Increasing the imaging capabilities of the VLTI using integrated optics

Several scientific topics linked to the observation of extended structures around astrophysical sources (dust torus around AGN, disks around young stars, envelopes around AGBs) require imaging capability with milli-arcsecond spatial resolution. The current VLTI instruments, AMBER and MIDI, will provide in the coming months the required high angular resolution, yet without actual imaging. As a rule of thumb, the image quality accessible with an optical interferometer is directly related to the number of telescopes used simultaneously: the more the apertures, the better and the faster the reconstruction of the image. We propose an instrument concept to achieve interferometric combination of N telescopes (4 ≤ N ≤ 8) thanks to planar optics technology: 4 x 8-m telescopes in the short term and/or 8 x 1.8-m telescopes in the long term. The foreseen image reconstruction quality in the visible and/or in the near infrared will be equivalent to the one achieved with millimeter radio interferometers. Achievable spatial resolution will be better than the one foreseen with ALMA. This instrument would be able to acquire routinely 1 mas resolution images. A 13 to 20 magnitude sensitivity in spectral ranges from 0.6 to 2.5 μm is expected depending on the choice of the phase referencing guide source. High dynamic range, even on faint objects, is achievable thanks to the high accuracy provided by integrated optics for visibility amplitude and phase measurements. Based on recent validations of integrated optics presented here an imaging instrument concept can be proposed. The results obtained using the VLTI facilities give a demonstration of the potential of the proposed technique

Increasing the imaging capabilities of the VLTI using integrated optics

Several scientific topics linked to the observation of extended structures around astrophysical sources (dust torus around AGN, disks around young stars, envelopes around AGBs) require imaging capability with milli-arcsecond spatial resolution. The current VLTI instruments, AMBER and MIDI, will provide in the coming months the required high angular resolution, yet without actual imaging. As a rule of thumb, the image quality accessible with an optical interferometer is directly related to the number of telescopes used simultaneously: the more the apertures, the better and the faster the reconstruction of the image. We propose an instrument concept to achieve interferometric combination of N telescopes (4 ≤ N ≤ 8) thanks to planar optics technology: 4 x 8-m telescopes in the short term and/or 8 x 1.8-m telescopes in the long term. The foreseen image reconstruction quality in the visible and/or in the near infrared will be equivalent to the one achieved with millimeter radio interferometers. Achievable spatial resolution will be better than the one foreseen with ALMA. This instrument would be able to acquire routinely 1 mas resolution images. A 13 to 20 magnitude sensitivity in spectral ranges from 0.6 to 2.5 μm is expected depending on the choice of the phase referencing guide source. High dynamic range, even on faint objects, is achievable thanks to the high accuracy provided by integrated optics for visibility amplitude and phase measurements. Based on recent validations of integrated optics presented here an imaging instrument concept can be proposed. The results obtained using the VLTI facilities give a demonstration of the potential of the proposed technique

Growing up -the completion of the VLTI

Abstract. The completed VLTI with eight Delay Lines and eight ATs forms the basis for the second generation instrumentation. We describe the events up to first fringes with the test instrument VINCI using the siderostats, and the planning for the immediate future. Multi beam combination for 'smoother images' will be briefly discussed as well as artificial guide stars for fringe tracking. New technological developments like fiber optics amplifiers and integrated optics in combination with STJ open the door for a new type of interferometric arrays. Baselines as long as a a few kilometres come into reach. Examples of these second generation interferometers will be given

Dix-septièmes Rencontres d'Aubrac : Les Imaginaires de l'Eldorado.<br>: Mardi 21 août après-midi

