Point Source Limiting Magnitudes

Limiting magnitudes for a 5$\sigma$ 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).

Figure 5: Point sources - SNR vs. magnitude for one 300s fowler exposure in different filters for IRCAL and ShARCS (8 or 16 subapertures).