977 research outputs found
The pupil-swapping coronagraph
A new coronagraph that performs destructive interference between copies of the telescope pupil in which "slices" have been swapped is studied in this paper. A fourth-order "pupil-swapping coronagraph" is particularly attractive for direct imaging of extrasolar terrestrial planets: it achieves 100% throughput at 1.4 lambda/d on a square pupil (72.5% at 1.77 lambda/d on a circular pupil), is compatible with a central obstruction and spiders, l/d and delivers sharp images of off-axis sources. Direct detection of extrasolar terrestrial planets appears theoretically feasible on a 2 to 3 m visible-wavelength telescope in space
Phase-Induced Amplitude Apodization of Telescope Pupils for Extrasolar Terrestrial Planet Imaging
In this paper, an alternative to the classical pupil apodization techniques
(use of an amplitude pupil mask) is proposed. It is shown that an apodized
pupil suitable for imaging of Extrasolar planets can be obtained by reflection
of an unapodized flat wavefront on 2 mirrors. By carefully choosing the shape
of these 2 mirrors, it is possible to obtain a contrast better than 10^{9} at a
distance smaller than 2 \lambda/d from the optical axis. Because this technique
preserves both the angular resolution and light gathering capabilities of the
unapodized pupil, it allows efficient detection of terrestrial extrasolar
planets with a 1.5m telescope in the visible.Comment: 9 pages, 9 figures, Accepted for publication in A&A. Postscript file
with full-resolution figures can be found at
http://www.naoj.org/staff/guyon/publications/PIAA.p
Wide field interferometric imaging with single-mode fibers
Classical single-mode fiber interferometers, using one fiber per aperture,
have very limited imaging capabilities and small field of view. Observations of
extended sources (resolved by one aperture) cannot be fully corrected for
wavefront aberrations: accurate measurements of object visibilities are then
made very difficult from ground-based fiber interferometers. These limitations
are very severe for the new generation of interferometers, which make use of
large telescopes equipped with adaptive optics, but can be overcome by using
several fibers per aperture. This technique improves the wide field imaging
capabilities of both ground-based and space interferometers.Comment: 14 pages, 14 figures. Accepted for publication in A&
The Subaru Coronagraphic Extreme Adaptive Optics System: Enabling High-Contrast Imaging on Solar-System Scales
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is a multipurpose high-contrast imaging platform designed for the discovery and detailed characterization of exoplanetary systems and serves as a testbed for high-contrast imaging technologies for ELTs. It is a multiband instrument which makes use of light from 600 to 2500 nm, allowing for coronagraphic direct exoplanet imaging of the inner 3λ/D from the stellar host. Wavefront sensing and control are key to the operation of SCExAO. A partial correction of low-order modes is provided by Subaru's facility adaptive optics system with the final correction, including high-order modes, implemented downstream by a combination of a visible pyramid wavefront sensor and a 2000-element deformable mirror. The well-corrected NIR (y-K bands) wavefronts can then be injected into any of the available coronagraphs, including but not limited to the phase-induced amplitude apodization and the vector vortex coronagraphs, both of which offer an inner working angle as low as 1λ/D. Noncommon path, low-order aberrations are sensed with a coronagraphic low-order wavefront sensor in the infrared (IR). Low noise, high frame rate NIR detectors allow for active speckle nulling and coherent differential imaging, while the HAWAII 2RG detector in the HiCIAO imager and/or the CHARIS integral field spectrograph (from mid-2016) can take deeper exposures and/or perform angular, spectral, and polarimetric differential imaging. Science in the visible is provided by two interferometric modules: VAMPIRES and FIRST, which enable subdiffraction limited imaging in the visible region with polarimetric and spectroscopic capabilities respectively. We describe the instrument in detail and present preliminary results both on-sky and in the laboratory
A Nulling Wide Field Imager for Exoplanets Detection and General Astrophysics
We present a solution to obtain a high-resolution image of a wide field with
the central source removed by destructive interference. The wide-field image is
created by aperture synthesis with a rotating sparse array of telescopes in
space. Nulling of the central source is achieved using a phase-mask
coronagraph. The full (u,v) plane coverage delivered by the 60m, six 3-meter
telescope array is particularly well-suited for the detection and
characterization of exoplanets in the infrared (DARWIN and Terrestrial Planet
Finder (TPF) missions) as well as for other generic science observations.
