Hokupa`a Anisoplanatism and Mauna Kea Turbulence Characterization

A data set of adaptive optics images has been analyzed in order to study the effects of angular anisoplanatism and to characterize Mauna Kea nighttime turbulence. The data set consists of a selection of Galactic center images obtained with the adaptive optics instrument Hokupa`a and the near‐infrared camera QUIRC on the Gemini‐North 8 m telescope. Using the Strehl ratio and the FWHM as tracers for anisoplanatism in the images, it is possible to draw conclusions about the effective turbulence height h - by model‐fitting synthetic data. From the relatively small statistical sample, we obtain a median h - = 3.5 km, with 10th and 90th percentiles being 2.2 and 5.6 km. The implications of these findings for a turbulence‐conjugated adaptive optics system are addressed. We also find the Zernike modal equivalent of Hokupa`a to be N ≈ 18, i.e., on the average slightly better than 4 radial degrees.