KEYWORDS: Point spread functions, Adaptive optics, Photometry, General relativity, Sensors, Data modeling, Stars, Optical transfer functions, Atmospheric modeling, Instrument modeling
General relativity can be tested in the strong gravity regime by monitoring stars orbiting the supermassive black hole at the Galactic Center with adaptive optics. However, the limiting source of uncertainty is the spatial PSF variability due to atmospheric anisoplanatism and instrumental aberrations. The Galactic Center Group at UCLA has completed a project developing algorithms to predict PSF variability for Keck AO images. We have created a new software package (AIROPA), based on modified versions of StarFinder and Arroyo, that takes atmospheric turbulence profiles, instrumental aberration maps, and images as inputs and delivers improved photometry and astrometry on crowded fields. This software package will be made publicly available soon.
The sky coverage and performance of laser guide star (LGS) adaptive optics (AO) systems is limited by the natural guide star (NGS) used for low order correction. This limitation can be dramatically reduced by measuring the tip and tilt of the NGS in the near-infrared where the NGS is partially corrected by the LGS AO system and where stars are generally several magnitudes brighter than at visible wavelengths. We present the design of a near-infrared tip-tilt sensor that has recently been integrated with the Keck I telescope’s LGS AO system along with some initial on-sky results. The implementation involved modifications to the AO bench, real-time control system, and higher level controls and operations software that will also be discussed. The tip-tilt sensor is a H2RG-based near-infrared camera with 0.05 arc second pixels. Low noise at high sample rates is achieved by only reading a small region of interest, from 2×2 to 16×16 pixels, centered on an NGS anywhere in the 100 arc second diameter field. The sensor operates at either Ks or H-band using light reflected by a choice of dichroic beamsplitters located in front of the OSIRIS integral field spectrograph.
There is great interest in the adaptive optics (AO) science community to overcome the limitations imposed by incomplete knowledge of the point spread function (PSF). To address this limitation a program has been initiated at the W. M. Keck Observatory (WMKO) to demonstrate PSF determination for observations obtained with Keck AO science instruments. This paper aims to give a broad view of the progress achieved in this area. The concept and the implementation are briefly described. The results from on-sky on-axis NGS AO measurements using the NIRC2 science instrument are presented. On-sky performance of the technique is illustrated by comparing the reconstructed PSFs to NIRC2 PSFs. Accuracy of the reconstructed PSFs in terms of Strehl ratio and FWHM are discussed. Science cases for the first phase of science verification have been identified. More technical details of the program are presented elsewhere in the conference.
With the commencement of shared-risk science observations in May 2012, the Keck I laser guide star (LGS) adaptive
optics (AO) system is the second LGS AO system to be commissioned at the W. M. Keck Observatory. This paper
reports on the Keck I LGS AO system itself and some of the initial performance results. The Keck I system differs from
the Keck II system primarily with regards to the laser and a beam transport system which projects the laser from behind
the telescope’s secondary mirror. The existing OSIRIS science instrument has been integrated with the Keck I system.
Anisoplanatism is a primary source of photometric and astrometric error in single-conjugate adaptive optics. We present initial results of a project to model the off-axis optical transfer function in the adaptive optics system at the Keck II telescope. The model currently accounts for the effects of atmospheric anisoplanatism in natural guide star observations. The model for the atmospheric contribution to the anisoplanatic transfer function uses contemporaneous MASS/ DIMM measurements. Here we present the results of a validation campaign using observations of naturally guided visual binary stars under varying conditions, parameterized by the r0 and θ0 parameters of the C2n atmospheric turbulence profile. We are working to construct a model of the instrumental field-dependent aberrations in the NIRC2 camera using an artificial source in the Nasmyth focal plane. We also discuss our plans to extend the work to laser guide star operation.
We discuss in this paper the last results of our adaptive optics point spread function reconstruction (PSF-R) project at theW. M. Keck Observatory. Objective of the project are recalled, followed by a short reintroduction of the basis of the method. Amongst the novelties, a method for a drastic reduction of the number of the so-called Ui,j functions for any pupil shape and an arbitrary number of actuators is presented, making the current PSF-R technique easily applicable to extremely large telescopes AO systems. Our success at reconstructing the PSF in bright natural guide star (NGS) conditions is revisited in details and confirmed. First results on PSF-R with faint NGS are presented and it is shown that our reconstructed PSF Strehl ratio drops with the NGS magnitude basically like the measured sky performance. These preliminary but encouraging results, in real conditions, can be considered as a validation of our PSF-R approach. Plans for the next steps of the project are discussed at the end of this progress report.
We present the results of a sky source based, phase diversity experiment at the W. M. Keck Observatory to
retrieve the global wavefront static aberration from the telescope primary mirror to the science imager (NIRC2).
