448 research outputs found
PSF reconstruction for NAOS-CONICA
Adaptive optics (AO) allows one to derive the point spread function (PSF)
simultaneously to the science image, which is a major advantage in
post-processing tasks such as astrometry/photometry or deconvolution. Based on
the algorithm of \citet{veran97}, PSF reconstruction has been developed for
four different AO systems so far: PUEO, ALFA, Lick-AO and Altair. A similar
effort is undertaken for NAOS/VLT in a collaboration between the group PHASE
(Onera and Observatoire de Paris/LESIA) and ESO. In this paper, we first
introduce two new algorithms that prevent the use of the so-called "
functions" to: (1) avoid the storage of a large amount of data (for both new
algorithms), (2) shorten the PSF reconstruction computation time (for one of
the two) and (3) provide an estimation of the PSF variability (for the other
one). We then identify and explain issues in the exploitation of real-time
Shack-Hartmann (SH) data for PSF reconstruction, emphasising the large impact
of thresholding in the accuracy of the phase residual estimation. Finally, we
present the data provided by the NAOS real-time computer (RTC) to reconstruct
PSF ({\em (1)} the data presently available, {\em (2)} two NAOS software
modifications that would provide new data to increase the accuracy of the PSF
reconstruction and {\em (3)} the tests of these modifications) and the PSF
reconstruction algorithms we are developing for NAOS on that basis.Comment: 12 pages & 13 figures. To be published in the proceedings of the SPIE
conference Advances in Adaptive Optics - Astronomical Telescopes &
Instrumentation, 24-31 May 2006, Orland
Optical vortex coronagraphs on ground-based telescopes
The optical vortex coronagraph is potentially a remarkably effective device,
at least for an ideal unobstructed telescope. Most ground-based telescopes
however suffer from central obscuration and also have to operate through the
aberrations of the turbulent atmosphere. This note analyzes the performance of
the optical vortex in these circumstances and compares to some other designs,
showing that it performs similarly in this situation. There is a large class of
coronagraphs of this general type, and choosing between them in particular
applications depends on details of performance at small off-axis distances and
uniformity of response in the focal plane. Issues of manufacturability to the
necessary tolerances are also likely to be important.Comment: 32 pages, 13 figure
An aperture masking mode for the MICADO instrument
MICADO is a near-IR camera for the Europea ELT, featuring an extended field
(75" diameter) for imaging, and also spectrographic and high contrast imaging
capabilities. It has been chosen by ESO as one of the two first-light
instruments. Although it is ultimately aimed at being fed by the MCAO module
called MAORY, MICADO will come with an internal SCAO system that will be
complementary to it and will deliver a high performance on axis correction,
suitable for coronagraphic and pupil masking applications. The basis of the
pupil masking approach is to ensure the stability of the optical transfer
function, even in the case of residual errors after AO correction (due to non
common path errors and quasi-static aberrations). Preliminary designs of pupil
masks are presented. Trade-offs and technical choices, especially regarding
redundancy and pupil tracking, are explained.Comment: SPIE 2014 Proceeding -- Montrea
Sous-traiter lâaccompagnement des chĂŽmeurs : Ă©lĂ©ments dâĂ©valuation
Sous-traiter des parcours dâaccompagnement des demandeurs dâemploi Ă des opĂ©rateurs privĂ©s reprĂ©sente une tendance commune Ă de nombreux pays, mais qui obĂ©it Ă des objectifs diffĂ©rents du fait de contextes nationaux spĂ©cifiques. LâAustralie, les Pays-Bas et le Royaume-Uni ont depuis longtemps recours Ă la sous-traitance ; cette tendance est plus rĂ©cente en France. Sâappuyer sur lâexpĂ©rience des trois premiers pays permet dâĂ©clairer la situation française. En effet, ces pays ont, sur la base des rĂ©sultats de premiĂšres Ă©valuations, appris de leurs Ă©checs et transformĂ© le cadre de rĂ©gulation de la sous-traitance. Tout particuliĂšrement, les processus dâappel dâoffres, de sĂ©lection et dâorientation des demandeurs dâemploi, comme le contenu des contrats Ă©tablis avec les opĂ©rateurs privĂ©s, ont Ă©tĂ© revus.Contracting-out case management of unemployed people to private providers represents one common trend to many countries, even if the objectives attributed in contracting-out and national context are specific. Australia, the Netherlands and the United Kingdom have a long experience on that subject : this trend is more recent in France. Actually, one can learn from such experience as far as theses countries have, on the basis of their first evaluations, learned of their failures and reformed the regulation framework of contracting-out. More precisely the tendering process, selection and orientation of unemployed people and also the contents of contracts have been transformed
A giant planet imaged in the disk of the young star Beta Pictoris
Here we show that the ~10 Myr Beta Pictoris system hosts a massive giant
planet, Beta Pictoris b, located 8 to 15 AU from the star. This result confirms
that gas giant planets form rapidly within disks and validates the use of disk
structures as fingerprints of embedded planets. Among the few planets already
imaged, Beta Pictoris b is the closest to its parent star. Its short period
could allow recording the full orbit within 17 years.Comment: 4 pages, 2 figures. Published online 10 June 2010;
10.1126/science.1187187. To appear in Scienc
A probable giant planet imaged in the Beta Pictoris disk
Since the discovery of its dusty disk in 1984, Beta Pictoris has become the
prototype of young early-type planetary systems, and there are now various
indications that a massive Jovian planet is orbiting the star at ~ 10 AU.
