2,048 research outputs found
Differential Imaging with a Multicolor Detector Assembly: A New ExoPlanet Finder Concept
Simultaneous spectral differential imaging is a high contrast technique by
which subtraction of simultaneous images reduces noise from atmospheric
speckles and optical aberrations. Small non-common wave front errors between
channels can seriously degrade its performance. We present a new concept, a
multicolor detector assembly (MCDA), which can eliminate this problem. The
device consists of an infrared detector and a microlens array onto the flat
side of which a checkerboard pattern of narrow-band micro-filters is deposited,
each micro-filter coinciding with a microlens. Practical considerations for
successful implementation of the technique are mentioned. Numerical simulations
predict a noise attenuation of 10^-3 at 0.5" for a 10^5 seconds integration on
a mH=5 star of Strehl ratio 0.9 taken with an 8-m telescope. This reaches a
contrast of 10^-7 at an angular distance of 0.5" from the center of the star
image.Comment: 13 pages, 5 figures, accepted APJ
Effects of Quasi-Static Aberrations in Faint Companion Searches
We present the first results obtained at CFHT with the TRIDENT infrared
camera, dedicated to the detection of faint companions close to bright nearby
stars. The camera's main feature is the acquisition of three simultaneous
images in three wavelengths (simultaneous differential imaging) across the
methane absorption bandhead at 1.6 micron, that enables a precise subtraction
of the primary star PSF while keeping the companion signal. The main limitation
is non-common path aberrations between the three optical paths that slightly
decorrelate the PSFs. Two types of PSF calibrations are combined with the
differential simultaneous imaging technique to further attenuate the PSF:
reference star subtraction and instrument rotation to smooth aberrations. It is
shown that a faint companion with a DeltaH of 10 magnitudes would be detected
at 0.5 arcsec from the primary.Comment: 12 pages, 10 figures, to appear in Astronomy with High Contrast
Imaging, EAS Publications Serie
Hydrogen maser development at Laval University
The physical construction of two hydrogen masers is described and results of measurements made on one of the masers are given. These include: cavity Q, thermal time constant, line Q, signal power output, magnetic shielding factor. Preliminary results indicate that the frequency stability will be mainly affected by the thermal of the cavity. The magnetic field and the barometric fluctuations should not affect the maser at the stability level above a few parts in 10 to the 15th power, which is the goal for averaging times of several hours
Preliminary vegetation map of the Espenberg Peninsula, Alaska, based on an Earth Resources Technology Satellite image
There are no author-identified significant results in this report
Scattering, Damping, and Acoustic Oscillations: Simulating the Structure of Dark Matter Halos with Relativistic Force Carriers
We demonstrate that self-interacting dark matter models with interactions
mediated by light particles can have significant deviations in the matter
power-spectrum and detailed structure of galactic halos when compared to a
standard cold dark matter scenario. While these deviations can take the form of
suppression of small scale structure that are in some ways similar to that of
warm dark matter, the self-interacting models have a much wider range of
possible phenomenology. A long-range force in the dark matter can introduce
multiple scales to the initial power spectrum, in the form of dark acoustic
oscillations and an exponential cut-off in the power spectrum. Using
simulations we show that the impact of these scales can remain observationally
relevant up to the present day. Furthermore, the self-interaction can continue
to modify the small-scale structure of the dark matter halos, reducing their
central densities and creating a dark matter core. The resulting phenomenology
is unique to this type of models.Comment: 23 pages, 11 figure
A Dark Census: Statistically Detecting the Satellite Populations of Distant Galaxies
In the standard structure formation scenario based on the cold dark matter
paradigm, galactic halos are predicted to contain a large population of dark
matter subhalos. While the most massive members of the subhalo population can
appear as luminous satellites and be detected in optical surveys, establishing
the existence of the low mass and mostly dark subhalos has proven to be a
daunting task. Galaxy-scale strong gravitational lenses have been successfully
used to study mass substructures lying close to lensed images of bright
background sources. However, in typical galaxy-scale lenses, the strong lensing
region only covers a small projected area of the lens's dark matter halo,
implying that the vast majority of subhalos cannot be directly detected in
lensing observations. In this paper, we point out that this large population of
dark satellites can collectively affect gravitational lensing observables,
hence possibly allowing their statistical detection. Focusing on the region of
the galactic halo outside the strong lensing area, we compute from first
principles the statistical properties of perturbations to the gravitational
time delay and position of lensed images in the presence of a mass substructure
population. We find that in the standard cosmological scenario, the statistics
of these lensing observables are well approximated by Gaussian distributions.
