The MagAO project hosted our Pre-Ship Review (PSR) last week at Arcetri Observatory in Florence. The purpose of this review was to ensure that lab work on the AO system is complete and that MagAO is ready to move to the telescope for on-sky commissioning.
Six external reviewers (4 in person and 2 by videocon) gave us their time and attention for 2 days in real time, as well as studying up beforehand and writing a report after the fact. The scope of their expertise covered subjects from large telescopes, commissioning AO systems, instrument development, logistical implementation, real-time software, and adaptive secondaries.
The review lasted 2 days and included presentations, discussions, and a demonstration of the AO system in the tower, controlled from the chem. lab. Topics included a description of the Magellan telescope, an overview of the MagAO project and instrument, the scientific justification, detailed technical descriptions of all subsystems, logistical considerations, and our plans for commissioning. The reviewers considered everything in detail and gave us a report in the format of Findings, Comments, and Recommendations.
The review went very well — the reviewers were extremely thorough and helpful. They included three requirements and four recommendations, as well as findings and comments. We are working to address the requirements identified by the panel, before we ship to Chile. Two have been addressed already this week, and the third is waiting for next week.
Here are some photos from the review:
The PSR panel visiting the solar tower lab during the review. The large black ring hanging from the ceiling, which we call 'The Nas', contains our wavefront sensor and the VisAO science camera. Below that are our electronics racks, which will actually mount on the side of The Nas at the telescope.The MagAO PSR had lunch at Galileo's house. Galileo once walked this very balcony. This is our "album cover" shot.A happy AO operator is a good AO operator. Katie Morzinski, MagAO's newest team member, operated the AO system for the PSR panel. On her screens you can see the 4 pyramid sensor pupils, the SDSS i' PSF, and a glimpse of our mirror status displays. In the background you can also catch a glimpse of the VisAO camera in action.Alfio Puglisi explains some of the finer points of AO with pyramid sensors and adaptive secondaries, while Katie Morzinski and Jared Males concentrate on the loop.At the after party in the MagAO home-away-from-home at Via Romana 89. The entire team celebrated a successful moment in the project after many years of 'blood sweat and tears'.The MagAO PSR team celebrates the end of an intense 2 weeks. Speakers provided by Enrico "How many Watts RMS?" Pinna and music provided by Katie "Girl Bands" Morzinski.The PI holds forth - toasting a job well done by the entire team. A beam of light descends down on him to mark the occasion.The MagAO team, Magellan telescope experts, and Pre-Ship Review panel on the balcony at Galileo's house, inspired by a place where Galileo pointed his telescope to the heavens. Back row: Povilas Palunas, Al Conrad, Doug Miller, Jared Males, Ian Bryson, Marco Xompero, Runa Briguglio. Front row: Alfio Puglisi, Katie Morzinski, Simone Esposito, Carmelo Arcidiacono, Laird Close, Mark Chun
Yesterday we tested closing the loop on a faint R=13 mag star. Ambient light from computer monitors in the test tower was too bright and so we closed the loop from the “control room” in the chem. lab. It’s a good thing we got all the computers, desks, and high-speed ethernet links so that our control room is all set up and we could darken the “dome”!
We closed the loop on this R=13 star with the conservative 75th %ile seeing we’ve been using, 0.8” FWHM (r_0~15cm) and 33 mph winds (~15 m/s). The frame rate was 200 Hz to get enough counts on the WFS with the pixels binned by 2. Our resulting Strehl was 13% in z’-band which is about 200 nm rms wavefront error. (The correction for our simulated turbulence not having high-order modes, and the correction for the double-pass on our DM in the test tower have a negligible contribution at this level). Here is the image in z’-band:
For comparison, typical Keck AO wavefront control on H~7-9 mag NGS is also around 200 nm, or ~50% Strehl in H-band (result from 1000 Keck images from my dissertation). So we are quite happy with this image quality!
Last week on Tuesday we closed the loop in the test tower, verifying our performance from the November run and validating our excellent wavefront control with MagAO.
We simulated 0.8” seeing (~15 cm r_0) in a 33 mph (~15 m/s) wind and closed the loop on an 8.5-mag guide star running at 1000 Hz with a pyramid modulation amplitude of 0.17 or about 3.5 lambda/D. We are correcting 400 modes, each one with an optimzed gain. The resulting image quality (right) is 85% Strehl at 982 nm effective wavelength, or about 65 nm residual wavefront error. The slight elongation manifested as subtle lobes on the first Airy ring at a position angle around ~60 deg. is most likely caused by time delay along the wind vector. Note that these images are linear scale, not log scale — and note the similarity of the ideal and the achieved PSFs!
Jared’s note at /uncategorized/a-better-closed-loop/ explains more about the differences between our simulated turbulence (limited to low and mid spatial frequencies by our 585-actuator DM) and Kolmogorov turbulence in the real atmosphere. We calculate that true atmospheric turbulence would add a moderate amount of wavefront error, and would bring our measured image quality of 65 nm WFE (85% Strehl) to more like 100 nm (68% Strehl).
Another difference between the test tower and the telescope is that our telescope simulator is double-pass on the ASM, so that our internal static error is doubled to ~75 nm rms as compared to what we should see on sky. Correcting for this effect improves our estimated on-sky WFE to ~70-80 nm rms (75-80% Strehl)! For comparison/sanity checking, LBT has thus far achieved 90% Strehl at H-band or ~85 nm rms WFE at best on sky in Arizona.
We (Laird, Jared, Katie, Alfio, Armando, Marco, Runa, Enrico, Simone, Luca, Carmelo, and Alessandro) have been working hard all week here at Arcetri to prepare for the Pre-Ship Review.
For today’s installment we have a video of the VisAO PSF as we test closing the loop and adjusting the gains. Laird is narrating and Katie is operating MagAO in this clip.
Descripion of video: The Magellan AO system loop closing and opening at 1kHz on an 8.5-mag guide star in 0.8” seeing with 33 mph (15 m/s) wind. The image viewer is showing our SDSS i’ PSF, and we have selected a 32×32 subwindow of the CCD 47 (our VisAO science detector) to operate at 42 frames per second. You can see the impact on Strehl ratio (calculated from slope telemetry) and FWHM (fitting the PSF in real time) when the loop gains are low.
First we see the closed-loop PSF. Then the loop is opened. When we close the loop, we start with low gain and slowly ramp up first the low-order gain and then the high-order gain. MagAO is operated with modal gains so that each mode (up to 400 controllable modes) can be operated with its own gain. The automated gain algorithm searches for the best gain for each mode that minimizes the WFE. However, gain can also be adjusted by hand, in groupings of low-order (tip/tilt), mid-frequencies, and high-order (above 100 modes for bin 1).
Laird and Katie on the walk to Arcetri, with the only snow we've found in Florence.
Due to the always too short amount of time we get to spend with our instrument here, we work some long hours. Late at night and on weekends the front gate to Arcetri is closed, so we have to go around the back way. It is actually a nice walk, and we discovered the last remaining snow in Florence. In the picture you can see the top of the Solar Tower, where our adaptive secondary mirror is mounted. It is performing very well, and we are putting the last touches on the amazing automation that was developed here at Arcetri.
