2. Instruments and data

 

Data presented here have been carried out with the adaptive optics system from the European Southern Observatory (ESO) called at this time Come-on+ (COP) and the adaptive optics system from the Starfire Optical Range (SOR) called Generation II (Gen II). Both systems are based on a Shack-Hartmann wavefront and a piezo-actuated deformable mirror.

The Come-on+ instrument (Beuzit et al. 1994 for a technical description) recently renamed ADONIS is currently used at the focus of the 3.6 meter ESO telescope in Chile for NGS AO imaging in the near-infrared. For simplicity, I have selected observations of bright binary sources. NGS AO data of sub-arcsecond binaries carried out on November 1993 and January 1994 with COP have been provided by C. Perrier and J. Bouvier (Observatory of Grenoble, France) respectively.

The Gen II instrument (Fugate et al. 1994) operates at the Starfire Optical Range 1.5 meter telescope facility located near Albuquerque, New-Mexico, U.S.A. and delivers AO corrected images in the I-band (m). Gen II provides a laser and natural guide star modes. B. Ellerbroek and J. Christou (U.S. Air Force Phillips Laboratory, NM, U.S.A.) provided a set of NGS Gen II observations carried out on December 1994 and July 1995.

 

AO system COP/Adonis SOR Gen II WFS geometry (subapertures)

Actuators number 52 241

WFS maximum frame rate 200 Hz 1667 Hz

-3dB close loop bandwidth 50-60 Hz 80-120 Hz

Table 1 (click here) gives the main characteristics for the two AO systems. We note that the WFS analyses in the V-R light. Here after, AO imaging data in the JHK bands and the I band come from COP and Gen II respectively. The experimental data correspond to various turbulence conditions (r₀, t₀). is currently 1 to 2 where d is the subaperture width and is the seeing parameter at the imaging wavelength , and the Greenwood frequency (which is inversely proportional to t₀) is often smaller than the AO system bandwidth. Unfortunately, for COP data, these atmospheric parameters are only estimations given by the observers. The guide source is always the astronomical target so that only the on-axis psf is considered here. Sources are bright so that continuous short exposure time frames were often used, there was no photon starvation in the WFS and photon, detector and background noises are expected to be small in order to stress the others fundamental limitations due to the turbulence or the AO control system.