Detection (S/N=10) of an Earth-like planet is achieved in less than 10 hours
with a 1 micron bandwidth at 10 micron.Comment: 18 pages, 16 figures. Accepted for publication in A&
Personalized Pancreatic Tumor Growth Prediction via Group Learning
Tumor growth prediction, a highly challenging task, has long been viewed as a
mathematical modeling problem, where the tumor growth pattern is personalized
based on imaging and clinical data of a target patient. Though mathematical
models yield promising results, their prediction accuracy may be limited by the
absence of population trend data and personalized clinical characteristics. In
this paper, we propose a statistical group learning approach to predict the
tumor growth pattern that incorporates both the population trend and
personalized data, in order to discover high-level features from multimodal
imaging data. A deep convolutional neural network approach is developed to
model the voxel-wise spatio-temporal tumor progression. The deep features are
combined with the time intervals and the clinical factors to feed a process of
feature selection. Our predictive model is pretrained on a group data set and
personalized on the target patient data to estimate the future spatio-temporal
progression of the patient's tumor. Multimodal imaging data at multiple time
points are used in the learning, personalization and inference stages. Our
method achieves a Dice coefficient of 86.8% +- 3.6% and RVD of 7.9% +- 5.4% on
a pancreatic tumor data set, outperforming the DSC of 84.4% +- 4.0% and RVD
13.9% +- 9.8% obtained by a previous state-of-the-art model-based method
Adaptive optics in high-contrast imaging
The development of adaptive optics (AO) played a major role in modern
astronomy over the last three decades. By compensating for the atmospheric
turbulence, these systems enable to reach the diffraction limit on large
telescopes. In this review, we will focus on high contrast applications of
adaptive optics, namely, imaging the close vicinity of bright stellar objects
and revealing regions otherwise hidden within the turbulent halo of the
atmosphere to look for objects with a contrast ratio lower than 10^-4 with
respect to the central star. Such high-contrast AO-corrected observations have
led to fundamental results in our current understanding of planetary formation
and evolution as well as stellar evolution. AO systems equipped three
generations of instruments, from the first pioneering experiments in the
nineties, to the first wave of instruments on 8m-class telescopes in the years
2000, and finally to the extreme AO systems that have recently started
operations. Along with high-contrast techniques, AO enables to reveal the
circumstellar environment: massive protoplanetary disks featuring spiral arms,
gaps or other asymmetries hinting at on-going planet formation, young giant
planets shining in thermal emission, or tenuous debris disks and micron-sized
dust leftover from collisions in massive asteroid-belt analogs. After
introducing the science case and technical requirements, we will review the
architecture of standard and extreme AO systems, before presenting a few
selected science highlights obtained with recent AO instruments.Comment: 24 pages, 14 figure
Influence of flow confinement on the drag force on a static cylinder
The influence of confinement on the drag force on a static cylinder in a
viscous flow inside a rectangular slit of aperture has been investigated
from experimental measurements and numerical simulations. At low enough
Reynolds numbers, varies linearly with the mean velocity and the viscosity,
allowing for the precise determination of drag coefficients and
corresponding respectively to a mean flow parallel and
perpendicular to the cylinder length . In the parallel configuration, the
variation of with the normalized diameter of the
cylinder is close to that for a 2D flow invariant in the direction of the
cylinder axis and does not diverge when . The variation of
with the distance from the midplane of the model reflects the
parabolic Poiseuille profile between the plates for while it
remains almost constant for . In the perpendicular configuration,
the value of is close to that corresponding to a 2D system
