206 research outputs found
Pupil stabilization for SPHERE's extreme AO and high performance coronagraph system
We propose a new concept of pupil motion sensor for astronomical adaptive
optics systems and present experimental results obtained during the first
laboratory validation of this concept. Pupil motion is an important issue in
the case of extreme adaptive optics, high contrast systems, such as the
proposed Planet Finder instruments for the ESO and Gemini 8-meter telescopes.
Such high contrast imaging instruments will definitively require pupil
stabilization to minimize the effect of quasi-static aberrations. The concept
for pupil stabilization we propose uses the flux information from the AO system
wave-front sensor to drive in closed loop a pupil tip-tilt mirror located in a
focal plane. A laboratory experiment validates this concept and demonstrates
its interest for high contrast imaging instrument.Comment: This paper was published in Optics Express and is made available as
an electronic reprint with the permission of OSA. The paper can be found at
http://www.opticsexpress.org/abstract.cfm?id=144687 on the OSA websit
Design of light concentrators for Cherenkov telescope observatories
The Cherenkov Telescope Array (CTA) will be the largest cosmic gamma ray
detector ever built in the world. It will be installed at two different sites
in the North and South hemispheres and should be operational for about 30
years. In order to cover the desired energy range, the CTA is composed of
typically 50-100 collecting telescopes of various sizes (from 6 to 24-m
diameters). Most of them are equipped with a focal plane camera consisting of
1500 to 2000 Photomultipliers (PM) equipped with light concentrating optics,
whose double function is to maximize the amount of Cherenkov light detected by
the photo-sensors, and to block any stray light originating from the
terrestrial environment. Two different optical solutions have been designed,
respectively based on a Compound Parabolic Concentrator (CPC), and on a purely
dioptric concentrating lens. In this communication are described the technical
specifications, optical designs and performance of the different solutions
envisioned for all these light concentrators. The current status of their
prototyping activities is also given
Characterization of integrated optics components for the second generation of VLTI instruments
Two of the three instruments proposed to ESO for the second generation
instrumentation of the VLTI would use integrated optics for beam combination.
Several design are studied, including co-axial and multi-axial recombination.
An extensive quantity of combiners are therefore under test in our
laboratories. We will present the various components, and the method used to
validate and compare the different combiners. Finally, we will discuss the
performances and their implication for both VSI and Gravity VLTI instruments.Comment: SPIE Astronomical Instrumentation 2008 in Marseille, France --
Equation (7) update
ExTrA: Exoplanets in Transit and their Atmospheres
The ExTrA facility, located at La Silla observatory, will consist of a
near-infrared multi-object spectrograph fed by three 60-cm telescopes. ExTrA
will add the spectroscopic resolution to the traditional differential
photometry method. This shall enable the fine correction of color-dependent
systematics that would otherwise hinder ground-based observations. With both
this novel method and an infrared-enabled efficiency, ExTrA aims to find
transiting telluric planets orbiting in the habitable zone of bright nearby M
dwarfs. It shall have the versatility to do so by running its own independent
survey and also by concurrently following-up on the space candidates unveiled
by K2 and TESS. The exoplanets detected by ExTrA will be amenable to
atmospheric characterisation with VLTs, JWST, and ELTs and could give our first
peek into an exo-life laboratory.Comment: 15 pages, 11 figures, SPIE 201
The FALCON concept: multi-object spectroscopy combined with MCAO in near-IR
A large fraction of the present-day stellar mass was formed between z=0.5 and
z~3 and our understanding of the formation mechanisms at work at these epochs
requires both high spatial and high spectral resolution: one shall
simultaneously} obtain images of objects with typical sizes as small as
1-2kpc(~0''.1), while achieving 20-50 km/s (R >= 5000) spectral resolution. The
obvious instrumental solution to adopt in order to tackle the science goal is
therefore a combination of multi-object 3D spectrograph with multi-conjugate
adaptive optics in large fields. A partial, but still competitive correction
shall be prefered, over a much wider field of view. This can be done by
estimating the turbulent volume from sets of natural guide stars, by optimizing
the correction to several and discrete small areas of few arcsec2 selected in a
large field (Nasmyth field of 25 arcmin) and by correcting up to the 6th, and
eventually, up to the 60th Zernike modes. Simulations on real extragalactic
fields, show that for most sources (>80%), the recovered resolution could reach
0".15-0".25 in the J and H bands. Detection of point-like objects is improved
by factors from 3 to >10, when compared with an instrument without adaptive
correction. The proposed instrument concept, FALCON, is equiped with deployable
mini-integral field units (IFUs), achieving spectral resolutions between R=5000
and 20000. Its multiplex capability, combined with high spatial and spectral
resolution characteristics, is a natural ground based complement to the next
generation of space telescopes.Comment: ESO Workshop Proceedings: Scientific Drivers for ESO Future VLT/VLTI
Instrumentation, 10 pages and 5 figure
MYSTIC: Michigan Young STar Imager at CHARA
