMar 27 2001The space $M_{\mu/i,j}$ spanned by all partial derivatives of the lattice polynomial $\Delta_{\mu/i,j}(X;Y)$ is investigated in math.CO/9809126 and many conjectures are given. Here, we prove all these conjectures for the $Y$-free component $M_{\mu/i,j}^0$ ... More
Infrared Photometric Analysis of White Dwarfs from The Two Micron All Sky Survey and the Spitzer Space TelescopeNov 29 2006We review the available near- and mid-infrared photometry for white dwarfs obtained from the Two Micron All-Sky Survey (2MASS) and by the Spitzer Space Telescope. Both data sets have recently been used to seek white dwarfs with infrared excesses due to ... More
Spectroscopic Analysis of DA White Dwarfs: Stark Broadening of Hydrogen Lines Including Non-Ideal EffectsFeb 24 2009We present improved calculations for the Stark broadening of hydrogen lines in dense plasmas typical of white dwarf atmospheres. Our new model is based on the unified theory of Stark broadening from Vidal, Cooper, & Smith. For the first time, we account ... More
Ideals of Quasi-Symmetric Functions and Super-Covariant Polynomials for S_nFeb 08 2002The aim of this work is to study the quotient ring R_n of the ring Q[x_1,...,x_n] over the ideal J_n generated by non-constant homogeneous quasi-symmetric functions. We prove here that the dimension of R_n is given by C_n, the n-th Catalan number. This ... More
A study of the Lyman-$α$ line profile in DBA white dwarfsOct 27 2016The hydrogen abundances in DBA white dwarfs determined from optical or UV spectra have been reported to differ significantly in some studies. We revisit this problem using our own model atmospheres and synthetic spectra, and present a theoretical investigation ... More
A comprehensive spectroscopic and photometric analysis of DA and DB white dwarfs from SDSS and GaiaJan 07 2019We present a detailed spectroscopic and photometric analysis of DA and DB white dwarfs drawn from the Sloan Digital Sky Survey with trigonometric parallax measurements available from the Gaia mission. The temperature and mass scales obtained from fits ... More
Comparison of Atmospheric Parameters Determined from Spectroscopy and Photometry for DA White Dwarfs in the Sloan Digital Sky SurveyOct 20 2014We present a comparative analysis of atmospheric parameters obtained with the so-called photometric and spectroscopic techniques. Photometric and spectroscopic data for 1360 DA white dwarfs from the Sloan Digital Sky Survey (SDSS) are used, as well as ... More
Model Atmosphere Analysis of Two Very Cool White DwarfsJul 31 2002A detailed analysis of the very cool white dwarfs SDSS 1337+00 and LHS 3250 is presented. Model atmosphere calculations with improved collision-induced absorptions by molecular hydrogen indicate that a pure hydrogen composition can be ruled out, and that ... More
Hopf Algebras and Edge-Labeled PosetsDec 17 1997May 04 1999Given a finite graded poset with labeled Hasse diagram, we construct a quasi- symmetric generating function for (saturated) chains whose labels have fixed descents. This is a common generalization of a generating function for the flag f-vector defined ... More
A Determination of the Luminosity Function of DA White Dwarfs from the Kiso SurveyMar 31 2009Apr 01 2009We rederive the luminosity function for the sample of DA white dwarfs from the Kiso Schmidt ultraviolet excess survey (KUV stars) using the spectroscopic method where the atmospheric parameters (Teff and log g) and absolute visual magnitudes for each ... More
A Spectroscopic Analysis of White Dwarfs in the Kiso SurveyMar 23 2010We present a spectroscopic analysis of white dwarfs found in the Kiso survey. Spectroscopic observations at high signal-to-noise ratio have been obtained for all DA and DB stars in the Kiso Schmidt ultraviolet excess survey (KUV stars). These observations ... More
Generating functions for the osp(1|2) Clebsch-Gordan coefficientsJun 30 2015Generating functions for Clebsch-Gordan coefficients of osp(1|2) are derived. These coefficients are expressed as q goes to - 1 limits of the dual q-Hahn polynomials. The generating functions are obtained using two different approaches respectively based ... More
A Detailed Spectroscopic and Photometric Analysis of DQ White DwarfsMar 21 2005We present an analysis of spectroscopic and photometric observations of cool DQ white dwarfs based on improved model atmosphere calculations. In particular, we revise the atmospheric parameters of the trigonometric parallax sample of Bergeron, Leggett, ... More
