With the new system, we retain the IRCAL filter curves, dust fraction of 3% and coating degradation described above. Strehl ratios are derived from . The predicted sky background and throughput for ShaneAO are given in Table 5.
Comparing Tables 5 and 3, the model predicts that the background in the band will be a magnitude fainter and throughput will increase by 20-30% across all bands. The reduced background for ShaneAO is illustrated by Figure 3.
Total background and emissivity comparison as determined by our model between the existing system (IRCAL) and the new system (ShARCS).
For limiting magnitudes, the comparison between current and new systems is one of what is and will be their usual modes of operation:
- LGS mode with 88 subapertures and 300 second Fowler-16 exposures.
- ShARCS+old laser:
- LGS mode with 88 subapertures (ShARCS 8 in the figures and tables below) and 300 second Fowler-16 exposures - this will be the modus operandi for a few months after ShARCS is installed (April 2014 onwards) until the new laser is operational.
- Full ShaneAO:
- LGS mode with 1616 subapertures (ShARCS 16 hereafter) and 300 second Fowler-32 exposures.