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NIRCam : Wavefronts , Images, and Science

NIRCam : Wavefronts , Images, and Science . Marcia Rieke NIRCam PI STScI June 7, 2011. What’s NIRCam ?. View of the Goddard clean room . NIRCam is the near-infrared camera (0.6-5 microns) for JWST Refractive design to minimize mass and volume

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NIRCam : Wavefronts , Images, and Science

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  1. NIRCam: Wavefronts, Images, and Science Marcia Rieke NIRCam PI STScI June 7, 2011

  2. What’s NIRCam? View of the Goddard clean room • NIRCam is the near-infrared camera (0.6-5 microns) for JWST • Refractive design to minimize mass and volume • Dichroic used to split range into short (0.6-2.3mm) and long (2.4-5mm) sections • Nyquist sampling at 2 and 4mm • 2.2 arc min x 4.4 arc min total field of view seen in two colors (40 MPixels) • Coronagraphic capability for both short and long wavelengths • NIRCam is the wavefront sensor • Must be fully redundant • Dual filter/pupil wheels to accommodate WFS hardware • Pupil imaging lens to check optical alignment

  3. Design Overview Short wave camera lens group Light from Telescope Short wave fold mirror First fold mirror Collimator lens group Dichroic beamsplitter Pupil imaging lens assembly Coronagraph occulting masks Short wave filter wheel assembly Focus and alignment mechanism Short wave focal plane housing Long wave filter wheel assembly Long wave focal plane housing Long wave camera lens group • Fully redundant with mirror image A and B modules • Refractive optical design • Thermal design uses entire instrument as thermal ballast ; cooling straps attached to the benches • SIDECAR ASICs digitize detector signals in cold region • Uses two detector types – short wavelength HgCdTe and long wavelength HgCdTe (this one is same as used on NIRSpec & FGS)

  4. 2 Channels Per Module Short wavelength channel Long wavelength channel • Each module has two bands (0.6 microns to 2.3 microns and 2.4 microns to 5 microns) • Deep surveys will use ~7 wide band filters (4 SW, 3 LW, 2x time on longest filter) • Survey efficiency is increased by observing the same field at long and short wavelength simultaneously • SW pixel scale is 0.032”/pix; long is 0.064”/pix Module A Module B 2.2’

  5. NIRCam as a Wavefront Sensor First Light After segment capture Coarse phasing w/DHS Spectra recorded by NIRCam DHS at pupil Fine phasing After coarse phasing Fully aligned • NIRCam provides the imaging data needed for wavefront sensing. • Two grisms have been added to the long wavelength channel to extend the segment capture range during coarse phasing and to provide an alternative to the Dispersed Hartmann Sensor (DHS) • Alignment steps include: • Telescope focus sweep • Segment ID and Search • Image array • Global alignment • Image stacking • Coarse phasing • Fine phasing uses in and out of focus images (similar to algorithms used for ground base adaptive optics)

  6. Following the Light: 1st Stop is the FAM POM Assembly Prototype  POM  FAM being prepped for connector installation. Sensor & Target Assy Linear Actuators • FAM = Focus Adjust Mechanism • Pick-off mirror (POM) is attached to the FAM; POM has some optical power to ensure that the pupil location does not move when FAM is moved • Ensures correct mapping of NIRCam pupil onto telescope exit pupil

  7. Light LiF ZnSe BaF2 Following the Light: 2nd Stop is the Collimator One of the flight collimator triplets Transmits over entire 0.6 – 5.0 micron band Most of the optical power is in the ZnSe lens with the other two largely providing color correction Excellent AR coatings available

  8. Following the Light: 3rd Stop is the Beam Splitter • LW beam is transmitted, SW beam is reflected • DBS made of Si which greatly reduces problems with short wavelength filter leaks in LW arm • Coatings have excellent performance Flight beam splitters

  9. Following the Light: 4th Stop is the Filter Wheel Assembly (FWA) One of the flight LW pupil wheels Dual wheel assembly has a pupil wheel and a filter wheel, twelve positions each, in a back-to-back arrangement Filters are held at 4 degree angle to minimize ghosting Pupil wheel includes an illumination fixture for internal flats and for use with special alignment fixtures Wheels are essential for wavefront sensing as they carry the weak lenses and the dispersed Hartmann sensor

  10. Bandpass Filters Filters have names indicating wavelength (100x microns) and width (Wide, Medium, or Narrow) Transmission of flight W filters.

