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The astrometric precision and accuracy of an imaging camera is often limited by geometric optical distortions. These must be calibrated and removed to measure precise proper motions, orbits, and gravitationally lensed positions of interesting astronomical objects. Here, we derive a distortion solution for the OSIRIS Imager fed by the Keck I adaptive optics system at the W. M. Keck Observatory. The distortion solution was derived from images of the dense globular clusters M15 and M92 taken with OSIRIS in 2020 and 2021. The set of 403 starlists, each containing ∼1000 stars, were compared to reference Hubble catalogs to measure the distortion-induced positional differences. OSIRIS was opened and optically realigned in 2020 November and the distortion solutions before and after the opening show slight differences at the ∼20 mas level. We find that the OSIRIS distortion closely matches the designed optical model: large, reaching 20 pixels at the corners, but mostly low order, with the majority of the distortion in the 2nd-order mode. After applying the new distortion correction, we find a median residual of [x, y] = [0.052, 0.056] pixels ([0.51, 0.56] mas) for the 2020 solution, and [x, y] = [0.081, 0.071] pixels ([0.80, 0.71] mas) for the 2021 solution. Comparison between NIRC2 images and OSIRIS images of the Galactic center show that the mean astrometric difference between the two instruments reduces from 10.7 standard deviations to 1.7 standard deviations when the OSIRIS distortion solution is applied. The distortion model is included in the Keck AO Imaging data-reduction pipeline and is available for use on OSIRIS data.

 

We present evaluations of the Keck Telescope’s adaptive optics (AO) performance on Milky Way Galactic center imaging and spectroscopic observations using three different AO setups: laser guide star with infrared (IR) tip-tilt correction, laser guide star with visible tip-tilt correction, and infrared natural guide star with a pyramid wavefront sensor. Observations of the Galactic Center can utilize a bright IR tip-tilt star (K′ = 7.4 mag) for corrections, which is over 10 arcseconds closer than the optical tip-tilt star. The proximity of this IR star enables the comparison of the aforementioned AO configurations. We present performance metrics such as full-width-at-half-maximum (FWHM), Strehl ratio, and spectral signal to noise ratio and their relations to atmospheric seeing conditions. The IR tip-tilt star decreases the median spatial FWHM by 31% in imaging data and 30% in spectroscopy. Median Strehl for imaging data improves by 24%. Additionally, the IR star removes the seeing dependence from differential tip-tilt error in both imaging and spectroscopic data. This evaluation provides important work for ongoing upgrades to AO systems, such as the Keck All sky Precision Adaptive Optics (KAPA) upgrade on the Keck I Telescope, and the development of new AO systems for extremely large telescopes. 

We calculate an optical distortion solution for the OSIRIS Imager on the Keck I telescope, by matching observations of globular clusters to a Hubble reference catalogue. This solution can be applied to correct astrometric distortions in OSIRIS frames, improving the astrometric accuracy of observations. We model the distortion with a 5th order Legendre polynomial. The distortion we find matches the expected OSIRIS distortion, and has a fit error of 0.6 mas, but has large residuals of 7 mas. We are currently iterating on an improved reference frame to improve the residual. Additionally, we have installed the Precision Calibration Unit (PCU) on the Keck I optical bench, which will generates an artificial grid of stars for use in future distortion calculations. 

We present the status and plans for the Keck All sky Precision Adaptive optics (KAPA) program. KAPA includes (1) an upgrade to the Keck I laser guide star adaptive optics (AO) facility to improve image quality and sky coverage, (2) the inclusion of AO telemetry-based point spread function estimates with all science exposures, (3) four key science programs, and (4) an educational component focused on broadening the participation of women and underrepresented groups in instrumentation. For this conference we focus on the KAPA upgrades since the 2020 SPIE proceedings1 including implementation of a laser asterism generator, wavefront sensor, real-time controller, asterism and turbulence simulators, the laser tomography system itself along with new operations software and science tools, and modifications to an existing near-infrared tip-tilt sensor to support multiple natural guide star and focus measurements. We will also report on the results of daytime and on-sky calibrations and testing. 

NIRSPEC is a high-resolution near-infrared echelle spectrograph on the Keck II telescope that was commissioned in 1999 and upgraded in 2018. This recent upgrade was aimed at improving the sensitivity and longevity of the instrument through the replacement of the spectrometer science detector (SPEC) and slit-viewing camera (SCAM). Commissioning began in 2018 December, producing the first on-sky images used in the characterization of the upgraded system. Through the use of photometry and spectroscopy of standard stars and internal calibration lamps, we assess the performance of the upgraded SPEC and SCAM detectors. First, we evaluate the gain, readnoise, dark current, and the charge persistence of the spec detector. We then characterize the newly upgraded spectrometer and the resulting improvements in sensitivity, including spectroscopic zero points, pixel scale, and resolving power across the spectrometer detector field. Finally, for SCAM, we present zero points, pixel scale, and provide a map of the geometric distortion of the camera.