Hokupa'a Performance Calulations: AOWFS star magnitude

The performance of Hokupa'a depends strongly on the seeing conditions and the brightness of the wavefront reference star. The following figures illustrates how the Strehl and FWHM are expected to vary as a function of guide star magnitude and atmospheric seeing. The values were generated using Francois Rigaut's AO simulation package. The following parameters were used:

• Intrinsic atmospheric seeing of roughly 0.3''through 1.0" (see legend in the first figure).
• Guide star on-axis and point-like.
• No high-order telescope aberrations are included.
• Residual telescope jitter of rms = 10mas.
• QUIRC aberrations modeled as a chromatic aberration which results in a Strehl degradation of 0.6. The aberration is modeled as a focus aberration across the band. Aberrations are assumed to be the same in J, H, and K.

A few points to note are:

• As the seeing increases, the performance of the system eventually becomes unstable and highly variable. This is reflected in the smoothness of the curves.
• The performance in J-band under 1" seeing or worse is extremely unstable and is not shown. Under these conditions there is very little improvement of the image quality.
• Hokupa'a-36 is undersized for an 8-meter telescope but it performs well in K-band under moderately good seeing conditions. Notice how the FWHMat 2.2 microns is insensitive to the seeing while the 50%EED is extremely sensitive. This illustrates the stability or instability under various conditions.

Last update 24 August 2000; Mark Chun
In original form; Mark Chun