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Search Results: 1 - 10 of 191402 matches for " D. Mouillet "
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HST/NICMOS2 observations of the HD 141569 A circumstellar disk
J. C. Augereau,A. M. Lagrange,D. Mouillet,F. Menard
Physics , 1999,
Abstract: We report the first resolved scattered light images of the circumstellar dust disk around the old Pre-Main Sequence star HD 141569 A. The disk seen in HST/NICMOS2 images shapes a bright annulus inclined at 37.5 degrees +/- 4.5 degrees from edge-on. This ring peaks at 325+/-10 AU from the star with a characteristic width of ~150 AU. At 1.6 microns, the dust grains scatter a total flux density of at least 4.5 +/- 0.5 mJy. Our disk model using the spatial distribution implied by the images does not explain the 10 microns excess and requires an additional grain population closer to the star. Some similarities and differences with the dust annulus surrounding HR 4796 A are pointed out.
Dust disks around old Pre Main-Sequence stars: HST/NICMOS2 scattered light images and modeling
J. C. Augereau,A. M. Lagrange,D. Mouillet,F. Menard
Physics , 2000,
Abstract: We present recent near-infrared detections of circumstellar disks around the two old PMS Herbig stars HD 141569 and HD 100546 obtained with the HST/NICMOS2 camera. They reveal extended structures larger than 350-400 AU in radius. While the HD 100546 disk appears as a continuous disk down to 40 AU, the HD 141569 environment seems more complex, splitted at least into two dust populations. As a convincing example, the full modeling of the disk surrounding HR 4796, another old PMS star, is detailed and confronted with more recent observations.
HST/NICMOS2 coronagraphic observations of the circumstellar environment of three old PMS stars: HD 100546, SAO 206462 and MWC 480
J. C. Augereau,A. M. Lagrange,D. Mouillet,F. Menard
Physics , 2000, DOI: 10.1051/0004-6361:20000328
Abstract: The close environment of four old Pre-Main Sequence stars has been observed thanks to the coronagraphic mode of the HST/NICMOS2 camera at lambda=1.6 micron. In the course of this program, the detection of a circumstellar annulus around HD 141569 has already been presented in Augereau et al.(1999b). In this paper, we report the detection of an elliptical structure around the Herbig Be star HD 100546 extending from the very close edge of the coronagraphic mask (~50 AU) to 350-380 AU (3.5-3.8 arcsec) from the star. The axis ratio gives a disk inclination of 51+/-3 degrees to the line-of-sight and a position angle of 161+/-5 degrees, measured east of north. At 50 AU, the disk has a surface brightness between 10.5 and 11 mag/arcsec^2, then follows a -2.92+/-0.04 radial power law up to 250-270 AU and finally falls as r^{-5.5+/-0.2}. The inferred optical thickness suggests that the disk is at least marginally optically thick inside 80 AU and optically thin further out. Combined with anisotropic scattering properties, this could explain the shape of a brightness asymmetry observed along the minor axis of the disk. This asymmetry needs to be confirmed. The circumstellar disks around SAO 206462 and MWC 480 are not resolved, leading to constraints on the dust distribution. A tight binary system separated by only 0.32+/-0.04 arcsec is nevertheless detected in the close vicinity of SAO 206462.
Bibliography Manager Computer Programs. The Example of EndNote
Mouillet E
Revue Médicale de l'Assurance Maladie , 2001,
Abstract: In order to perform many editing tasks, scientists must be able to create a personal reference database and periodically update it by online retrievals, indexing, storing, managing and reference searching in view of formatting a bibliography which follows the international rules for scientific publication. Specific computer tools and bibliographic softwares, all of which work in a similar fashion, have been developed and marketed in order to lighten the successive stages of this repetitive and meticulous task. This article presents the main bibliographic softwares presently available and illustrates how they function by using the example of EndNote version 4.0, a program which is often used by the life-science community. We offer a step-by-step explanation of its features in order to allow the reader to directly use it. EndNote is an efficient tool for managing reference databases, search for bibliographic databases or library catalogues on Internet and for formatting bibliographies. It is hoped that this article written in French will enable French-language users to better understand and make use of presently available software user guides, which are all written in English.
