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Hokupa'a Performance Calulations |
The system performance was simulated using a complete AOS simulation package written by Francois Rigaut. The simulated point spread functions (PSFs) account for uncorrected atmospheric aberrations, aberrations in QUIRC, and residual telescope jitter (1-D rms=10 mas). Note that QUIRC was not designed to be used with an adaptive optics system. A consequence of this is that the performance of Hokupa'a with QUIRC is limited in the K-band by static aberrations. Also note that the residual jitter is strongly dependent on the performance of the telescope dynamics (e.g. wind shake). PSFs generated with this simulation package for conditions occuring during the dedication image observations agree well with the images taken during the commissioning of Hokupaa.
A web-based tool
is provided that may be helpful in estimating the
type of performance you can obtain: see the
Hokupa'a Image Quality Calculator.
The following examples illustrate how to estimate the Strehl, FWHM, and 50% encircled energy diameter under various conditions. Please refer to the following pages for more information of the performance dependence on:
Note that the degradation in performance resulting from these factors is cumulative.
Example 1: H-band observation in 0.7" seeing conditions, with an on-axis guide star of magnitude R=13, observed at the zenith.
For a guide star of R=13 under 0.7" seeing conditions we find from the guide star magnitude dependence that the FWMH, Strehl and 50%EED are FWHM= 75mas, Strehl=0.08, and 50%EED=0.4".
Example 2: K-band observation in 0.5" seeing conditions, with an AOWFS reference source 20" off-axis of magnitude R=17, observed at a zenith angle of 50 degrees.
Observing a zenith angle > 1 means that the path length for turbulence grows. At a zenith angle of 50 degrees, the zenith angle dependence page gives an increase of the seeing of 55%. In other words, if the seeing at zenith is 0.5", then at a zenith angle of 50 degrees the seeing will be 55% worse or 0.8".
For a guide star of brightness R=17 under 0.8" seeing conditions we find from the guide star magnitude dependence that FWHM= 0.3", Strehl=0.02, and 50%EED=0.6".
Now take into account the performance degradation due to the field offset. From this page we see that in K, the Strehl degrades by 50%, the FWHM increases by about 20%, and the 50%EED increases by 40%.
The estimated performance on this target is therefore FWHM = 0.36", Strehl=1%, and a 50%EED=0.84".
Example PSFS from these simulationscan be downloaded from the link below. These contain simulations of the Hokupaa/QUIRC PSF for J,H, and K-bands under 0.5" and 0.7" seeing at zenith on a bright guide star.
Last update 11 February 2001; Mark Chun
In original form; Mark Chun