KEYWORDS: Telescopes, High dynamic range imaging, Imaging systems, Single mode fibers, Adaptive optics, Range imaging, Stars, Observatories, Space telescopes, Wavefronts
We present the laboratory demonstration of a very high-dynamic range imaging instrument FIRST (Fibered Imager foR
Single Telescope). FIRST combines the techniques for aperture masking and a single-mode fiber interferometer to
correct wavefront errors, which leads to a very high-dynamic range up to 106 around very near the central object (~ λ/D)
at visible to near-infrared wavelengths. Our laboratory experiments successfully demonstrated that the original image
can be reconstructed through a pupil remapping system. A first on-sky test will be performed at the Lick Observatory 3-
m Shane telescope for operational tests in the summer of 2010.
KEYWORDS: High dynamic range imaging, Range imaging, Telescopes, Astronomy, Point spread functions, Visibility, Diffraction, Imaging systems, Exoplanets, Prototyping
We describe the present status of the development of a very high-dynamic range, diffraction limited imaging instrument FIRST (Fibered Imager foR Single Telescope), among which goals is the detection of nearby extra-solar planets at visible to near-infrared wavelengths from the ground. We have started to develop a prototype system which consists of a number of novel designs such as a segmented micro mirror array and silicon micro machined single-mode fiber arrays. Furthermore, we have proposed to build a FIRST instrument for the CFHT, which will be complementary to high-dynamic range instruments developed for 8m class telescopes at near-infrared wavelengths.
To detect Earth-like planets in the visible with a coronagraphic telescope, two major noise sources have to be overcome: the photon noise of the diffracted star light, and the speckle noise due to the star light scattered by instrumental defects. Coronagraphs tackle only the photon noise contribution. In order to decrease the speckle noise below the planet level, an active control of the wave front is required. We have developed analytical methods to measure and correct the speckle noise behind a coronagraph with a deformable mirror. In this paper, we summarize these methods, present numerical simulations, and discuss preliminary experimental results obtained with the High-Contrast Imaging Testbed at NASA's Jet Propulsion Laboratory.
In stellar interferometry, the raw fringe visibilities must be calibrated to obtain the intrinsic object visibilities and then object parameters which can be interpreted in term of astrophysical parameters. The selection of suitable calibration stars is crucial to reach the ultimate precision of the interferometric instruments like VLTI. So, we have developed a user-dedicated software to create an evolutive catalog of such calibration stars. This gives useful information for the selection of calibrators with respect to the requirements of the astrophysical program and of the instrumental configuration. A list of potential calibrators is obtained from a set of catalogs available at the Centre de Donnees Astronomiques de Strasbourg (CDS). The CDS request is based on some selection criteria like the maximum angular distance and the range of magnitude around the scientific target. This calibrator selection tool is integrated into ASPRO the interferometric observing preparation software developed by the Jean-Marie Marriotti Center (JMMC), and which is accessible at http://mariotti.ujf-grenoble.fr/~aspro/
We present a catalog of reference stars suitable for calibrate long
baseline interferometric observations in the infrared. This work
includes and extends the previous catalog by Bord\'e et al. (2002): in
the K band, a precision of 1~\% or better can be achieved on the
visibility with interferometric baselines up to $\sim 200$ meters
instead of $\sim 100$ in the preceding version. Angular diameters are
computed by way of the absolute spectro-photometric calibration method
proposed by Cohen et al. (1999), using IRAS and 2MASS photometric
measurements. Our updated catalog contains G8--M0 stars with angular
diameters 0.6--1.8~mas (median 1.1~mas) and a median error of
2.1~\%. The median magnitudes are 3.5 in K and 6.5 in V. Our grid is
dense enough that one would find a calibrator star closer than 10
degrees to any direction on the sky.
The fibered beam combiner FLUOR, which has provided high accuracy
visibility measurements on the IOTA interferometer, is being moved to
the CHARA array which provides five 1m telescopes on baselines ranging from 35 to 330m. The combination CHARA/FLUOR makes it possible for the first time to achieve sub-milliarcsecond resolution in the K band, with a dynamic range of 100 or more.
We explore the scientific potential of CHARA/FLUOR, most notably in the domains of high contrast binaries and the characterization of Cepheid pulsations, and present some of the anticipated developements.
The calibration process of long baseline stellar interferometers requires the use of reference stars with accurately determined angular diameters. We present a catalog of 374 carefully chosen stars among the all-sky network of infrared sources provided by Ref. 1. The catalog benefits from a very good sky coverage and a median formal error on the angular diameters of only 1.2%. Besides, its groups together in a homogeneous handy set stellar coordinates, uniform and limb-darkened angular diameters, photometric measurements, and other parameters relevant to optical interferometry. In this paper, we describe the selection criteria applied to qualify stars as reference sources. Then, we discuss the catalog's statistical properties such as the sky coverage or the distributions of magnitudes and angular diameters. We study the number of available reference stars as a function of the baseline and the precision needed on the visibility measurements. Finally, we compare the angular diameters predicted in Ref. 1 with existing determinations in the literature, and find a very good agreement.
Wavefront cleaning by single-mode fibers has proved to be efficient in optical-infrared interferometry to improve calibration quality. For instance, the FLUOR instrument has demonstrated the capability of fluoride glass single-mode fibers in this respect in the K and L bands. New interferometric instruments developed for the mid-infrared require the same capability for the 8-12 μm range. We have initiated a program to develop single-mode fibers in the prospect of the VLTI mid-infrared instrument MIDI and of the ESA/DARWIN and NASA/TPF missions that require excellent wavefront quality. In order to characterize the performances of chalcogenide fibers we are developing, we have set up an experiment to measure the far-field pattern radiated at 10 μm. In this paper, we report the first and promising results obtained with this new component.
Present projects of space interferometers dedicated to the detection and analysis of extrasolar planets (DARWIN in Europe, TPF in the United States) are based on the nulling interferometry concept. This concept has been proposed by Bracewell in 1978 but has never been demonstrated with high values of rejection, in the thermal infrared range, where the planet detection should be performed (6 - 18 micrometers ). We have thus built a two-beam laboratory interferometer to validate this concept in a monochromatic case (at 10 micrometers ). The keypoint of our interferometer is the use of optical filtering by pinhole and optical fibers to clean the interfering beams. We present in this paper the principle of the experimental setup, its realization, and the first measurements of rejection it allowed. We also present the future developments of this interferometer.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.