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Search Results: 1 - 10 of 1032 matches for " Karine Perraut "
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The case for optical interferometric polarimetry
Nicholas M. Elias II,Carol E. Jones,Henrique R. Schmitt,Anders M. Jorgensen,Michael J. Ireland,Karine Perraut
Physics , 2008,
Abstract: Within the last 10 years, long-baseline optical interferometry (LBOI) has benefited significantly from increased sensitivity, spatial resolution, and spectral resolution, e.g., measuring the diameters and asymmetries of single stars, imaging/fitting the orbits of multiple stars, modeling Be star disks, and modeling AGN nuclei. Similarly, polarimetry has also yielded excellent astrophysical results, e.g., characterizing the atmospheres and shells of red giants/supergiants, modeling the envelopes of AGB stars, studying the morphology of Be stars, and monitoring the short- and long- term behavior of AGNs. The next logical evolutionary step in instrumentation is to combine LBOI with polarimetry, which is called optical interferometric polarimetry (OIP). In other words, measurements of spatial coherence are performed simultaneously with measurements of coherence between orthogonal polarization states.
First spectro-interferometric survey of Be stars I. Observations and constraints on the disks geometry and kinematics
Anthony Meilland,Florentin Millour,Samer Kanaan,Philippe Stee,Romain G. Petrov,Karl-Heinz Hofmann,Antonella Natta,Karine Perraut
Physics , 2011, DOI: 10.1051/0004-6361/201117955
Abstract: Context. Classical Be stars are hot non-supergiant stars surrounded by a gaseous circumstellar disk that is responsible for the observed infrared-excess and emission lines. The phenomena involved in the disk formation still remain highly debated. Aims. To progress in the understanding of the physical process or processes responsible for the mass ejections and test the hypothesis that they depend on the stellar parameters, we initiated a survey on the circumstellar environment of the brightest Be stars. Methods. To achieve this goal, we used spectro-interferometry, the only technique that combines high spectral (R=12000) and high spatial ($\theta_{\rm min}$=4\,mas) resolutions. Observations were carried out at the Paranal observatory with the VLTI/AMBER instrument. We concentrated our observations on the Br$\gamma$ emission line to be able to study the kinematics within the circumstellar disk. Our sample is composed of eight bright classical Be stars : $\alpha$ Col, $\kappa$ CMa, $\omega$ Car, p Car, $\delta$ Cen, $\mu$ Cen, $\alpha$ Ara, and \textit{o} Aqr. Results. We managed to determine the disk extension in the line and the nearby continuum for most targets. We also constrained the disk kinematics, showing that it is dominated by rotation with a rotation law close to the Keplerian one. Our survey also suggests that these stars are rotating at a mean velocity of V/V$_{\rm c}$\,=\,0.82\,$\pm$\,0.08. This corresponds to a rotational rate of $\Omega/\Omega_{\rm c}$\,=\,0.95\,$\pm$\,0.02 Conclusions. We did not detect any correlation between the stellar parameters and the structure of the circumstellar environment. Moreover, it seems that a simple model of a geometrically thin Keplerian disk can explain most of our spectrally resolved K-band data. Nevertheless, some small departures from this model have been detected for at least two objects (i.e, $\kappa$ CMa and $\alpha$ Col). Finally, our Be stars sample suggests that rotation is the main physical process driving the mass-ejection. Nevertheless, smaller effects from other mechanisms have to be taken into account to fully explain how the residual gravity is compensated.
Radii, masses, and ages of 18 bright stars using interferometry. And new estimations of exoplanetary parameters
Roxanne Ligi,Orlagh Creevey,Denis Mourard,Aurélien Crida,Anne-Marie Lagrange,Nicolas Nardetto,Karine Perraut,Mathias Schultheis
Physics , 2015,
Abstract: Accurate stellar parameters are needed in numerous domains of astrophysics. The position of stars on the H-R diagram is an important indication of their structure and evolution, and it helps improve stellar models. Furthermore, the age and mass of stars hosting planets are required elements for studying exoplanetary systems. We aim at determining accurate parameters of a set of 18 bright exoplanet host and potential host stars from interferometric measurements, photometry, and stellar models. Using the VEGA/CHARA interferometer, we measured the angular diameters of 18 stars, ten of which host exoplanets. We combined them with their distances to estimate their radii. We used photometry to derive their bolometric flux and, then, their effective temperature and luminosity to place them on the H-R diagram. We then used the PARSEC models to derive their best fit ages and masses, with error bars derived from MC calculations. Our interferometric measurements lead to an average of 1.9% uncertainty on angular diameters and 3% on stellar radii. There is good agreement between measured and indirect estimations of angular diameters (from SED fitting or SB relations) for MS stars, but not as good for more evolved stars. For each star, we provide a likelihood map in the mass-age plane; typically, two distinct sets of solutions appear (an old and a young age). The errors on the ages and masses that we provide account for the metallicity uncertainties, which are often neglected by other works. From measurements of its radius and density, we also provide the mass of 55 Cnc independently of models. From the stellar masses, we provide new estimates of semi-major axes and minimum masses of exoplanets with reliable uncertainties. We also derive the radius, density, and mass of 55 Cnc e, a super-Earth that transits its stellar host. Our exoplanetary parameters reflect the known population of exoplanets.
