In the coming year, the CHARA 1-meter telescopes will be equipped with Adaptive Optics (AO) systems. This improvement opens the possibility to apply, in the visible domain, the principle of spatial filtering with single mode fibers well demonstrated in the near-infrared. It will clearly open new astrophysical fields by taking benefit of an improved sensitivity and state-of-the-art precision and accuracy on interferometric observables. A demonstrator called FRIEND (Fibered and spectrally Resolved Interferometric Experiment - New Design) has been developed. FRIEND combines the beams coming from 3 telescopes after injection in single mode optical fibers and provides photometric channels as well as some spectral capabilities for characterization purposes. It operates around the R spectral band (from 600nm to 750nm) and uses the fast and sensitive analog detector OCAM2. On sky tests at the focus of the CHARA interferometer have been performed during the last year to get the optimal DIT or an estimation of the stability of the instrumental visibility. Complementary lab tests have permitted to characterize the birefringence of the fibers, and the characteristics of the detector. In this paper, we present the results of these tests.

Visibility

10.1117/12.2231704

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Citations (4)

Towards the monitoring of atmospheric turbulence model

Astronomy and Astrophysics (2004)

A. Ziad J. Borgnino F. Martin Jérôme Maîre D. Mourard

A new method is proposed for the verification of the atmospheric turbulence model. It is based on the reconstruction of the phase structure function from simultaneous measurements of the Angle-of-Arrival longitudinal covariance at different baselines with the Generalized Seeing Monitor (GSM). In addition, with this new technique we obtain the first non-model dependent estimates of the outer scale with the GSM. Preliminary results of the reconstructed phase structure function with this technique are presented and compared to those obtained theoretically with the most known atmospheric turbulence models.

GSM

Structure function

Phase function

Atmospheric models

10.1051/0004-6361:20031770

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Citations (7)

Recent progress and future prospects of the GI2T interferometer

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2006)

D. Mourard A. Blazit D. Bonneau J. L. Chevassut J. M. Clausse

We give an overview of recent results obtained with the GI2T interferometer. On the technical side, great improvements have been obtained on photon counting detectors, especially in terms of quantum efficiency and of photon centroiding algorithms. Piston measurements with the GI2T dispersed fringes have been made during coordinate observations with the Generalized Seeing Monitor GSM. These observations have lead to wavefront outer scale determinations. The last topic we will present concerns the polarimetric measurements done with the SPIN device on the GI2T spectrograph. We conclude this paper by a summary of the results obtained with the GI2T during its scientific life.

Piston (optics)

10.1117/12.669899

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Citations (22)

VEGA: Visible spEctroGraph and polArimeter for the CHARA array: principle and performance

Astronomy and Astrophysics (2009)

D. Mourard J. M. Clausse A. Marcotto K. Perraut I. Tallon–Bosc

Context. Among optical stellar interferometers, the CHARA Array located at Mt Wilson in California offers the potential of very long baselines (up to 330 m) and the prospect of coupling multiple beam combiners. This paper presents the principle and the measured performance of VEGA, Visible spEctroGraph and polArimeter installed in September 2007 at the coherent focus of the array.Aims. With 0.3 ms of arc of spatial resolution and up to of spectral resolution, VEGA intends to measure fundamental parameters of stars, to study stellar activities and to image and analyze circumstellar environments. We describe the observing modes that have been implemented for this spectro-polarimeter and show actual performances measured on the sky during the first observing runs.Methods. The astrophysical programs are described in relation to the observing modes of the instrument, the presentation of the spectrograph and of the interface table is shown and finally the data is presented. We discuss the perspectives of further development in the framework of the CHARA Array.Results. We show that VEGA/CHARA is fully operational. The current limiting magnitude is nearly 7 but the results depend on the observing conditions (seeing, spectral resolution, etc.). We have validated the stability of the instrumental visibility at the level of 1 to 2% over half an hour and of the instrumental polarization for various declinations. Some examples of squared visibility and differential visibility are presented.Conclusions. The spectro-polarimeter VEGA has been installed and successfully tested on CHARA. It will permit stellar physics studies at unprecedented spectral and spatial resolutions.

