Adaptive Optics Research Papers - Academia.edu (original) (raw)
Direct imaging of exoplanetary systems is a powerful technique that can reveal Jupiter-like planets in wide orbits, can enable detailed characterization of planetary atmospheres, and is a key step toward imaging Earth-like planets.... more
Direct imaging of exoplanetary systems is a powerful technique that can reveal Jupiter-like planets in wide orbits, can enable detailed characterization of planetary atmospheres, and is a key step toward imaging Earth-like planets. Imaging detections are challenging because of the ...
Angular differential imaging is a high-contrast imaging technique that reduces quasistatic speckle noise and facilitates the detection of nearby companions. A sequence of images is acquired with an altitude/azimuth telescope while the... more
Angular differential imaging is a high-contrast imaging technique that reduces quasistatic speckle noise and facilitates the detection of nearby companions. A sequence of images is acquired with an altitude/azimuth telescope while the instrument field derotator is switched off. This keeps the instrument and telescope optics aligned and allows the field of view to rotate with respect to the instrument. For
OCT is a non-invasive technique for three-dimensional imaging at high axial resolution. Due to aberrations in the eye, OCT systems for retinal imaging have a limited lateral resolution. The lateral resolution can be increased by using... more
OCT is a non-invasive technique for three-dimensional imaging at high axial resolution. Due to aberrations in the eye, OCT systems for retinal imaging have a limited lateral resolution. The lateral resolution can be increased by using adaptive optics (AO) to correct for static and dynamic wavefront aberrations. The combination of these two technologies results in high quality AO-OCT images to image photoreceptors, capillaries and nerve fiber bundles, which can help retinal specialists to better understand and diagnose retinal diseases. Here we review the basic principles of AO-OCT and discuss future opportunities for the technology.
The Keck Observatory began science observations with a laser guide star adaptive optics system, the first such system on an 8-10 m class telescope, in late 2004. This new capability greatly extends the scientific potential of the Keck II... more
The Keck Observatory began science observations with a laser guide star adaptive optics system, the first such system on an 8-10 m class telescope, in late 2004. This new capability greatly extends the scientific potential of the Keck II Telescope, allowing near-diffraction-limited observations in the near-infrared using natural guide stars as faint as 19th magnitude. This paper describes the conceptual approach and technical implementation followed for this system, including lessons learned, and provides an overview of the early science capabilities.
We present the results of a spectroscopic survey of the kinematic structure of star-forming galaxies at redshift z ~ 2 - 3 using Keck/OSIRIS integral field spectroscopy. Our sample is comprised of 12 galaxies between redshifts z ~ 2.0 and... more
We present the results of a spectroscopic survey of the kinematic structure of star-forming galaxies at redshift z ~ 2 - 3 using Keck/OSIRIS integral field spectroscopy. Our sample is comprised of 12 galaxies between redshifts z ~ 2.0 and 2.5 and one galaxy at z ~ 3.3 which are well detected in either HAlpha or [O III] emission. These observations were obtained in conjunction with the Keck laser guide star adaptive optics system, with a typical angular resolution after spatial smoothing ~ 0.15" (approximately 1 kpc at the redshift of the target sample). At most five of these 13 galaxies have spatially resolved velocity gradients consistent with rotation while the remaining galaxies have relatively featureless or irregular velocity fields. All of our galaxies show local velocity dispersions ~ 60 - 100 km/s, suggesting that (particularly for those galaxies with featureless velocity fields) rotation about a preferred axis may not be the dominant mechanism of physical support. While some galaxies show evidence for major mergers such evidence is unrelated to the kinematics of individual components (one of our strongest merger candidates also exhibits unambiguous rotational structure), refuting a simple bimodal disk/merger classification scheme. We discuss these data in light of complementary surveys and extant UV-IR spectroscopy and photometry, concluding that the dynamical importance of cold gas may be the primary factor governing the observed kinematics of z ~ 2 galaxies. We conclude by speculating on the importance of mechanisms for accreting low angular-momentum gas and the early formation of quasi-spheroidal systems in the young universe.(abridged)
The remarkable progress made in infrared (IR) astronomical instruments over the last 10–15 years has radically changed our vision of the extragalactic IR sky, and overall understanding of galaxy evolution. In particular, this has been the... more
The remarkable progress made in infrared (IR) astronomical instruments over the last 10–15 years has radically changed our vision of the extragalactic IR sky, and overall understanding of galaxy evolution. In particular, this has been the case for the study of active galactic nuclei (AGN), for which IR observations provide a wealth of complementary information that cannot be derived from data in other wavelength regimes. In this review, I summarize the unique contribution that IR astronomy has recently made to our understanding of AGN and their role in galaxy evolution, including both physical studies of AGN at IR wavelengths, and the search for AGN among IR galaxies in general. Finally, I identify and discuss key open issues that should be possible to address with forthcoming IR telescopes.
