Author: Katie Morzinski

• Information for Observers

The director of Arizona’s telescope time at Magellan has just issued a call for proposals for MagAO for 2013A.  This is for shared-risk observing during our second commissioning run, during early April of next year.  These observations will demonstrate our new AO system and science cameras in the best way possible — with science!  Eligible astronomers are at public universities in Arizona (those sharing Magellan telescope time with us).  This is an exciting opportunity to get involved in the first high-order AO system having broad O/IR spectral coverage!

Please see our webpage with information for observers for help in planning your telescope proposals.  The optical wavelengths will be available for observation with VisAO and the near-infrared with Clio2.

Note that we (the commissioning team) will execute, in a “mini-queue”, the top TAC ranked MagAO proposals (for Clio2 or VisAO or both) in a shared-risk manner. The proposal PI would participate with the team, and could optionally join us in person, but attendance at Magellan would not be required. All proposals for this special call need to be signed off on by the MagAO PI (Laird Close, lclose at as.arizona.edu, 520 626 5992) before TAC submission. The MagAO commissioning team would receive proper credit (co-authorship) for our efforts in accomplishing any of the proposed science programs.

This video demonstrates the MagAO high-level software GUIs used to acquire the star, set up the AO system, and close the loop.  The entire process takes about ~3-4 min. at this time.

(Filmed by Alfio, narrated by Laird, cameo by Katie operating the VisAO camera)

Go to https://www.youtube.com/watch?v=wSiFoG8qgKI to view the video in high-def.

Description:
After the telescope slews to a new target, the guider will acquire the star to within 4” on the Technical Viewer (CCD 47 in AO acquisition mode; otherwise CCD 47 is the VisAO array).  Next, the MagAO Command GUI controls the AO system and is operated as follows:

1. PresetVisAO — Transforms the CCD 47 from its role as the Science Camera (VisAO) to its role as the AO acquisition camera (Technical Viewer).
   • Takes control of the CCD 47, gimbal, and filter-wheel 2 and 3
   • Opens up filter-wheel 3 (coronagraph stops and SDI narrow-band filters)
   • Centers the gimbal
2. PresetAO — Configures the board for acquisition, and uses the estimated NGS magnitude in order to determine the AO system parameters (frame rate, modulation, binning).
   • Start with a guess of the NGS mag (entered by hand, or will be read in from the starlist provided by the astronomer) — required for appropriate speed and binning to get good SNR photometry. These settings are read from a lookup table
   • Opens up filter-wheel 2 (SDSS r’, i’, z’, and 950 long-pass filters)
   • Moves gimbal to point off axis to take CCD 47 darks
   • Sets binning and framerate on both CCD 39 and CCD 47 based on the estimated NGS magnitude.
   • Places the beamsplitter wheel in the dark position for CCD 39 darks
   • Once darks are taken, re-centers the gimbal
   • Wait for all movements to finish (stages, filterwheels, etc)
3. AcquireRef — Aligns the guide star onto the pyramid.  Metric is position of the star on the Technical Viewer (CCD 47).
   • Finds star on Technical Viewer
   • Finds offset from pre-determined home position (green cross)
   • Moves X,Y Bayside stages (entire W-unit) to remove offset
   • The above steps are performed iteratively until the star is on the green cross to within 0.2 mm of stage movement
   • Set filter-wheels for AO. Filter-wheel 1 (beam splitter) will be placed in the correct position based on star magnitude.
4. AutoCenter — Fine-tuning of the alignment onto the tip of the pyramid.  Metric is pupil illumination on WFS camera (CCD 39).
   • Button on the CCD 39 image viewer
   • Moves X,Y Bayside stages to even out the illumination (i.e. zero out tip and tilt)
   • Iterative process; Final precision is ~few microns
5. StartAO — Closes the loop.
   • First closes the loop with only 10 low-order modes to center up the camera lens (the camera lens loop aligns the pupil images to keep the illuminated pixels constant to 1/10th pixel)
   • You can next load artifical turbulence in the lab to simulate on-sky AO
   • Sets the frame rate, modulation, and binning determined in PresetAO
   • Closes the loop with all modes (400 modes in bin 1; 120 modes in bin 2; 50 modes in bin 3; 28 modes in bin 4) and low gain
   • AutoGain starts and iteratively guesses-and-checks the gain for each mode grouping (low, mid, and high) that minimizes the slope RMS
6. Finally, we have an optimized closed loop. The instrument can be turned over to the astronomer for diffraction-limited data acquisition

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!