183 research outputs found
Experimental study of a low-order wavefront sensor for the high-contrast coronagraphic imager EXCEDE
The mission EXCEDE (EXoplanetary Circumstellar Environments and Disk
Explorer), selected by NASA for technology development, is designed to study
the formation, evolution and architectures of exoplanetary systems and
characterize circumstellar environments into stellar habitable zones. It is
composed of a 0.7 m telescope equipped with a Phase-Induced Amplitude
Apodization Coronagraph (PIAA-C) and a 2000-element MEMS deformable mirror,
capable of raw contrasts of 1e-6 at 1.2 lambda/D and 1e-7 above 2 lambda/D. One
of the key challenges to achieve those contrasts is to remove low-order
aberrations, using a Low-Order WaveFront Sensor (LOWFS). An experiment
simulating the starlight suppression system is currently developed at NASA Ames
Research Center, and includes a LOWFS controlling tip/tilt modes in real time
at 500 Hz. The LOWFS allowed us to reduce the tip/tilt disturbances to 1e-3
lambda/D rms, enhancing the previous contrast by a decade, to 8e-7 between 1.2
and 2 lambda/D. A Linear Quadratic Gaussian (LQG) controller is currently
implemented to improve even more that result by reducing residual vibrations.
This testbed shows that a good knowledge of the low-order disturbances is a key
asset for high contrast imaging, whether for real-time control or for post
processing.Comment: 12 pages, 20 figures, proceeding of the SPIE conference
Optics+Photonics, San Diego 201
Efficient injection from large telescopes into single-mode fibres: Enabling the era of ultra-precision astronomy
Photonic technologies offer numerous advantages for astronomical instruments
such as spectrographs and interferometers owing to their small footprints and
diverse range of functionalities. Operating at the diffraction-limit, it is
notoriously difficult to efficiently couple such devices directly with large
telescopes. We demonstrate that with careful control of both the non-ideal
pupil geometry of a telescope and residual wavefront errors, efficient coupling
with single-mode devices can indeed be realised. A fibre injection was built
within the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument.
Light was coupled into a single-mode fibre operating in the near-IR (J-H bands)
which was downstream of the extreme adaptive optics system and the pupil
apodising optics. A coupling efficiency of 86% of the theoretical maximum limit
was achieved at 1550 nm for a diffraction-limited beam in the laboratory, and
was linearly correlated with Strehl ratio. The coupling efficiency was constant
to within <30% in the range 1250-1600 nm. Preliminary on-sky data with a Strehl
ratio of 60% in the H-band produced a coupling efficiency into a single-mode
fibre of ~50%, consistent with expectations. The coupling was >40% for 84% of
the time and >50% for 41% of the time. The laboratory results allow us to
forecast that extreme adaptive optics levels of correction (Strehl ratio >90%
in H-band) would allow coupling of >67% (of the order of coupling to multimode
fibres currently). For Strehl ratios <20%, few-port photonic lanterns become a
superior choice but the signal-to-noise must be considered. These results
illustrate a clear path to efficient on-sky coupling into a single-mode fibre,
which could be used to realise modal-noise-free radial velocity machines,
very-long-baseline optical/near-IR interferometers and/or simply exploit
photonic technologies in future instrument design.Comment: 15 pages, 16 figures, 1 table, published in A&
Post-processing CHARIS integral field spectrograph data with PyKLIP
We present the pyKLIP-CHARIS post-processing pipeline, a Python library that
reduces high contrast imaging data for the CHARIS integral field spectrograph
used with the SCExAO project on the Subaru Telescope. The pipeline is a part of
the pyKLIP package, a Python library dedicated to the reduction of direct
imaging data of exoplanets, brown dwarfs, and discs. For PSF subtraction, the
pyKLIP-CHARIS post-processing pipeline relies on the core algorithms
implemented in pyKLIP but uses image registration and calibrations that are
unique to CHARIS. We describe the pipeline procedures, calibration results, and
capabilities in processing imaging data acquired via the angular differential
imaging and spectral differential imaging observing techniques. We showcase its
performance on extracting spectra of injected synthetic point sources as well
as compare the extracted spectra from real data sets on HD 33632 and HR 8799 to
results in the literature. The pipeline is a python-based complement to the
SCExAO project supported, widely used (and currently IDL-based) CHARIS data
post-processing pipeline (CHARIS DPP) and provides an additional approach to
reducing CHARIS data and extracting calibrated planet spectra.Comment: 17 pages, 13 figure
EXCEDE Technology Development III: First Vacuum Tests
This paper is the third in the series on the technology development for the
EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer) mission
concept, which in 2011 was selected by NASA's Explorer program for technology
development (Category III). EXCEDE is a 0.7m space telescope concept designed
to achieve raw contrasts of 1e6 at an inner working angle of 1.2 l/D and 1e7 at
2 l/D and beyond. This will allow it to directly detect and spatially resolve
low surface brightness circumstellar debris disks as well as image giant
planets as close as in the habitable zones of their host stars. In addition to
doing fundamental science on debris disks, EXCEDE will also serve as a
technological and scientific precursor for any future exo-Earth imaging
mission. EXCEDE uses a Starlight Suppression System (SSS) based on the PIAA
coronagraph, enabling aggressive performance.
