Transcript Near Infrared Camera (NIRCam) for JWST Michael Meyer, John Stansberry, Erick Young and the NIRCam Team Steward Observatory, University of Arizona Overview: NIRCam.

Near Infrared Camera (NIRCam) for JWST
Michael Meyer, John Stansberry, Erick Young and the NIRCam Team
Steward Observatory, University of Arizona
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 critical design review, and is beginning its construction phase. 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. Development of NIRCam is supported by NASA contract NAS5-02105.
Temperatures of Planets and Brown Dwarfs
Detection of Brown Dwarfs
• Survey filters can measure temperatures with an accuracy of 20K
The plot below shows model two brown dwarf
Optical Bench
spectra from Burrows et al. 2003. These spectra are
for an age of 1 Gyr and a distance of 10 pc. NIRCam
NIRCam’s optics need a
easily detects such objects in broadband filters in
rigid base if they are to
10,000 secs which will enable surveys for low mass
achieve the required level
objects.
of performance. The
competing need to
1.0E+00
minimize mass dictated
1 Gyr
the choice of Be as the
bench material. The top
1.0E-02
two pictures show a
plastic bench being used
1.0E-04
in a practice run of
bonding the two halves of
1.0E-06
a module bench together.
The third picture shows
part of the Be engineering
1.0E-08
test unit bench at AXSYS.
1.0
2.0
3.0
4.0
5.0
• 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!
5 Mj
500
900
450
800
400
700
350
600
300
500
400
150
200
100
100
50
2.00
4.00
6.00
8.00
Models
Pupil
Wheel
Filter
Wheel
Not to scale
Not to scale
Coronagraph
Image Masks
NIRCam
Optics
Field-of-View
Without Coronagraph Wedge
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 4-5mm 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.
Camera
Optics
Coronagraph
Wedge
FPA
0
-0.20
12.00
NIRCam Coronagraphy
Collimator
Optics
Telescope
Focal
Surface
10.00
F356W-F444W
Coronagraph
Image
Masks
NIRCam
Pickoff
Mirror
250
300
NIRCam Broad Filters (10-sigma, 10,000sec)
JWST Telescope
Aluminum prototype Focal Plane
Assembly for holding four 2Kx2K arrays
(one shown in the background).
200
0
0.00
l (mm)
1 Mj
1000
Teff (K)
T eff(K)
Fn (mJy at 10pc)
• Caveat is that this analysis used models (Burrows et al. 2003) –
real objects may be less well behaved
Calibration Source
FPA
With Coronagraph Wedge
Prototype lens mount.
Coronagraph Background at 4.8 um
Near 5 or 10 mag Star
1.E+07
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+06
Background Intensity (MJy/sr)
NIRCam EPO
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.
3
2
1
1.0
1.25
1.6
2.0
2.5
Wavelength (µm)
3.2
4.0
5.0
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
Weak lens
2
Weak
lens 1
F225N
SWP3
Grism 1
F162M
Outward
pinholes
SWF
Weak lens
3
WFS
Filter
F150W2
F212N
DHS 1
F115W
F150W
F200W
F250M
Flat field
pinholes
LWP3
F323N
F418N
F466N
F470N
SWF3
F322W2
Imaging
pupil
F405N
F090W
F210M
Corona-graph
pupil
LWP
Grism 2
Flat field
pinholes
F140M
Coronagraph pupil
F070W
SWF12
Corona-graph
pupil 2 with
wedge
F277W
F480M
LWF
F460M
F356W
LWF3
LWF6
0
2.5
LWF12
Signal (linear units)
4
2
Separation (arcsec)
LWP6
CO ice
H2O ice
CO2 ice
N2 ice
CH4 ice
NH3 ice
Pholus
WR106
PAH
EI 18
L-dwarf
T-dwarf
W33A
1.5
SWF6
5
1
SWP6
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
LWP12
NIRCam Filters
0
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.