摘要：ʻImaka is a ground-layer adaptive optics (GLAO) demonstrator on the University of Hawaii 2.2 m telescope with a24′×18′ field of view, nearly an order of magnitude larger than previous AO instruments. In 15 nights ofobserving with natural guide star asterisms ∼16′ in diameter, we measure median AO-off and AO-on empiricalFWHMs of 0 95 and 0 64 in R band, 0 81 and 0 48 in I band, and 0 76 and 0 44 at 1 μm. This factor of 1.5–1.7reduction in the size of the point-spread function (PSF) results from correcting both the atmosphere and telescopetracking errors. The AO-on PSF is uniform out to field positions ∼5′ off-axis, with a typical standard deviation inthe FWHM of 0 018. Images exhibit variation in FWMM by 4.5% across the field, which has been applied as acorrection to the aforementioned quantities. The AO-on PSF is also 10×more stable in time compared to the AO-off PSF. In comparing the delivered image quality to proxy measurements, we find that in both AO-off and AO-ondata delivered image quality is correlated with ʻImaka’s telemetry, with R-band correlation coefficients of 0.68 and0.70, respectively. At the same wavelength, the data are correlated to DIMM and MASS seeing with coefficients of0.45 and 0.55, respectively. Our results are an essential first step to implementing facility-class, wide-field GLAOon Maunakea telescopes, enabling new opportunities to study extended astronomical sources, such as deep galaxyfields, nearby galaxies, or star clusters, at high angular resolution.