An Improved Spectroscopic Analysis of DA White Dwarfs from the Sloan Digital Sky Survey Data Release 4Feb 01 2011We present an improved spectroscopic and photometric analysis of hydrogen-line DA white dwarfs from the Sloan Digital Sky Survey Data Release 4 based on model atmospheres that include improved Stark broadening profiles with non-ideal gas effects. We also ... More
Parameter-free Stark Broadening of Hydrogen Lines in DA White DwarfsApr 06 2009We present new calculations for the Stark broadening of the hydrogen line profiles in the dense atmospheres of white dwarf stars. Our improved model is based on the unified theory of Stark broadening from Vidal, Cooper & Smith, but it also includes non-ideal ... More
Detailed Spectroscopic and Photometric Analysis of DQ White DwarfsMar 04 2005We present an analysis of spectroscopic and photometric data for cool DQ white dwarfs based on improved model atmosphere calculations. In particular, we revise the atmospheric parameters of the trigonometric parallax sample of Bergeron et al.(2001), and ... More
Discovery of a Cool, Massive, and Metal-Rich DAZ White DwarfOct 28 2004We report the discovery of a new metal-rich DAZ white dwarf, GD 362. High signal-to-noise optical spectroscopy reveals the presence of spectral lines from hydrogen as well as CaI, CaII, MgI, and FeI. A detailed model atmosphere analysis of this star yields ... More
Analysis of DA White Dwarfs from the McCook & Sion CatalogMar 04 2005Mar 04 2005The Sloan Digital Sky Survey has already doubled the number of spectroscopically identified white dwarfs. However, there remains a wealth of white dwarfs in the McCook & Sion catalog for which little or nothing is known. We have thus undertaken a spectroscopic ... More
Schur Partial Derivative OperatorsNov 22 2001A lattice diagram is a finite list L=((p_1,q_1),...,(p_n,q_n) of lattice cells. The corresponding lattice diagram determinant is \Delta_L(X;Y)=\det \| x_i^{p_j}y_i^{q_j} \|. These lattice diagram determinants are crucial in the study of the so-called ... More
Catalan paths, Quasi-symmetric functions and Super-Harmonic SpacesSep 20 2001We investigate the quotient ring $R$ of the ring of formal power series $\Q[[x_1,x_2,...]]$ over the closure of the ideal generated by non-constant quasi-\break symmetric functions. We show that a Hilbert basis of the quotient is naturally indexed by ... More
Obscured and powerful AGN and starburst activities at z~3.5Oct 14 2008Nov 14 2008We report the discovery of two sources at z=3.867 and z=3.427 that exhibit powerful starburst and AGN activities. They benefit from data from radio to X rays from the CFHTLS-D1/SWIRE/XMDS surveys. Follow-up optical and near-infrared spectroscopy, and ... More
Dust depletion and abundance pattern in damped Lyman-alpha systems: a sample of Mn and Ti abundances at z<2.2Feb 06 2002We analyse a sample of 24 damped Lyman-alpha (DLA)/moderate DLA systems at 0.3<z<2.2, all with measurement of the weak MnII absorption lines, to investigate which elemental ratios could possibly be used as tracers of either dust depletion or nucleosynthesis ... More
Observationnal constraints on the nature of the low redshift Lyman-alpha absorbersSep 28 1995We present results from a spectroscopic and imaging survey of galaxies in the fields of quasars from the HST Quasar Absorption Line Key Project. The aim of this survey is to identify galaxies within 3.5' from the quasar sightline, to a limiting r-band ... More
Spectroscopic confirmation of UV-bright white dwarfs from the Sandage Two-Color Survey of the Galactic PlaneFeb 03 2011We present spectroscopic observations confirming the identification of hot white dwarfs among UV-bright sources from the Sandage Two-color Survey of the Galactic plane and listed in the Lanning (Lan) catalog of such sources. A subsample of 213 UV bright ... More
Discovery of Spectroscopic Variations in the DAB White Dwarf GD 323Jan 27 2005We report the discovery of spectroscopic variations in GD 323, the prototypical DAB white dwarf. Simultaneous optical spectroscopic observations over five consecutive nights of GD 323 and of PG 1234+482, a non-variable comparison DA white dwarf of similar ... More
Spectroscopic analysis of DA white dwarfs from the McCook & Sion catalogOct 29 2008For some years now, we have been gathering optical spectra of DA white dwarfs in an effort to study and define the empirical ZZ Ceti instability strip. However, we have recently expanded this survey to include all the DA white dwarfs in the McCook & Sion ... More
The Formation Rate, Mass and Luminosity Functions of DA White Dwarfs from the Palomar Green SurveyJun 29 2004Sep 07 2004Spectrophotometric observations at high signal-to-noise ratio were obtained of a complete sample of 347 DA white dwarfs from the Palomar Green (PG) Survey. Fits of observed Balmer lines to synthetic spectra calculated from pure-hydrogen model atmospheres ... More