The formalism developed as part of this calculation is very general and can be
applied to any halo geometry and choice of subhalo mass function. Our results
significantly reduce the computational cost of including a large substructure
population in lens models and enable the use of Bayesian inference techniques
to detect and characterize the distributed satellite population of distant lens
galaxies.Comment: 21 pages + appendices, 7 figures. v2: Some derivations streamlined,
extended appendices. Matches version published in PR
Future Prospects: Deep Imaging of Galaxy Outskirts using Telescopes Large and Small
The Universe is almost totally unexplored at low surface brightness levels.
In spite of great progress in the construction of large telescopes and
improvements in the sensitivity of detectors, the limiting surface brightness
of imaging observations has remained static for about forty years. Recent
technical advances have at last begun to erode the barriers preventing
progress. In this Chapter we describe the technical challenges to low surface
brightness imaging, describe some solutions, and highlight some relevant
observations that have been undertaken recently with both large and small
telescopes. Our main focus will be on discoveries made with the Dragonfly
Telephoto Array (Dragonfly), which is a new telescope concept designed to probe
the Universe down to hitherto unprecedented low surface brightness levels. We
conclude by arguing that these discoveries are probably only scratching the
surface of interesting phenomena that are observable when the Universe is
explored at low surface brightness levels.Comment: 27 pages, 10 figures, Invited review, Book chapter in "Outskirts of
Galaxies", Eds. J. H. Knapen, J. C. Lee and A. Gil de Paz, Astrophysics and
Space Science Library, Springer, in pres
Benchmarking quantum control methods on a 12-qubit system
In this letter, we present an experimental benchmark of operational control
methods in quantum information processors extended up to 12 qubits. We
implement universal control of this large Hilbert space using two complementary
approaches and discuss their accuracy and scalability. Despite decoherence, we
were able to reach a 12-coherence state (or 12-qubits pseudo-pure cat state),
and decode it into an 11 qubit plus one qutrit labeled observable pseudo-pure
state using liquid state nuclear magnetic resonance quantum information
processors.Comment: 11 pages, 4 figures, to be published in PR
TRIDENT: an infrared camera optimized for the detection of methanated substellar companions around nearby stars
A near-infrared (0.85-2.5 microns) camera in use at the Canada-France-Hawaii
Telescope and at the 1.6m telescope of the Observatoire du Mont-Megantic is
described. The camera is based on a Hawaii-1 1024x1024 HgCdTe array detector.
Its main feature is to acquire three simultaneous images at three wavelengths
(simultaneous differential imaging) across the methane absorption bandhead at
1.6 micron, enabling an accurate subtraction of the stellar point spread
function (PSF) and the detection of faint close methanated companions. The
instrument has no coronagraph and features a fast (1 MHz) data acquisition
system without reset anomaly, yielding high observing efficiencies on bright
stars. The performance of the instrument is described, and it is illustrated by
CFHT images of the nearby star Ups And. TRIDENT can detect (3 sigma) a
methanated companion with DeltaH=10 at 0.5 arcsec from the star in one hour of
observing time. Non-common path aberrations between the three optical paths are
the limiting factors preventing further PSF attenuation. Reference star
subtraction and instrument rotation improve the detection limit by one order of
magnitude.Comment: 8 pages, 6 figures, to appear in SPIE 486
- …