The context of this study is a point spread function reconstruct (PSF-R) project for the Keck-II and Gemini-
North adaptive optics systems. We demonstrate that if we select couples of in/out-of-focus PSF with identical
seeing (determined with a deformable mirror based seeing monitor), retrieving the global static wavefront from
AO corrected sky images is indeed possible. A sensitivity analysis shows that the reconstructed wavefront
accuracy is very sensitive to errors in the knowledge of the system's optical parameters, and an accuracy of less
than 1% is required. Recommendations for an accurate sky-based phase diversity static wavefront reconstruction
are given, as well as our plan for the next steps of this project at the W. M. Keck Observatory.
With the much anticipated delivery of the Lockheed Martin Coherent Technology Quasi-CW laser, the W. M. Keck
Observatory was able to complete the installation and integration of the Laser Guide Star Adaptive Optics System on the
Keck I telescope. The Keck I LGSAO system was developed to provide redundancy for the Keck II system as well as
balancing the instrumentation load between the two telescopes and interferometers. With the improved sodium coupling
efficiency of the laser and a center launching system, the Keck I laser performance is expected to exceed those on the
Keck II system.
We present the challenges of integrating the Keck I Laser Guide Star Adaptive Optics System on an operational
telescope. We will present issues and performance data related to the primary subsystem components such as the laser
itself, the Selex Galileo Avionica launch telescope, the Mitsubishi fiber transport, and the Adaptive Optics System. The
paper will also focus on the integration and testing performed at the W. M. Keck headquarters as well as the summit of
Mauna Kea. We will present initial first light performance of the Keck I LGSAO System and compare those to the
existing Keck II LGSAO System.
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.
W. M. Keck Observatory (WMKO) is currently engaged in the design of a powerful new Adaptive Optics (AO) science
capability providing precision correction in the near-IR, good correction in the visible, and faint object multiplexed
integral field spectroscopy. Improved sensitivity will result from significantly higher Strehl ratios over narrow fields (<
30" diameter) and from lower backgrounds. Quantitative astronomy will benefit from improved PSF stability and
knowledge. Strehl ratios of 15 to 25% are expected at wavelengths as short as 750 nm. A multi-object AO approach
will be taken for the correction of multiple science targets over modest fields of regard (< 2' diameter) and to achieve
high sky coverage using AO compensated near-IR tip/tilt sensing. In this paper we present the conceptual design for this
system including discussion of the requirements, system architecture, key design features, performance predictions and
implementation plans.
The W. M. Keck Observatory is currently engaged in the conceptual design of a powerful new adaptive optics (AO)
science capability providing precision AO correction in the near infrared (NIR) and visible and faint object multiplexed
integral field spectroscopy. In this poster, we present the conceptual design of the Science Operations for this Next
Generation Adaptive Optics (NGAO) facility. We summarize the main requirements for science operations resulting
from the science cases and the Observatory requirements. We give an overview of the science operation paradigm and
design that will meet these requirements. We then illustrate the pre-observing, observing and post-observing interfaces
by looking into various observing scenarios. We conclude by briefly outlining the project milestones.
The Next Generation Adaptive Optics (NGAO) system will represent a considerable advancement for high resolution
astronomical imaging and spectroscopy at the W. M. Keck Observatory. The AO system will incorporate multiple laser
guidestar tomography to increase the corrected field of view and remove the cone effect inherent to single laser guide
star systems. The improvement will permit higher Strehl correction in the near-infrared and diffraction-limited correction
down to R band. A high actuator count micro-electromechanical system (MEMS) deformable mirror will provide the
on-axis wavefront correction to a number of instrument stations and additional MEMS devices will feed multiple
channels of a deployable integral-field spectrograph. In this paper we present the status of the AO system design and
describe its various operating modes.
A laser guide star (LGS) adaptive optics (AO) system generally requires additional tip/tilt information derived using a
natural guide star (NGS), while multi-LGS systems will benefit from measurement of additional low-order wavefront
modes using one or more NGS's. If we use AO sharpened NGS's, we can improve both the measurement accuracy and
accessible sky fraction while also minimizing the observational overhead of faint NGS acquisition. Multi-object
adaptive optics (MOAO) sharpening of NGS is possible where a good estimate of the NGS wavefront can be made, for
example where tomographic wavefront information is available. We describe a new approach for high Strehl ratio
sharpening, based on additional patrolling laser beacons, to eliminate generalized anisoplanatism and minimize
tomography error in the NGS direction.
The W. M. Keck Observatory has completed the development and initial deployment of MAGIQ, the Multi-function
Acquisition, Guiding and Image Quality monitoring system. MAGIQ is an integrated system for acquisition, guiding and
image quality measurement for the Keck telescopes. This system replaces the acquisition and guiding hardware and
software for existing instruments at the Observatory and is now the standard for visible wavelength band acquisition
cameras for future instrumentation. In this paper we report on the final design and implementation of this new system,
which includes three major components: a visible wavelength band acquisition camera, image quality measurement
capability, and software for acquisition, guiding and image quality monitoring. The overall performance is described, as
well as the details of our approach to integrating low order wavefront sensing capability in order to provide closed loop
control of telescope focus.
