Transcript NIRCam - STScI

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
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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
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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
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• 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
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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
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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
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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.
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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
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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.
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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
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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)
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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
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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
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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.
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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
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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
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Sensitivity
40
35
“Shallow”
30
25
nJy
NIRCam will have the
sensitivity to find z~10
galaxies and low mass
galaxies at lower redshifts.
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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
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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
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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?
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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)
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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)
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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:
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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
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Fine Phasing Images from ETU: Samples of
Defocussed Images Useful for Transits
-8
-4
0
+8
+4
+12
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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!
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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
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