A hot compact dust disk around a massive young stellar object
Stefan Kraus,Karl-Heinz Hofmann,Karl Menten,Dieter Schertl,Gerd Weigelt,Friedrich Wyrowski,Anthony Meilland,Karine Perraut,Romain Petrov,Sylvie Robbe-Dubois,Peter Schilke,Leonardo Testi
Physics , 2010, DOI: 10.1038/nature09174
Abstract: Circumstellar disks are an essential ingredient of the formation of low-mass stars. It is unclear, however, whether the accretion-disk paradigm can also account for the formation of stars more massive than about 10 solar masses, in which strong radiation pressure might halt mass infall. Massive stars may form by stellar merging, although more recent theoretical investigations suggest that the radiative-pressure limit may be overcome by considering more complex, nonspherical infall geometries. Clear observational evidence, such as the detection of compact dusty disks around massive young stellar objects, is needed to identify unambiguously the formation mode of the most massive stars. Here we report near-infrared interferometric observations that spatially resolve the astronomical unit-scale distribution of hot material around a high-mass (approx. 20 solar masses) young stellar object. The image shows an elongated structure with a size of about 13 x 19 astronomical units, consistent with a disk seen at an inclination angle of 45 degree. Using geometric and detailed physical models, we found a radial temperature gradient in the disk, with a dust-free region less than 9.5 astronomical units from the star, qualitatively and quantitatively similar to the disks observed in low-mass star formation. Perpendicular to the disk plane we observed a molecular outflow and two bow shocks, indicating that a bipolar outflow emanates from the inner regions of the system.
First results from VLTI near-infrared interferometry on high-mass young stellar objects
Stefan Kraus,Karl-Heinz Hofmann,Karl Menten,Dieter Schertl,Gerd Weigelt,Friedrich Wyrowski,Anthony Meilland,Karine Perraut,Romain Petrov,Sylvie Robbe-Dubois,Peter Schilke,Leonardo Testi
Physics , 2010, DOI: 10.1117/12.858285
Abstract: Due to the recent dramatic technological advances, infrared interferometry can now be applied to new classes of objects, resulting in exciting new science prospects, for instance, in the area of high-mass star formation. Although extensively studied at various wavelengths, the process through which massive stars form is still only poorly understood. For instance, it has been proposed that massive stars might form like low-mass stars by mass accretion through a circumstellar disk/envelope, or otherwise by coalescence in a dense stellar cluster. After discussing the technological challenges which result from the special properties of these objects, we present first near-infrared interferometric observations, which we obtained on the massive YSO IRAS 13481-6124 using VLTI/AMBER infrared long-baseline interferometry and NTT speckle interferometry. From our extensive data set, we reconstruct a model-independent aperture synthesis image which shows an elongated structure with a size of 13x19 AU, consistent with a disk seen under an inclination of 45 degree. The measured wavelength-dependent visibilities and closure phases allow us to derive the radial disk temperature gradient and to detect a dust-free region inside of 9.5 AU from the star, revealing qualitative and quantitative similarities with the disks observed in low-mass star formation. In complementary mid-infrared Spitzer and sub-millimeter APEX imaging observations we detect two bow shocks and a molecular out ow which are oriented perpendicular to the disk plane and indicate the presence of a bipolar outflow emanating from the inner regions of the system.
Análisis de la producción científica de los estudios de traducción en Espa a
Palomares Perraut, R.
Revista Espa?ola de Documentación Científica , 1998,
Abstract: This article studies the literature produced on Translation Studies in Spain between 1960 and 1994. An analytical subject database named TRADES has been created and is used to obtain results regarding quinquennial productivity, productivity of different types of documents, pairs of languages, academic research, and most developed topics in all documents and in journals. The results show the volume of publications on Translation Studies is directly related to the implementation of the Spanish undergraduate degree in Translation. Se estudia la producción bibliográfica de los Estudios de Traducción en Espa a durante el período 1960-1994. A partir de la información documental seleccionada en la base de datos TRADES se analizan las siguientes variables: productividad por quinquenios, productividad por tipología documental, pares de lenguas, investigación (tesis y tesinas), materias y líneas temáticas preferentes de las revistas de traducción. Los resultados aportados muestran una correlación entre el volumen de publicaciones y la implantación de la licenciatura de Traducción e Interpretación.
