Evaluation of the on-sky performance of Altair

Abstract

In this paper we evaluate the on-sky performance of Altair, the facility adaptive optics instrument at the Gemini North telescope. We describe the method for doing this on-sky evaluation, which includes: 1) the choice of suitable stellar fields for PSF observations that must cover a range of guide star magnitudes and angular separations from the guide star; 2) the observation strategy and data reduction pipeline; and 3) the PSF database from which the performance results are queried. The database stores observatory system parameters and performance observations such as FWHM, Strehl, encircled energy, wave front sensor flux, as well as coherence length (r o ) and outer scale (L o ) of the turbulence measured in closed loop and therefore coincident with the focal plane observations of the telescope. From the database we derive 20 to 24% Noll efficiency of the system and an estimated distribution of effective turbulence height above the summit to be 3.3 ± 0.6km. The performance evaluation strategy used on Altair is quite general and could be used for other adaptive optics systems.

OPERA, an automatic PSF reconstruction software for Shack-Hartmann AO systems: application to Altair

“…The fit gave r 0 = 13 ± 1 cm, and an apparent outer scale (it is a turbulator) L 0 = 24 ± 6 m. We do not know for the outer scale, but at least r 0 is compatible with the value we were expecting for these phase screens (in the range 10-15 cm), giving us good confidence on the accuracy of the algorithm. In fact, the module of OPERA which is doing the r 0 and L 0 calculation (seeing.pro) has been tested on-sky during Altair's commissioning (see Stoesz,5 this conference), and values obtained showed very good agreement with the expected seeing on top of Mauna Kea.…”

Adaptive Optics Simulations for Siding Spring

“…Evidence of this fact is the success of AO demonstrated with the modern 8–10 m class telescopes. Good performance has been reported with the 10-m Keck II Telescope (van Dam et al 2006), the 8-m Very Large Telescope (Rousset et al 2003), the 8.2-m Subaru Telescope (Iye et al 2004), and 8-m Gemini North Telescope (Stoesz et al 2004), and others.…”

Constraining the GLAO parameter space with turbulence profile models

“…An outer scale of L o = 30 meters is often measured (e.g. [6]) and is adopted here. The outer scale only affects ITR and ITRS in an absolute sense and has a negligible effect on the optimization of ∆ and ∆t.…”