Transcript Slide 1
Near Infrared Camera (NIRCam) for JWST Marcia 1 Rieke , 1Steward Doug 1 Kelly , 2, Horner Scott and the NIRCam Team Observatory, University of Arizona; 2Lockheed Martin Advanced Technology Center Overview: NIRCam provides diffraction-limited imaging over the 0.6 to 5 mm 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-s a 10 nJy source at 2mm and a 14 nJy source at 3.6mm. A beamsplitter divides the input light at 2.4 mm 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: 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. Temperatures of Planets and Brown Dwarfs Distant Galaxy Survey • Survey filters can measure temperatures with an accuracy of 20K 1000 • 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! 100 10 • Log g can be estimated from F466N – F470N with limited accuracy – spectra better! 1 • Caveat is that this analysis used models (Burrows et al. 2003) – real objects may be less well behaved 0.1 1.5 2.5 3.5 l(m m) 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. 1000 500 900 450 800 400 700 350 600 300 500 400 Above assumes 50,000 sec/filter with 2x time on longest wavelength. Deeper surveys should reach ~1nJy and detect the earliest galaxies. 300 150 200 100 100 50 0 0.00 2.00 4.00 6.00 Camera Optics Pupil Wheel Filter Wheel Not to scale Not to scale Coronagraph Image Masks Without Coronagraph Wedge NIRCam Optics Field-of-View 12.00 0.00 0.20 0.40 0.60 0.80 F460M-F480M Fit Models Fit 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 45mm region as shown below. This plot gives the background as function of distance from a star in a coronagraphic observation and shows that at 4.8mm, groundbased telescopes are always limited by thermal background. Coronagraph Wedge FPA 10.00 NIRCam Coronagraphy Collimator Optics Telescope Focal Surface 8.00 0 -0.20 F356W-F444W Coronagraph Image Masks NIRCam Pickoff Mirror 250 200 Models JWST Telescope Aluminum prototype Focal Plane Assembly for holding four 2Kx2K arrays (one shown in the background). 4.5 Teff (K) 0.5 T eff(K) 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. nJy Optical Bench Calibration Source FPA With Coronagraph Wedge Protoype bearings for the NIRCam filter wheels. Coronagraph Background at 4.8 um Near 5 or 10 mag Star NIRCam EPO 1.E+07 1.E+06 Background Intensity (MJy/sr) 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!). 1.E+05 JWST10 Keck10 Gem10 TMT10 JWST5 Keck5 Gem5 TMT5 1.E+04 1.E+03 1.E+02 1.E+01 1.E+00 1.E-01 Coronagraph occulting masks are just above the pickoff mirror. 0 1 1.5 2 3 Plot courtesy of C. Beichman and J. Green. F187N Imaging pupil F182M SWP12 Corona-graph pupil 1 with wedge DHS 2 SWP Outward pinholes Flat field pinholes F162M SWF Weak lens 3 WFS Filter F150W2 F212N F140M DHS 1 LWP Grism 2 Flat field pinholes LWP3 F323N F418N F466N F470N F250M F277W F480M LWF F460M F356W LWF3 LWF6 F405N F200W F322W2 Imaging pupil LWP6 Outward pinholes F115W F150W LWF12 Grism 1 SWF3 F210M LWP12 Coronagraph pupil Coronagraph pupil F090W SWF6 SWP6 Weak lens 2 F225N SWP3 F070W SWF12 Corona-graph pupil 2 with wedge Weak lens 1 Filter wheel model with top removed to show the dual wheels and element attach points. 2.5 Separation (arcsec) 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 0.6-5mm range and will enable a broad variety of projects. Other components in the filter and pupil wheels aid calibration and wavefront sensing. 0.5 F430M F410M F300M F335M F360M F444W 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.