162 research outputs found
W. M. Keck Observatory's next-generation adaptive optics facility
We report on the preliminary design of W.M. Keck Observatory's (WMKO's) next-generation adaptive optics (NGAO) facility. This facility is designed to address key science questions including understanding the formation and evolution of today's galaxies, measuring dark matter in our galaxy and beyond, testing the theory of general relativity in the Galactic Center, understanding the formation of planetary systems around nearby stars, and exploring the origins of our own solar system. The requirements derived from these science questions have resulted in NGAO being designed to have near diffraction-limited performance in the near-IR (K-Strehl ~ 80%) over narrow fields (< 30" diameter) with modest correction down to ~ 700 nm, high sky coverage, improved sensitivity and contrast and improved photometric and astrometric accuracy. The resultant key design features include multi-laser tomography to measure the wavefront and correct for the cone effect, open loop AO-corrected near-IR tip-tilt sensors with MEMS deformable mirrors (DMs) for high sky coverage, a high order MEMS DM for the correction of atmospheric and telescope static errors to support high Strehls and high contrast companion sensitivity, point spread function (PSF) calibration to benefit quantitative astronomy, a cooled science path to reduce thermal background, and a high-efficiency science instrument providing imaging and integral field spectroscopy
The science case for the Next Generation AO system at W. M. Keck Observatory
The W. M. Keck Observatory is designing a new adaptive optics system providing precision AO correction in the near infrared, good correction at visible wavelengths, and multiplexed spatially resolved spectroscopy. We discuss science cases for this Next Generation AO (NGAO), and show how the system requirements were derived from these science cases. Key science drivers include asteroid companions, planets around low-mass stars, general relativistic effects around the Galactic Center black hole, nearby active galactic nuclei, and high-redshift galaxies (including galaxies lensed by intervening galaxies or clusters). The multi-object AO-corrected integral field spectrograph will be optimized for high-redshift galaxy science
Exploring the Structure of Distant Galaxies with Adaptive Optics on the Keck-II Telescope
We report on the first observation of cosmologically distant field galaxies
with an high order Adaptive Optics (AO) system on an 8-10 meter class
telescope. Two galaxies were observed at 1.6 microns at an angular resolution
as high as 50 milliarcsec using the AO system on the Keck-II telescope. Radial
profiles of both objects are consistent with those of local spiral galaxies and
are decomposed into a classic exponential disk and a central bulge. A
star-forming cluster or companion galaxy as well as a compact core are detected
in one of the galaxies at a redshift of 0.37+/-0.05. We discuss possible
explanations for the core including a small bulge, a nuclear starburst, or an
active nucleus. The same galaxy shows a peak disk surface brightness that is
brighter than local disks of comparable size. These observations demonstrate
the power of AO to reveal details of the morphology of distant faint galaxies
and to explore galaxy evolution.Comment: 5 pages, Latex, 3 figures. Accepted for publication in P.A.S.
Dynamical Masses of Young Stars in Multiple Systems
We present recent measurements of the orbital motion in the young binaries DF
Tau and ZZ Tau, and the hierarchical triple Elias 12, that were obtained with
the Fine Guidance Sensors on the HST and at the Keck Observatory using adaptive
optics. Combining these observations with previous measurements from the
literature, we compute preliminary orbital parameters for DF Tau and ZZ Tau. We
find that the orbital elements cannot yet be determined precisely because the
orbital coverage spans only about 90 degr in position angle. Nonetheless, the
range of possible values for the period and semi-major axis already defines a
useful estimate for the total mass in DF Tau and ZZ Tau, with values of
0.90{+0.85}{-0.35} M_sun and 0.81{+0.44}{-0.25} M_sun, respectively, at a
fiducial distance of 140 pc.Comment: 26 pages, 9 figures, accepted for publication in A
Science with the Keck Interferometer ASTRA Program
The ASTrometric and phase-Referenced Astronomy (ASTRA) project will provide
phase referencing and astrometric observations at the Keck Interferometer,
leading to enhanced sensitivity and the ability to monitor orbits at an
accuracy level of 30-100 microarcseconds. Here we discuss recent scientific
results from ASTRA, and describe new scientific programs that will begin in