  11. Medium & Narrow Filters Isolate Spectral Features “M” filters useful for distinguishing ices, brown dwarfs.

  12. Following the Light: 6th Stop is the Camera Triplet Operates over SW 0.6 – 2.3 microns Operates over LW 2.4 – 5.0 microns Camera triplets come in two flavors for the two arms of NIRCam Using same AR coatings as on collimator because they give good performance and it is cheaper to use the same coatings everywhere

  13. Following the Light: Last Stop is the Focal Plane Assembly (FPA) LW FPA w/ one 2Kx2K readied for performance tests SW FPA with four 2kx2K arrays Qual focal plane assembly mated to ASICs. NIRCam has two types of detectors: 2.5-mm cutoff and 5-mm cutoff HgCdTe (5-mm same as NIRSpec, FGS) Basic performance is excellent with read noise ~7 e- in 1000 secs, dark current < 0.01 e/sec, and QE > 80% Other performance factors such as latent images and linearity are excellent

  14. Latent Testing of Flight Arrays • All IR arrays suffer from latent images after exposure to light • An issue for NIRCam because there will be an over-exposed star in every long exposure 1 ADU = 4 e- DARK Illuminate strongly, remove illumination, reset, read non-destructively. Repeat 5x Signal Time

  15. Coronagraph Image Masks JWST Telescope NIRCam Pickoff Mirror Collimator Optics Camera Optics Telescope Focal Surface Pupil Wheel Filter Wheel Coronagraph Wedge Not to scale Not to scale Coronagraph Image Masks Calibration Source FPA NIRCamOptics Field-of-View FPA Collimator Optics Camera Optics Without Coronagraph Wedge With Coronagraph Wedge Wedge Following the Light: Optional Coronagraph FWHM = 0.40” (6l/D @ 2.1 mm) FWHMc = 0.58” (4l/D @ 4.6 mm) FWHMc = 0.27” (4l/D @ 2.1 mm) FWHM = 0.82” (6l/D @ 4.3 mm) FWHM = 0.64” (6l/D @ 3.35 mm)

  16. Lyot Stops Mask clear regions (white) superposed on JWST pupil (grey) Lyot stop for 6l/D spot occulters Lyot stop for 4l/D wedge occulters Throughput of each is ~19%. Masks similar to those defined by John Trauger & Joe Green

  17. Bench Holds it all Together

  18. Inflation Inflation Quark Soup Quark Soup Clusters & Clusters & Morphology Morphology Modern Universe Modern Universe First Galaxies First Galaxies Reionoization Reionoization Recombination Recombination Forming Atomic Nuclei Forming Atomic Nuclei NIRCam NIRCam NIRCAM_X000 young solar system Kuiper Belt Planets The First Light in the Universe: Discovering the first galaxies, Reionization NIRCam executes deep surveys to find and categorize objects. Period of Galaxy Assembly: Establishing the Hubble sequence, Growth of galaxy clusters NIRCam provides details on shapes and colors of galaxies, identifies young clusters NIRCam’s Role in JWST’s Science Themes Stars and Stellar Systems: Physics of the IMF, Structure of pre-stellar cores, Emerging from the dust cocoon NIRCam measures colors and numbers of stars in clusters, measure extinction profiles in dense clouds Planetary Systems and the Conditions for Life:Disks from birth to maturity, Survey of KBOs, Planets around nearby stars NIRCam and its coronagraph image and characterize disks and planets, classifies surface properties of KBOs

  19. NIRCam Team Observing Plan Team has embraced the JWST Science Themes and is divided into an Extragalactic Team, a Star Formation Team, and an Exo-planet-Debris Disk Team. Use of all instruments and collaboration with the other instrument team is assumed.

  20. NIRCam Team Theme Groups Extragalactic Leader: Daniel Eisenstein Deputy: Alan Dressler Members: Marcia Rieke Stefi Baum Laura Ferrarese Simon Lilly Don Hall Chad Engelbracht Christopher Wilmer Star Formation Leader: Michael Meyer Deputy: Tom Greene Members: Klaus Hodapp Doug Johnstone Peter Martin John Stauffer Tom Roellig Erick Young Doug Kelly Karl Misselt Massimo Robberto Dan Jaffe Exoplanets & Disks Leader: Chas Beichman Deputy: Don McCarthy Members: René Doyon Tom Greene George Rieke Scott Horner John Trauger John Stansberry John Krist KailashSahu

