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

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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

Mod

ule

AM

odul

e 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)

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Coarse phasing w/DHS

After coarse phasing Fully 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

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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

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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

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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

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One of the flight LW pupil wheels

Bandpass Filters

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Filters have names indicating wavelength (100x microns) and width (Wide, Medium, or Narrow)

Transmission of flight W filters.

Medium & Narrow Filters Isolate Spectral Features

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“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

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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

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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

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Illuminate strongly, remove illumination, reset, read non-destructively.

DARK

Time

Sig

nal

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)

Nor

mal

ized

Sig

nal 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

rat

e AD

U/s

ec

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Following the Light: Optional Coronagraph

PupilWheel

CollimatorOptics Camera

OpticsNIRCamPickoffMirror

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

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NIRCam’s Role in JWST’s Science Themes

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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 clustersStars and Stellar Systems: Physics of the IMF,

Structure of pre-stellar cores, Emerging from the dust cocoon

NIRCam 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

Infla

tion

Form

ing

Ato

mic

Nuc

lei

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ombi

natio

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Firs

t Gal

axie

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Rei

onoi

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Clu

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s &

M

orph

olog

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Mod

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Uni

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NIRCam

Qua

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oup

Infla

tion

Form

ing

Atom

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ucle

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Rec

ombi

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Firs

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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 GroupsExtragalactic Leader:Daniel EisensteinDeputy: Alan Dressler

Members: Marcia Rieke Stefi BaumLaura FerrareseSimon Lilly Don HallChad EngelbrachtChristopher Wilmer

Star FormationLeader:Michael MeyerDeputy: Tom Greene

Members:Klaus HodappDoug JohnstonePeter MartinJohn StaufferTom RoelligErick YoungDoug KellyKarl MisseltMassimo RobbertoDan Jaffe

Exoplanets & DisksLeader:Chas BeichmanDeputy: Don McCarthy

Members:René DoyonTom GreeneGeorge RiekeScott HornerJohn TraugerJohn StansberryJohn KristKailash Sahu

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Extragalactic ProgramNIRCam 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 8.505

10152025303540

~900Myr ~40Myr NIRCam MIRIl(mm)

nJy

“Shallow”

0123456789

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/ s

q ar

c se

c

0 2 4 6 8 10 12 14 16 18 200

2

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Redshift

NIR

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NIRCam Surface Brightness Limit 3-sigma/pix

WFC3

JWST

2 mm

3.6 mm

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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

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More on Star FormationDo 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

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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 MJup 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 Inclin

ationPro

b D

etec

t

0.4-1.0 -0.4Log Mass (MJup)

Orb

it (A

U)

10

40

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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

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+4

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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

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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 athttp://ircamera.as.arizona.edu/nircam/And athttp://www.stsci.edu/jwst/instruments/nircam