Robert Stobie Prime Focus Imaging Spectrograph Status

1
Robert StobiePrime Focus Imaging
SpectrographStatus

• On-telescope throughput analysis
• Ghost analysis
• Repair plan
• Status of other current control and mechanical
  issues
• Commissioning progress
• Budget

2
RSS Optics Throughput Shortfall

• Telescope system testing found RSS optics
  throughput 60 of expected in visible, lt 25
  below 375 nm
• Either blank absorption or coatings at fault

3
Blank Absorption Investigation

• Polished and measured spare NaCl blank - good
• Remaining possibility of effect found for UVES
  coating process causing development of "color
  centers" in CaF2. Curable by UV Flooding

4
Throughput Test Apparatus

• To isolate optical subsystems with problem and
  narrow range of causes, develop apparatus to
  measure throughput of integrated optics at 375
  and 635 nm
• Tests performed 23 - 30 Sept, 2006

5
Throughput Experiments
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Subsystem Throughput

• Throughput of 7 subsystems derived
• MgF2 coatings, LLNL fold flat exonerated
• Visible loss in collimator main group and camera
• UV loss also in collimator doublet
• Multiplying losses consistent with on-sky system
  results

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Conclusions

• no common coatings gt at least 2 separate
  problems.
• doublet shows transmission lt 1 - reflectivity gt
  CaF2 color center possible. Definitely
  multilayer coating problem.
• problem in collimator main group means instrument
  must come off.

8
Ghost

• Flatfield ghost with interference filter imaging
  and Fabry-Perot
• in interference filter sky images and flat fields
  see 10 doughnut which appears to be an image
  of the pupil
• does not show up with clear or color filters gt
  one ghost surface is the filter (reflection 10
  100 depending on wavelength)
• a severe problem for FP mode
• determined to be internal to RSS
• Ghost investigation
• take flats with various pupil masks inserted in
  grating holder, field mask at slit
• raytrace analysis to find surface that forms
  pupil image
• circular polaroid between ghost surfaces should
  eliminate it

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Ghost Geometry

• Mask experiments -gt 2nd surface in camera
• Polaroid experiment -gt after filter
• Raytrace -gt dewar front surface

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The trouble with the dewar window

• Predict surface reflectivity from observed ghost
  intensity vs wavelength up to 20 peaking at 540
  nm
• remove detector, measure and inspect window
  yellow-green
• Another (different) multilayer problem
• Fix during throughput repair

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Repair plan
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Control Issues

• Grating insertion interlock problem
• not interlocked against inserting grating when
  etalon or articulation is in wrong status.
• this works on built-up spare at UW. Suggests
  wiring or board problem in RSS electronics box.
• Found error and fixed.
• Waveplate homing problem
• found that we need to turn off the waveplate
  rotator encoder when not moving it (stray light).
  Rotator homing then does not work.
• again, this works on built-up spare at UW.
  Suspect a software or firmware incompatibility.
• hardware verified with encoder diagnostic
  software.
• software not waiting long enough after turning
  encoder on. Software problem identified

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Mechanical Issues

• Slitmask mechanism
• severe reliability problems due to difficulty of
  aligning magazine, carrier, and focal plane chute
• temporarily removing magazine, using insertor to
  inset and remove a manually loaded slitmask
• SAAO redesigning slitmask assembly to make it
  monolithic, aligned on bench
• install during down time
• Articulation fall arrestor
• safety restraint to prevent catastrophic damage
  in case articulation motor fails during
  articulation
• installation and testing within a few days
• Polarizing Beamsplitter
• SAAO task to redesign and manufacture
  beamsplitter insertor to allow for beamsplitter
  removal/ rotation/ insertion in situ
• clearance issues resolved. Now installed

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Commissioning - Longslit Spectroscopy

• Mostly done. Many PV proposals used.
• Autoguide setup procedure mature
• Calibration procedures developed

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Commissioning - MOS

• Slitmask cutting process tested
• Manual acquisition with MOS painful (10 - 20 m),
  but surprisingly possible
• Orientation control issue identified with
  slitmask cutting/ TCS software
• Needs slitmask magazine, more automated
  acquisition procedure to be practical

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Commissioning - Fabry-Perot

• On 20060922, first light RSS on-sky Fabry Perot
  observations two spiral galaxies, NGC 1535 and
  NGC 1365, at Ha through the LR etalon.
• roughly 20-step etalon scans through the line.
• An initial reduction of the data cubes shows a
  velocity map for NGC 1365 which compares well
  with data obtained on other telescopes
• throughput is within 2x of expected

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Commissioning - Continued

• Polarimetric. Next two weeks
• linear polarization lamp calibration
• spectropolarimetry on-sky first light
• linear standards, high and low-res PV
• circular mCV
• High speed awaiting detector software issue
• All UV commissioning after repair (starting May?)

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Cost to Completion

• Does not include 50 - 100 K for optics repair
  costs (mostly optomechanical)
• Predicting CTC 20 over CDR budget