1. The Active Optics System S. Thomas and the AO team

2. The Active Optics System 2 Wavefront Sensor Estimation (WEP) Active Optics Control System Maintain system alignment Maintain surface figure on three mirrors M1M3 Controller M2 Controller M2 hexapod Controller Camera hexapod Controller Camera DAQ for WFS images Science images from DM? For each detector: -Instrument Signature Removal -Source Selection -Masters computation -Compute the Zernike Coefficients Zernike Coefficients for each detectors Crosstalk corrected images -Optimal estimator -Control algorithm using a cost function Catalog Calibration Product Focal plane map Sensitivity matrix Prior knowledge of the system Bending modes Forces

3. 3 WEP 3 Curvature sensing enables significant flexibility in selecting sources due to the large field of view of the area sensors split sensors: because of the fast f-number (f/1.23) and crowded focal plane, using a beam splitter and delay line or physically moving the detector will not work. Use multiple sources to increase S/N, to help average out atmosphere noise, and to alleviate problems due to vignetting. LSST WFS challenges - 61% Central Obscuration - f/1.23 - Off-axis Distortion & Vignetting (~1.7 o ) - Field Dependence (covering 1.51° to 1.84°) The defocus for the WFS detectors is +/- 1mm (TBC)

4. WEP Status -Publication of the update to the basic curvature sensing algorithm by Bo Xin (large central obscuration, small f/number, distortion and vignetting) -Requirement document close to completion -Understand interfaces -Understand calibrations -WEP translated from Matlab to Python -Start to include the WEP in the DM stack 4

5. On sky tests 5 Chuck Claver and Bo Xin had a one-night observing run on Magellan (3/30/2015) To test LSST curvature wavefront sensing software IMACS f/2, SLOAN r filter, 26.5% central obscuration Piston secondary mirror to get defocused donut images Nominal setup: 3.5mm image defocus. Analysis of wavefront was done in real time. Good agreement in general between system input and the curvature wavefront estimates

6. AOCS Status An algorithm written in Matlab exists and Paul Lotz will be in charge of the translation in Labview. Include the telescope models and use PhoSim to built the look-up-table (temperature, elevation and azimuthal angle). “closed-loop” done using Zemax simulations and bending modes of the mirrors Need to close the loop using PhoSim 6

7. 7

8. Data Quality Control In the WEP: – Source Selection – Master Consequence: The Zernike coefficient for the specific wavefront sensor is truncated. In the AOCS: – Check forces sent to the various controllers Consequence: TBD? 8

9. Future Work Write the ICDs for the different mirrors and hexapods, and also with Data Management Include the telescope models in the look-up- table (temperature, elevation and azimuthal angle). Include the AOS code in the DM software stack (one first step is to add the code on github) 9

10. Issues -Should we send the offsets to the mirrors or the actual forces -Need to update the interface documents (to the mirrors and hexapods) -How to make this system automatic and robust? -Still a few unknown, some of which we won’t know before going on sky (such as how often do we want to update the forces) 10

11. 11

12. 12 Wavefront sensor camera 12 ICD provides specifications and tolerances: Offset distance for intra/extra focal sensors +/- 2mm?? Flatness 10 microns rms Placement wrt science FPA +/- 20 microns in along z-axis Sensor noise and QE Matches science sensors Useable effective sensor area 80 arcmin 2 x two halves Data exchange and format

13. Image quality drives AOS related requirements Science Requirements Document (LPM-17) LSST System Requirement (LSE-29) – Mandates 0.4 arcsec FWHM from the system (Telescope + Camera) – Plate scale control not required Observatory System Specifications (LSE-30) – Optical prescription – Allocates 0.30 arcsec to the Camera – Allocates 0.25 arcsec to the Telescope – Additional AOS error is captured fully in the Telescope allocation – Mean slew and settle time of 5 sec. between visits Telescope and Site Requirements (LSE-60) – AOS functional requirements – Alignment and Compensation Detailed Image budgets – Telescope & Site image budget (LTS-123, LTS-124) – Camera System (LCA-17) Title TMA Review Tucson, Arizona May 9-10, 2013 13

14. Covariance Analysis 14 (Algorithmic + atmospheric) Covariance matrix Total covariance is almost entirely dominated by atmosphere – Diagonal elements (lower left) similar – Singular values (lower right) also similar; some increase for low singular values Variance Singular values