Baseline Specification of GLAO

By S. Oya and Subaru ngAO working group

[2013/03/21]

Notes

The performance of GLAO depends not only the integrated turbulence strength, but also the height distribution.
The turblence profile is based on Andersen+12,PASP,124,469 developed for RAVEN (MOAO demonstrator at Subaru), which consists of 7 turbulence layers. The basic idea is to use the turbulence profile obtained by the site testing at 13N (Mauna Kea) for TMT. The the difference between the 13N seeing and Subaru image quality statistics is ascribed to the dome seeing and added to the ground-layer.
Four sodium Laser Guide Stars (LGSs) in square configuration surrounding the field-of-view. A Tip/Tilt/Focus Natural Guide Star (TTF NGS) is located between two LGSs, i.e. four NGSs in total. The ground-layer is determined as average wavefront determined by these guide stars.
The brightness of LGS is quivalent to 10th magnitude and NGS is 18th magnitude. The effective readout noise of 0.22 is assumed for WFS.

Specifications

Field of View	15 arcmin^*1
Focus	Cassegrain
Corrector	Deformable secondary, 33 actuator across the diameter
Sky Coverage	almost all sky
AO system throughput	100%^*2

*1: Performance little change betwen 10 arcmin and 20 arcmin (but it may depend on turbulence height).
*2: The throughput of AO system itself, excluding the telescope mirrors, i.e., 100% means no additional AO optics needed in the case of GLAO (cf. 90% for AO36, 70% for AO188).

Expected Correction in FWHM

The simulation results are shown for three atmospheric condtions:

'moderate' (the probablity to have better seeing is 50%),
'bad' (the probability to have better seeing is 75%),
'good', (the probability to have better seeing is 25%).

GLAO corrected results (="GLAO average FWHM" the average on 5 points in the FoV) are compared with seeing (no GLAO correction) resuts (="Natural Seeing FWHM")

Note that the following FWHM corrections are for observation at the Zenith. The dependency on zenith angle has been simulated. Please refer page 18 and 19 of "Subaru Next-Gen Wide-Field AO: Ground Layer AO Simulation" (PDF), in which performance has been measured by NEA (Noise Equivalent Area).

"Moderate" (50%-ile)

	R-band	J-band	H-band	K-band
Natural Seeing FWHM (1)	0.65"	0.51"	0.49"	0.44"
GLAO average FWHM (2)	0.41"	0.27"	0.23"	0.20"
(1) / (2)	1.58	1.91	2.14	2.19
(1) - (2)	0.23"	0.24"	0.26"	0.24"

"Bad" (75%-ile)

	R-band	J-band	H-band	K-band
Natural Seeing FWHM (1)	0.88"	0.75"	0.66"	0.62"
GLAO average FWHM (2)	0.67"	0.46"	0.40"	0.35"
(1) / (2)	1.31	1.62	1.65	1.75
(1) - (2)	0.21"	0.29"	0.26"	0.27"

"Good" (25%-ile)

	R-band	J-band	H-band	K-band
Natural Seeing FWHM (1)	0.51"	0.43"	0.37"	0.30"
GLAO average FWHM (2)	0.33"	0.22"	0.19"	0.16"
(1) / (2)	1.55	1.96	1.97	1.86
(1) - (2)	0.18"	0.21"	0.18"	0.24"

Expected Correction in Ensquared Energy

The conditions are the same as that for FWHM.

"Moderate" (50%-ile)

	0.24" x 0.24"				0.48" x 0.48"
	R-band	J-band	H-band	K-band	R-band	J-band	H-band	K-band
Natural Seeing EE (1)	0.09	0.12	0.15	0.17	0.29	0.38	0.42	0.46
GLAO average EE (2)	0.16	0.29	0.36	0.41	0.43	0.59	0.65	0.71
(2) / (1)	1.8	2.4	2.4	2.4	1.5	1.6	1.5	1.5

"Bad" (75%-ile)

	0.24" x 0.24"				0.48" x 0.48"
	R-band	J-band	H-band	K-band	R-band	J-band	H-band	K-band
Natural Seeing EE (1)	0.05	0.07	0.09	0.10	0.19	0.26	0.28	0.32
GLAO average EE (2)	0.08	0.13	0.17	0.21	0.26	0.39	0.45	0.52
(2) / (1)	1.6	1.9	1.9	2.1	1.4	1.5	1.6	1.6

"Good" (25%-ile)

	0.24" x 0.24"				0.48" x 0.48"
	R-band	J-band	H-band	K-band	R-band	J-band	H-band	K-band
Natural Seeing EE (1)	0.14	0.20	0.23	0.26	0.42	0.52	0.56	0.60
GLAO average EE (2)	0.23	0.38	0.44	0.49	0.56	0.69	0.73	0.76
(2) / (1)	1.6	1.9	1.9	1.9	1.3	1.3	1.3	1.3

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