283 research outputs found
Comparative study of manufacturing techniques for coronagraphic binary pupil masks: masks on substrates and free-standing masks
We present a comparative study of the manufacture of binary pupil masks for
coronagraphic observations of exoplanets. A checkerboard mask design, a type of
binary pupil mask design, was adopted, and identical patterns of the same size
were used for all the masks in order that we could compare the differences
resulting from the different manufacturing methods. The masks on substrates had
aluminum checkerboard patterns with thicknesses of 0.1/0.2/0.4/0.8/1.6m
constructed on substrates of BK7 glass, silicon, and germanium using
photolithography and chemical processes. Free-standing masks made of copper and
nickel with thicknesses of 2/5/10/20m were also realized using
photolithography and chemical processes, which included careful release from
the substrate used as an intermediate step in the manufacture. Coronagraphic
experiments using a visible laser were carried out for all the masks on BK7
glass substrate and the free-standing masks. The average contrasts were
8.4, 1.2, and 1.2 for the masks on
BK7 substrates, the free-standing copper masks, and the free-standing nickel
masks, respectively. No significant correlation was concluded between the
contrast and the mask properties. The high contrast masks have the potential to
cover the needs of coronagraphs for both ground-based and space-borne
telescopes over a wide wavelength range. Especially, their application to the
infrared space telescope, SPICA, is appropriate.Comment: 21 pates, 12 figures, 2 tables, accepted to PAS
DISCO: a Spatio-Spectral Recombiner for Pupil Remapping Interferometry
Pupil-remapping is a new high-dynamic range imaging technique that has
recently demonstrated feasibility on sky. The current prototypes present
however deceiving limiting magnitude, restricting the current use to the
brightest stars in the sky. We propose to combine pupil-remapping with
spatio-spectral encoding, a technique first applied to the VEGA/CHARA
interferometer. The result is an instrument proposal, called "Dividing
Interferometer for Stars Characterizations and Observations" (DISCO). The idea
is to take profit of wavelength multiplexing when using a spectrograph in order
to pack as much as possible the available information, yet providing a
potential boost of 1.5 magnitude if used in existing prototypes. We detail in
this paper the potential of such a concept.Comment: Improving the performances of current optical interferometers \&
future designs, France (2013
Multi-Color Coronagraph Experiment in a Vacuum Testbed with a Binary Shaped Pupil Mask
We conducted a number of multi-band coronagraph experiments using a vacuum
chamber and a binary-shaped pupil mask which in principle should work at all
wavelengths, in the context of the research and development on a coronagraph to
observe extra-solar planets (exoplanets) directly. The aim of this work is to
demonstrate that subtraction of Point Spread Function (PSF) and multi-band
experiments using a binary-shaped pupil mask coronagraph would help improve the
contrast in the observation of exoplanets. A checkerboard mask, a kind of
binary-shaped pupil mask, was used. We improved the temperature stability by
installing the coronagraph optics in a vacuum chamber, controlling the
temperature of the optical bench, and covering the vacuum chamber with thermal
insulation layers. We evaluated how much the PSF subtraction contributes to the
high contrast observation by subtracting the images obtained through the
coronagraph. We also carried out multi- band experiments in order to
demonstrate a more realistic observation using Super luminescent Light Emitting
Diodes (SLEDs) with center wavelengths of 650nm, 750nm, 800nm and 850nm. A
contrast of 2.3x10-7 was obtained for the raw coronagraphic image and a
contrast of 1.3x10-9 was achieved after PSF subtraction with a He-Ne laser at
632.8nm wavelength. Thus, the contrast was improved by around two orders of
magnitude from the raw contrast by subtracting the PSF. We achieved contrasts
of 3.1x10-7, 1.1x10-6, 1.6x10-6 and 2.5x10-6 at the bands of 650nm, 750nm,
800nm and 850nm, respectively, in the multi-band experiments. The results show
that contrast within each of the wavelength bands was significantly improved
compared with non-coronagraphic optics. We demonstrated PSF subtraction is
potentially beneficial for improving contrast of the coronagraph, and this
coronagraph produces a significant improvement in contrast with multi-band
light sources.Comment: 14 pages, 7 figures, accepted for publication in PAS
Sub-Arcsecond Near-Infrared Images of Massive Star Formation Region NGC 6334 V
We present high spatial resolution (0\farcs3) polarimetric images in the
and bands and direct images in the and bands of the NGC 6334
V infrared nebulae. The images show complex structures including the
multi-shells and various knots in the nebulae. The appearances and colors of
the eastern and western nebulae differ considerably. Our polarization images
also show differences between the illuminating sources of the nebulae: the
eastern nebula is illuminated by a deeply embedded mid-infrared source, KDJ 4,
and the western nebula by our newly detected near-infrared source, WN-A1. The
degree of polarization of the nebulae is very large, up to 70% at and 60%
at , which is consistent with a single scattering of near-infrared radiation
from each source at the walls of the mass outflows
C2PU: 1-Meter Telescopes for the GAIA-FUN
3 p.International audienceC2PU stands in french for "Centre Pédagogique Planète Univers" (Planet and Universe Pedagogic Center). It is a project both for pedagogic and research purposes. It relies on the renewal of two 1-meter diameter telescopes. These two telescopes were earlier coupled as part of an interferometric instrument called SOIRDETE (for "Synthèse d'Ouverture en Infra Rouge avec DEux Telescopes"), described in Rabbia et al. 1990
First Two-Micron Imaging Polarimetry of Beta Pictoris
High-resolution K band imaging polarimetry of the beta Pic dust disk has been
conducted with adaptive optics and a coronagraph using the Subaru 8.2-m
telescope. Polarization of ~10 % is detected out to r ~ 120 AU with a
centro-symmetric vector pattern around the central star, confirming that the
disk is seen as an infrared reflection nebula. We have modeled our
near-infrared and previous optical polarization results in terms of dust
scattering in the disk and have found that both the degrees of polarization and
the radial intensity profiles are well reproduced. We argue that the observed
characteristics of the disk dust are consistent with the presence of ice-filled
fluffy aggregates consisting of submicron grains in the beta Pic system. There
is a gap around 100 AU in both the intensity and polarization profiles, which
suggests a paucity of planetesimals in this region. The radial intensity
profile also shows ripple-like structures, which are indicative of the presence
of multiple planetesimal belts, as in the case of the M-type Vega-like star AU
Mic.Comment: 18 pages, 6 figures, accepted for Jp
Apodized Lyot Coronagraph for VLT-SPHERE: Laboratory tests and performances of a first prototype in the visible
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
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