The purpose of this paper is to report on new adaptive optics (AO) developments at the W. M. Keck Observatory since the 2004 SPIE meeting.1 These developments include commissioning of the Keck II laser guide star (LGS) facility, development of new wavefront controllers and sensors, design of the Keck I LGS facility and studies in support of a next generation Keck AO system.
The purpose of this paper is to report on new adaptive optics (AO) developments at the W. M. Keck Observatory since the 2002 SPIE meeting. These developments include continued improvements to the natural guide star (NGS) facilities, first light for our laser guide star (LGS) system and the commencement of several new Keck AO initiatives.
The visibility science mode of the Keck Interferometer fully transitioned into operations with the successful completion of its operational readiness review in April 2004. The goal of this paper is to describe this science mode and the operations structure that supports it.
The Keck Interferometer includes an autoalignment system consisting of pop-up targets located at strategic locations along the beam trains of each arm of the instrument along with a sensor and control system. We briefly describe the hardware of the system and then proceed to a description of the two operational modes of the system. These are: 1) to provide an initial alignment of the coude paths in each arm, and 2) to recover coude alignments between changes of the static delay sled positions. For the initial alignment mode, we review the system performance requirements along with the software used for image acquisition and centroiding. For coudé alignment recovery, we describe beam-train surveys through the static delay (Long Delay Line) and criteria for a successful recovery of a coudé alignment. Finally, we describe the results of testing of the autoalignment system.
We present the final results of the injection tests of adaptive optics corrected light into single mode fibers, conducted at Canada-France-Hawaii Telescope, W.M. Keck Observatory and Gemini North Observatory, in the prospect of 'OHANA Phase I (preparatory phase). We emphasize on the impact of the results on both the 'OHANA Phase II (interferometric demonstration phase) sensitivity and observational protocol and the behavior of the different adaptive optics.
This paper describes the upgrades to the Keck II Adaptive Optics (K2 AO) system needed for laser guide star observing. The upgrade, including integration with the laser, is scheduled for completion in the winter of 2003. This upgrade includes the addition of a Low Bandwidth Wavefront Sensor (LBWFS) measuring focus and higher order terms, and a Lawrence Livermore National Lab quad-lens avalanche photodiode detector which monitors tip/tilt. Both observe a dim natural guide star. LBWFS corrections are applied as corrections to the high bandwidth wavefront sensor, which is observing the laser beacon. These subsystems drive focus stages, a deformable mirror, a tip/tilt mirror for the incoming starlight, and a tip/tilt mirror for pointing the propagating laser beam. Taken together, and in concert with the rest of the components of the K2 AO system, they provide the tools and the means to observe the universe as never before.
A laser guided adaptive optics system called UnISIS -- University of Illinois Seeing Improvement System -- has been commissioned at the Mt. Wilson 2.5-m Telescope. The UnISIS laser guide star is created via Rayleigh scattering of 351 nm photons from a 30 W excimer laser. The laser guide star is focused at an altitude of 20 km above msl. The UnISIS adaptive optics system sits at the fixed f/30 Coude focus of the 2.5-m telescope while the 30 W excimer laser sits on the observatory ground floor. The collimated laser beam is projected first into the Coude room where it is converted to f/30 and projected into the sky off the 2.5-m primary mirror. We describe the practical experience gained in installing and commissioning UnISIS, and we present simulations of the expected system performance based on the characteristic Cn2 distribution above Mt. Wilson.
The purpose of this paper is to report on new adaptive optics (AO) developments at the W. M. Keck Observatory since the 2000 SPIE meeting. These developments include completion of the Keck I AO system, interferometric combination of the full apertures of the two Keck telescopes using AO on both telescopes, commissioning of two science instruments with the Keck II AO system, first projection of the Keck II sodium laser beacon, progress on laser guide star AO, improved automation of the AO systems and a diversity of AO science programs.
SCIDAR (SCIntillation Detection And Ranging) is a technique for recovering atmospheric Cn2 profiles from the scintillation pattern in or near the telescope's entrance pupil plane. The generalized SCIDAR technique allows the measurement of the entire atmospheric Cn2 profile. We report on a program of generalized SCIDAR measurements at the Air Force Maui Optical Station (AMOS). We discuss how a short exposure imaging system at AMOS was modified to record SCIDAR data. We also discuss the use of computer simulations of atmospheric propagation to aid in the development of data analysis techniques. Results from the first set of SCIDAR observations are presented.
The relative wander in the positions of the laser beacons in a multiple beacon system limits the accuracy to which the wavefront can be measured. We describe the design of an experiment to test methods for reducing laser beacon wander. The system employs an excimer laser producing Rayleigh guide stars at an altitude of 10 km mounted at the Coude focus of the Mt. Laguna 1 m telescope. The experimental tests are based on simultaneously creating two guide stars and measuring their apparent differential motion in a set of projection and detection schemes that includes: full aperture broadcast, partial aperture broadcast, full aperture reception, and partial aperture reception.
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