CRIRES is a cryogenic, pre-dispersed, infrared echelle spectrograph designed to provide a resolving power lambda/(Delta lambda) of 105 between 1 and 5mu m at the Nasmyth focus B of the 8m VLT unit telescope #1 (Antu). A curvature sensing... more
CRIRES is a cryogenic, pre-dispersed, infrared echelle spectrograph designed to provide a resolving power lambda/(Delta lambda) of 105 between 1 and 5mu m at the Nasmyth focus B of the 8m VLT unit telescope #1 (Antu). A curvature sensing adaptive optics system feed is used to minimize slit losses and to provide diffraction limited spatial resolution along the slit. A mosaic of 4 Aladdin~III InSb-arrays packaged on custom-fabricated ceramics boards has been developed. This provides for an effective 4096x512 pixel focal plane array, to maximize the free spectral range covered in each exposure. Insertion of gas cells to measure high precision radial velocities is foreseen. For measurement of circular polarization a Fresnel rhomb in combination with a Wollaston prism for magnetic Doppler imaging is foreseen. The implementation of full spectropolarimetry is under study. This is one result of a scientific workshop held at ESO in late 2003 to refine the science-case of CRIRES. Installation at the VLT is scheduled during the first half of 2005. Here we briefly recall the major design features of CRIRES and describe its current development status including a report of laboratory testing.
We report the detection of an extrasolar planet of mass ratio q ~ 2 x 10^(-4) in microlensing event MOA-2007-BLG-192. The best fit microlensing model shows both the microlensing parallax and finite source effects, and these can be... more
We report the detection of an extrasolar planet of mass ratio q ~ 2 x 10^(-4) in microlensing event MOA-2007-BLG-192. The best fit microlensing model shows both the microlensing parallax and finite source effects, and these can be combined to obtain the lens masses of M = 0.060 (+0.028 -0.021) M_sun for the primary and m = 3.3 (+4.9 -1.6) M_earth for the planet. However, the observational coverage of the planetary deviation is sparse and incomplete, and the radius of the source was estimated without the benefit of a source star color measurement. As a result, the 2-sigma limits on the mass ratio and finite source measurements are weak. Nevertheless, the microlensing parallax signal clearly favors a sub-stellar mass planetary host, and the measurement of finite source effects in the light curve supports this conclusion. Adaptive optics images taken with the Very Large Telescope (VLT) NACO instrument are consistent with a lens star that is either a brown dwarf or a star at the bottom of the main sequence. Follow-up VLT and/or Hubble Space Telescope (HST) observations will either confirm that the primary is a brown dwarf or detect the low-mass lens star and enable a precise determination of its mass. In either case, the lens star, MOA-2007-BLG-192L, is the lowest mass primary known to have a companion with a planetary mass ratio, and the planet, MOA-2007-BLG-192Lb, is probably the lowest mass exoplanet found to date, aside from the lowest mass pulsar planet.
We present precise Doppler measurements of five stars obtained during the past decade at Keck Observatory. These stars, namely, HD 34445, HD 126614, HD 24496, HD 13931, and Gl 179, all show evidence for a single planet in Keplerian... more
We present precise Doppler measurements of five stars obtained during the past decade at Keck Observatory. These stars, namely, HD 34445, HD 126614, HD 24496, HD 13931, and Gl 179, all show evidence for a single planet in Keplerian motion. The orbital ...
Analytical theory is combined with extensive numerical simulations to compare different flavours of centroiding algorithms: thresholding, weighted centroid, correlation, quad cell (QC). For each method, optimal parameters are defined in... more
Analytical theory is combined with extensive numerical simulations to compare different flavours of centroiding algorithms: thresholding, weighted centroid, correlation, quad cell (QC). For each method, optimal parameters are defined in function of photon flux, readout noise and turbulence level. We find that at very low flux the noise of QC and weighted centroid leads the best result, but the latter method can provide linear and optimal response if the weight follows spot displacements. Both methods can work with average flux as low as 10 photons per subaperture under a readout noise of three electrons. At high-flux levels, the dominant errors come from non-linearity of response, from spot truncations and distortions and from detector pixel sampling. It is shown that at high flux, centre of gravity approaches and correlation methods are equivalent (and provide better results than QC estimator) as soon as their parameters are optimized. Finally, examples of applications are given to illustrate the results obtained in the paper.
Wave-front distortion compensation using direct system performance metric optimization is studied both theo-retically and experimentally. It is shown how different requirements for wave-front control can be incorpo-rated, and how... more
Wave-front distortion compensation using direct system performance metric optimization is studied both theo-retically and experimentally. It is shown how different requirements for wave-front control can be incorpo-rated, and how information from different wave-front sensor types can be fused, within a generalized gradient descent optimization paradigm. In our experiments a very-large-scale integration (VLSI) system implement-ing a simultaneous perturbation stochastic approximation optimization algorithm was applied for real-time adaptive control of multielement wave-front correctors. The custom-chip controller is used in two adaptive laser beam focusing systems, one with a 127-element liquid-crystal phase modulator and the other with beam steering and 37-control channel micromachined deformable mirrors. The submillisecond response time of the micromachined deformable mirror and the parallel nature of the analog VLSI control architecture provide for high-speed adaptive compensation ...