A planet on an inclined orbit as an explanation of the warp in the Beta Pictoris disk
D. Mouillet,J. D. Larwood,J. C. B. Papaloizou,A. M. Lagrange
Physics , 1997, DOI: 10.1093/mnras/292.4.896
Abstract: We consider the deformation that has recently been observed in the inner part of the circumstellar disk around Beta Pictoris with the HST. Our recent ground based adaptive optics coronographic observations confirm that the inner disk is warped. We investigate the hypothesis that a yet undetected planet is responsible for the observed warp, through simulations of the effect of the gravitational perturbation due to a massive companion on the disk. The physical processes assumed in the simulations are discussed: since the observed particles do not survive collisions, the apparent disk shape is driven by the underlying collisionless parent population. The resulting possible parameters for the planet that are consistent with the observed disk deformation are reviewed.
Impact of angular differential imaging on circumstellar disk images
J. Milli,D. Mouillet,A. M. Lagrange,A. Boccaletti,D. Mawet,G. Chauvin,M. Bonnefoy
Physics , 2012, DOI: 10.1051/0004-6361/201219687
Abstract: Direct imaging of circumstellar disks requires high-contrast and high-resolution techniques. The angular differential imaging (ADI) technique is one of them, initially developed for point-like sources but now increasingly applied to extended objects. This new field of application raises many questions because the disk images reduced with ADI depend strongly on the amplitude of field rotation and the ADI data reduction strategy. Both of them directly affect the disk observable properties. Our aim is to characterize the applicability and biases of some ADI data reduction strategies for different disk morphologies. A particular emphasis is placed on parameters mostly used for disks: their surface brightness, their width for a ring, and local features such as gaps or asymmetries. We first present a general method for predicting and quantifying those biases. In a second step we illustrate them for some widely used ADI algorithms applied to typical debris disk morphologies: inclined rings with various inner/outer slopes and width. Last, our aim is also to propose improvements of classical ADI to limit the biases on extended objects. Simulated disks seen under various observing conditions were used to reduce ADI data and quantify the resulting biases. These conclusions complements previous results from NaCo L' real-disk images of HR4796A. ADI induces flux losses on disks. This makes this technique appropriate only for low- to medium-inclination disks. A theoretical criterion is derived to predict the amount of flux loss for a given disk morphology, and quantitative estimates of the biases are given in some specific configurations. These biases alter the disk observable properties, such as the slopes of their surface brightness or their radial/azimuthal extent. Additionally, this work demonstrates that ADI can very easily create artificial features without involving astrophysical processes.
On the HR 4796A circumstellar disk
J. C. Augereau,A. M. Lagrange,D. Mouillet,J. C. B. Papaloizou,P. A. Grorod
Physics , 1999,
Abstract: We investigate in details the properties of the disk surrounding the 8 Myr old star HR 4796A, one of the few stars bringing precious clues to better understand the scenario which lead to planetary system formation. We propose a model able to reproduce all the available observations : the full spectral energy distribution from the mid-infrared to the millimeter wavelengths, resolved scattered light and thermal emission observations. We show that the circumstellar matter splits into two dust components : a cold annulus, peaked at 70 AU from the star, made of ISM-like grains (amorphous composition, porosity ~ 0.6) larger than 10 microns and a population of hot dust close to the star (at about 9 AU) made of comet-like grains (crystalline composition, porosity ~ 0.97). Both dust populations are highly collisional and the grain size distribution in the cold annulus is found to be cut-off by radiation pressure. At 70 AU, bodies as large as a few meters are required to fit the data leading to a minimum disk mass of a few Earth masses and to a gas to dust ratio less than 1. We discuss aftewards some implications on the disk structure and effects of larger bodies.
