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Search Results: 1 - 10 of 448316 matches for " J-L. Beuzit "
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No disk needed around HD 199143 B
G. Chauvin,T. Fusco,A-M. Lagrange,D. Mouillet,J-L. Beuzit,M. Thomson,J-C. Augereau,F. Marchis,C. Dumas,P. Lowrance
Physics , 2002, DOI: 10.1051/0004-6361:20021114
Abstract: We present new, high angular resolution images of HD 199143 in the Capricornus association, obtained with the adaptive optics system ADONIS+SHARPII at the ESO 3.6m Telescope of La Silla Observatory. HD 199143 and its neighbour star HD 358623 (separation 5'away) have previously been imaged with adaptive optics. For each star, a companion has been detected in the J and K bands at respective separations of 1.1'' and 2.2'' (Jayawardhana & Brandeker 2001). Our new photometry of HD 199143 B suggests that it is a M2 star and that the presence of circumstellar dust proposed by Van den Ancker et al. (2000) is no longer necessary. We show that the 12 microns flux detected by IRAS previously interpreted as an IR excess, can be explained by the presence of the late-type companion.
Adaptive optics imaging of the MBM 12 association
G. Chauvin,F. Ménard,T. Fusco,A-M. Lagrange,J-L. Beuzit,D. Mouillet,J-C. Augereau
Physics , 2002, DOI: 10.1051/0004-6361:20021215
Abstract: We report adaptive optics (AO) observations of the young and nearby association MBM 12 obtained with the Canada-France-Hawaii Telescope. Our main observational result is the discovery of six new binary systems, LkHa 264, E 0255+2018, RX J0255.4+2005, S18, MBM 12-10, RX J0255.3+1915, and the confirmation of HD 17332, already known as a binary. We also detected a possible quadruple system. It is composed of the close binary LkHa 263 AB (separation of 0.41 ''), of LkH\alpha 262 located 15.25 '' from LkHa 263 A, and of LkHa 263 C, located 4.1 '' from LkH\alpha 263 A. A preliminary study of the binary fraction suggests a binary excess in the MBM 12 association as compared to the field and IC 348. Because of the high binarity rate, previous estimations of spectral types and measurements of IR excesses for several candidate members of MBM 12 have to be revised. LkH\alpha 263 C is a nebulous object that we interpret as a disk oriented almost perfectly edge-on and seen in scattered light. This object has already been reported by Jayawardhana et al. (2002). Scattered light models allow us to estimate some of the structural parameters (i.e. inclination, diameter and to a lesser extent dust mass) of the circumstellar disk. We find an inclination of 89^o and a outer radius for the disk, 165 AU if the distance to MBM 12 is 275 pc. With the present data set, we do not attempt to re-assess the distance to MBM 12. We estimate however that the distance to the candidate member RX J0255.3+1915 is d > 175 pc.
Adaptive optics imaging survey of the Tucana-Horologium association
G. Chauvin,M. Thomson,C. Dumas,J-L. Beuzit,P. Lowrance,T. Fusco,A-M. Lagrange,B. Zuckerman,D. Mouillet
Physics , 2003, DOI: 10.1051/0004-6361:20030352
Abstract: We present the results of an adaptive optics (AO) imaging survey of the common associations of Tucana and Horologium, carried out at the ESO 3.6m telescope with the ADONIS/SHARPII system. Based on our observations of two dozen probable association members, HIP 1910 and HIP 108422 appear to have low-mass stellar companions, while HIP 6856 and GSC 8047-0232 have possible sub-stellar candidate companions. Astrometric measurements, performed in November 2000 and October 2001, indicate that HIP 1910 B likely is bound to its primary, but are inconclusive in the case of the candidate companion to HIP 6856. Additional observations are needed to confirm the HIP 6856 companionship as well as for HIP 108422 and GSC 8047-0232.
The young, tight and low mass binary TWA22AB: a new calibrator for evolutionary models ? Orbit, spectral types and temperatures determination
M. Bonnefoy,G. Chauvin,C. Dumas,A-M. Lagrange,H. Beust,M. Desort,R. Texeira,C. Ducourant,J-L. Beuzit,I. Song
Physics , 2009, DOI: 10.1051/0004-6361/200810921
Abstract: Tight binaries discovered in young, nearby associations, with known distances, are ideal targets to provide dynamical mass measurements to test the physics of evolutionary models at young ages and very low masses. We report for the first time the binarity of TWA22, possible new dynamical calibrator for evolutionary models at young ages. Based on an accurate trigonometric distance (17.53 +- 0.21 pc) determination, we infer a total dynamical mass of 220 +- 21 MJup for the system. From the resolved near-infrared integral-field spectroscopy, we find an effective temperature Teff=2900+200-200 K for TWA22 A and Teff=2900+200-100 K for TWA22 B and surface gravities between 4.0 and 5.5 dex. From our photometry and a M6 +- 1 spectral type for both components, we find luminosities of log(L/Lsun)=-2.11 +- 0.13 dex and log(L/Lsun)=-2.30 +- 0.16 dex for TWA22 A and B respectively. By comparing these parameters with evolutionary models, we question the age and the multiplicity of this system. We also discuss a possible underestimation of the mass predicted by evolutionary models for young stars close to the substellar boundary.