Spectroscopic Analysis of the White Dwarf KUV 02196+2816: A New Unresolved DA+DB Degenerate BinaryFeb 20 2009A spectroscopic analysis of the DBA (or DAB) white dwarf KUV 02196+2816 is presented. The observed hydrogen and helium line profiles are shown to be incompatible with model spectra calculated under the assumption of a homogeneous hydrogen and helium chemical ... More
A Progress Report on the Empirical Determination of the ZZ Ceti Instability StripDec 01 2006Although the Sloan Digital Sky Survey has permitted the discovery of an increasing number of new ZZ Ceti stars, recent published analyses have shown that there are still many relatively bright (V < 17) ZZ Ceti stars waiting to be found. We will discuss ... More
Towards an Empirical Determination of the ZZ Ceti Instability StripJun 20 2005We present atmospheric parameters for a large sample of DA white dwarfs that are known to be photometrically constant. For each star, we determine the effective temperature and surface gravity by comparing high signal-to-noise ratio optical spectra to ... More
Physical Properties of the Current Census of Northern White Dwarfs within 40 pc of the SunMay 09 2015We present a detailed description of the physical properties of our current census of white dwarfs within 40 pc of the Sun, based on an exhaustive spectroscopic survey of northern hemisphere candidates from the SUPERBLINK proper motion database. Our method ... More
The True Incidence of Magnetism among Field White DwarfsOct 15 2002Oct 15 2002We study the incidence of magnetism in white dwarfs from three large and well-observed samples of hot, cool, and nearby white dwarfs in order to test whether the fraction of magnetic degenerates is biased, and whether it varies with effective temperature, ... More
The Mass Distribution of White Dwarfs: An Unwavering ObsessionNov 29 2006We discuss some of our current knowledge of the mass distribution of DA and non-DA stars using various methods for measuring white dwarf masses including spectroscopic, trigonometric parallax, and gravitational redshift measurements, with a particular ... More
New SUSYQM coherent states for Poschl-Teller potentials: a detailed mathematical analysisDec 05 2011Feb 02 2012In a recent short note [Bergeron H, Gazeau J P, Siegl P and Youssef A 2010 EPL 92 60003], we have presented the nice properties of a new family of semi-classical states for P\"oschl-Teller potentials. These states are built from a supersymmetric quantum ... More
Toward a Spectroscopic Census of White Dwarfs Within 40 parsecs of the SunMar 08 2013We present the preliminary results of a survey aimed at significantly increasing the range and completeness of the local census of spectroscopically confirmed white dwarfs. The current census of nearby white dwarfs is reasonably complete only to about ... More
A Census of White Dwarfs Within 40 Parsecs of the SunOct 06 2010Our aim is to compile a catalog of white dwarfs within 40 parsecs of the Sun, in which newly discovered objects would significantly increase the completeness of the current census. White dwarf candidates are identified from the SUPERBLINK proper motion ... More
Astrophysical Implications of a New Dynamical Mass for the Nearby White Dwarf 40 Eridani BSep 01 2017The bright, nearby DA-type white dwarf (WD) 40 Eridani B is orbited by the M dwarf 40 Eri C, allowing determination of the WD's mass. Until recently, however, the mass depended on orbital elements determined four decades ago, and that mass was so low ... More
Mapping the ZZ Ceti Instability Strip: Discovery of 6 New PulsatorsJun 07 2006As part of an ongoing program to map better the empirical instability strip of pulsating ZZ Ceti white dwarfs, we present a brief progress report based on our last observing season. We discuss here high-speed photometric measurements for 6 new pulsators. ... More
Taking Advantage of the COS Time-Tag Capability: Observations of Pulsating Hot DQ White Dwarfs and Discovery of a New OneApr 13 2011We present an analysis of the ultraviolet light curves of five Hot DQ white dwarfs recently observed with the Cosmic Origins Spectrograph (COS) on board the Hubble Space Telescope (HST). These light curves were constructed by extracting the time-tag information ... More
The Potential of Multi-Colour Photometry for Pulsating Subdwarf B StarsJul 26 2005We investigate the potential of multi-colour photometry for partial mode identification in both long- and short-period variable subdwarf B stars. The technique presented is based on the fact that the frequency dependence of an oscillation's amplitude ... More
