149 research outputs found
SCExAO, an instrument with a dual purpose: perform cutting-edge science and develop new technologies
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is an extremely modular high- contrast instrument installed on the Subaru telescope in Hawaii. SCExAO has a dual purpose. Its position in the northern hemisphere on a 8-meter telescope makes it a prime instrument for the detection and characterization of exoplanets and stellar environments over a large portion of the sky. In addition, SCExAOâs unique design makes it the ideal instrument to test innovative technologies and algorithms quickly in a laboratory setup and subsequently deploy them on-sky. SCExAO benefits from a first stage of wavefront correction with the facility adaptive optics AO188, and splits the 600-2400 nm spectrum towards a variety of modules, in visible and near infrared, optimized for a large range of science cases. The integral field spectrograph CHARIS, with its J, H or K-band high-resolution mode or its broadband low-resolution mode, makes SCExAO a prime instrument for exoplanet detection and characterization. Here we report on the recent developments and scientific results of the SCExAO instrument. Recent upgrades were performed on a number of modules, like the visible polarimetric module VAMPIRES, the high-performance infrared coronagraphs, various wavefront control algorithms, as well as the real-time controller of AO188. The newest addition is the 20k-pixel Microwave Kinetic Inductance Detector (MKIDS) Exoplanet Camera (MEC) that will allow for previously unexplored science and technology developments. MEC, coupled with novel photon-counting speckle control, brings SCExAO closer to the final design of future high-contrast instruments optimized for Giant Segmented Mirror Telescopes (GSMTs)
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
Diffraction-limited polarimetric imaging of protoplanetary disks and mass-loss shells with VAMPIRES
Both the birth and death of a stellar system are areas of key scientific importance. Whether it's understanding the process of planetary formation in a star's early years, or uncovering the cause of the enormous mass-loss that takes place during a star's dying moments, a key to scientific understanding lies in the inner few AU of the circumstellar environment. Corresponding to scales of 10s of milli-arcseconds, these observations pose a huge technical challenge due to the high angular-resolutions and contrasts required. A major stumbling block is the problem of the Earth's own atmospheric turbulence. The other difficulty is that precise calibration is required to combat the extremely high contrast ratios and high resolutions faced. By taking advantage of the fact that starlight scattered by dust in the circumstellar region is polarized, differential polarimetry can help achieve this calibration. Spectral features can also be utilized
The Subaru Coronagraphic Extreme AO project
High contrast coronagraphic imaging is a challenging task for telescopes with
central obscurations and thick spider vanes, such as the Subaru Telescope. Our
group is currently assembling an extreme AO bench designed as an upgrade for
the newly commissionned coronagraphic imager instrument HiCIAO, that addresses
these difficulties. The so-called SCExAO system combines a high performance
PIAA coronagraph to a MEMS-based wavefront control system that will be used in
complement of the Subaru AO188 system. We present and demonstrate good
performance of two key optical components that suppress the spider vanes, the
central obscuration and apodize the beam for high contrast coronagraphy, while
preserving the throughput and the angular resolution.Comment: 4 pages, 2nd Subaru International Conference on Exoplanets and Disks:
Their Formation and Diversity, Keauhou - Hawaii, 9-12 March 200
On-sky demonstration of low-order wavefront sensing and control with focal plane phase mask coronagraphs
The ability to characterize exoplanets by spectroscopy of their atmospheres
requires direct imaging techniques to isolate planet signal from the bright
stellar glare. One of the limitations with the direct detection of exoplanets,
either with ground- or space-based coronagraphs, is pointing errors and other
low-order wavefront aberrations. The coronagraphic detection sensitivity at the
diffraction limit therefore depends on how well low-order aberrations upstream
of the focal plane mask are corrected. To prevent starlight leakage at the
inner working angle of a phase mask coronagraph, we have introduced a
Lyot-based low-order wavefront sensor (LLOWFS), which senses aberrations using
the rejected starlight diffracted at the Lyot plane. In this paper, we present
the implementation, testing and results of LLOWFS on the Subaru Coronagraphic
Extreme Adaptive Optics system (SCExAO) at the Subaru Telescope.
We have controlled thirty-five Zernike modes of a H-band vector vortex
coronagraph in the laboratory and ten Zernike modes on sky with an integrator
control law. We demonstrated a closed-loop pointing residual of 0.02 mas in the
laboratory and 0.15 mas on sky for data sampled using the minimal 2-second
exposure time of the science camera. We have also integrated the LLOWFS in the
visible high-order control loop of SCExAO, which in closed-loop operation has
validated the correction of the non-common path pointing errors between the
infrared science channel and the visible wavefront sensing channel with
pointing residual of 0.23 mas on sky.Comment: 12 pages, 15 figures, Accepted and scheduled for publication in
September 2015 issue of the PAS
Phase-induced amplitude apodization complex mask coronagraph tolerancing and analysis
Phase-Induced Amplitude Apodization Complex Mask Coronagraphs (PIAACMC) offer
high-contrast performance at a small inner-working angle ( 1
/D) with high planet throughput ( 70%). The complex mask is a
multi-zone, phase-shifting mask comprised of tiled hexagons which vary in
depth. Complex masks can be difficult to fabricate as there are many
micron-scale hexagonal zones ( 500 on average) with continuous depths
ranging over a few microns. Ensuring the broadband PIAACMC design performance
carries through to fabricated devices requires that these complex masks are
manufactured to within well-defined tolerances. We report on a simulated
tolerance analysis of a "toy" PIAACMC design which characterizes the effect of
common microfabrication errors on on-axis contrast performance using a simple
Monte Carlo method. Moreover, the tolerance analysis provides crucial
information for choosing a fabrication process which yields working devices
while potentially reducing process complexity. The common fabrication errors
investigated are zone depth discretization, zone depth errors, and edge
artifacts between zones.Comment: 8 pages, 6 figures, SPIE Astronomical Telescopes + Instrumentatio
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