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NIRCam: Wavefronts, Images, and Science Marcia Rieke NIRCam PI STScI June 7, 2011 What’s NIRCam? • NIRCam is the near-infrared camera (0.6-5 microns) for JWST View of the Goddard clean room – Refractive design to minimize mass and volume – Dichroic used to split range into short (0.6-2.3mm) and long (2.45mm) 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 2 Design Overview • Fully redundant with mirror image A and B modules • Refractive optical design Short wave camera lens group First fold mirror Light from Telescope Short wave fold mirror Collimator lens group • Thermal design uses entire instrument as Dichroic beamsplitter thermal ballast ; cooling straps Coronagraph attached to the occulting masks benches SIDECAR ASICs Focus and digitize detector alignment signals in cold region mechanism • Uses two detector types – short wavelength HgCdTe Long wave filter wheel and long assembly wavelength HgCdTe (this one is same as used on NIRSpec & FGS) Pupil imaging lens assembly Short wave filter wheel assembly • Short wave focal plane housing Long wave camera lens group Long wave focal plane housing 2 Channels Per Module • SW pixel scale is 0.032”/pix; long is 0.064”/pix 4 Module A 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 Module B • Each module has two bands (0.6 microns to 2.3 microns and 2.4 microns to 5 microns) Short wavelength channel 2.2’ Long wavelength channel NIRCam as a Wavefront Sensor First Light After segment capture – Telescope focus sweep Coarse phasing w/DHS Spectra recorded by NIRCam DHS at pupil Fine phasing After coarse phasing 5 • 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: Fully aligned – 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) Following the Light: 1st Stop is the FAM • 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 POM Assembly Prototype POM FAM being prepped for connector installation. Sensor & Target Assy Linear Actuators 6 Following the Light: 2nd Stop is the Collimator • 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 16:40:53 Light LiF ZnSe One of the flight collimator triplets BaF2 NIRCam Mono OTE 03/02/04 7 20.00 Scale: 1.25 MM 10-Mar-05 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 8 Following the Light: 4th Stop is the Filter Wheel Assembly (FWA) • 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 One of the flight LW pupil wheels 9 Bandpass Filters Filters have names indicating wavelength (100x microns) and width (Wide, Medium, or Narrow) Transmission of flight W filters. 10 Medium & Narrow Filters Isolate Spectral Features “M” filters useful for distinguishing ices, brown dwarfs. 11 Following the Light: 6th Stop is the Camera Triplet • 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 Operates over SW 0.6 – 2.3 microns 12 Operates over LW 2.4 – 5.0 microns Following the Light: Last Stop is the Focal Plane Assembly (FPA) • 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 LW FPA w/ one 2Kx2K readied for performance tests SW FPA with four 2kx2K arrays Qual focal plane assembly mated to ASICs. 13 Latent Testing of Flight Arrays Normalized Signal ADU/sec 1.2 • 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 1.0 0.8 0.6 0.4 1 ADU = 4 e- 0.2 0.0 10 100 DARK 1.0 Post rate ADU/sec Signal Repeat 5x 0.8 0.6 0.4 0.2 0.0 1000 Time 10000 Time Since Illumination (sec) C045 Data integrated fit 1.2 Illuminate strongly, remove illumination, reset, read nondestructively. 1000 10000 100000 1000000 Total illumination ADUs 14 C045 C038 C043 C044 10000000 Following the Light: Optional Coronagraph Coronagraph Image Masks JWST Telescope NIRCam Pickoff Mirror Collimator Optics Telescope Focal Surface Camera Optics Pupil Wheel Filter Wheel Coronagraph Wedge Not to scale Not to scale Coronagraph Image Masks FPA NIRCam Optics Field-of-View Without Coronagraph Wedge Calibration Source FPA Collimator Optics Camera Optics With Coronagraph Wedge Wedge 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) FWHM = 0.40” (6l/D @ 2.1 mm) 15 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 Bench Holds it all Together 17 NIRCam NIRCAM_X000 Modern Universe Clusters & Morphology Reionoization First Galaxies Discovering the first galaxies, Reionization NIRCam executes deep surveys to find and categorize objects. Recombination Forming Atomic Nuclei Inflation Quark Soup NIRCam’s Role in JWST’s Science Themes The First Light in the Universe: Period of Galaxy Assembly: Establishing the Hubble sequence, Growth of galaxy clusters NIRCam provides details on shapes and colors of galaxies, identifies young clusters Stars and Stellar Systems: Physics of the IMF, young solar system Kuiper Belt Planets 18 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 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. 19 NIRCam Team Theme Groups Extragalactic Star Formation Exoplanets & Disks Leader: Leader: Leader: Daniel Eisenstein Michael Meyer Chas Beichman Deputy: Alan Dressler Deputy: Tom Greene Deputy: Don McCarthy Members: Members: Members: Marcia Rieke Klaus Hodapp René Doyon Stefi Baum Doug Johnstone Tom Greene Laura Ferrarese Peter Martin George Rieke Simon Lilly John Stauffer Scott Horner Don Hall Tom Roellig John Trauger Chad Engelbracht Erick Young John Stansberry Christopher Wilmer Doug Kelly John Krist Karl Misselt Kailash Sahu Massimo Robberto Dan Jaffe 20 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 21 Sensitivity 40 35 “Shallow” 30 25 nJy NIRCam will have the sensitivity to find z~10 galaxies and low mass galaxies at lower redshifts. 20 15 10 5 0 0.5 2.5 4.5 6.5 8.5 l(mm) (~20ksecs) ~900Myr ~40Myr NIRCam MIRI 10 9 Z=5 M=4x109Msun 8 nJy 7 6 “Deep” 5 Z=10 M=4x108Msun 4 3 2 1 0 0.5 Finlator et al. 2010 22 1.5 NIRCam 2.5 l( mm) z=5.0 3.5 4.5 z=10.1 Angular Resolution NIRCam Pixels per 1 kpc 14 12 2 mm 10 8 6 4 3.6 mm 2 0 0 5 10 15 20 Redshift Jy/ sq arc sec 1.E-02 1.E-03 Bulge 1.E-04 Disk 1.E-05 WFC3 50,000 sec JWST 3.56um 1.E-06 1.E-07 1.E-08 1.E-09 NIRCam Surface Brightness Limit 3-sigma/pix 1.E-10 0 5 10 Redshift 15 20 JWST 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? 24 More on Star Formation Do any of these 8 parameters vary with initial conditions of 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 From Bastian, Meyer, & Covey (2010) 25 Will need multicolor images 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 slitless grisms (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) 26 Coronagraphic Capabilities: Ground and Space 11 mm 4.4 mm spot TFI 4.4 mm 1.65 mm 1.65 mm 1.65 mm • 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: 40 Orbit (AU) GTO Imaging Program • 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 Prob Detect – Faint, young, host stars difficult for ground 10 base AO, e.g. M stars with sensitivity to 0.11 MJup at 10-30 AU. – Debris disk systems suggestive of planets -1.0 – Face-on systems offer 10-20% improved probability of detection (Durst, Meyer, CAB) – High metallicity – Systems with strong RV – Monitoring for temporal changes -0.4 Log Mass (MJup) 0. 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 29 Fine Phasing Images from ETU: Samples of Defocussed Images Useful for Transits -8 -4 0 +8 +4 +12 30 Transit Spectroscopy • 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 Will concentrate on a limited number of interesting targets NIRCam grism range very useful! 31 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 32