ABSTRACT. 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 have searched the four brightest objects in the Kuiper belt for the presence of satellites using the newly commissioned Keck Observatory Laser Guide Star Adaptive Optics system. Satellites are seen around three of the four objects: Pluto (whose satellite Charon is well-known), 2003 EL61, and 2003 UB313. The object 2005 FY9, the brightest Kuiper belt object after Pluto, does not have a satellite detectable within 0.4 arcseconds with a brightness of more than 0.5% of the primary. The presence of satellites to 3 of the 4 brightest Kuiper belt objects is inconsistent with the fraction of satellites in the Kuiper belt at large at the 99.1% confidence level, suggesting a different formation mechanism for these largest KBO satellites. The satellites of 2003 EL61 and 2003 UB313, with fractional brightnesses of 5% and 2% of their primaries, respectively, are significantly fainter relative to their primaries than other known Kuiper belt object satellites, again pointing to possible differences in their origin.

ABSTRACT. The Keck II Telescope is the first 8-10 m class telescope equipped with a laser guide star adaptive optics (LGS AO) system. Under normal seeing conditions, the LGS AO system produces K-band Strehl ratios between 30% and 40% using bright tip-tilt guide stars, and it works well with tip-tilt guide stars as faint as , with partial correction for stars up to a magnitude fainter. This paper presents the algorithms implemented m p 18 R in the LGS AO system, as well as experimental performance results. A detailed error budget shows excellent agreement between the measured and expected image quality for both bright and faint guide stars.

We present the first Laser Guide Star Adaptive Optics (LGS-AO) observations of the Galactic center. LGS-AO has dramatically improved the quality and robustness with which high angular resolution infrared images of the Galactic center can be obtained with the W. M. Keck II 10-meter telescope. Specifically, Strehl ratios of 0.7 and 0.3 at L'[3.8 µm] and K'[2.1 µm], respectively, are achieved in these LGS-AO images; these are at least a factor of two higher and a factor of four to five more stable against atmospheric fluctuations than the Strehl ratios delivered thus far with the Keck Natural Guide Star AO system on the Galactic center. Furthermore, these observations are the first that cover a large area (76 ′′ × 76 ′′ ) surrounding the central black hole at diffractionlimited resolution for an 8-10 meter class telescope. During our observations, the infrared counterpart to the central supermassive black hole, Sgr A*-IR, showed significant infrared intensity variations, with observed L' magnitudes ranging from 12.6 to 14.5 mag and a decrease in flux density of a factor of two over an 8 minute interval. The faintest end of our L' detections, 1.3 mJy (dereddened), is the lowest level of emission yet observed for this source by a factor of 3. No significant variation in the location of SgrA*-IR is detected as a function of either wavelength or intensity. Previous claims of such positional variations are easily attributable to a nearby (0. ′′ 09 or 720 AU, projected), extended, very red source, which we suggest arises from a locally heated dust feature. Near a peak in its intensity, we obtained the first measurement of SgrA*-IR's K'-L' color; its K'-L' of 3.0 ± 0.2 mag (observed) or 1.4 ± 0.2 (dereddened) corresponds to an intrinsic spectral index of α -0.5 ± 0.3 for F ν ∼ ν α . This is significantly bluer than other recent infrared measurements from the literature, which suggest α = -4 ± 1. Because our measurement was taken at a time when Sgr A* was ∼6 times brighter in the infrared than the other measurements, we posit that the spectral index of the emission arising from the vicinity of our Galaxy's central black hole may depend on the strength of the flare, with stronger flares giving rise to a higher fraction of high energy electrons in the emitting region.

The existence of binary asteroidal systems has been confirmed observationally during the past decade with spacecraft exploration 3 , ground-based imaging 4 , radar observations 4 , and light curve measurements 5 . Most recently, the discovery of two moons orbiting around the irregular rubble pile asteroid 87 Sylvia 6 with adaptive optics system observations confirms that collision and disruption is the main formation mechanism for multiple main-belt systems. The system 617 Patroclus, the only binary Trojan known 1 , was discovered with the Hokupa'a Gemini 8-m adaptive optics system 7 under excellent seeing conditions. Because of their faintness (with a magnitude in the visible spectrum of m v >15.5), Trojan asteroids cannot be directly observed by most of the adaptive optics systems. Using related techniques such as stellar appulse 8 and LaserGuide Star (LGS) observations 9 at the Lick 3-m telescope, our group failed to detect any new companions of Trojans, indicating that the proportion of multiple systems in the Trojan population larger than 40 km in diameter is less than 4% (ref. 9). The study of a