Dynamical modeling of large scale asymmetries in the beta Pictoris dust disk
J. C. Augereau,R. P. Nelson,A. M. Lagrange,J. C. B. Papaloizou,D. Mouillet
Physics , 2001, DOI: 10.1051/0004-6361:20010199
Abstract: We report a new and complete model of the beta Pictoris disk, which succeeds in accounting for both the surface brightness distribution, warp characteristics, the outer ``butterfly'' asymmetry as observed by HST/STIS in scattered light, as well as the infrared emission. Our model includes the presence of a disk of planetesimals extending out to 120-150 AU, perturbed gravitationally by a giant planet on an inclined orbit, following the approach of Mouillet et al. (1997b). At any time, the planetesimal disk is assumed to be the source of a distribution of grains produced through collisional evolution, with the same initial orbital parameter distribution. The steady state spatial grain distribution is found incorporating the effects of radiation pressure which can cause the distribution of the smallest particles to become very distended. With realistic assumptions about the grains' chemical properties, the modeling confirms the previously evident need for an additional population of hot grains close to the star, to account for the 12 microns fluxes at short distances from the star. It also indicates that this population cannot explain the outer 12 microns flux distribution when the effects of gravity and radiation pressure determine the distribution. Very small grains, produced by collisions among aggregates, are tentatively proposed to account for this 12 microns outer emission.
A giant planet imaged in the disk of the young star Beta Pictoris
A. -M. Lagrange,M. Bonnefoy,G. Chauvin,D. Apai,D. Ehrenreich,A. Boccaletti,D. Gratadour,D. Rouan,D. Mouillet,S. Lacour,M. Kasper
Physics , 2010, DOI: 10.1126/science.1187187
Abstract: Here we show that the ~10 Myr Beta Pictoris system hosts a massive giant planet, Beta Pictoris b, located 8 to 15 AU from the star. This result confirms that gas giant planets form rapidly within disks and validates the use of disk structures as fingerprints of embedded planets. Among the few planets already imaged, Beta Pictoris b is the closest to its parent star. Its short period could allow recording the full orbit within 17 years.
Orbital characterization of the βPictoris b giant planet
G. Chauvin,A. -M. Lagrange,H. Beust,M. Bonnefoy,A. Boccaletti,D. Apai,F. Allard,D. Ehrenreich,J. H. V. Girard,D. Mouillet,D. Rouan
Physics , 2012, DOI: 10.1051/0004-6361/201118346
Abstract: In June 2010, we confirmed the existence of a giant planet in the disk of the young star Beta Pictoris, located between 8 AU and 15 AU from the star. This young planet offers the rare opportunity to monitor a large fraction of the orbit using the imaging technique over a reasonably short timescale. Using the NAOS-CONICA adaptive-optics instrument (NACO) at the Very Large Telescope (VLT), we obtained repeated follow-up images of the Bpic system in the Ks and L' filters at four new epochs in 2010 and 2011. Complementing these data with previous measurements, we conduct a homogeneous analysis, which covers more than eight yrs, to accurately monitor the Bpic b position relative to the star. On the basis of the evolution of the planet's relative position with time, we derive the best-fit orbital solutions for our measurements. More reliable results are found with a Markov-chain Monte Carlo approach. The solutions favor a low-eccentricity orbit e < 0.17, with semi-major axis in the range 8--9 AU corresponding to orbital periods of 17--21 yrs. Our solutions favor a highly inclined solution with a peak around i=88.5+-1.7 deg, and a longitude of ascending node tightly constrained at Omega = -147.5+-1.5 deg. These results indicate that the orbital plane of the planet is likely to be above the midplane of the main disk, and compatible with the warp component of the disk being tilted between 3.5 deg and 4.0 deg. This suggests that the planet plays a key role in the origin of the inner warped-disk morphology of the Bpic disk. Finally, these orbital parameters are consistent with the hypothesis that the planet is responsible for the transit-like event observed in November 1981, and also linked to the cometary activity observed in the Bpic system.
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