This is the final version of the article. Available from SPIE via the DOI in this record.We present the design for MYSTIC, the Michigan Young STar Imager at CHARA. MYSTIC will be a K-band, cryogenic, 6-beam combiner for the Georgia State University CHARA telescope array. The design follows the image-plane combination scheme of the MIRC instrument where single-mode fibers bring starlight into a non-redundant fringe pattern to feed a spectrograph. Beams will be injected in polarization-maintaining fibers outside the cryogenic dewar and then be transported through a vacuum feedthrough into the ~220K cold volume where combination is achieved and the light is dispersed. We will use a C-RED One camera (First Light Imaging) based on the eAPD SAPHIRA detector to allow for near-photon-counting performance. We also intend to support a 4-telescope mode using a leftover integrated optics component designed for the VLTI-GRAVITY experiment, allowing better sensitivity for the faintest targets. Our primary science driver motivation is to image disks around young stars in order to better understand planet formation and how forming planets might influence disk structures.MYSTIC is funded by the USA National Science Foundation (PI: Monnier, NSF-ATI 1506540) while the MIRC-X project is funded by the European Research Council (PI: Kraus, ERC, Grant # 639889)
The Fringe Detection Laser Metrology for the GRAVITY Interferometer at the VLTI
Interferometric measurements of optical path length differences of stars over
large baselines can deliver extremely accurate astrometric data. The
interferometer GRAVITY will simultaneously measure two objects in the field of
view of the Very Large Telescope Interferometer (VLTI) of the European Southern
Observatory (ESO) and determine their angular separation to a precision of 10
micro arcseconds in only 5 minutes. To perform the astrometric measurement with
such a high accuracy, the differential path length through the VLTI and the
instrument has to be measured (and tracked since Earth's rotation will
permanently change it) by a laser metrology to an even higher level of accuracy
(corresponding to 1 nm in 3 minutes). Usually, heterodyne differential path
techniques are used for nanometer precision measurements, but with these
methods it is difficult to track the full beam size and to follow the light
path up to the primary mirror of the telescope. Here, we present the
preliminary design of a differential path metrology system, developed within
the GRAVITY project. It measures the instrumental differential path over the
full pupil size and up to the entrance pupil location. The differential phase
is measured by detecting the laser fringe pattern both on the telescopes'
secondary mirrors as well as after reflection at the primary mirror. Based on
our proposed design we evaluate the phase measurement accuracy based on a full
budget of possible statistical and systematic errors. We show that this
metrology design fulfills the high precision requirement of GRAVITY.Comment: Proc. SPIE in pres
Integrated optics for astronomical interferometry - VI. Coupling the light of the VLTI in K band
Our objective is to prove that integrated optics (IO) is not only a good
concept for astronomical interferometry but also a working technique with high
performance. We used the commissioning data obtained with the dedicated K-band
integrated optics two-telescope beam combiner which now replaces the fiber
coupler MONA in the VLTI/VINCI instrument. We characterize the behaviour of
this IO device and compare its properties to other single mode beam combiner
like the previously used MONA fiber coupler. The IO combiner provides a high
optical throughput, a contrast of 89% with a night-to-night stability of a few
percent. Even if a dispersive phase is present, we show that it does not bias
the measured Fourier visibility estimate. An upper limit of 0.005 for the
cross-talk between linear polarization states has been measured. We take
advantage of the intrinsic contrast stability to test a new astronomical
prodecure for calibrating diameters of simple stars by simultaneously fitting
the instrumental contrast and the apparent stellar diameters. This method
reaches an accuracy with diameter errors of the order of previous ones but
without the need of an already known calibrator. These results are an important
step of integrated optics and paves the road to incoming imaging interferometer
projects
Searching for faint companions with VLTI/PIONIER. I. Method and first results
Context. A new four-telescope interferometric instrument called PIONIER has
recently been installed at VLTI. It provides improved imaging capabilities
together with high precision. Aims. We search for low-mass companions around a
few bright stars using different strategies, and determine the dynamic range
currently reachable with PIONIER. Methods. Our method is based on the closure
phase, which is the most robust interferometric quantity when searching for
faint companions. We computed the chi^2 goodness of fit for a series of binary
star models at different positions and with various flux ratios. The resulting
chi^2 cube was used to identify the best-fit binary model and evaluate its
significance, or to determine upper limits on the companion flux in case of non
detections. Results. No companion is found around Fomalhaut, tau Cet and
Regulus. The median upper limits at 3 sigma on the companion flux ratio are
respectively of 2.3e-3 (in 4 h), 3.5e-3 (in 3 h) and 5.4e-3 (in 1.5 h) on the
search region extending from 5 to 100 mas. Our observations confirm that the
previously detected near-infrared excess emissions around Fomalhaut and tau Cet
are not related to a low-mass companion, and instead come from an extended
source such as an exozodiacal disk. In the case of del Aqr, in 30 min of
observation, we obtain the first direct detection of a previously known
companion, at an angular distance of about 40 mas and with a flux ratio of
2.05e-2 \pm 0.16e-2. Due to the limited u,v plane coverage, its position can,
however, not be unambiguously determined. Conclusions. After only a few months
of operation, PIONIER has already achieved one of the best dynamic ranges
world-wide for multi-aperture interferometers. A dynamic range up to about
1:500 is demonstrated, but significant improvements are still required to reach
the ultimate goal of directly detecting hot giant extrasolar planets.Comment: 11 pages, 6 figures, accepted for publication in A&
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