La régression parent-descendant dans le cas d'un nombre variable de mesures par parent
J-L Foulley
Genetics Selection Evolution , 1981, DOI: 10.1186/1297-9686-13-2-181
Mémoires d’Océans et d’Ailleurs: Traversées interocéaniques
J-L Cornille
Tydskrif vir letterkunde , 2013,
Abstract: Inter-oceanic passages: from the French Antilles to Madagascar and back In order to gauge the possibilities of producing a minor literature in French, as defined by Deleuze and Guattari in their groundbreaking work on Kafka, we have confronted two books of contemporary authors who position themselves at the forefront of francophone postcolonial literature: Le Nègre et l’Amiral (1988) by Rapha l Confiant, a writer from Martinique famous for his praise of creolity; and Za (2008) by Jean-Luc Raharimanana, a lesser-known and seemingly more radical writer from Madagascar, based in Paris. They both seem to share a common purpose of representing the population of their respective islands by their particular way of pronouncing the French language: either by creolizing it, as is the case with Confiant, or by pronouncing it with a lisp, as in Za. But these variations of the French language lead to totally opposite aesthetics. Whereas the first attempt is marked by excessive verbal display, the second one seems to function almost by default: a painful scream wrapped in near silence. Indeed, Le Nègre et l’Amiral is dominated by images of verticality and erection, which translates in the cooccurrence of multiple version of the same events, while Za favours the horizontality of bodies and corpses lying down. From within the politico-literary context in which they were published, these works offer two different solutions to the same problem: how to escape the normative tendencies enshrined in a major language such as French, and flee or chase the discourse of the master.
A simple empirical redshift indicator for gamma-ray bursts
J-L Atteia
Physics , 2003, DOI: 10.1051/0004-6361:20030958
Abstract: We propose a new empirical redshift indicator for gamma-ray bursts. This indicator is easily computed from the gamma-ray burst spectral parameters, and its duration, and it provides ``pseudo-redshifts'' accurate to a factor two. Possible applications of this redshift indicator are briefly discussed.
Gamma-ray bursts: towards a standard candle luminosity
J-L. Atteia
Physics , 1997,
Abstract: It is usual, in gamma-ray burst (GRB) studies, to compare the average properties of bright and faint GRBs, with the assumption that brightness classes reflect distance classes. When brightness is intented to reflect the distance to the sources, it is nevertheless important to use a quantity with a small intrinsic dispersion. We propose here a method to compare the intrinsic dispersion of various measures of GRB brightness. This method assumes that nearby bursters are homogeneously distributed in an Euclidean space with no density or luminosity evolution. We then use it to compare 5 measures of GRB brightness in the BATSE Catalog. Our analysis reveals that better (i.e. less dispersed) measures of brightness are obtained at low energy and that GRBs are much closer to standard candles below 100 keV than above. We suggest that a beaming of the emission above 100 keV could explain this behaviour.
Choosing a measure of GRB brightness that approaches a standard candle
J-L. Atteia
Physics , 1997, DOI: 10.1063/1.55422
Abstract: Studies using the GRB brightness as a distance indicator require a measure of brightness with a small intrinsic dispersion (close to a standard candle). There is unfortunately no general agreement on the definition of such a quantity. We show here that the comparison of the size-frequency curves obtained with various measures of brightness can be used to select the quantity which is closer to a standard candle. Our method relies on a few general assumptions on the burster spatial distribution, namely that nearby bursters are homogeneously distributed in an Euclidean space with no density or luminosity evolution. We apply it to 5 measures of GRB brightness in the Current BATSE Catalog and we find that the GRB size-frequency distribution depends significantly on the energy window used to measure the GRB brightness. The influence of the time window being, in comparison, negligible. Our method suggests that the best distance indicator in this Catalog is the fluence measured below 100 keV, indicating that GRB luminosities have a smaller intrinsic dispersion below 100 keV than above.
Are bright gamma-ray bursts a fair sample ?
J-L. Atteia
Physics , 1999,
Abstract: We conjecture that bright gamma-ray bursts (GRBs) are bright because they come from sources which are intrinsically over luminous and not because they come from nearby sources. We show that this hypothesis is supported by theoretical and observational arguments and that it explains some well-known properties of GRBs such as their Hardness-Intensity Correlation or the No-Host problem. We discuss the consequences of this hypothesis on our understanding of the properties of the GRB population.
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