2010-2011. We begin with results from the "self phase referencing" (SPR) mode
of ASTRA, which uses continuum light to correct atmospheric phase variations
and produce a phase-stabilized channel for spectroscopy. We have observed a
number of protoplanetary disks using SPR and a grism providing a spectral
dispersion of ~2000. In our data we spatially resolve emission from dust as
well as gas. Hydrogen line emission is spectrally resolved, allowing
differential phase measurements across the emission line that constrain the
relative centroids of different velocity components at the 10 microarcsecond
level. In the upcoming year, we will begin dual-field phase referencing (DFPR)
measurements of the Galactic Center and a number of exoplanet systems. These
observations will, in part, serve as precursors to astrometric monitoring of
stellar orbits in the Galactic Center and stellar wobbles of exoplanet host
stars. We describe the design of several scientific investigations capitalizing
on the upcoming phase-referencing and astrometric capabilities of ASTRA.Comment: Published in the proceedings of the SPIE 2010 conference on "Optical
and Infrared Interferometry II
The Discovery of a Companion to the Very Cool Dwarf Gl~569~B with the Keck Adaptive Optics Facility
We report observations obtained with the Keck adaptive optics facility of the
nearby (d=9.8 pc) binary Gl~569. The system was known to be composed of a cool
primary (dM2) and a very cool secondary (dM8.5) with a separation of 5" (49
Astronomical Units). We have found that Gl~569~B is itself double with a
separation of only 0".1010".002 (1 Astronomical Unit). This detection
demonstrates the superb spatial resolution that can be achieved with adaptive
optics at Keck. The difference in brightness between Gl~569~B and the companion
is 0.5 magnitudes in the J, H and K' bands. Thus, both objects have
similarly red colors and very likely constitute a very low-mass binary system.
For reasonable assumptions about the age (0.12~Gyr--1.0~Gyr) and total mass of
the system (0.09~M--0.15~M), we estimate that the orbital
period is 3 years. Follow-up observations will allow us to obtain an
astrometric orbit solution and will yield direct dynamical masses that can
constrain evolutionary models of very low-mass stars and brown dwarfs
Keck Observatory Laser Guide Star Adaptive Optics Discovery and Characterization of a Satellite to the Large Kuiper Belt Object 2003 EL_(61)
The newly commissioned laser guide star adaptive optics system at Keck Observatory has been used to discover and characterize the orbit of a satellite to the bright Kuiper Belt object 2003 EL_(61). Observations over a 6 month period show that the satellite has a semimajor axis of 49,500 ± 400 km, an orbital period of 49.12 ± 0.03 days, and an eccentricity of 0.050 ± 0.003. The inferred mass of the system is (4.2 ± 0.1) × 10^(21) kg, or ~32% of the mass of Pluto and 28.6% ± 0.7% of the mass of the Pluto-Charon system. Mutual occultations occurred in 1999 and will not occur again until 2138. The orbit is fully consistent neither with one tidally evolved from an earlier closer configuration nor with one evolved inward by dynamical friction from an earlier more distant configuration
W. M. Keck Observatory's next-generation adaptive optics facility
We report on the preliminary design of W.M. Keck Observatory's (WMKO's) next-generation adaptive optics (NGAO) facility. This facility is designed to address key science questions including understanding the formation and evolution of today's galaxies, measuring dark matter in our galaxy and beyond, testing the theory of general relativity in the Galactic Center, understanding the formation of planetary systems around nearby stars, and exploring the origins of our own solar system. The requirements derived from these science questions have resulted in NGAO being designed to have near diffraction-limited performance in the near-IR (K-Strehl ~ 80%) over narrow fields (< 30" diameter) with modest correction down to ~ 700 nm, high sky coverage, improved sensitivity and contrast and improved photometric and astrometric accuracy. The resultant key design features include multi-laser tomography to measure the wavefront and correct for the cone effect, open loop AO-corrected near-IR tip-tilt sensors with MEMS deformable mirrors (DMs) for high sky coverage, a high order MEMS DM for the correction of atmospheric and telescope static errors to support high Strehls and high contrast companion sensitivity, point spread function (PSF) calibration to benefit quantitative astronomy, a cooled science path to reduce thermal background, and a high-efficiency science instrument providing imaging and integral field spectroscopy
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