  21. Extragalactic Program NIRCam Team will concentrate on z> 10 = deep survey but lower zs also important -- Survey details TBD but will take data using 6 or 7 filters in SW/LW pairs so 3 or 4 settings will be needed -- likely will spend at least ~15 hours setting -- will collaborate w/ NIRSpec, MIRI, FGS teams Deep Survey Questions What is the luminosity function and size/SB distributions of z>10 galaxies? Is the SF only in the core or spread over the halo? Is there any evidence for cooperative formation, mediated by radiation or reionization? What are the halo masses of these galaxies? What can we learn of reionization from these galaxies? NIRCam footprint compared to Goods, UDF

  22. Sensitivity NIRCam will have the sensitivity to find z~10 galaxies and low mass galaxies at lower redshifts. (~20ksecs) Z=5 M=4x109Msun “Deep” Z=10 M=4x108Msun Finlator et al. 2010

  23. 2 mm Angular Resolution 3.6 mm WFC3 NIRCam Surface Brightness Limit 3-sigma/pix JWST

  24. Star Formation Program • Program takes advantage of JWST’s high sensitivity in the near- and mid-infrared • Program will be executed in collaboration with the MIRI and TFI Teams • Making of Stars and Planets:Testing the Standard Model(s) 1) What physical variables determine the shape of the IMF? 2) How do cloud cores collapse to form isolated protostars? 3) Does mass loss play a crucial role in regulating star formation? 4) What are the initial conditions for planet formation? 5) How do disks evolve in structure and composition?

  25. More on Star Formation Use imaging of clusters to -- determine IMF to ~ 1MJupiter -- measure cluster kinematics -- find variable YSOs Will want both high and low metallicity targets Will need multi-color images Do any of these 8 parameters vary with initial conditions of star formation? From Bastian, Meyer, & Covey (2010)

  26. Exo-planet and Debris Disk Program • Program is aimed at characterizing exo-planets and debris disks, not at finding them • JWST’s angular resolution and 1-5 micron capabilities are keys • Will be done in collaboration with MIRI and TFI teams • NIRCam has three sets of features to enable this program: • Coronagraphic masks and Lyot stops • Long wavelength slitlessgrisms (installed to support wavefront sensing but useful for science) Because the SW side can also be readout when using one of the grisms, jitter can be tracked directly. • Internal defocusing lenses for high precision photometry = transits (installed for wavefront sensing, only available in the short wavelength arms)

  27. Coronagraphic Capabilities: Ground and Space 11 mm 4.4 mm spot TFI 4.4 mm 1.65 mm 1.65 mm 1.65 mm

  28. GTO Imaging Program 40 Orbit (AU) • Large scale surveys of 100s of young stars best left to ground-based AO and/or JWST/GO programs • Small targeted surveys take advantage of various criteria to enhance probability of success: • Faint, young, host stars difficult for ground base AO, e.g. M stars with sensitivity to 0.1-1 MJup at 10-30 AU. • Debris disk systems suggestive of planets • Face-on systems offer 10-20% improved probability of detection (Durst, Meyer, CAB) • High metallicity • Systems with strong RV • Monitoring for temporal changes • Majority of GTO program will be imaging and spectra to characterize 10-15 known systems • Complete spectra (1-5 mm w NIRCam and <10 mm with MIRI) to compare w. physical models • Search for additional planets • Refine orbits 10 -0.4 0.4 -1.0 Log Mass (MJup) Prob Detect Inclination Eccentricity

  29. Transits With NIRCAM Lenses introduce 4,8,12 l of defocus to spread light over many hundreds of pixels compared with 25 pixels when in-focus Reduce flat-field errors for bright stars 5<K<10 mag Max defocus is 12l, ultra-high precision data for bright transits Diffused images (weak lenses) or spectrally dispersed images (grism) reduce brightness/pixel by >5 mag. K=3-5 mag stars not saturated. LED Pupil

  30. -8 -4 0 +8 +4 +12 Fine Phasing Images from ETU: Samples of Defocussed Images Useful for Transits

  31. NIRCamgrism range very useful! Transit Spectroscopy Will concentrate on a limited number of interesting targets If an instrument+telescope combination is sufficiently stable, spectra of a transiting planet’s atmosphere can be obtained. Both emission spectra and transmission spectra can be obtained. HST and Spitzer have produced such data. This is likely to be a very powerful technique for JWST. Whether NIRSpec or NIRCam will be best will depend on systematics that may be difficult to predict

  32. NIRCam has been designed to take advantage of JWST’s large and cold primary mirror… and the NIRCam team will scratch the surface of several sciences areas BUT most of the work will done by the general observing community! NIRCam Cheat Sheet and more at http://ircamera.as.arizona.edu/nircam/ And at http://www.stsci.edu/jwst/instruments/nircam

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