893 research outputs found
Adaptive Optics Observations of Exoplanets, Brown Dwarfs, & Binary Stars
The current direct observations of brown dwarfs and exoplanets have been
obtained using instruments not specifically designed for overcoming the large
contrast ratio between the host star and any wide-separation faint companions.
However, we are about to witness the birth of several new dedicated observing
platforms specifically geared towards high contrast imaging of these objects.
The Gemini Planet Imager, VLT-SPHERE, Subaru HiCIAO, and Project 1640 at the
Palomar 5m telescope will return images of numerous exoplanets and brown dwarfs
over hundreds of observing nights in the next five years. Along with
diffraction-limited coronagraphs and high-order adaptive optics, these
instruments also will return spectral and polarimetric information on any
discovered targets, giving clues to their atmospheric compositions and
characteristics. Such spectral characterization will be key to forming a
detailed theory of comparative exoplanetary science which will be widely
applicable to both exoplanets and brown dwarfs. Further, the prevalence of
aperture masking interferometry in the field of high contrast imaging is also
allowing observers to sense massive, young planets at solar system scales
(~3-30 AU)---separations out of reach to conventional direct imaging
techniques. Such observations can provide snapshots at the earliest phases of
planet formation---information essential for constraining formation mechanisms
as well as evolutionary models of planetary mass companions. As a demonstration
of the power of this technique, I briefly review recent aperture masking
observations of the HR 8799 system. Moreover, all of the aforementioned
techniques are already extremely adept at detecting low-mass stellar companions
to their target stars, and I present some recent highlights.Comment: Invited Review for IAU Symposium 28
Characterization of microdot apodizers for imaging exoplanets with next-generation space telescopes
A major science goal of future, large-aperture, optical space telescopes is
to directly image and spectroscopically analyze reflected light from
potentially habitable exoplanets. To accomplish this, the optical system must
suppress diffracted light from the star to reveal point sources approximately
ten orders of magnitude fainter than the host star at small angular separation.
Coronagraphs with microdot apodizers achieve the theoretical performance needed
to image Earth-like planets with a range of possible telescope designs,
including those with obscured and segmented pupils. A test microdot apodizer
with various bulk patterns (step functions, gradients, and sinusoids) and 4
different dot sizes (3, 5, 7, and 10 m) made of small chrome squares on
anti-reflective glass was characterized with microscopy, optical laser
interferometry, as well as transmission and reflectance measurements at
wavelengths of 600 and 800 nm. Microscopy revealed the microdots were
fabricated to high precision. Results from laser interferometry showed that the
phase shifts observed in reflection vary with the local microdot fill factor.
Transmission measurements showed that microdot fill factor and transmission
were linearly related for dot sizes >5 m. However, anomalously high
transmittance was measured when the dot size is <5x the wavelength and the fill
factor is approximately 50%, where the microdot pattern becomes periodic. The
transmission excess is not as prominent in the case of larger dot sizes
suggesting that it is likely to be caused by the interaction between the
incident field and electronic resonances in the surface of the metallic
microdots. We used our empirical models of the microdot apodizers to optimize a
second generation of reflective apodizer designs and confirmed that the
amplitude and phase of the reflected beam closely matches the ideal wavefront.Comment: Space Telescopes and Instrumentation 2018: Optical, Infrared, and
Millimeter Wav
Pupil stabilization for SPHERE's extreme AO and high performance coronagraph system
We propose a new concept of pupil motion sensor for astronomical adaptive
optics systems and present experimental results obtained during the first
laboratory validation of this concept. Pupil motion is an important issue in
the case of extreme adaptive optics, high contrast systems, such as the
proposed Planet Finder instruments for the ESO and Gemini 8-meter telescopes.
