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NIRCam: Wavefronts, Images, and Science
Marcia RiekeNIRCam PI
STScI June 7, 2011
What’s NIRCam?• 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 alignment2
View of the Goddard clean room
Design Overview• 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)
Focus and alignment
mechanism
Coronagraphocculting masks
First fold mirror
Collimator lens group
Dichroic beamsplitter
Long wave filter wheel assembly Long wave
camera lens group
Long wave focal plane housing
Short wave filter wheel assembly
Short wave fold mirror
Pupil imaging lens assembly
Short wave focal plane housing
Light from Telescope Short wave camera lens group
4
2 Channels Per Module
• 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
Long wavelength channelShort wavelength channel
Mo
du
le A
Mo
du
le B
2.2’
NIRCam as a Wavefront Sensor• 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)
5
Coarse phasing w/DHS
After coarse phasingFully aligned
Fine phasing
First Light
After segment capture
DHS at pupil Spectra recorded by NIRCam
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
6
FAM being prepped for connector installation.
POM Assembly
Linear Actuators
Sensor & Target Assy
Prototype
POM
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
7
16:40:53
NIRCam Mono OTE 03/02/04 Scale: 1.25 10-Mar-05
20.00 MM
LiF
BaF2
ZnSe
Light
One of the flight collimator triplets
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
8
Flight beam splitters
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
9
One of the flight LW pupil wheels
Bandpass Filters
10
Filters have names indicating wavelength (100x microns) and width (Wide, Medium, or Narrow)
Transmission of flight W filters.
Medium & Narrow Filters Isolate Spectral Features
11
“M” filters useful for distinguishing ices, brown dwarfs.
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
12
Operates over SW 0.6 – 2.3 microns 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
13
LW FPA w/ one 2Kx2K readied for performance tests
SW FPA with four 2kx2K arrays
Qual focal plane assembly mated to ASICs.
Latent Testing of Flight Arrays
14
Illuminate strongly, remove illumination, reset, read non-destructively.
DARK
Time
Sig
na
l
Repeat 5x
• 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-
10 100 1000 100000.0
0.2
0.4
0.6
0.8
1.0
1.2
C045 Data integrated fitTime Since Illumination (sec)
Norm
alized S
ignal A
DU
/sec
1000 10000 100000 1000000 100000000.0
0.2
0.4
0.6
0.8
1.0
1.2
C045 C038 C043 C044
Total illumination ADUs
Post
rate
AD
U/s
ec
15
Following the Light: Optional Coronagraph
PupilWheel
CollimatorOptics Camera
Optics
NIRCamPickoffMirror
TelescopeFocal
Surface
Coronagraph ImageMasks
Coronagraph Wedge
JWST Telescope
Not to scale
NIRCamOptics
Field-of-View
FPA FPA
Coronagraph Image Masks
Without Coronagraph Wedge With Coronagraph Wedge
Not to scale
FilterWheel
Calibration Source
CollimatorOptics
CameraOptics
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)
Lyot Stops
Lyot stop for 6l/D spot occulters
Lyot stop for 4l/D wedge occulters
Mask clear regions (white) superposed on JWST pupil (grey)
Throughput of each is ~19%.Masks similar to those defined by John Trauger & Joe Green
Bench Holds it all Together
17
NIRCam’s Role in JWST’s Science Themes
18
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 clustersNIRCam provides details on shapes and colors
of galaxies, identifies young clusters
Stars and Stellar Systems: Physics of the IMF, Structure of pre-stellar cores, Emerging from the
dust cocoonNIRCam measures colors and numbers of stars in clusters, measure extinction profiles in dense
cloudsPlanetary 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_X000
Infl
atio
n
Fo
rmin
g A
tom
ic N
ucl
ei
Rec
om
bin
atio
n
Fir
st G
alax
ies
Rei
on
oiz
atio
n
Clu
ster
s &
Mo
rph
olo
gy
Mo
der
n U
niv
erse
NIRCam
Qu
ark
So
up
Infl
atio
n
Fo
rmin
g A
tom
ic N
ucl
ei
Rec
om
bin
atio
n
Fir
st G
alax
ies
Rei
on
oiz
atio
n
Clu
ster
s &
Mo
rph
olo
gy
Mo
der
n U
niv
erse
NIRCam
Qu
ark
So
up
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 FormationLeader:
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 & DisksLeader:
Chas Beichman
Deputy: Don McCarthy
Members:
René Doyon
Tom Greene
George Rieke
Scott Horner
John Trauger
John Stansberry
John Krist
Kailash Sahu
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
NIRCam footprint compared to Goods, UDF
Deep Survey QuestionsWhat 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?
Sensitivity
22Finlator et al. 2010
(~20ksecs)
0.5 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.50
5
10
15
20
25
30
35
40
~900Myr ~40Myr NIRCam MIRIl(mm)
nJ
y
“Shallow”
0
1
2
3
4
5
6
7
8
9
10
0.5 1.5 2.5 3.5 4.5
nJy
(l mm)NIRCam z=5.0 z=10.1
Z=10 M=4x108Msun
Z=5 M=4x109Msun
“Deep”
NIRCam will have the sensitivity to find z~10 galaxies and low mass galaxies at lower redshifts.
Angular Resolution
0 2 4 6 8 10 12 14 16 18 201E-10
1E-09
1E-08
1E-07
1E-06
1E-05
1E-04
1E-03
1E-02
Bulge
Disk
50,000 sec JWST 3.56um
Redshift
Jy/
sq a
rc s
ec
0 2 4 6 8 10 12 14 16 18 200
2
4
6
8
10
12
14
Redshift
NIR
Cam
Pix
els
per
1 k
pc
NIRCam Surface Brightness Limit 3-sigma/pix
WFC3
JWST
2 mm
3.6 mm
24
Star Formation Program
• 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?
• 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
25
More on Star Formation
Do any of these 8 parameters vary with initial conditions of star formation?
From Bastian, Meyer, & Covey (2010)
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
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 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)
Coronagraphic Capabilities: Ground and Space
11 mm
4.4 mm spot
TFI 4.4 mm
1.65 mm1.65 mm
1.65 mm
GTO Imaging Program• 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 M Jup 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
Eccentricity Incli
natio
n
Pro
b D
etec
t
0.4-1.0 -0.4
Log Mass (MJup)
Orb
it (A
U)
10
40
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 12 ,l 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
Fine Phasing Images from ETU: Samples of Defocussed Images Useful
for Transits
-8
+8
-4
+4
0
+12
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
31
Will concentrate on a limited number of interesting targets
NIRCam grism range very useful!
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 athttp://ircamera.as.arizona.edu/nircam/And athttp://www.stsci.edu/jwst/instruments/nircam