HST Cal Conf -- Oct 27, 2005 Calibration Status and Results for Wide Field Camera 3 – R....

HST Cal Conf -- Oct 27, 2005 Calibration Status and Results for Wide Field Camera 3 – R. Kimble/GSFC, [email protected]

Calibration Status and Results for

Wide Field Camera 3

Randy A. Kimble (GSFC) and the

WFC3 Team


Outline

• Purpose/potential of WFC3

• Configuration of instrument

• Ambient and thermal-vac calibration results

• Improvements in work – filters, crosstalk, IR detector

• Future calibration plans


Key Team MembersSupporting Calibration

• WFC3 also supported by Science Oversight Committee, chaired by Bob O’Connell/University of Virginia

Science IPT (STScI)

J. MacKenty

Detector Characterization Laboratory (GSFC)

Filter Evaluation

S. Baggett B. Hill (also Science IPT) R. Boucarut

T. Brown G. Delo P. Arsenovic

H. Bushouse R. Foltz J. Kim Quijano

D. Figer E. Malumuth M. Quijada

G. Hartig A. M. Russell R. Telfer

B. Hilbert A. Waczynski

N. Reid Y. Wen

M. Robberto


Origins/Purpose of WFC3

• WFC3 originated when HST’s nominal observing lifetime was first extended from 2005 to 2010: facility instrument conceived for installation during Servicing Mission 4, to extend and enhance HST’s imaging capability

• If SM4 approved, era of WFC3 operation now likely to be late 2007/2008 2013 and beyond?

• WFC3 has been designed as a powerful general purpose camera:

– widest spectral coverage of any HST instrument

– 200-1000 nm in UVIS channel; 850-1700 nm in IR channel

– complementary to ACS


Key Aspects of WFC3

• Unique capabilities in the near-UV– 200 to 400 nm

• Unique capabilities in the near-IR – without cryogen or mechanical cryocooler!– 850 to 1700 nm (though warm, HST is very powerful in this range)

• Large and diverse set of filters and grisms: 63 UVIS, 16 IR

• Very capable accompaniment to ACS in the red, with more filters, fresh start with respect to radiation damage, and greater tolerance of CTE degradation


WFC3’s Intended Destination

WFC3 is intended to replace the extraordinarily successful but aging WFPC2 in its radial instrument bay.


Overall WFC3 Configuration

Dimensions: 7.5’ x 7’ x 3’ Weight: 907 lbs

B-Latch


WFC3 Interior Configuration


UVIS Channel Summary

Key Properties

• 200 – 1000 nm • 4K x 4K CCD mosaic (two 2K x 4K UV-optimized CCDs)• 0.04” x 0.04” pixels, 160” x 160” field of view

The WFC3 UVIS channel will extend high-sensitivity, large-format imaging at HST’s sharp angular resolution to the near UV.

Relative fields of view of HST’s NUV imagers


UVIS Channel Science Goals

The UVIS channel will be particularly well suited to the study of:• Star formation history of galaxies (see figure at right)• Chemical enrichment history of galaxies• Ly dropouts at z = 1 – 2.• It will also probe one of the darkest spectral regions of the natural sky background (~200 nm).

NUV Observations Probe Age of Stellar Populations


CCD Detectors

• The WFC3 CCDs, developed by Marconi (now e2v) are shown in their flight housing (left) and mounted in the instrument (right).

• The end-to-end read noise for the flight CCDs and electronics is 3 e- rms for all four readout amplifiers.


IR Channel Summary

Key Properties

• 850 – 1700 nm • 1K x 1K HgCdTe array with 1.7 micron cutoff• 0.13” x 0.13” pixels, 139” x 123” field of view• zodiacal-background-limited sensitivity in broadband filters

The WFC3 IR channel will provide a 10-20+ x increase in survey speed vs. NICMOS + cryocooler, with finer angular resolution and improved stability, photometric accuracy, and cosmetics.

Relative fields of view of HST’s IR imagers


IR Channel Science Goals

The IR channel will take advantage of the dark IR sky in space to study:

• Type Ia supernovae and the accelerating universe

• High-redshift galaxy formation (high-z dropouts) – note the strong NIR color-color discrimination of high-z galaxies in the figure at right

• Sources of cosmic re-ionization

• Dust-enshrouded star formation

• Water and ices in the solar system.

IR Color-Color Identification of High-z Galaxies


IR Detectors

• The novel 1.7 micron cutoff wavelength of the IR array (left), developed by Rockwell Scientific, permits low-dark-current operation at a temperature of <150 K, achievable with thermo-electric cooling alone.

