When Do I need LGS-AO?
In general, NGS-AO produces better results than LGS-AO for on-axis observations of bright targets. As the guide star becomes fainter or moves off axis, it might be advisable to switch to LGS-AO. The following plot and tables show the best regimes for both observing modes.
On-axis K-band Strehl vs. Magnitude
NGS: Green line; LGS: Orange line
Reference: AO System Performance -
KAON 489
Use NGS-AO |
Use LGS-AO |
Guide Star is:
- R brighter than 14th mag
- separation under 10"
| Guide Star is:
- R dimmer than 14th mag
- separation over 10"
|
Absolute Performance Limits (with excellent seeing)
NGS-AO |
LGS-AO |
NIRC2:
- R brighter than mag 15.5
- separation under 30"
| NIRC2:
- R brighter than mag 18.5
- separation under 60"
|
NIRSPAO:
- R brighter than mag 15.5
- separation under 30"
| NIRSPAO:
- R brighter than mag 18.5
- separation under 60"
|
OSIRIS:
- R brighter than mag 15.5
- separation under 35"
| OSIRIS:
- R brighter than mag 18.5
- separation under 65"
|