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).
  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

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

Srikar Srinath 2013-10-09