114 research outputs found

    Spatially resolved PAH emission in the inner disks of Herbig Ae/Be stars

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    We present adaptive optics high angular resolution (\sim0.1\arcsec) spectroscopic observations in the 3 \um region of eight well known Herbig Ae/Be stars with circumstellar disks. We detect the aromatic emission feature at 3.3 \um for four out of six of our objects with flared disks (HD 169142, HD 97048, HD 100453, HD 100546), some weaker additional features at 3.4 and 3.46 ÎĽ\mum and nanodiamond features at 3.43 and 3.53 \um in two of our flared object (HD 100546 and HD 97048 respectively). We also detect hydrogen recombination line at 3.74 \um in practically all objects. The emission in the polycyclic aromatic hydrocarbons (PAHs) feature at 3.3 \um, additional and nanodiamond features in the 3.4-3.5 \um region is, for the first time, spatially resolved in all the sources where the features are detected. The full-width at half-maximum sizes that we derive are typical of emission arising in a circumstellar disk. On the other hand, the continuum emission is unresolved, with the exception of HD 97048 where it is marginally resolved. We compare the observed spatial distribution of the 3.3 ÎĽ\mum PAH feature and the adjacent continuum to the predictions of a disk model that includes transiently heated small grains and PAHs in addition to large grains in thermal equilibrium \cite[]{habart2004a}. The model predicts that, as observed, the 3.3 ÎĽ\mum PAH emission feature is significantly broader than that of the adjacent continuum and that about 50% of its integrated intensity comes from a radius R<R< 30 AU. We find that the predicted brightness profiles reproduce very well the observed ones. This proves beyond doubt that the energetic 3.3 ÎĽ\mum PAH emission feature takes its origin in the inner disk regions.Comment: 7 figures, accepted to A&

    Discretized aperture mapping for wavefront sensing

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    DAM (Discretized Aperture Mapping) is an original filtering device able to improve the performance in high-angular resolution and high-contrast imaging by the present class of large telescopes equipped with adaptive optics (Patru et al. 2011, 2014, 2015). DAM is a high-spatial frequency filter able to remove the problematic phase errors produced by the small scale defects in the wavefront. Various effects are related to high-order aberrations (ie the high-spatial frequency content) which are neither seen by any wavefront sensor (WFS) nor corrected by any adaptive optics (AO) and is thus transmitted up to the final detector. In particular, any wavefront sensor, due to its finite sub-apertures size, is fundamentally limited by the well-known aliasing effect, where high-spatial frequencies are seen as spurious low frequencies. DAM can be used as an anti-aliasing filter in order to improve both the accuracy of the WFS measurements and the stability of the AO compensation

    Eléments orbitaux d'étoiles doubles: WDS 02193-0259 (JOY 1 Aa ADS 1778)

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    Nous présentons de nouveaux éléments orbitaux pour l'étoile double visuelle WDS~02193-0259 (JOY~1~Aa ADS~1778). Ces éléments ont été obtenus en utilisant les dernières mesures que nous avons effectuées avec le tavelographe PISCO et le télescope Bernard Lyot de 2 m du Pic du Midi, et celles déjà disponibles dans la littérature

    Apodized Lyot Coronagraph for VLT-SPHERE: Laboratory tests and performances of a first prototype in the visible

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    We present some of the High Dynamic Range Imaging activities developed around the coronagraphic test-bench of the Laboratoire A. H. Fizeau (Nice). They concern research and development of an Apodized Lyot Coronagraph (ALC) for the VLT-SPHERE instrument and experimental results from our testbed working in the visible domain. We determined by numerical simulations the specifications of the apodizing filter and searched the best technological process to manufacture it. We present the results of the experimental tests on the first apodizer prototype in the visible and the resulting ALC nulling performances. The tests concern particularly the apodizer characterization (average transmission radial profile, global reflectivity and transmittivity in the visible), ALC nulling performances compared with expectations, sensitivity of the ALC performances to misalignments of its components

    Discretized aperture mapping with a micro-lenses array for interferometric direct imaging

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    Discretized Aperture Mapping (DAM) appears as an original filtering technique easy to play with existing adaptive optics (AO) systems. In its essential DAM operates as an optical passive filter removing part of the phase residuals in the wavefront without introducing any difficult-to-align component in the Fourier conjugate of the entrance pupil plane. DAM reveals as a new interferometric technique combined with spatial filtering allowing direct imaging over a narrow field of view (FOV). In fact, the entrance pupil of a single telescope is divided into many sub-pupils so that the residual phase in each sub-pupil is filtered up to the DAM cut-off frequency. DAM enables to smooth the small scale wavefront defects which correspond to high spatial frequencies in the pupil plane and to low angular frequencies in the image plane. Close to the AO Nyquist frequency, such pupil plane spatial frequencies are not well measured by the wavefront sensor (WFS) due to aliasing. Once bigger than the AO Nyquist frequency, they are no more measured by the WFS due to the fitting limit responsible for the narrow AO FOV. The corresponding image plane angular frequencies are not transmitted by DAM and are useless to image small FOVs, as stated by interferometry. That is why AO and DAM are complementary assuming that the DAM cut-off frequency is equal to the AO Nyquist frequency. Here we describe the imaging capabilities when DAM is placed downstream an AO system, over a convenient pupil which precedes the scientific detector. We show firstly that the imaging properties are preserved on a narrow FOV allowing direct imaging throughout interferometry. Then we show how the residual pupil plane spatial frequencies bigger than the AO Nyquist one are filtered out, as well as the residual halo in the image is dimmed

    Study of the atmospheric refraction in a single mode instrument - Application to AMBER/VLTI

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    International audienceThis paper presents a study of the atmospheric refraction and its effect on the light coupling efficiency in an instrument using single-mode optical fibers. We show the analytical approach which allowed us to assess the need to correct the refraction in J- and H-bands while observing with an 8-m Unit Telescope. We then developed numerical simulations to go further in calculations. The hypotheses on the instrumental characteristics are those of AMBER (Astronomical Multi BEam combineR), the near infrared focal beam combiner of the Very Large Telescope Interferometric mode (VLTI), but most of the conclusions can be generalized to other single-mode instruments. We used the software package caos (Code for Adaptive Optics Systems) to take into account the atmospheric turbulence effect after correction by the ESO system MACAO (Multi-Application Curvature Adaptive Optics). The opto-mechanical study and design of the system correcting the atmospheric refraction on AMBER is then detailed. We showed that the atmospheric refraction becomes predominant over the atmospheric turbulence for some zenith angles z and spectral conditions: for z larger than 30° in J-band for example. The study of the optical system showed that it allows to achieve the required instrumental performance in terms of throughput in J- and H-bands. First observations in J-band of a bright star, alpha Cir star, at more than 30° from zenith clearly showed the gain to control the atmospheric refraction in a single mode instrument, and validated the operating law
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