Performance of Subaru AO188

Performance of AO is characterized by a Strehl ratio (a peak intensity normalized by that of PSF without any turbulence) and FWHM of the PSF. These depend on a the AO guide star magnitude, seeing, sky background and angular separation between the target and guide star. In general, performance of the AO system is better with a brighter guide star, at a better seeing, or longer wavelength.

On-source Strehl ratio and FWHM (NGS mode)
Encircled energy (NGS mode)
Isoplanatic field
Further information

On-source Strehl ratio and FWHM (NGS mode)

The plots below show a Strehl ratio and FWHM as a function of AO guide star magnitude (seeing = 0''.5-0''.6) and observed wavelength. We also show a FWHM as a function of seeing based on the data obtained by AO36 (Oya et al. 2004, SPIE Proc., 5490, 409), for your information. Seeing statistics at Subaru is shown here.

FWHM as a function of R-magnitude of the NGS and the observed wavelength. FWHM of the AO36 and seeing condition are also plotted for comparison.

Strehl ratio (SR) as a function of R-magnitude of the NGS and the observed wavelength. SR of the AO36 and seeing condition are also plotted for comparison.

Natural seeing vs. FWHM of the AO corrected PSF. The data points are color coded along the guide star magnitude. Note that this plot is based on the data obtained by AO36.

Encircled energy (NGS mode)

The plot below shows the encircled flux plot of the point sources obtained by the AO188 with R=9.0 guide star at 0.5-0.6 arcsec seeing condition. Half-flux radius, within which half of the total flux is contained, is 0.1 arcsec for JHKL'M' band, 0.2 arcsec for shorter z band, and 0.5 arcsec for normal seeing condition. The higher flux concentration due to the AO correction resulted in much higher sensitivity. The expected sensitivity gain by AO188 for point sources is about 2.0 mag for K band in best case (SR~0.5).

Isoplanatic field

Note: Since the estimation of the isoplanatic field is based on the AO36 observations, the isoplanatic angle described below could be smaller for the AO188 observations with higher strehl ratio.

The isoplanatic field has approximately 1' in diameter. The image quality degrades at distances of more than 30'' from the AO guide star (see figure below). This indicates that the height of the effective turbulent layer is less than 2 km. These values may vary from night to night, or even during a night.

Further information

Questions and further information regarding this page should be directed to Yutaka Hayano.

6 February 2008