Limiting magnitudes for a 5
detection (i.e. SNR=5) of point sources for the current and new systems is shown in Table 6. ShaneAO should be able to image point sources 1.3-2 magnitudes fainter than the existing system can.
Table 6:
Point source limiting magnitudes (Vega system) in LGS mode: IRCAL predicted (300s Fowler sample - 16 reads) and ShARCS (8 or 16 subapertures) predicted (300s Fowler sample - 32 reads).
Filter |
IRCAL |
ShARCS 8 |
ShARCS 16 |
|
predicted |
predicted |
predicted |
K strehl |
0.42 (LGS) |
0.6 (LGS) |
0.8 (LGS) |
J |
19.97 |
21.30 |
22.28 |
H |
19.62 |
20.48 |
21.03 |
K |
17.67 |
18.71 |
19.02 |
Ks |
17.84 |
18.92 |
19.24 |
|
Graphically, the results for point sources for current and new systems are displayed in Figures 4 and 5. Figure 4 illustrates the prediction that ShaneAO will be faster by a factor of 10-13 in reaching a fiducial SNR. Figure 5 is a representation of Table 6. The curves change slope at the transition between sky background noise dominance (fainter sources) and source photon Poisson noise dominance (bright sources).
Figure 4:
Point sources - Exposure time required to reach SNR=5 vs. magnitude (Vega system) in different filters for IRCAL, ShARCS 8 (ShARCS + old laser) and full ShaneAO (ShARCS 16).
![Image exptVmag-ircsha](./exptVmag-ircsha.png) |
Figure 5:
Point sources - SNR vs. magnitude for one 300s fowler exposure in different filters for IRCAL and ShARCS (8 or 16 subapertures).
![Image snrVmag-ircsha](./snrVmag-ircsha.png) |
Srikar Srinath
2013-10-09