Performance of the W.M. Keck Observatory Natural Guide Star Adaptive Optic Facility: the first year at the telescope

First light for the Keck II Natural Guide Star (NGS) Adaptive Optics (AO) facility was on the night of February 4, 1999. On the firs attempt at closing the AO loops the image full-width- at-half-maximum (FWHM) went from 0.6 to 0.04 arcsec at H-band (1.65 micrometer wavelength), with a Strehl ratio of 25%. The AO system became an officially scheduled Keck science facility in August 1999; 30 science nights are scheduled in the first half of 2000. The primary purpose of this paper is to present results from this first year at the telescope.