Robert Stobie Prime Focus Imaging Spectrograph Status. On-Sky Grating Spectroscopy Performance: Method

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1 Board Papers: * * Robert Stobie Prime Focus Imaging Spectrograph Status On-Sky Performance/ Acceptance Data Package Throughput/ grating performance Still to complete: Fabry Perot, PSF, Polarimetry Fixes Throughput Beamsplitter Fabry Perot dual etalon mode Calibration/ Reduction issues Bias Imaging and Spectral Flats Spectrophotometric Standards Nov 7, 2012 RSS Status - SALT Board #32 1 On-Sky Grating Spectroscopy Performance: Method 579 spec standard observations, 4/1/2011 8/1/2012 all gratings, 21 stars, 118 configs saltclean, spec model wavelengths, python extraction from obs/ expect remove: Sutherland mean extinction P Vaisanen telescope throughput, pupil RSS QE from SAAO, 2008 grating efficiency model from lab data fit left with: RSS optics x transparency x telescope mirror cleanliness remove grey variation by shifting to max => rms of mean a few percent plausible transparency vs time Nov 7, 2012 RSS Status - SALT Board # l/mm Lab data, Kogelnik fit 1800 l/mm (46 observations) response Optics Throughput Wavelength (Ang) 4 gratings (265 observations) transparency vs time median: 78% Efficiency PG1300 PG1800 PG2300 PG % 80% 60% 1800 l/mm cor Mean 40% 28.6 deg Fit deg 20% Fit deg Fit 0% Wavelength (nm) 2 1

2 Optics Throughput On-Sky Throughput Results, To Do 0.3 FPRD Min 2008 Monochrom Fixed Coll Dblt 0.2 Laser PG1300 PG1800 PG2300 PG Wavelength (Ang) 4 gratings done independently, agree to 10%, plus agree with 2012 SALT laser measurements Falls like 35% below expected (grey-blue) from predelivery monochromator, consistent with fluid transmission problem in collimator triplet Possible ~20% drop at 380 nm; feature seen in monochromator for collimator doublet (not a large effect) Possible time dependent drop below 320 nm Still to do: 900 l/mm grating. Lab data not fit by Kogelnik, not even by RCWA detailed model. Get grating model using on-sky data + optics throughput from 4 gratings Update Acceptance Package, simulators with new throughput, grating models Nov 7, 2012 RSS Status - SALT Board #32 3 Acceptance Package, To Do Done Fabry Perot numbers (TW) Optics imaging performance, PSF (KN, January) Polarimetry: Use 2011 commissioning data (KN, February) Nov 7, 2012 RSS Status - SALT Board #32 4 2

3 Acceptance Package I FPRD Description Specification Pre-Delivery Req # Imaging Field Size 8 arcminute diameter PASS; 8.12 arcminutes Slit Mask Capability Arbitrary features down to PASS 0.45 arcsec Collimation 60 micron defocus < at CONCEDE detector Post-Delivery On-telescope # Collimation measured with Fabry-Perot ghosts Image Quality See FPRD Table 1 PASS Imaging mode tested at 629 nm 4 full +/ Focus Range +/- 400 microns PASS; +/- 500 PASS: 1.5 mm 600 microns microns range Comments Set by machined aperture in slitmask frame. Extended to accomodate actual filter thicknesses Detector Pixel Scale0.128 arcsec/pixel PASS Flexure Dispersion direction: FAIL <0.1 arcsec/track Perp. to dispersion: <0.15 arcsec/track Transmission See FPRD Table 2 PASS arcsec/pixel 6 CONCEDE: Detailed Imaging mode flexure Dispersion data at rho +/- 100 deg direction: 0.2 arcsechrack 7 Perp. To dispersion: 0.3 arcsechrack ~70% of expected (grey) ~65% of FPRD Min 8 After SALT ADC remount Stray Light Collimator/Camera ghost brightness < 10 4 PASS: 434 nm: 1.6x nm: 2.9x10-5 Disperser (focused) ghost brightness <1 0-3 CONCEDE Spectroscopy FOV 8 arcmin diameter PASS Max Resolution 1.25 arcsec slit R=5300 PASS arcsec slit R= Grating efficiency See FPRD Tables 3 and 4PASS 12 No values <350nm Central Wavelength AA, <1 nm x (300/a) PASS Repeatability retested PASS after 13 Precision modifications to grating mechanism Etalon Resolution Low Res: R= CONCEDE: TF: LR: Mid Res: R=2500 CONCEDE: Nov 7, 2012 RSS Status - SALT Board # Acceptance Package II FPRD Description Specification Pre-Delivery Post-Delivery On-telescope # Comments Req # High Res: R=12500 CONCEDE: FP Spectral Range nm PASS FP Field of View 8 arcminute diameter PASS FP Wavelength 2r=i1c cos(4.877 x r/4) PASS 17 Gradient FP Wavelength FWHM/50 PASS Precision TF: /120 LR: /220 MR: /170 HR: / FP Wavelength FWHM/3 per hour LR: PASS HR: PASS Stability MR: PASS HR: NO TEST FP Wavelength Set 2 msec CONCEDE Time 2 msec in controller, 100 msec practical in Labview FP Efficiency 75% minimum CONCEDE 60% Blue (approximately achromatic); 85% Red 80% expected (approximately achromatic) Parasitic Light Polarimetric FOV Polarimetric Efficiency Low Res: <1.5% NO TEST PASS Mid Res: <1.0% NO TEST NO TEST High Res: <6.0% NO TEST NO TEST Linear: 4x7.2 arcmin NO TEST PASS: Unvignetted to 7.3 arcmin diam Circular: 3 arcmin diam NO TEST CONCEDE: Unvignetted to 2.8 arcmin diam Linear: >95%, calibrated NO TEST PASS: Have data to better than ±0.5%. Linear: >95% nm Circular: >92%, Circular: >94% calibrated to better than ±0.5% Nov 7, 2012 RSS Status - SALT Board #32 6 3

