232 research outputs found
SPHERE: a `Planet Finder' Instrument for the VLT
No full textSPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) is a second generation instrument for the VLT optimized for the very high-contrast imaging around bright stars [J.-L. Beuzit, M. Feldt, K. Dohlen et al. in Messenger 125, 29 (2006)]. The primary goal is the detection and characterization of new giant planets around a variety of nearby stars. Together with the observation of early planetary systems and disks, and in association with the results of other planet search techniques, SPHERE will be a primary contributor to get a complete picture of the variety of planetary systems and to better understand their mechanisms of formation and evolution. Such results will be obtained before even more ambitious projects for the direct imaging of planets either from the ground with ELTs or from space
Direct characterization of young giant exoplanets at high spectral resolution by coupling SPHERE and CRIRES+
No full textThis is the final version. Available on open access from EDP Sciences via the DOI in this recordStudies of atmospheres of directly imaged extrasolar planets with high-resolution spectrographs have shown that their characterization
is predominantly limited by noise on the stellar halo at the location of the studied exoplanet. An instrumental combination of highcontrast imaging and high spectral resolution that suppresses this noise and resolves the spectral lines can therefore yield higher quality
spectra. We study the performance of the proposed HiRISE fiber coupling between the direct imager SPHERE and the spectrograph
CRIRES+ at the Very Large Telescope for spectral characterization of directly imaged planets. Using end-to-end simulations of
HiRISE we determine the signal-to-noise ratio (S/N) of the detection of molecular species for known extrasolar planets in H and K
bands, and compare them to CRIRES+. We investigate the ultimate detection limits of HiRISE as a function of stellar magnitude, and
we quantify the impact of different coronagraphs and of the system transmission. We find that HiRISE largely outperforms CRIRES+
for companions around bright hosts like β Pictoris or 51 Eridani. For an H = 3.5 host, we observe a gain of a factor of up to 36 in
observing time with HiRISE to reach the same S/N on a companion at 200 mas. More generally, HiRISE provides better performance
than CRIRES+ in two-hour integration times between 50–400 mas for hosts with H < 8.5 and between 50–800 mas for H < 7. For
fainter hosts like PDS 70 and HIP 65426, no significant improvements are observed. We find that using no coronagraph yields the
best S/N when characterizing known exoplanets due to higher transmission and fiber-based starlight suppression. We demonstrate
that the overall transmission of the system is in fact the main driver of performance. Finally, we show that HiRISE outperforms the
best detection limits of SPHERE for bright stars, opening major possibilities for the characterization of future planetary companions
detected by other techniquesEuropean Union Horizon 202
ESSAI DE MISE EN ÉVIDENCE DES ÉTATS A DEUX PARTICULES-UN TROU DANS 41Sc PAR LA DIFFUSION INÉLASTIQUE DES PROTONS SUR 40Ca
No full textDes états à 2 particules-1 trou dans 41Sc, analogues à ceux excités par 39K (3He, p) dans 41Ca, ont été étudiés par diffusion inélastique des protons sur 40Ca par la méthode suggérée par Bolsterli et al. (Phys. Rev. Letters, 1966, 17, 878). Une certaine correspondance entre ces deux ensembles d'états a été trouvée.Two-particleone-hole states in 41Sc analogous to those excited by 39K (3He, p) in 41Ca, were studied by inelastic scattering of protons on 40Ca by the method suggested by Bolsterli et al. (Phys. Rev. Letters, 1966, 17, 878). A certain correspondence in the excitation energies of the two sets of states has been found
Coronagraphic near-IR photometry of AB Doradus C
No full textInternational audienceContext: Observations of low-mass companions for which the dynamical masses are well constrained help to improve the calibration of evolutionary models. Such observations thereby provide more confidence in the estimation of the mass of a companion using the photometric methods expected for the next generation of planet finder instruments. Aims: The commissioning of a new coronagraph at the Very Large Telescope (VLT) was the occasion to test the performance of this technique on the well-known object AB Dor A and its 0.09 M_ȯ companion AB Dor C. The purpose of this paper is to refine the photometric analysis on this object and to provide an accurate photometric error budget. Methods: In addition to coronagraphy, we