New Insights into the Problem of the Surface Gravity Distribution of Cool DA White DwarfsFeb 18 2010We review at length the longstanding problem in the spectroscopic analysis of cool hydrogen-line (DA) white dwarfs (Teff < 13,000 K) where gravities are significantly higher than those found in hotter DA stars. The first solution that has been proposed ... More
The HST Large Programme on NGC 6752. III. Detection of the Peak of the White Dwarf Luminosity FunctionJul 15 2019We report on the white dwarf cooling sequence of the old globular cluster NGC 6752, which is chemically complex and hosts a blue horizontal branch. This is one of the last globular cluster white dwarf (WD) cooling sequences accessible to imaging by the ... More
Semi-classical behavior of Pöschl-Teller coherent statesJul 22 2010We present a construction of semi-classical states for P\"oschl-Teller potentials based on a supersymmetric quantum mechanics approach. The parameters of these "coherent" states are points in the classical phase space of these systems. They minimize a ... More
Hopf monoids from class functions on unitriangular matricesMar 07 2012Oct 16 2012We build, from the collection of all groups of unitriangular matrices, Hopf monoids in Joyal's category of species. Such structure is carried by the collection of class function spaces on those groups, and also by the collection of superclass function ... More
Generating functions for the Bannai-Ito polynomialsMay 11 2016Mar 13 2018The generating function of the Bannai-Ito polynomials is derived using the fact that these polynomials are known to be essentially the Racah or $6j$ coefficients of the $\mathfrak{osp}(1|2)$ Lie superalgebra. The derivation is carried in a realization ... More
Combinatorial Hopf algebras and Towers of AlgebrasOct 19 2007Bergeron and Li have introduced a set of axioms which guarantee that the Grothendieck groups of a tower of algebras $\bigoplus_{n\ge0}A_n$ can be endowed with the structure of graded dual Hopf algebras. Hivert and Nzeutzhap, and independently Lam and ... More
Signal processing, orthogonal polynomials, and Heun equationsMar 01 2019A survey of recents advances in the theory of Heun operators is offered. Some of the topics covered include: quadratic algebras and orthogonal polynomials, differential and difference Heun operators associated to Jacobi and Hahn polynomials, connections ... More
The sub-DLA toward HE0001-2340: galaxy formation at z=2May 17 2005We present a detailed analysis of chemical abundances in a sub-damped Ly alpha absorber (sub-DLA) at z=2.187 towards the quasar HE0001-2340 (z_em=2.28) using VLT/UVES data. This sub-DLA system consists of at least 25 individual subcomponents spanning ... More
An upper bound for the volumes of complements of periodic geodesicsDec 08 2014May 10 2016A periodic geodesic on a surface has a natural lift to the unit tangent bundle; when the complement of this lift is hyperbolic, its volume typically grows as the geodesic gets longer. We give an upper bound for this volume which is linear in the geometric ... More
The masses of the millisecond pulsar J1012+5307 and its white-dwarf companionJun 07 1996We report on spectroscopy of the white-dwarf companion of the millisecond radio pulsar PSR J1012+5307. We find strong Balmer absorption lines, as would be expected for a cool DA white dwarf. The profiles are much narrower than usual, however, and lines ... More
Cool White Dwarfs Identified in the Second Data Release of the UKIRT Infrared Deep Sky SurveyOct 22 2008We have paired the Second Data Release of the Large Area Survey of the UKIRT Infrared Deep Sky Survey with the Fifth Data Release of the Sloan Digital Sky Survey to identify ten cool white dwarf candidates, from their photometry and astrometry. Of these ... More
A comparative analysis of the observed white dwarf cooling sequence from globular clustersDec 10 2015We report our study of features at the observed red end of the white dwarf cooling sequences for three Galactic globular clusters: NGC\,6397, 47\,Tucanae and M\,4. We use deep colour-magnitude diagrams constructed from archival Hubble Space Telescope ... More
A Photometric Analysis of ZZ Ceti Stars: A Parameter-Free Temperature Indicator?Mar 30 2009We present a model atmosphere analysis of optical VRI and infrared JHK photometric data of about two dozen ZZ Ceti stars. We first show from a theoretical point of view that the resulting energy distributions are not particularly sensitive to surface ... More
