Dome C Site Characterization in 2006 with Single-Star SCIDAR

We present observations made in 2006 with the single-star SCIDAR (SSS) at Dome C in Antarctica, allowing us to determine optical turbulence C-N(2)(h) and velocity V(h) profiles from ice levels up to about 25 km above sea level (a.s.l.). SSS is a 16 inch telescope placed on an equatorial mount that continuously tracks the Canopus star. About 90,000 individual profiles are analyzed from March to September, where surface-layer contribution to seeing can be separated from the rest of the atmosphere. Medians of high angular resolution parameters relevant to astronomy are statistically studied, such as seeing (1.0''), isoplanatic angle (6.9''), and wavefront coherence time (3.4 ms). For a telescope placed above the turbulent surface layer, superb conditions are encountered (medians of seeing better than 0.3'', isoplanatic angle better than 6.9'', and coherence time larger than 10 ms). Astronomical conditions are twice as good at the beginning of the night, with epsilon(0) approximate to 0.5,theta(0) approximate to 11.5, and T-0 approximate to 15 ms. SSS wind-velocity profiles are consistent with National Oceanic and Atmospheric Administration analysis up to 17 km (a.s.l.), within a +/- 2 m s(-1) error bar. Coherence etendue (which is a combination of epsilon(0),theta(0) , and T-0), well adapted to adaptive optics performances, is likely 4 times better at Dome C than at the already-known observatories such as Mauna Kea or ORM.