However, no planets have been detected around this star so far. Our goal was to
investigate the close environment of Beta Pic, searching for planetary
companion(s). Deep adaptive-optics L'-band images of Beta Pic were recorded
using the NaCo instrument at the Very Large Telescope. A faint point-like
signal is detected at a projected distance of ~ 8 AU from the star, within the
North-East side of the dust disk. Various tests were made to rule out with a
good confidence level possible instrumental or atmospheric artifacts. The
probability of a foreground or background contaminant is extremely low, based
in addition on the analysis of previous deep Hubble Space Telescope images. The
object L'=11.2 apparent magnitude would indicate a typical temperature of ~1500
K and a mass of ~ 8 Jovian masses. If confirmed, it could explain the main
morphological and dynamical peculiarities of the Beta Pic system. The present
detection is unique among A-stars by the proximity of the resolved planet to
its parent star. Its closeness and location inside the Beta Pic disk suggest a
formation process by core accretion or disk instabilities rather than a
binary-like formation process.Comment: 5 pages, 3 figures, 1 table. A&A Letters, in pres
Model-free reinforcement learning with a non-linear reconstructor for closed-loop adaptive optics control with a pyramid wavefront sensor
We present a model-free reinforcement learning (RL) predictive model with a supervised learning non-linear reconstructor for adaptive optics (AO) control with a pyramid wavefront sensor (P-WFS). First, we analyse the additional problems of training an RL control method with a P-WFS compared to the Shack-Hartmann WFS. From those observations, we propose our solution: a combination of model-free RL for prediction with a non-linear reconstructor based on neural networks with a U-net architecture. We test the proposed method in simulation of closed-loop AO for an 8m telescope equipped with a 32x32 P-WFS and observe that both the predictive and non-linear reconstruction add additional benefits over an optimised integrator.This project has received funding from the European Unionâs Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 873120.Peer ReviewedPostprint (author's final draft
An original interferometric study of NGC 1068 with VISIR BURST mode images
We present 12.8 microns images of the core of NGC 1068 obtained with the
BURST mode of the VLT/VISIR. We trace structures under the diffraction limit of
one UT and we investigate the link between dust in the vicinity of the central
engine of NGC 1068, recently resolved by interferometry with MIDI, and more
extended structures. This step is mandatory for a multi-scale understanding of
the sources of mid-infrared emission in AGNs. A speckle processing of VISIR
BURST mode images was performed to extract very low spatial-frequency
visibilities, first considering the full field of VISIR BURST mode images and
then limiting it to the mask used for the acquisition of MIDI data. Extracted
visibilities are reproduced with a multi-component model. We identify two major
sources of emission: one compact < 85 mas, associated with the dusty torus, and
an elliptical one, (< 140) mas x 1187 mas at P.A.=-4 degrees from N to E. This
is consistent with previous deconvolution processes. The combination with MIDI
data reveals the close environment of the dusty torus to contribute to about 83
percent of the MIR flux seen by MIDI. This strong contribution has to be
considered in modeling long baseline interferometric data. It must be related
to the NS elongated component which is thought to originate from individually
unresolved dusty clouds and is located inside the ionization cone. Low
temperatures of the dusty torus are not challenged, emphasizing the scenarios
of clumpy torus.Comment: 10 pages, 7 figures, accepted for publication in A&
Unveiling the central parsec region of an AGN: the Circinus nucleus in the near infrared with the VLT
VLT J- to M\p-band adaptive optics observations of the Circinus Galaxy on
parsec scales resolve a central bright Ks-band source with a FWHM size of 1.9
0.6 pc. This source is only visible at wavelengths longward of 1.6 m
and coincides in position with the peak of the [Si VII]~2.48 m coronal
line emission. With respect to the peak of the central optical emission, the
source is shifted by 0.15\arcsec (2.8 pc) to the south-east. Indeed, it
defines the vertex of a fairly collimated beam which extends for 10 pc,
and which is seen in both continuum light shortward of 1.6 m and in
H line emission. The source also lies at the center of a 19 pc
size [Si VII] ionization {\it bicone}.
Identifying this source as the nucleus of Circinus, its size is compatible
with a putative parsec-scale torus. Its spectral energy distribution,
characterized by a prominent narrow peak, is compatible with a dust temperature
of 300 K. Hotter dust within a 1 pc radius of the center is not detected. The
AGN luminosity required to heat this dust is in the range of X-ray luminosities
that have been measured toward the central source. This in turn supports the
existence of highly obscuring material, with column densities of
cm, that must be located within 1 pc of the core.Comment: 15 pages, 4 figures; To appear in The Astrophysical Journa
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