Limb-Darkening Coefficients for Eclipsing White DwarfsJan 29 2013Feb 20 2013We present extensive calculations of linear and non-linear limb-darkening coefficients as well as complete intensity profiles appropriate for modeling the light-curves of eclipsing white dwarfs. We compute limb-darkening coefficients in the Johnson-Kron-Cousins ... More
A high resolution study of intergalactic O VI absorbers at z~2.3Dec 06 2011[Abridged] We present a detailed study of the largest sample of intervening O VI systems in the redshift range 1.9 < z < 3.1 detected in high resolution (R ~ 45,000) spectra of 18 bright QSOs observed with VLT/UVES. Based on Voigt profile and apparent ... More
XMM-Newton observations of the Lockman Hole : Spectral analysisFeb 11 2002We present the results of the X-ray spectral analysis of the deep survey obtained with the XMM-Newton observatory on the Lockman Hole. The X-ray data and the cumulative source counts were reported by Hasinger et al. (2001). Our sample contains 104 sources ... More
The nature of intermediate-redshift damped Ly-alpha absorbersNov 05 1996We present HST/WFPC2 high-spatial resolution images in the R and B bands of the close environment of the sightlines to seven quasars which spectra show either a damped Ly-alpha absorption line, 21cm absorption, or a very strong MgII/FeII absorption system ... More
The Luminosity Function for White Dwarfs in the SuperCOSMOS Sky SurveyMar 24 2009We present the techniques and early results of our program to measure the luminosity function for White Dwarfs in the SuperCOSMOS Sky Survey. Our survey covers over three quarters of the sky to a mean depth of I~19.2, and finds ~9,500 Galactic disk WD ... More
Photometric and Spectroscopic Analysis of Cool White Dwarfs with Trigonometric Parallax MeasurementsNov 15 2000A photometric and spectroscopic analysis of 152 cool white dwarf stars is presented. The discovery of 7 new DA white dwarfs, 2 new DQ white dwarfs, 1 new magnetic white dwarf, and 3 weak magnetic white dwarf candidates, is reported, as well as 19 known ... More
The Solar Neighborhood. XIX. Discovery and Characterization of 33 New Nearby White Dwarf SystemsApr 06 2007We present spectra for 33 previously unclassified white dwarf systems brighter than V = 17 primarily in the southern hemisphere. Of these new systems, 26 are DA, 4 are DC, 2 are DZ, and 1 is DQ. We suspect three of these systems are unresolved double ... More
The Solar Neighborhood. XX. Discovery and Characterization of 21 New Nearby White Dwarf SystemsMay 16 2008We present medium resolution spectroscopy and multi-epoch VRI photometry for 21 new nearby (< 50 pc) white dwarf systems brighter than V ~ 17. Of the new systems, ten are DA (including a wide double degenerate system with two DA components), eight are ... More
Combinatorial Cellular Decompositions for the Space of Complex Coefficient PolynomialsJan 26 2009May 05 2011We describe a classification of degree n complex coefficient polynomials with respect to combinatorial patterns that arise from the two real algebraic curves obtained as the zero sets for their real and imaginary part. In particular, we work out explicitly ... More
Propriétés de Lefschetz automorphes pour les groupes unitaires et orthogonauxMar 03 2005Let $G$ be a connected semisimple group over ${\Bbb Q}$. Given a maximal compact subgroup and a convenient arithmetic subgroup $\Gamma\subset G({\Bbb Q})$, one constructs an arithmetic manifold $S=S(\Gamma)=\Gamma\backslash X$. If $H\subset G$ is a connected, ... More
Atomic resolution STM imaging of a twisted single-wall carbon nanotubeApr 16 1998We present atomically-resolved STM images of single-wall carbon nanotubes (SWNTs) embedded in a crystalline nanotube rope. Although they may be interpreted as of a chiral nanotube, the images are more consistently explained a an achiral armchair tube ... More
A Quantitative Analysis of the Available Multicolor Photometry for Rapidly Pulsating Hot B SubdwarfsJun 20 2006We present a quantitative and homogeneous analysis of the broadband multicolor photometric data sets gathered so far on rapidly pulsating hot B subdwarf stars. This concerns seven distinct data sets related to six different stars. Our analysis is carried ... More
A q-Analog of Foulke's conjectureFeb 25 2016Jul 01 2016We propose a $q$-analog of classical plethystic conjectures due to Foulkes. In our conjectures, a divided difference of plethysms of Hall-Littlewood polynomials $H_n(\mathbf{x};q)$ replaces the analogous difference of plethysms of complete homogeneous ... More
La conjecture des sous-groupes de surfaces (d'après Jeremy Kahn et Vladimir Markovic)Jul 13 2012This is the text of my Bourbaki seminar on the proof of the surface subgroup conjecture by Jeremy Kahn and Vladimir Markovic.
