91 research outputs found
Shaped pupil design for the Gemini Planet Imager
The Gemini Planet Imager (GPI) is an instrument designed for the Gemini South
telescope to image young Jupiter-mass planets in the infrared. To achieve the
high contrast needed for this, it employs an apodized pupil Lyot coronagraph
(APLC) to remove most of the starlight. Current designs use a
partially-transmitting apodizer in the pupil; we examine the use of binary
apodizations in the form of starshaped shaped pupils, and present a design that
could achieve comparable performance, along with a series of design guidelines
for creating shaped pupil versions of APLCs in other systems.Comment: 20 pages, 7 figures, accepted for publication in Ap
Fast computation of Lyot-style coronagraph propagation
We present a new method for numerical propagation through Lyot-style
coronagraphs using finite occulting masks. Standard methods for coronagraphic
simulations involve Fast Fourier Transforms (FFT) of very large arrays, and
computing power is an issue for the design and tolerancing of coronagraphs on
segmented Extremely Large Telescopes (ELT) in order to handle both the speed
and memory requirements. Our method combines a semi-analytical approach with
non-FFT based Fourier transform algorithms. It enables both fast and
memory-efficient computations without introducing any additional
approximations. Typical speed improvements based on computation costs are of
about ten to fifty for propagations from pupil to Lyot plane, with thirty to
sixty times less memory needed. Our method makes it possible to perform
numerical coronagraphic studies even in the case of ELTs using a contemporary
commercial laptop computer, or any standard commercial workstation computer.Comment: 17 pages, 9 figures, accepted for publication in Optics Expres
The Solar-System-Scale Disk Around AB Aurigae
The young star AB Aurigae is surrounded by a complex combination of gas-rich
and dust dominated structures. The inner disk which has not been studied
previously at sufficient resolution and imaging dynamic range seems to contain
very little gas inside a radius of least 130 astronomical units (AU) from the
star. Using adaptive-optics coronagraphy and polarimetry we have imaged the
dust in an annulus between 43 and 302 AU from the star, a region never seen
before. An azimuthal gap in an annulus of dust at a radius of 102 AU, along
with a clearing at closer radii inside this annulus, suggests the formation of
at least one small body at an orbital distance of about 100 AU. This structure
seems consistent with crude models of mean motion resonances, or accumulation
of material at two of the Lagrange points relative to the putative object and
the star. We also report a low significance detection of a point source in this
outer annulus of dust. This source may be an overdensity in the disk due to
dust accreting onto an unseen companion. An alternate interpretation suggests
that the object's mass is between 5 and 37 times the mass of Jupiter. The
results have implications for circumstellar disk dynamics and planet formation.Comment: 11 pages, 5 figures, accepted for publication in Astrophysical
Journal, V. 680, June 10, 200
Speckle noise and dynamic range in coronagraphic images
This paper is concerned with the theoretical properties of high contrast
coronagraphic images in the context of exoplanet searches. We derive and
analyze the statistical properties of the residual starlight in coronagraphic
images, and describe the effect of a coronagraph on the speckle and photon
noise. Current observations with coronagraphic instruments have shown that the
main limitations to high contrast imaging are due to residual quasi-static
speckles. We tackle this problem in this paper, and propose a generalization of
our statistical model to include the description of static, quasi-static and
fast residual atmospheric speckles. The results provide insight into the
effects on the dynamic range of wavefront control, coronagraphy, active speckle
reduction, and differential speckle calibration. The study is focused on
ground-based imaging with extreme adaptive optics, but the approach is general
enough to be applicable to space, with different parameters.Comment: 31 pages, 18 figure
Constraining mass ratio and extinction in the FU Orionis binary system with infrared integral field spectroscopy
We report low resolution near infrared spectroscopic observations of the
eruptive star FU Orionis using the Integral Field Spectrograph Project 1640
installed at the Palomar Hale telescope. This work focuses on elucidating the
nature of the faint source, located 0.5" south of FU Ori, and identified in
2003 as FU Ori S. We first use our observations in conjunction with published
data to demonstrate that the two stars are indeed physically associated and
form a true binary pair. We then proceed to extract J and H band
spectro-photometry using the damped LOCI algorithm, a reduction method tailored
for high contrast science with IFS. This is the first communication reporting
the high accuracy of this technique, pioneered by the Project 1640 team, on a
faint astronomical source. We use our low resolution near infrared spectrum in
conjunction with 10.2 micron interferometric data to constrain the infrared
excess of FU Ori S. We then focus on estimating the bulk physical properties of
FU Ori S. Our models lead to estimates of an object heavily reddened, A_V
=8-12, with an effective temperature of ~ 4000-6500 K . Finally we put these
results in the context of the FU Ori N-S system and argue that our analysis
provides evidence that FU Ori S might be the more massive component of this
binary syste
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