The binary Be star δ Sco at high spectral and spatial resolution: Disk geometry and kinematics before the 2011 periastron
Anthony Meilland,O. Delaa,Philippe Stee,Samer Kanaan,Florentin Millour,Denis Mourard,Daniel Bonneau,Romain Petrov,Nicolas Nardetto,Aurelie Marcotto,Jean-Michel Clausse,Karine Perraut,H. Mcalister,Theo A. Ten Brummelaar,J. Sturmann,L. Sturmann,N. Turner,S. T. Ridgway,C. Farrington,P. J. Goldfinger,C. Farrington
Physics , 2011, DOI: 10.1051/0004-6361/201116798
Abstract: Classical Be stars are hot non-supergiant stars surrounded by a gaseous circumstellar disk that is responsible for the observed IR-excess and emission lines. The influence of binarity on these phenomena remains controversial. delta Sco is a binary system whose primary suddently began to exhibit the Be phenomenon at the last periastron in 2000. We want to constrain the geometry and kinematics of its circumstellar environment. We observed the star between 2007 and 2010 using spectrally-resolved interferometry with the VLTI/AMBER and CHARA/VEGA instruments. We found orbital elements that are compatible with previous estimates. The next periastron should take place around July 5, 2011 (+- 4,days). We resolved the circumstellar disk in the HAlpha (FWHM = 4.8+-1.5mas), BrGamma (FWHM = 2.9 0.,mas), and the 2.06$ \mu$m HeI (FWHM = 2.4+-0.3mas) lines as well as in the K band continuum (FWHM ~2.4mas). The disk kinematics are dominated by the rotation, with a disk expansion velocity on the order of 0.2km/s. The rotation law within the disk is compatible with Keplerian rotation. As the star probably rotates at about 70% of its critical velocity the ejection of matter doesn't seems to be dominated by rotation. However, the disk geometry and kinematics are similar to that of the previously studied quasi-critically rotating Be stars, namely Alpha Ara, Psi Per and 48 Per.
The GRAVITY Coudé Infrared Adaptive Optics (CIAO) system for the VLT Interferometer
Sarah Kendrew,Stefan Hippler,Wolfgang Brandner,Yann Clénet,Casey Deen,Eric Gendron,Armin Huber,Ralf Klein,Werner Laun,Rainer Lenzen,Vianak Naranjo,Udo Neumann,José Ramos,Ralf-Rainer Rohloff,Pengqian Yang,Frank Eisenhauer,Enrico Fedrigo,Marcos Suarez-Valles,Antonio Amorim,Karine Perraut,Guy Perrin,Christian Straubmeier
Physics , 2012, DOI: 10.1117/12.926558
Abstract: GRAVITY is a second generation instrument for the VLT Interferometer, designed to enhance the near-infrared astrometric and spectro-imaging capabilities of VLTI. Combining beams from four telescopes, GRAVITY will provide an astrometric precision of order 10 micro-arcseconds, imaging resolution of 4 milli-arcseconds, and low and medium resolution spectro-interferometry, pushing its performance far beyond current infrared interfero- metric capabilities. To maximise the performance of GRAVITY, adaptive optics correction will be implemented at each of the VLT Unit Telescopes to correct for the effects of atmospheric turbulence. To achieve this, the GRAVITY project includes a development programme for four new wavefront sensors (WFS) and NIR-optimized real time control system. These devices will enable closed-loop adaptive correction at the four Unit Telescopes in the range 1.4-2.4 {\mu}m. This is crucially important for an efficient adaptive optics implementation in regions where optically bright references sources are scarce, such as the Galactic Centre. We present here the design of the GRAVITY wavefront sensors and give an overview of the expected adaptive optics performance under typical observing conditions. Benefiting from newly developed SELEX/ESO SAPHIRA electron avalanche photodiode (eAPD) detectors providing fast readout with low noise in the near-infrared, the AO systems are expected to achieve residual wavefront errors of \leq400 nm at an operating frequency of 500 Hz.
Una agricultura de regadío racional: El Salobral - Albacete (Espa a)
Karine Collet
Papeles de Geografía , 2004,
Abstract: Presentar la agricultura de regadío de El Salobral (polígono 90), en el término municipal de Albacete (Espa a), permitirá entrever una gestión racional e integrada de los recursos hídricos. Es un espacio de regadío donde se practica una agricultura intensiva (muy consumidora de agua) más o menos impulsada por la nueva Política Agrícola Común.
Le regadío à Albacete à l aube du XXI E siècle: du riego a pie au riego por aspersión
Karine Collet
Papeles de Geografía , 2002,
Abstract: Este trabajo tiene por ambición presentar un espacio concreto de cerealicultura de regadío en el umbral del siglo XXI, en el seno de la Llanura de Albacete, en Castilla la NuevaEl análisis se enfoca en el municipio de Albacete y más precisamente en el pueblo de colonización de Aguas Nuevas, ordenado por el Instituto Nacional de Colonización luego el Instituto de Reforma y Desarrollo Agrarios en el ámbito de la política de modernización espa ola impulsada por el régimen franquista. La idea ha sido regenerar Espa a por la aportación de agua a la agricultura a través de reformas de estructuras moderadas, tal la ley de bases de colonización de las grandes áreas de regadío. Se trata, entre otras cosas, determinar el origen del recurso de agua de riego, el sistema de riego y los cultivos de regadío. La conclusión pone en evidencia que en el a o 2000 en Albacete el movimiento de difusión de los regadíos ha alcanzado su óptimo en razón a la sobreexplotación de los recursos hídricos, es decir de los acuíferos. (Espa a)
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