Produits dans la cohomologie des variétés arithmétiques : quelques calculs sur les séries thêtaDec 15 2006For abelian varieties $A$, in the most interesting cohomology theories $H^* (A)$ is the exterior algebra of $H^1(A)$. In this paper we study a weak generalization of this in the case of arithmetic manifolds associated to orthogonal or unitary groups. ... More
Représentations cohomologiques isolées, applications cohomologiquesNov 28 2005We give a new proof of a Theorem of Vogan which classify the cohomological representations of a real semisimple Lie group $G$ which are isolated in the unitary dual of $G$. We investigate the same question in the automorphic dual, and obtain partial results. ... More
Shifted Quasi-Symmetric Functions and the Hopf algebra of peak functionsApr 20 1999In his work on P-partitions, Stembridge defined the algebra of peak functions Pi, which is both a subalgebra and a retraction of the algebra of quasi-symmetric functions. We show that Pi is closed under coproduct, and therefore a Hopf algebra, and describe ... More
The topology of nilpotent representations in reductive groups and their maximal compact subgroupsOct 18 2013Aug 06 2014Let G be a complex reductive linear algebraic group and let K be a maximal compact subgroup of G. Given a nilpotent group \Gamma generated by r elements, we consider the representation spaces Hom(\Gamma,G) and Hom(\Gamma,K) with the natural topology induced ... More
Tentative d'épuisement de la cohomologie d'une variété de Shimura par restriction à ses sous-variétésMar 24 2004Let $G$ be a connected semisimple group over ${\Bbb Q}$. Given a maximal compact subgroup $K\subset G({\Bbb R})$ such that $X=G({\Bbb R})/K$ is a Hermitian symmetric domain, and a convenient arithmetic subgroup $\Gamma\subset G({\Bbb Q})$, one constructs ... More
New Formulas and Conjectures for the Nabla OperatorMay 29 2011The operator nabla, introduced by Garsia and the author, plays a crucial role in many aspect of the study of diagonal harmonics. Besides giving several new formulas involving this operator, we show how one is lead to representation theoretic explanations ... More
Multivariate Diagonal Coinvariant Spaces for Complex Reflection GroupsMay 22 2011Nov 02 2011For finite complex reflexion groups, we consider the graded $W$-modules of diagonally harmonic polynomials in $r$ sets of variables, and show that associated Hilbert series may be described in a global manner, independent of the value of $r$.
Open Questions for operators related to Rectangular Catalan CombinatoricsMar 14 2016Mar 20 2016We formulate many open questions regarding the Schur positivity of the effect of interesting operators on symmetric functions, and give supporting evidence for why one should expect such behavior.
