329 research outputs found
Component-resolved Near-infrared Spectra of the (22) Kalliope System
We observed (22) Kalliope and its companion Linus with the integral-field
spectrograph OSIRIS, which is coupled to the adaptive optics system at the W.M.
Keck II telescope on March 25 2008. We present, for the first time,
component-resolved spectra acquired simultaneously in each of the Zbb (1-1.18
um), Jbb (1.18-1.42 um), Hbb (1.47-1.80 um), and Kbb (1.97-2.38 um) bands. The
spectra of the two bodies are remarkably similar and imply that both bodies
were formed at the same time from the same material; such as via incomplete
re-accretion after a major impact on the precursor body.Comment: 20 pages, 5 figures, 1 table. Accepted for publication in Icaru
Determination of binary asteroid orbits with a genetic-based algorithm
Reproduced with permission. Copyright ESO. The original publication is available at www.aanda.org.International audienceAims: Over the past decade, discoveries of multiple and binary asteroid systems have played a significant role in our general understanding of small solar system bodies. Direct observations of satellites of asteroids are rare and difficult since they require the use of already over-subscribed facilities such as adaptive optics (AO) on large 8-10 m class telescopes and the Hubble Space Telescope (HST). The scarcity of data and the long temporal baseline of observations (up to 10 years) significantly complicate the determination of the mutual orbits of these systems. Methods: We implemented a new approach for determining the mutual orbits of directly-imaged multiple asteroids using a genetic-based algorithm. This approach was applied to several known binary asteroid systems (22 Kalliope, 3749 Balam, and 50 000 Quaoar) observed with AO systems and HST. This statistical method is fast enough to permit the search for an orbital solution across a large parameter space and without a priori information about the mutual orbit. Results: From 10 years of observation, we derived an orbital solution for Linus, companion of (22) Kalliope, with an accuracy close to the astrometric limit provided by the AO observations, assuming a purely Keplerian orbit. A search for non-Keplerian orbit confirmed that a J2 ~ 0 is the best-fitting solution. We show that the precession of the nodes could be detected without ambiguity, implying that Kalliope's primary may have an inhomogeneous internal structure. HST astrometric observations of Weywot, companion of the trans-Neptunian object (50 000) Quaoar, were used to derive its mass and its bulk density, which appears to be higher than the density of other TNOs. Finally, we derived a bundle of orbital solutions for (3749) Balam, with equally good fits, from the limited set of astrometric positions. They provide a realistic density between 1.3 and 3.7 g/cm3 for this S-type asteroid
MOEMS deformable mirror testing in cryo for future optical instrumentation
MOEMS Deformable Mirrors (DM) are key components for next generation
instruments with innovative adaptive optics systems, in existing telescopes and
in the future ELTs. These DMs must perform at room temperature as well as in
cryogenic and vacuum environment. Ideally, the MOEMS-DMs must be designed to
operate in such environment. We present some major rules for designing /
operating DMs in cryo and vacuum. We chose to use interferometry for the full
characterization of these devices, including surface quality measurement in
static and dynamical modes, at ambient and in vacuum/cryo. Thanks to our
previous set-up developments, we placed a compact cryo-vacuum chamber designed
for reaching 10-6 mbar and 160K, in front of our custom Michelson
interferometer, able to measure performances of the DM at actuator/segment
level as well as whole mirror level, with a lateral resolution of 2{\mu}m and a
sub-nanometric z-resolution. Using this interferometric bench, we tested the
Iris AO PTT111 DM: this unique and robust design uses an array of single
crystalline silicon hexagonal mirrors with a pitch of 606{\mu}m, able to move
in tip, tilt and piston with strokes from 5 to 7{\mu}m, and tilt angle in the
range of +/-5mrad. They exhibit typically an open-loop flat surface figure as
good as <20nm rms. A specific mount including electronic and opto-mechanical
interfaces has been designed for fitting in the test chamber. Segment
deformation, mirror shaping, open-loop operation are tested at room and cryo
temperature and results are compared. The device could be operated successfully
at 160K. An additional, mainly focus-like, 500 nm deformation is measured at
160K; we were able to recover the best flat in cryo by correcting the focus and
local tip-tilts on some segments. Tests on DM with different mirror thicknesses
(25{\mu}m and 50{\mu}m) and different coatings (silver and gold) are currently
under way.Comment: 11 pages, 12 Figure
Gemini Planet Imager Observational Calibrations III: Empirical Measurement Methods and Applications of High-Resolution Microlens PSFs
The newly commissioned Gemini Planet Imager (GPI) combines extreme adaptive
optics, an advanced coronagraph, precision wavefront control and a
lenslet-based integral field spectrograph (IFS) to measure the spectra of young
extrasolar giant planets between 0.9-2.5 um. Each GPI detector image, when in
spectral model, consists of ~37,000 microspectra which are under or critically
sampled in the spatial direction. This paper demonstrates how to obtain
high-resolution microlens PSFs and discusses their use in enhancing the
wavelength calibration, flexure compensation and spectral extraction. This
method is generally applicable to any lenslet-based integral field spectrograph
including proposed future instrument concepts for space missions.Comment: 10 pages, 6 figures. Proceedings of the SPIE, 9147-282 v2: reference
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Titan imagery with Keck adaptive optics during and after probe entry
We present adaptive optics data from the Keck telescope, taken while the Huygens probe descended through Titan's atmosphere and on the days following touchdown. No probe entry signal was detected. Our observations span a solar phase angle range from 0.05° up to 0.8°, with the Sun in the west. Contrary to expectations, the east side of Titan's stratosphere was usually brightest. Compiling images obtained with Keck and Gemini over the past few years reveals that the east-west asymmetry can be explained by a combination of the solar phase angle effect and an enhancement in the haze density on Titan's morning hemisphere. While stratospheric haze was prominent over the northern hemisphere, tropospheric haze dominated the south, from the south pole up to latitudes of âŒ45°S. At 2.1 ÎŒm this haze forms a polar cap, while at 1.22 ÎŒm it appears in the form of a collar at 60°S. A few small clouds were usually present near the south pole, at altitudes of 30â40 km. Our narrowband J,H,K images of Titan's surface compare extremely well with that obtained by Cassini ISS, down to the small-scale features. The surface contrast between dark and bright areas may be larger at 2 ÎŒm than at 1.6 and 1.3 ÎŒm, which would imply that the dark areas may be covered by a coarser-grained frost than the bright regions and/or that there is additional 2 ÎŒm absorption there
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