First astro images with altair LGS
That's it. We've done it. Well, not entirely, but it's looking fairly good. here are the two first images we did with altair LGS the other night (past Wednesday night). We first did M13. Four pointings with NIRI F/14 (51"x51" FoV each). Pixel size 49.8mas. Resolution about 0.16" (see comment below):
Then we pointed M16, the Eagle Nebula. We concentrated on the central pillar/bridge, but we did it in Kprime and H. I have here only the K' reduction. Haven't done the H yet, as I believe it's gonna be bad (not a lot of signal in H). The FWHM of the stars in this image is about 0.14", quite uniform across the field.
So, why is the angular resolution so bad w.r.t to the diffraction limit? Because we did not get the time to refine the NCPAs. We did a first pass, and got about 4.8 pixels at F/32 (so about 100mas), but we lost the setting as we were pointing other objects (during a slew, the TCC loads the default NIRI MCPA file, which is a good thing). Also, the focus was not perfect. Focus stays a problem with altair LGS, we'll have to do something about the open loop model (trombone position vs zenith angle). Note that the PSF was usually quite stable, but affected by a very strong quadrufoil. The PSF was actually like a cross, with no core when far enough from focus. Details in this PSF were of the order of the diffraction limit, so I am confident that TT correction was adequate.
Note: These images have been basically: sky subtracted, average-combined, and slightly contrast enhanced (see datared.i in Data/Altair-MK/2006may04/NIRI/)