4 Acceptance Package III FPRD Description Specification Pre-Delivery Req # Instrumental Linear: <0.4%, calibrated Polarization to <0.04%. Linear to circular<3x10-3, calibrated to <3x10-4 Post-Delivery On-telescope Linear: ~ 0.2% # Comments Position Angle Repeatability Repeatability <6 arcminutes Transmission 70% of spectroscopic/imaging modes at 650 nm CTE CTE= % (typical), % (guaranteed) Full Well 200 k e7pix (typical) 150 k e7pix (guaranteed). NO TEST PASS: <1.8 arcminutes Have Data NO TEST PASS: >70% Have Data NO TEST NO TEST PASS: > % PASS: >153 ke" Sensitivity see FPRD Table 5. PASS. See Table below Dark Current Dark current of 1 e7pix/hr NO TEST LATER: (typical) at 163 K <1.5e"/pix/hr Readout Noise 3.0 e7pix at 100kHz (10.0 See table below See table below See Table psec/pix) TBC4; 5.0 e7pix at 345 khz (2.9 psec/pix) TBC Gain Software selectable from : See table below PASS: see table See Table xl; x2; x4.75; x9.5 below Prebinning /x/ to 9x9, independently in PASS each direction Readout Speed Frame transfer architecture: 4microsec/pix sec frame transfer FAST; time khz ( microsec/pix psec/pix) See FPRD Table 34 SLOW 6 for detector readout times BRIGHT/ FAST changed to high dynamic range Nov 7, 2012 RSS Status - SALT Board #32 7 Fix I - Throughput Suggest focusing effort on collimator triplet fix on-sky throughput data indicates collimator doublet UV drop is much smaller (~ 20x) than triplet greyish problem. doublet can be replaced in situ if future evidence suggests the value Triplet options complete replacement (Ockert Table 19) NaCl complete spare + cleaning (Ockert Table 18) Completely a budget/schedule/risk issue Nov 7, 2012 RSS Status - SALT Board #32 8 4

5 Fix II - Polarimetric Beamsplitter During Nov 2011 polarimetric commissioning, beamsplitter found to have developed a slow coupling fluid leak Decision to re-engineer beamsplitter to do without fluid UW, TPG, BB, KLC Analysis: Two fluidless options fluid -> thick glue. Con: calcite E and O have large thermal mismatch (breakage risk). fluid -> air gap. Con: lose mosaic alignment capability, require inner AR coat (risk). Plan Phase I: lab investigation of glue option (preferred) Phase II: glue, if it works, else air beamsplitter Nov 7, 2012 RSS Status - SALT Board # Updated: 5-Nov-2012 Dec-12 Jan-13 Feb-13 Mar-13 Phase I: Lab Work Fabricate Test Cell Assembly, Align Testing Transmission Beam Deviation Thermal Survival Cold/Hot Optical Phase II: Remount grating Fix III - Dual-Etalon Ghosts Dual etalon on-sky images reveal extensive ghosting between etalons verified by insertion of circular polarizer between etalons: ghosts vanish probably not usable as is Proposed fix rework etalon fixtures to align etalons sufficiently to superpose ghosts UW design awaits approval awaits demonstration that alignment would be held during swap of etalons on telescope to be implemented by SALT mechanical team, installed on telescope Nov 7, 2012 RSS Status - SALT Board #

6 Calibration I - Biases Courtesy of Arthur Eigenbrot, UW Current saltclean pipeline default does overscan subtraction only, leaves bias structure Better method: remove overscan from both program images and from sum of biases, subtract immediately conceivably, one can do this using pipeline master bias option, running clean by steps details of method at Bias Overscan cor n only Overscan + master cor n master overscan Nov 7, 2012 RSS Status - SALT Board #32 11 Calibration II Standards, Flats Imaging flats suggesting use of tracked sky flats with moving baffle placed at center position of previous images requested as commissioning proposal by Jenna Ryon, UW Spectral flats suggesting spectral flats obtained during daytime with moving baffle repeating observation track intended to correct for VPH grating nonuniformity which causes blaze to be a function of position in pupil daytime data obtained for Arthur Eigenbrot, under analysis Spectrophotometric standards not able to successfully self-calibrate standard stars using current pipeline routine. Ben Brown, UW, has hacked a version of pipeline to work correctly Nov 7, 2012 RSS Status - SALT Board #

7 Questions? Nov 7, 2012 RSS Status - SALT Board #32 13 CCD Optics (Etalons) Fabry-Perot (Grating) Shutter VPH Spectroscopy (maximum articulation) CCD Nov 7, 2012 RSS Status - SALT Board #

8 Monochromator Collimator Field Lens repair: UV loss was very small - repaired as precaution went to fluorosilicone lens fluid for NIR beam Triplet repair: interrupted by accident: final transmission as predicted went to fluorosilicone lens fluid for NIR beam Doublet repair UV loss gone except 20% dip at 350 nm ~10% grey loss still seen Nov 7, 2012 RSS Status - SALT Board #32 15 Monochromator- Camera/ Spec Quartet Repair. Looks good. Triplet Repair surface contact fix remedies grey loss fluid repair improves UV, leaves some loss at 320 nm Remeasurements after 8-12 months show no degradation Project visible ~FPRD spec, 40% low at 320 nm Nov 7, 2012 RSS Status - SALT Board #