calibrated the residual stellar halo with a reference star. We used standard techniques for photometric extraction. Results: The companion AB Dor C is easily detected at 0.185'' from the primary star, and its magnitudes in H and Ks are in agreement with an M 5.5 object, as already known from spectroscopic observations. However, these new measurements make the earlier J-band photometry less reliable. Finally, the comparison with evolutionary models supports an age of (75 ± 25) Myr, contrary to previous analyses. These observations demonstrate that coronagraphic observations can be more efficient than direct imaging, not only to improve contrast, but also to provide a better photometric estimation as long as a good calibration of the stellar halo is achieved
The X-ray position and optical counterpart of the accretion-powered millisecond pulsar XTE J1814−338
No full textWe report the precise optical and X-ray localization of the 3.2 ms accretion-powered X-ray pulsar XTE J1814-338 with data from the Chandra X-Ray Observatory as well as optical observations conducted during the 2003 June discovery outburst. Optical imaging of the field during the outburst of this soft X-ray transient reveals an R = 18 star at the X-ray position. This star is absent (R > 20) from an archival 1989 image of the field and brightened during the 2003 outburst, and we therefore identify it as the optical counterpart of XTE J1814-338. The best source position derived from optical astrometry is R.A. = 18h13m39.s04, decl. = -33°46'223 (J2000). The featureless X-ray spectrum of the pulsar in outburst is best fit by an absorbed power law (with photon index γ = 1.41 ± 0.06) plus blackbody (with kT = 0.95 ± 0.13 keV) model, where the blackbody component contributes approximately 10% of the source flux. The optical broadband spectrum shows evidence for an excess of infrared emission with respect to an X-ray heated accretion disk model, suggesting a significant contribution from the secondary or from a synchrotron-emitting region. A follow-up observation performed when XTE J1814-338 was in quiescence reveals no counterpart to a limiting magnitude of R = 23.3. This suggests that the secondary is an M3 V or later-type star and therefore very unlikely to be responsible for the soft excess, making synchrotron emission a more reasonable candidate
Le parcours de Pierre-Jakez Hélias vu par l'historien de l'éducation ou La mythologie de l'école républicaine
No full textColloque inaugural du Pôle universitaire Pierre-Jakez Hélias organisé et publié avec le soutien du Conseil Général du Finistère et de la Ville de Quimper. Édité dans la revue KREIZ, n° 15. Resp. de la publication D. Guillou-Beuzit, J.-L. Le Cam, mise en page Cl. Roy, cartographie G. CouixBased on the autobiographical passages of the work of P.-J. Hélias and archives of his secondary school in Quimper (France, Brittany), this text presents the educational travel of the Breton writer as emblematic of the great social and cultural change the most dynamic elements of rural society experienced, through the school of the Republic, in the first half of the twentieth century.Sur la base des passages autobiographiques de l'œuvre de P.-J. Hélias et des archives du Lycée de Quimper (France, Finistère), ce texte présente le parcours scolaire de l'écrivain breton comme emblématique de la grande mutation culturelle et sociale qu'ont vécue, grâce à l'école de la République, les éléments les plus dynamiques de la société rurale dans la première moitié du XXe siècle
Discovery of concentric broken rings at sub-arcsec separations in the HD 141569A gas-rich, debris disk with VLT/SPHERE
No full textObservations with SPHERE of HD141569A revealed a series of concentric ringlets located at 116-46AU and matching the formerly detected extended emission in the mid-IR and visible, although finer details are detected here. The brightest ring at 46AU has sharp edges and presents an unusual strong north/south asymmetry. Such structures may result from planet sheperding or gas/dust interactions.A. Boccaletti, E. Pantin, J-C. Augereau, A-M. Lagrange, R. Galicher, A-L. Maire, J. Mazoyer, J. Milli, G. Rousset, R. Gratton, M. Bonnefoy, W. Brandner, E. Buenzli, M. Langlois, J. Lannier, D. Mesa, S. Peretti, G. Salter, E. Sissa, G. Chauvin, S. Desidera, M. Feldt, A. Vigan, E. Di Folco, A. Dutrey, J. Pércaud, P. Baudoz, M. Benisty, J. De Boer, A. Garufi, J. H. Girard, F. Menard, J. Olofsson, S. P. Quanz, D. Mouillet, V. Christiaens, 17, S. Casassus, J.-L. Beuzit, P. Blanchard, M. Carle, T. Fusco, E. Giro, N. Hubin, D. Maurel, O. Moeller-Nilsson, A. Sevin, L. Webe
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