From: Knut Olsen Date: May 23, 2006 4:28:02 PM PDT To: Claire Max Subject: Re: sky backgrounds and current LGS AO psfs Dear Claire, Ok, so I've managed to produce something for your next-generation AO system. I'm attaching the plots of the photometry and the result of attempting to solve for the mix of stellar populations. The images are available at http://www.ctio.noao.edu/ftp/pub/olsen/claire . The images are FITS format, and assume an hour-long exposure in J and K. This is probably overkill for these crowded fields. For the ELT simulations, we used 20 arcsec sq. fields, so in order to be able to do this in a day, that's what I used here, too. For the photometry, I ran a straightforward DAOPHOT/ALLSTAR pipeline on the data, but didn't attempt to measure the zero point from the images themselves; it was fixed to the agree with the input magnitudes of the stars. The plot has two CMDs in it. The one at top left is just the PSF-fit photometry with the zero point applied; the one at top right is using my knowledge of the Strehl of the PSFs as a function of position to correct the photometry, as if a PSF observation (a relatively uncrowded star cluster, say) had been taken near the time of observation. The encouraging thing, I think, is that the scatter in the CMD on the left is not very much higher than the one on the right, meaning that MCAO produces a great deal of improvement over singe guide star AO. The plot at bottom left shows the parameters of the input stellar population mix. The plot at bottom right is what I was able to recover from the CMD at top right. I don't know if I'll be able to do much more than this until mid-June, but will see how far I can get with the current LGS AO PSFs this evening... Hope this is more or less what you were hoping to see. Let me know if you have questions... Cheers, Knut