Nonadiabatic bounce and an inflationary phase in the quantum mixmaster universeNov 18 2015Jun 24 2016Following our previous paper, Bergeron et al, Smooth quantum dynamics of the mixmaster universe, Phys. Rev. D 92, 061302(R) (2015), concerning the quantization of the vacuum Bianchi IX model and the Born-Huang-Oppenheimer framework, we present a further ... More
Combinatorics of r-Dyck paths, r-Parking functions, and the r-Tamari latticesFeb 28 2012Mar 03 2012This paper's aim is to present recent combinatorial considerations on r-Dyck paths, r-Parking functions, and the r-Tamari lattices. Giving a better understanding of the combinatorics of these objects has become important in view of their (conjectural) ... More
ELT Observations of Supernovae at the Edge of the UniverseApr 05 2005We discuss the possibility of using Supernovae as tracers of the star formation history of the Universe for the range of stellar masses $\sim 3-30$ M$_\odot$ and possibly beyond. We simulate the observations of 350 SNe, up to $z\sim 15$, made with OWL ... More
Pure-helium 3D model atmospheres of white dwarfsSep 03 2018We present the first grid of 3D simulations for the pure-helium atmospheres of DB white dwarfs. The simulations were computed with the CO5BOLD radiation-hydrodynamics code and cover effective temperatures and surface gravities between 12000 K < Teff < ... More
Detailed compositional analysis of the heavily polluted DBZ white dwarf SDSS J073842.56+183509.06: A window on planet formation?Jan 30 2012We present a new model atmosphere analysis of the most metal contaminated white dwarf known, the DBZ SDSS J073842.56+183509.06. Using new high resolution spectroscopic observations taken with Keck and Magellan, we determine precise atmospheric parameters ... More
An Ultramassive 1.28 M$_\odot$ White Dwarf in NGC 2099Mar 01 2016With the Keck I Low-Resolution Imaging Spectrometer we have observed nine white dwarf candidates in the very rich open cluster NGC 2099 (M37). The spectroscopy shows seven to be DA white dwarfs, one to be a DB white dwarf, and one to be a DZ white dwarf. ... More
Solution to the problem of the surface gravity distribution of cool DA white dwarfs from improved 3D model atmospheresJun 29 2011Jul 09 2011The surface gravities of cool (Teff < 13,000 K) hydrogen-atmosphere DA white dwarfs, determined from spectroscopic analyses, are found to be significantly higher than the canonical value of log g ~ 8 expected for these stars. It was recently concluded ... More
Precise Atmospheric Parameters for the Shortest Period Binary White Dwarfs: Gravitational Waves, Metals, and PulsationsAug 13 2014Aug 16 2014We present a detailed spectroscopic analysis of 61 low mass white dwarfs and provide precise atmospheric parameters, masses, and updated binary system parameters based on our new model atmosphere grids and the most recent evolutionary model calculations. ... More
Cool White Dwarfs Found in the UKIRT Infrared Deep Sky SurveyApr 20 2011We present the results of a search for cool white dwarfs in the United Kingdom InfraRed Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS). The UKIDSS LAS photometry was paired with the Sloan Digital Sky Survey (SDSS) to identify ... More
Search for cold gas in strong MgII absorbers at 0.5<z<1.5: nature and evolution of 21-cm absorbersMay 17 2012May 26 2012We report 4 new detections of 21-cm absorption from a systematic search of 21-cm absorption in a sample of 17 strong (Wr(MgII 2796)>1A) intervening MgII absorbers at 0.5<z<1.5. We also present 20-cm milliarcsecond scale maps of 40 quasars having 42 intervening ... More
The Montreal White Dwarf Database: a Tool for the CommunityOct 04 2016We present the "Montreal White Dwarf Database" (MWDD), an accessible database with sortable/filterable table and interactive plots that will, when fully completed, allow the community to explore the physical properties of all white dwarfs ever analyzed ... More
Time variations of narrow absorption lines in high resolution quasar spectraJun 09 2015Aims. We have searched for temporal variations of narrow absorption lines in high resolution quasar spectra. A sample of 5 distant sources have been assembled, for which 2 spectra - VLT/UVES or Keck/HIRES - taken several years apart are available. Methods. ... More
A Double White-Dwarf Cooling Sequence in ω CentauriMay 01 2013May 03 2013We have applied our empirical-PSF-based photometric techniques on a large number of calibration-related WFC3/UVIS UV-B exposures of the core of {\omega} Cen, and found a well-defined split in the right part of the white-dwarf cooling sequence (WDCS). ... More
A Helium White Dwarf of Extremely Low MassApr 15 2004We analyze the spectrum of an unusually-low mass white dwarf, SDSSJ123410.37-022802.9 (0335-264-52000), found in our recent, white dwarf catalog from the SDSS DR1 data release. Two independent, model atmosphere fits result in an accurate determination ... More