Blog

The MagAO team (or at least part of it) has returned to Florence for another round of integration and testing. I (Jared) have been here for 2 weeks, and Laird and Derek just arrived. As soon as I arrived we successfully closed the loop again, with only minimal adjustments of the alignment using the X-Y-Z stages. The system came right back up, with less than 5 minutes of work, after 3 months of down time.

The last two weeks have been mostly uneventful, consisting of a lot of software development and debugging. In preparation for the next 2 weeks of work on the ASM and the CRO tests we removed the NAS from the tower on Friday. The two videos below show the process of lowering, and then tilting the NAS upright on its handling cart.

While the NAS is off the tower we will be fine tuning the WFS and VisAO camera alignment, as well as testing the AO to Magellan software interface. In about two weeks we’ll reverse the process, and mount everything back in the tower for some more exciting closed loop action.

Last week Laird and I had the pleasure of attending the Arizona Board of Regents meeting in Phoenix, and presenting a poster about the Magellan AO system and the VisAO camera. The session we were invited to was on the impact of scientific research on student’s education at Arizona’s universities. Click the image below to download the poster as a pdf. It contains an introduction to AO in general and visible AO in particular, as well as an overview of the MagAO project. We also took the opportunity to show off some of our exciting results from the test tower in Florence.

Here is a short film of the VisAO camera at i’ (765 nm) in 0.8″ seeing (33mph wind) with the loop open (0.3% SR, FWHM~0.6″) and closed (55% Strehl, FWHM=0.027″) at 800 Hz (400 modes) in the test tower.

This is a >180 increase in peak counts (and >20x gain resolution) obtained by turning on the loop!

Note that the PSF is saturated out to the first Airy ring in this (rather poor) stretch. The red dot is the focus light from the videocamera (ignore it).

On July 21 we closed the loop again (but without wind on the outside of the tower). In these calm conditions we were able to obtain 55% Strelh at i’ (765 nm) which is excellent correction in 0.8″ seeing and 33mph winds. I attach a log10 stretch image below to show the very high contrast PSFs that are obtained with the Magellan AO system. This is slightly better performance then was predicted for an R=8 mag guide star in a 33 mph wind with ro=14cm at 0.55um. Normally at Magellan the seeing should be better (and the wind lower) than what we simulated here, giving us some confidence that VisAO will be an excellent visible AO science camera in >75% of the weather seen at the Magellan telescope.(clockwise) perfect PSF, the MagAO PSF, The AO ON PSF, and the AO OFF PSF (Log Scale)

Note by Jared: due to the way turbulence is simulated in the tower using the mirror itself, there is some missing power in the modes higher than ~585 (the number of actuators on our mirror). This results in an optimistic fitting error during these tests. We can estimate how much lower Strehl at the telescope would be due to this unsimulated turbulence using some AO theory (see Noll 1976). Our most conservative estimate for this correction brings our telescope Strehl down to 37%, from the 55% measured in the tower. Compared to the correction calculated by a more empirical method for the LBT (see Esposito 2010) this correction is probably a little large (resulting in a low estimate for Strehl). Even with this conservative correction, our tower results are exceeding our performance predictions for an 8th magnitude guide star by more than 5% Strehl. This is very exciting!