Polarimeter

Vega

Visibility

Spectral resolution

10.1051/0004-6361/200913016

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Citations (141)

Spectro-Interferometry of γ Cas by GI2T

R. Hirata D. Le Mignant P. Stee F. Vakili D. Mourard

Source

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<title>REGAIN: a new optical beam combiner for the G12T</title>

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (1994)

D. Mourard A. Blazit D. Bonneau D. Merlin I. Tallon-Bosc

A new focal instrumentation for the Grand Interferometre a 2 Telescopes (GI2T) called REGAIN (REcombinaison pour GrAnd INterferometre) is under study at the Observatoire de la Cote d'Azur (OCA) and the Laboratoire d'Astronomie Spatiale (LAS) in Marseille, France. The objectives of the REGAIN project are multiple. Priority number 1 is a more efficient astrophysical exploitation of the GI2T. Next is the possibility for observing simultaneously at visible and near-infrared wavelengths. Finally REGAIN should ensure the test of the OVLA prototype telescope added to the present GI2T. Therefore, the resulting GI3T could be used for phase-closure imaging with 1.5-m apertures. At the same time reservations will be made for implementing adaptive optics units for each telescope whilst the VLT interferometer fringe- sensor currently studied at the OCA, should be tested on the GI3T.

Instrumentation

Optical telescope

Very Large Telescope

10.1117/12.177277

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Kinematics and geometrical study of the Be stars 48 Persei andψPersei with the VEGA/CHARA interferometer

Astronomy and Astrophysics (2011)

O. Delaa P. Stee A. Meilland J. Zorec D. Mourard

Context. Five different physical processes might be responsible for the formation of decretion disks around Be stars: fast rotation of the star, stellar pulsations, binarity, stellar winds, and magnetic fields. Our observations indicate that fast rotation seems to produce a disk in Keplerian rotation, at least in the specific case of the two stars observed. We do not know if this observational result is a generality or not.

Stellar rotation

Vega

10.1051/0004-6361/201015639

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Citations (53)

Design Enhancements of the Fourier Kelvin Stellar Interferometer to Enable Detection of Earth Twins

Richard Barry W. C. Danchi Bruno Lopez Stephan Rinehart J.‐C. Augereau

During the last few years, considerable effort has been directed towards very large-scale (> $5 billion) missions to detect and characterize Mars-radius to Earth-radius planets around nearby stars; such as the Terrestrial Planet Finder Interferometer and Darwin missions. However, technological issues such as formation flying and control of systematic noise sources will likely prevent these missions from entering Phase A until at least the end of the next decade. Presently more than 350 planets have been discovered by a variety of techniques, and little is known about the majority of them other than their approximate mass. However, a simplified nulling interferometer operating in the near- to mid-infrared (e.g. approx. 5-15 microns), like the enhanced version of the Fourier Kelvin Stellar Interferometer (FKSI), can characterize the atmospheres of a large sample of the known planets - including Earth twins. Many other scientific problems can be addressed with a system like FKSI, including the studies of debris disks, active galactic nuclei, and low mass companions around nearby stars. We report results of a recent engineering study on an enhanced version of FKSI that includes 1-meter primary mirrors, 20-meter boom length, and an advanced sun shield that will provide a 45-degree FOR and 40K operating temperature for all optics including siderostats.

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The hypertelescope at work with a BIGRE integral field unit

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2011)

J. Antichi Patrick Rabou Fabien Patru E. Giro J. H. Girard

Dense Aperture Masking (DAM) is a high-contrast imaging technique which enhances the capabilities of the current direct imaging instrumentation, mainly to detect low bright companions at small separation from their parent star. DAM benefits from the experience achieved with the integral field unit installed on SPHERE spectrograph at the VLT (BIGRE, Antichi et al. 2009) with a very similar optical design. More in detail, it is obtained by exploiting the BIGRE integral field unit - composed of two consecutive micro-lens arrays - to subdivide the telescope pupil in many sub-pupils, preserving their relative position and providing the same amount of spatial filtering to each one. We present here results of a system study we pursued for a proficient implementation of BIGRE-DAM. We focus on the case of an 8 m class telescope coupled with the instrument NACO at the VLT. We detail on how the optical design and the related mechanical implementation of a DAM unit could be successfully achieved within NACO thanks to a wise optimization of the BIGRE micro-lenses array, adopted as sub-pupils re-imager instead of integral field unit. Diffraction limit is achieved by optical design and good apochromatic performances are proven for a narrow-band filter around 2.18 micron.

Integral field spectrograph

Aperture (computer memory)

10.1117/12.896926

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Citations (5)