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Introduction to NIRSpec

Introduction to NIRSpec. Michael Regan. JWST Project Manager P. Jensen. Project Scientist P. Jakobsen. Contracts Officer V. D’Hoedt. Admin. Assistant A. Plitzke. Deputy Project Scientist T. Boeker. System Group. Subsystem Expert Group. PA Manager J. van Dooren.

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Introduction to NIRSpec

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  1. Introduction to NIRSpec Michael Regan

  2. JWST Project Manager P. Jensen Project Scientist P. Jakobsen Contracts Officer V. D’Hoedt Admin. Assistant A. Plitzke Deputy Project Scientist T. Boeker System Group Subsystem Expert Group PA Manager J. van Dooren Project Control Manager Z. El Hamel Science Support NN NIRSpec Pr. System Engineer G. Bagnasco Ops, SW & Detector System P. Strada Documentation & Conf. Control D. Green Science Operations Team NN MIRI Principal System Engineer A. Marini Electr. System Engineer & AIV P. Rumler Schedule Control J. Molleman Launcher System Engineer P. Rumler Optical System Engineer M. Te Plate Optical Support P. Marenaci (YGT) Mechanism Engineer* B. Henson Mech. Thermal System Engineer J-C. Salvignol * leaving

  3. JWST Architecture Integrated Science Instrument Module (ISIM) Element Optical Telescope Element (OTE) Sunshield Spacecraft Bus Sun

  4. Telescope

  5. Telescope

  6. ISIM & Regions

  7. Thus Spoke ASWG

  8. Current Mission Requirements (the TAC will decide anyway…)

  9. NIRSpec

  10. Enter NIRSpec NIRSpec: A Pretty Picture is Not Enough

  11. NIRSpec: Thus Spoke ASWG • 3 x 3 arcmin FOV • 1-5 µm coverage • R~1000, R~100 multiplexed • >100 sources simultaneously • Configurable slit width/length • MEMS array preferred

  12. NIRSpec Procurement • Instrument built by European industry under ESA project leadership • Under study since 2001 • Presently entering implementation phase • Two NASA-provided components: • 2 x 2k x 2k HgCdTe Detector Array • 4 x 384 x 185 Micro-Shutter Array

  13. NIRSpec Modes • R=100 (exploratory spectroscopy) • Single prism 0.6 - 5.0 µm • Micro-shutter array or fixed Slits • R=1000 (emission line diagnostics) • 3 gratings 1.0 - 5.0 µm • Micro-shutter array or fixed slit(s) • R=3000 (emission line kinematics) • 3 gratings 1.0 - 5.0 µm • Fixed slit or integral field unit

  14. Wavelength Coverage • R=1000 & R=3000 modes • 1.0 - 5.0 µm • Covered by three overlapping first order gratings: • 1.0 - 1.8 µm • 1.7 - 3.0 µm • 2.9 - 5.0 µm • R=100 mode • 0.6 - 5.0 µm (as NIRCAM) • Covered by single dual-pass prism • Coverage below 1.0 µm is not allowed to drive anything • Resolution to be kept within factor 2 of R=100 1.0 - 5.0 µm • Resolution below 1.0 µm to follow

  15. You Can’t Fight Red shift ! ! NIR MIR

  16. Micro Shutter Array IFU Single 200 mas x 450 mas slits surrounded by 60 mas wide bars >100 objects simultaneously 4 x 384 x 185 Shutters 9 Square Arcmin of MSA Area

  17. A Bit of MEMS History • Initially both Micro Mirrors and Shutters • Mirrors eliminated due to excessive diffraction effects • Initially slit to be made up of several shutters • Later transitioned to “fat MEMS” • Huge simplification of optics • Factor ~4 reduction in MSA array • Reduced slit loss • At expense of multiplexing loss

  18. Diffraction & Slit Loss Spectrograph Entrance Pupil Telescope Exit Pupil Diffracted Output Beam Footprint of PSF

  19. MSA Close-up Key Requirements: Contrast: >2000 (!) Open Fill factor >70% (60 mas bars on 200 mas wide slits)

  20. MSA Magnet Mechanism

  21. MSA in Action

  22. Integral Field Unit

  23. Integral Field Unit • FOV: 3” x 3” • Sampling: 0.1” • ~30 Slicers • Entirely passive device (no moving parts) • Shuttered by MSA magnet mechanism • Main use R~3000 single object • But R~1000 and R~100 too.... • Superb backup in case of MSA failure • Point and shoot operations