We report on our continuing progress of developing the SSS for EXCEDE, and in
particular (a) the reconfiguration of our system into a more flight-like
layout, with an upstream deformable mirror and an inverse PIAA system, as well
as a LOWFS, and (b) testing this system in a vacuum chamber, including IWA,
contrast, and stability performance. The results achieved so far are 2.9e-7
contrast between 1.2-2.0 l/D and 9.7e-8 contrast between 2.0-6.0 l/D in
monochromatic light; as well as 1.4e-6 between 2.0-6.0 l/D in a 10% band, all
with a PIAA coronagraph operating at an inner working angle of 1.2 l/D. This
constitutes better contrast than EXCEDE requirements (in those regions) in
monochromatic light, and progress towards requirements in broadband light. Even
though this technology development is primarily targeted towards EXCEDE, it is
also germane to any exoplanet direct imaging space-based telescopes because of
the many challenges common to different coronagraph architectures and mission
requirements.Comment: 12 pages, 12 figures, to be published in proceedings of SPIE
Astronomical Telescopes + Instrumentation (2014
Co-phasing the Large Binocular Telescope: status and performance of LBTI/PHASECam
The Large Binocular Telescope Interferometer is a NASA-funded nulling and
imaging instrument designed to coherently combine the two 8.4-m primary mirrors
of the LBT for high-sensitivity, high-contrast, and high-resolution infrared
imaging (1.5-13 um). PHASECam is LBTI's near-infrared camera used to measure
tip-tilt and phase variations between the two AO-corrected apertures and
provide high-angular resolution observations. We report on the status of the
system and describe its on-sky performance measured during the first semester
of 2014. With a spatial resolution equivalent to that of a 22.8-meter telescope
and the light-gathering power of single 11.8-meter mirror, the co-phased LBT
can be considered to be a forerunner of the next-generation extremely large
telescopes (ELT).Comment: 8 pages, 5 figures, SPIE Conference proceeding
Bifurcations of periodic and chaotic attractors in pinball billiards with focusing boundaries
We study the dynamics of billiard models with a modified collision rule: the
outgoing angle from a collision is a uniform contraction, by a factor lambda,
of the incident angle. These pinball billiards interpolate between a
one-dimensional map when lambda=0 and the classical Hamiltonian case of elastic
collisions when lambda=1. For all lambda<1, the dynamics is dissipative, and
thus gives rise to attractors, which may be periodic or chaotic. Motivated by
recent rigorous results of Markarian, Pujals and Sambarino, we numerically
investigate and characterise the bifurcations of the resulting attractors as
the contraction parameter is varied. Some billiards exhibit only periodic
attractors, some only chaotic attractors, and others have coexistence of the
two types.Comment: 30 pages, 17 figures. v2: Minor changes after referee comments.
Version with some higher-quality figures available at
http://sistemas.fciencias.unam.mx/~dsanders/publications.htm
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