Such high contrast imaging instruments will definitively require pupil
stabilization to minimize the effect of quasi-static aberrations. The concept
for pupil stabilization we propose uses the flux information from the AO system
wave-front sensor to drive in closed loop a pupil tip-tilt mirror located in a
focal plane. A laboratory experiment validates this concept and demonstrates
its interest for high contrast imaging instrument.Comment: This paper was published in Optics Express and is made available as
an electronic reprint with the permission of OSA. The paper can be found at
http://www.opticsexpress.org/abstract.cfm?id=144687 on the OSA websit
Simultaneous exoplanet detection and instrument aberration retrieval in multispectral coronagraphic imaging
High-contrast imaging for the detection and characterization of exoplanets
relies on the instrument's capability to block out the light of the host star.
Some current post-processing methods for calibrating out the residual speckles
use information redundancy offered by multispectral imaging but do not use any
prior information on the origin of these speckles. We investigate whether
additional information on the system and image formation process can be used to
more finely exploit the multispectral information. We developed an inversion
method in a Bayesian framework that is based on an analytical imaging model to
estimate both the speckles and the object map. The model links the instrumental
aberrations to the speckle pattern in the image focal plane, distinguishing
between aberrations upstream and downstream of the coronagraph. We propose and
validate several numerical techniques to handle the difficult minimization
problems of phase retrieval and achieve a contrast of 10^6 at 0.2 arcsec from
simulated images, in the presence of photon noise. This opens up the the
possibility of tests on real data where the ultimate performance may override
the current techniques if the instrument has good and stable coronagraphic
imaging quality. This paves the way for new astrophysical exploitations or even
new designs for future instruments
First Light with ALES: A 2-5 Micron Adaptive Optics Integral Field Spectrograph for the LBT
Integral field spectrographs are an important technology for exoplanet
imaging, due to their ability to take spectra in a high-contrast environment,
and improve planet detection sensitivity through spectral differential imaging.
ALES is the first integral field spectrograph capable of imaging exoplanets
from 3-5m, and will extend our ability to characterize self-luminous
exoplanets into a wavelength range where they peak in brightness. ALES is
installed inside LBTI/LMIRcam on the Large Binocular Telescope, taking
advantage of existing AO systems, camera optics, and a HAWAII-2RG detector. The
new optics that comprise ALES are a Keplerian magnifier, a silicon lenslet
array with diffraction suppressing pinholes, a direct vision prism, and
calibration optics. All of these components are installed in filter wheels
making ALES a completely modular design. ALES saw first light at the LBT in
June 2015.Comment: 13 pages, 9 figures, Proc. SPI
Low-mass star formation in CG1: a diffraction limited search for pre-main sequence stars next to NX Puppis
Using adaptive optics at the ESO 3.6m telescope, we obtained diffraction
limited JHK-images of the region around the Herbig AeBe star NX Pup. We clearly
resolved the close companion (sep. 0.128") to NX Pup -- originally discovered
by HST -- and measured its JHK magnitudes. A third object at a separation of
7.0" from NX Pup was identified as a classical T Tauri star so that NX Pup may
in fact form a hierarchical triple system. We discuss the evolutionary status
of these stars and derive estimates for their spectral types, luminosities,
masses and ages.Comment: Latex using l-aa-ps.sty with links to 5 postscript figures. Complete
postscript version also available at http://lucky.astro.uni-wuerzburg.de/
Accepted for publication in A&
Frame Combination Techniques for Ultra High-Contrast Imaging
We summarize here an experimental frame combination pipeline we developed for
ultra high-contrast imaging with systems like the upcoming VLT SPHERE
instrument. The pipeline combines strategies from the Drizzle technique, the
Spitzer IRACproc package, and homegrown codes, to combine image sets that may
include a rotating field of view and arbitrary shifts between frames. The
pipeline is meant to be robust at dealing with data that may contain non-ideal
effects like sub-pixel pointing errors, missing data points, non-symmetrical
noise sources, arbitrary geometric distortions, and rapidly changing point
spread functions. We summarize in this document individual steps and
strategies, as well as results from preliminary tests and simulations.Comment: 9 pages, 4 figures, SPIE conference pape
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