Fonds audiovisuel du programme "ESCoM-AAR" (Equipe Sémiotique Cognitive et nouveaux Médias - Archives Audiovisuelles de la Recherche. Paris, France, 2000 - 2016).Chaque été, depuis 1994, l’Aveyron s’anime d’une couleur particulière, avec le festival littéraire des Rencontres d’Aubrac. Vrai festival littéraire, ces rencontres de trois jours sont devenues un rendez-vous incontournable pour un public de lecteurs enthousiastes - amateurs, érudits et professionnels mêlés.Après les "Imaginaires de Jérusalem" qui ouvraient un cycle dédié à l'esprit des lieux, l'édition 2012 se consacre aux "IMAGINAIRES DE L'ELDORADO" qui se conçoivent comme la représentation d'un idéal terrestre et accessible dans lequel l'homme fait irruption pour s'emparer de l'abondance. Or, cette irruption de l'humanité au sein d'une nature bienveillante qui offre tout ce qu'elle cache ordinairement au fond de ses entrailles, à commencer par l'or, semble déboucher non pas sur l'avènement d'une humanité meilleure, mais sur la faute de l'homme corrompu.La programmation s'est ainsi construite sur les figures de l'Eldorado, approché comme contrée mythique, univers utopique, lieu de fantasmes de pouvoir aux multiples résonances littéraires et historiques, quête matérielle marquée par des réussites éphémères, des échecs, des drames retentissants, mais aussi, derrière l'avidité, comme une quête d'absolu.Si nous puiserons aux sources historiques des représentations de l'Eldorado, nous aborderons également des actualités de la quête eldoradienne, particulièrement en interrogeant les ravages environnementaux et culturels produits par les exploitations minières ou l'orpaillage incontrôlé. La question du mirage de la richesse des pays occidentaux pour les migrants du Sud apparaîtra elle aussi tout à fait brûlante [...] (Francis Cransac)Le tournage et le montage des vidéos de ces rencontres ont été réalisés par Simon Gerland (Festivisuel, 34770 Gigean, France)

VINCI, the VLTI commissioning instrument: status after one year of operations at Paranal

International audienc

VINCI, the VLTI commissioning instrument: status after one year of operations at Paranal

International audienc

VINCI, the VLTI commissioning instrument: status after one year of operations at Paranal

International audienc

Revealing asymmetrical dust distribution in the inner regions of HD 141569

Context. The combination of high-contrast imaging with spectroscopy and polarimetry offers a pathway to studying the grain distribution and properties of debris disks in exquisite detail. Here, we focus on the case of a gas-rich debris disk around HD 141569A, which features a multiple-ring morphology first identified with SPHERE in the near-infrared. Aims. We obtained polarimetric differential imaging with SPHERE in the H-band to compare the scattering properties of the innermost ring at 44 au with former observations in total intensity with the same instrument. In polarimetric imaging, we observed that the intensity of the ring peaks in the south-east, mostly in the forward direction, whereas in total intensity imaging, the ring is detected only at the south. This noticeable characteristic suggests a non-uniform dust density in the ring. With these two sets of images, we aim to study the distribution of the dust to solve for the actual dust distribution. Methods. We implemented a density function varying azimuthally along the ring and generated synthetic images both in polarimetry and in total intensity, which are then compared to the actual data. The search for the best-fit model was performed both with a grid-based and an MCMC approach. Using the outcome of this modelization, we further measured the polarized scattering phase function for the observed scattering angle between 33° and 147° as well as the spectral reflectance of the southern part of the ring between 0.98 and 2.1 μm. We tentatively derived the grain properties by comparing these quantities with MCFOST models and assuming Mie scattering. Results. We find that the dust density peaks in the south-west at an azimuthal angle of 220°~238° with a rather broad width of 61°~127°. The difference in the intensity distributions observed in polarimetry and total intensity is the result of this particular morphology. Although there are still uncertainties that remain in the determination of the anisotropic scattering factor, the implementation of an azimuthal density variation to fit the data proved to be robust. Upon elaborating on the origin of this dust density distribution, we conclude that it could be the result of a massive collision when we account for the effect of the high gas mass that is present in the system on the dynamics of grains. In terms of grain composition, our preliminary interpretation indicates a mixture of porous sub-micron sized astro-silicate and carbonaceous grains. Conclusions. The SPHERE observations have allowed, for the first time, for meaningful constraints to be placed on the dust distribution beyond the standard picture of a uniform ring-like debris disk. However, future studies with a multiwavelength approach and additional detailed modeling would be required to better characterize the grain properties in the HD 141569 system.ISSN:0004-6361ISSN:1432-074

The VLTI and Its Subsystems

International audienc