  24. Integral Field Unit Relay optics Slicer Stack (30 slices) Slit mirror Line (30 elements) Pupil mirror Line (30 elements) IFU aperture

  25. Detector Array • 2K4K FPA comprised of two 2K2Ksensor chip assemblies (SCAs) • =0.6–5.0 µm HgCdTe detectors (Rockwell) • FPA passively cooled to T=34–37 K • Key Performance Parameters: • Total noise =6 electrons rms per t=1000 seconds exposure) • QE = >80% • NIRSpec is detector background limited in nearly all modes (!) • Non-stop (“up the ramp”) read and telemetry • 12 s frame time, 1 frame downlink each 50 s

  26. Why R=1000?

  27. Ha [NII] [NII] Why R=1000? • Science requirement • Clean emission line separation • Main challenge: • [NII] 6548.1 :1 • Ha 6562.8 metallicity diagnostic • [NII] 6583.4 :3 • and also: • [SII] 6716.4 density diagnostic • [SII] 6730.8 R=446 R=319 R=467

  28. Why 200 mas Slit? 1:2 MSA aspect ratio fixed 1.4 µm - Band I 2.4 µm - Band II 4.0 µm - Band III

  29. Why 200 mas Slit? 2 pixels across slit 200 mas optimal?

  30. Optical Schematic 200 mas per 79.5 µm wide shutter 2.52 “/mm, f/12.5 100 mas per 18 µm pixel 5.56 “/mm, f/5.67 1.58 “/mm, f/20

  31. Optical Layout • Buzzwords: • TMA’s • Scheimflug

  32. Focal Plane Layout & Scheimflug NIRCam NIRSpec

  33. Physical Layout

  34. Physical Layout

  35. SiC The wonder of modern ceramics

  36. WFE at MSA • Requirement: • Diffraction-limited at 2.4 µm • WFE = 180 nm rms or better • 131 nm rms OTE input specified • Fore optics challenging • Relaxation requires degrading sensitivity • Increased slit losses • Reduced photometric accuracy

  37. Ha [NII] [NII] WFE at FPA • Requirement: • Diffraction-limited at 3.0 µm • WFE = 225 nm rms or better • Camera optics challenging • Relaxation requires degrading sensitivity • Larger resolution element • Decreased sensitivity • Jeopardize spectral resolution

  38. NIRSpec Image Quality FPA with Cross-talk PSF at FPA PSF at MSA FPA 100 mas pixels PSF at MSA

  39. Grating Wheel 8 Positions: 1. R=100 Prism 2. Band I R=1000 Grating 3. Band II R=1000 Grating 4. Band III R=1000 Grating 5. Band I R=3000 Grating 6. Band II R=3000 Grating 7. Band III R=3000 Grating 8. Provision for imaging mode

  40. Filter Wheel 8 Positions: 1. Clear Aperture 2. Closed 3. Band I Long Pass l >1.0 µm 4. Band II Long Pass l >1.7 µm 5. Band III Long Pass l >2.9 µm 6. Narrow Band TA l =1.1 µm 7. Broad Band TA 0.9 < l1.1 µm 8. Broad Prism 0.9 < l5 µm Current Issue: Filters in pupil – should they second as pupil stops?

  41. Why Long Pass?One Object per Row

  42. Calibration Unit Carries both continuum and (FP-filtered) line sources

  43. NIRSpec Sensitivity Formal Level I Specs

  44. Mission Requirements

  45. Mission Requirements

  46. Target Acquisition Accuracy Goal: 12.5 mas (1s) • Partially documented in gory detail… • NIRSpec Operations Concept • Two dedicated tech notes (more to come)

  47. Image Mode Simulation 2.2 µm Centroid shift!

  48. Target Acquisition will be interesting

  49. STScI is currently working on several NIRSpec related studies • MSA planning tool (J. Valenti) • NIRSpec Target Acquisition Alternatives (M. Regan) • What’s in phase 1 and phase 2 with JWST (J. Valenti)

  50. STScI plays a crucial role in NIRSpec • MSA planning tool (J. Valenti) • NIRSpec Target Acquisition Alternatives (M. Regan) • What’s in phase 1 and phase 2 with JWST (J. Valenti) • NIRSpec Calibration Plan ( T. Keyes) • Guide Star Availability and planning (J. Valenti) • Do we use Observing templates? (J. Valenti)

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