only if and/or if the clearance between the ends of the cylinder
and the side walls is very small: in that latter case,
diverges as due to the blockage of the flow. In other cases, the
side flow between the ends of the cylinder and the side walls plays an
important part to reduce : a full 3D description of the flow is
needed to account for these effects
The Subaru Coronagraphic Extreme Adaptive Optics System: Enabling High-Contrast Imaging on Solar-System Scales
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is a multipurpose high-contrast imaging platform designed for the discovery and detailed characterization of exoplanetary systems and serves as a testbed for high-contrast imaging technologies for ELTs. It is a multiband instrument which makes use of light from 600 to 2500 nm, allowing for coronagraphic direct exoplanet imaging of the inner 3λ/D from the stellar host. Wavefront sensing and control are key to the operation of SCExAO. A partial correction of low-order modes is provided by Subaru's facility adaptive optics system with the final correction, including high-order modes, implemented downstream by a combination of a visible pyramid wavefront sensor and a 2000-element deformable mirror. The well-corrected NIR (y-K bands) wavefronts can then be injected into any of the available coronagraphs, including but not limited to the phase-induced amplitude apodization and the vector vortex coronagraphs, both of which offer an inner working angle as low as 1λ/D. Noncommon path, low-order aberrations are sensed with a coronagraphic low-order wavefront sensor in the infrared (IR). Low noise, high frame rate NIR detectors allow for active speckle nulling and coherent differential imaging, while the HAWAII 2RG detector in the HiCIAO imager and/or the CHARIS integral field spectrograph (from mid-2016) can take deeper exposures and/or perform angular, spectral, and polarimetric differential imaging. Science in the visible is provided by two interferometric modules: VAMPIRES and FIRST, which enable subdiffraction limited imaging in the visible region with polarimetric and spectroscopic capabilities respectively. We describe the instrument in detail and present preliminary results both on-sky and in the laboratory
Near Infrared Adaptive Optics Imaging of QSO Host Galaxies
We report near-infrared (primarily H-band) adaptive optics (AO) imaging with
the Gemini-N and Subaru Telescopes, of a representative sample of 32 nearby
(z<0.3) QSOs selected from the Palomar-Green (PG) Bright Quasar Survey (BQS),
in order to investigate the properties of the host galaxies. 2D modeling and
visual inspection of the images shows that ~36% of the hosts are ellipticals,
\~39% contain a prominent disk component, and ~25% are of undetermined type.
30% show obvious signs of disturbance. The mean M_H(host) = -24.82 (2.1L_H*),
with a range -23.5 to -26.5 (~0.63 to 10 L_H*). At <L_H*, all hosts have a
dominant disk component, while at >2 L_H* most are ellipticals. "Disturbed"
hosts are found at all M_H(host), while "strongly disturbed" hosts appear to
favor the more luminous hosts. Hosts with prominent disks have less luminous
QSOs, while the most luminous QSOs are almost exclusively in ellipticals or in
mergers (which presumably shortly will be ellipticals). At z<0.13, where our
sample is complete at B-band, we find no clear correlation between M_B(QSO) and
M_H(host). However, at z>0.15, the more luminous QSOs (M_B<-24.7), and 4/5 of
the radio-loud QSOs, have the most luminous H-band hosts (>7L_H*), most of
which are ellipticals. Finally, we find a strong correlation between the
"infrared-excess", L_IR/L_BB, of QSOs with host type and degree of disturbance.
Disturbed and strongly disturbed hosts and hosts with dominant disks have
L_IR/L_BB twice that of non-disturbed and elliptical hosts, respectively. QSOs
with "disturbed" and "strongly-disturbed" hosts are also found to have
morphologies and mid/far-infrared colors that are similar to what is found for
"warm" ultraluminous infrared galaxies, providing further evidence for a
possible evolutionary connection between both classes of objects.Comment: 80 pages, accepted for publication in ApJ Supp
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