The background for this poster shows a life size drawing of one NIRCam module. The other side is a mirror image. The two modules are mounted back-to-back with their FOVs adjacent on the sky.
Near Infrared Camera (NIRCam) for JWSTNear Infrared Camera (NIRCam) for JWSTMarcia Rieke1, Doug Kelly1, Scott Horner2, and the NIRCam Team
1Steward Observatory, University of Arizona; 2Lockheed Martin Advanced Technology Center
Filter wheel model with top removed to show the dual wheels and element attach points.
Protoype bearings for the NIRCam filter wheels.
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Ground (Keck/VLT) Space (HST or SPITZER) NIRCam z=5.0 z=10.1
Five-sigma detection limits are shown above. NIRCam’s spatial resolution corresponds to 1 Kpc for these distant objects. The z=10 galaxy has a mass of 4x108MSun while the mass of the z=5 galaxy is 4x109MSun.
Above assumes 50,000 sec/filter with 2x time on longest wavelength. Deeper surveys should reach ~1nJy and detect the earliest galaxies.
Coronagraph Background at 4.8 um Near 5 or 10 mag Star
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JWST10Keck10Gem10TMT10JWST5Keck5Gem5TMT5
PupilWheel
CollimatorOptics Camera
Optics
NIRCamPickoffMirror
TelescopeFocal
Surface
Coronagraph ImageMasks
Coronagraph Wedge
JWST Telescope
Not to scale
NIRCamOptics
Field-of-View
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Coronagraph Image Masks
Without Coronagraph Wedge With Coronagraph Wedge
Not to scale
FilterWheel
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Temperatures of Planets and Brown Dwarfs
• Survey filters can measure temperatures with an accuracy of 20K
• For cold objects which may only be detected in the longest wavelength survey filter, temperatures using two medium filters can be measured to 10K. Should be good for coronagraphy of planets!
• Log g can be estimated from F466N – F470N with limited accuracy – spectra better!
• Caveat is that this analysis used models (Burrows et al. 2003) – real objects may be less well behaved
OverviewOverview: : NIRCam provides diffraction-limited imaging over the 0.6 to 5 m range. Two science examples are shown below. It uses HgCdTe arrays with a total of 40Mpixels to cover 2.2’x4.4’ arc minutes in two wavelengths simultaneously for efficient surveying. These arrays have excellent performance at the projected ~37K operating temperatures expected on JWST. In 10,000 seconds, NIRCam should detect at 10- a 10 nJy source at 2m and a 14 nJy source at 3.6m. A beamsplitter divides the input light at 2.4 m enabling the observation of two wavelengths at once. In addition to its role as a science instrument, NIRCam is also the facility wavefront sensor. The same arrays used for science imaging will take images using weak lenses in the NIRCam pupil wheel to enable focus diverse wavefront sensing. NIRCam’s optics need to be exquisite to avoid imprinting any NIRCam aberrations on the telescope and hence other JWST instruments. The University of Arizona is leading the NIRCam development effort, Lockheed Martin Advanced Technology Center is responsible for building NIRCam, and Rockwell Scientific Company is providing the detector arrays.
Status: Status: NIRCam has already passed its preliminary design review, and has completed critical design reviews (CDR) on most subsystems. The instrument CDR is scheduled for May of this year. Two versions of NIRCam will be built: an engineering test unit which will be used in verifying performance of the telescope and associated wavefront sensing and control procedures, and the flight model. Many of the parts for the engineering test unit such as the Be bench, lenses, and detectors are already in production. Prototypes of the cryogenic mechanisms such as the filter wheels and focus adjust mechanism have been built and tested. Several problems that have cropped up have been solved: 1) Detector arrays delaminated from their molybdenum mounts, and 2) cracks developed at two sites on the Be bench as a result of tapping holes. The detector problem was solved by using a stronger epoxy and improved cleaning procedures. The Be bench problem was solved by switching to carbide taps which stay sharp longer and produce cleaner threads.
See also posters 115.10 (NIRCam Optics) and 115.11 (NIRCam Detectors). Development of NIRCam is supported by NASA contract NAS5-02105.
NIRCam Filters
NIRCam’s filter set supports extragalactic surveys, characterization of extra-solar planets, and studies of star formation regions. The filter set covers the entire 0.6-5m range and will enable a broad variety of projects. Other components in the filter and pupil wheels aid calibration and wavefront sensing.
NIRCam EPO
The NIRCam Team is using facilities on Mt. Lemmon, near Tucson, to run Astronomy Camps for Girl Scout leaders. Other activities include “Ask an Astronomer” days (colorful white board shown from one of these!).
NIRCam Coronagraphy
NIRCam implements a simple coronagraph that requires no extra moving parts by using a wedge in the pupil wheel to deflect the beam to masks located at the telescope focus. NIRCam will be very effective in studying planets and brown dwarfs in the 4-5m region as shown below. This plot gives the background as function of distance from a star in a coronagraphic observation and shows that at 4.8m, groundbased telescopes are always limited by thermal background.
Coronagraph occulting masks are just above the pickoff mirror.
Plot courtesy of C. Beichman and J. Green.
Distant Galaxy Survey
Optical Bench
NIRCam’s optics need a rigid base if they are to achieve the required level of performance. The competing need to minimize mass dictated the choice of Be as the bench material. The top two pictures show a plastic bench being used in a practice run of bonding the two halves of a module bench together. The third picture shows part of the Be engineering test unit bench at AXSYS.
Aluminum prototype Focal Plane Assembly for holding four 2Kx2K arrays (one shown in the background).
