201 research outputs found
High-contrast imaging in the Hyades with snapshot LOCI
To image faint substellar companions obscured by the stellar halo and
speckles, scattered light from the bright primary star must be removed in
hardware or software. We apply the "locally-optimized combination of images"
(LOCI) algorithm to 1-minute Keck Observatory snapshots of GKM dwarfs in the
Hyades using source diversity to determine the most likely PSF. We obtain a
mean contrast of 10^{-2} at 0.01", 10^{-4} at <1", and 10^{-5} at 5". New brown
dwarf and low-mass stellar companions to Hyades primaries are found in a third
of the 84 targeted systems. This campaign shows the efficacy of LOCI on
snapshot imaging as well as on bright wide binaries with off-axis LOCI,
reaching contrasts sufficient for imaging 625-Myr late-L/early-T dwarfs purely
in post-processing.Comment: 12 pages, 12 figures, to appear in SPIE Astronomy 2012, paper
8447-16
Exoplanet Detection Techniques
We are still in the early days of exoplanet discovery. Astronomers are
beginning to model the atmospheres and interiors of exoplanets and have
developed a deeper understanding of processes of planet formation and
evolution. However, we have yet to map out the full complexity of multi-planet
architectures or to detect Earth analogues around nearby stars. Reaching these
ambitious goals will require further improvements in instrumentation and new
analysis tools. In this chapter, we provide an overview of five observational
techniques that are currently employed in the detection of exoplanets: optical
and IR Doppler measurements, transit photometry, direct imaging, microlensing,
and astrometry. We provide a basic description of how each of these techniques
works and discuss forefront developments that will result in new discoveries.
We also highlight the observational limitations and synergies of each method
and their connections to future space missions.Comment: 24 pages, 19 figures, PPVI proceedings. Appears as 2014, Protostars
and Planets VI, Henrik Beuther, Ralf S. Klessen, Cornelis P. Dullemond, and
Thomas Henning (eds.), University of Arizona Press, Tucson, 914 pp.,
p.715-73
Astrometric Gravitational-Wave Detection via Stellar Interferometry
We evaluate the potential for gravitational-wave (GW) detection in the
frequency band from 10 nHz to 1 Hz using extremely high-precision
astrometry of a small number of stars. In particular, we argue that
non-magnetic, photometrically stable hot white dwarfs (WD) located at
kpc distances may be optimal targets for this approach. Previous studies of
astrometric GW detection have focused on the potential for less precise surveys
of large numbers of stars; our work provides an alternative optimization
approach to this problem. Interesting GW sources in this band are expected at
characteristic strains around . The astrometric angular precision
required to see these sources is after integrating for
a time . We show that jitter in the photometric center
of WD of this type due to starspots is bounded to be small enough to permit
this high-precision, small- approach. We discuss possible noise arising from
stellar reflex motion induced by orbiting objects and show how it can be
mitigated. The only plausible technology able to achieve the requisite
astrometric precision is a space-based stellar interferometer. Such a future
mission with few-meter-scale collecting dishes and baselines of
is sufficient to achieve the target precision.
This collector size is broadly in line with the collectors proposed for some
formation-flown, space-based astrometer or optical synthetic-aperature
imaging-array concepts proposed for other science reasons. The proposed
baseline is however somewhat larger than the km-scale baselines discussed for
those concepts, but we see no fundamental technical obstacle to utilizing such
baselines. A mission of this type thus also holds the promise of being one of
the few ways to access interesting GW sources in this band.Comment: 19 page
Detection of Carbon Monoxide and Water Absorption Lines in an Exoplanet Atmosphere
Determining the atmospheric structure and chemical composition of an
exoplanet remains a formidable goal. Fortunately, advancements in the study of
exoplanets and their atmospheres have come in the form of direct imaging -
spatially resolving the planet from its parent star - which enables
high-resolution spectroscopy of self-luminous planets in Jovian-like orbits.
Here, we present a spectrum with numerous, well-resolved, molecular lines from
both water and carbon monoxide from a massive planet orbiting less than 40 AU
from the star HR 8799. These data reveal the planet's chemical composition,
atmospheric structure, and surface gravity, confirming that it is indeed a
young planet. The spectral lines suggest an atmospheric carbon-to-oxygn ratio
greater than the host star's, providing hints about the planet's formation.Comment: Accepted for publication in Science. Published online on March 14,
2013. 24 pages (main text and supplementary materials), 8 figures.
Attachments to the supplementary material are available on Science websit
Science yield estimate with the Wide-Field Infrared Survey Telescope coronagraph
The coronagraph instrument (CGI) on the Wide-Field Infrared Survey Telescope will directly image and spectrally characterize planets and circumstellar disks around nearby stars. Here we estimate the expected science yield of the CGI for known radial-velocity (RV) planets and potential circumstellar disks. The science return is estimated for three types of coronagraphs: the hybrid Lyot and shaped pupil are the currently planned designs, and the phase-induced amplitude apodizing complex mask coronagraph is the backup design. We compare the potential performance of each type for imaging as well as spectroscopy. We find that the RV targets can be imaged in sufficient numbers to produce substantial advances in the science of nearby exoplanets. To illustrate the potential for circumstellar disk detections, we estimate the brightness of zodiacal-type disks, which could be detected simultaneously during RV planet observations
MEMS practice, from the lab to the telescope
Micro-electro-mechanical systems (MEMS) technology can provide for deformable
mirrors (DMs) with excellent performance within a favorable economy of scale.
Large MEMS-based astronomical adaptive optics (AO) systems such as the Gemini
Planet Imager are coming on-line soon. As MEMS DM end-users, we discuss our
decade of practice with the micromirrors, from inspecting and characterizing
devices to evaluating their performance in the lab. We also show MEMS wavefront
correction on-sky with the "Villages" AO system on a 1-m telescope, including
open-loop control and visible-light imaging. Our work demonstrates the maturity
of MEMS technology for astronomical adaptive optics.Comment: 14 pages, 15 figures, Invited Paper, SPIE Photonics West 201
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