• A cooled inner shield (center) within the detector housing (right) helps to minimize the thermal background radiation incident on the array.


Ambient and Thermal-Vac Calibrations Performed

• During “cancellation period” of 2004, instrument was fully integrated in a “non-final” mode, in which a number of hardware issues were tagged as “liens”, but not closed out

• We targetted a “performance characterization” in which WFC3’s performance could be demonstrated for the purposes of contemplating non-HST use

• Extensive suite of tests and calibrations performed, both in ambient and thermal-vac conditions

– Ambient tests of UVIS channel

– Thermal-vac tests of both channels – 1st opportunity for end-to-end look at IR channel

– Not a full science calibration, but all critical performance issues examined


Flight Subsystems Integrated for End-to-End Testing in 2004


Thermal/Vac Test Setup

Optical Stimulus

RIAF

WFC3

Cryopanels


Thermal/Vac Performance Highlights

• Overall instrument performed very well – never came up to air for an instrument issue

• 13,000 images obtained, assessing all aspects of WFC3 performance

• Detailed results documented in several dozen Instrument Science Reports– http://www.stsci.edu/hst/wfc3/documents/ISRs

– Easy to find: STScI → HST → Instruments → WFC3 → ISRs

• Results confirm the powerful performance of WFC3 across its wide spectral range


UVIS Results

Characteristic CEI spec; goal Measured

Dark current <20 e/pix/hour 0.2-0.4 e/pix/hour

Read noise (rms) <4 e/pix; <3 e/pix 2.98-3.08 e/pix

Linearity <5% deviation over 100-50,000 e <3% deviation

Full-well >50,000 e/pix; >85,000 e/pix ~68,000 e/pix

Encircled energy 250nm: >0.75; >0.80 in 0.20”

633nm: >0.75; >0.80 in 0.25”

250nm: 0.78-0.81*

633nm: 0.77-0.81*

Cal System 10,000 e/pix in <10 min <1 min

Uniform to <2x ~7x

Filter ghosts <0.2% of incident in a ghost Up to ~15%

Image stability <10 milli-arcseconds over 2 orbits 15-50 mas

*Specs apply to performance with OTA. Measurements obtained with CASTLE require corrections for differences in the optical systems. 250nm EE likely to fall just below CEI requirement (~0.72).


UVIS Channel Shows ExcellentEnd-to-End Image Quality

810nm250nm

350nm

633nm

810nm

GoalsSpecs


UVIS System Throughput

UVIS throughput very close to or better than predictions


IR Results

Characteristic CEI spec; goal Measured

Dark current <0.4 e/pix/sec; <0.1 e/pix/sec ~0.1 e/pix/sec

Read noise (rms) <15 e/pix; <10 e/pix (CDS pair) ~23 e/pix

Full-well >100,000 e/pix; >150,000 e/pix ~100,000 e/pix

Encircled energy 1000nm: >0.56; >0.61 in 0.25” 0.52-0.56*

>0.72; >0.80 in 0.37” 0.73-0.77*

1600nm: >0.48; >0.54 in 0.25” 0.40-0.44*

>0.75; >0.80 in 0.60” 0.77-0.81*

Filter ghosts <0.2% of incident in a ghost <0.2%

Cal System 10,000 e/pix in <10 min <1 min

Uniform to <2x ~25x

Image stability <20 milli-arcseconds over 2 orbits 15-50 mas*Corrections for OTA vs. CASTLE likely to cause 1.0μm core EE to meet CEI spec (~0.60), while 1.6μm core EE likely to fall just below spec (~0.46).


IR Channel Shows ExcellentEnd-to-End Image Quality

• Thermal/vac was first opportunity to see IR channel operate end-to-end. Very gratifying to see how well it worked overall.

• Below: Image, encircled energy vs. radius at 1 micron wavelength.


WFC3 IR Throughput

IR throughput 10-15% below component predictions; this discrepancy is a bit beyond the expected error bars.


Discovery Efficiency (Throughput x FOV) Based on Thermal-Vac Results

Curves connect values at central wavelengths of available broadband filters – instruments’ spectral coverage is wider


UVIS Filter Ghosts

• Nasty ghost images in a small subset of UVIS filters

• Inter-reflections between “air-gap” substrates or coating layers

• Excellent replacements in hand for all severe cases; two less critical shipping this week

• Strong field-dependent ghosts in current F225W

New F225W


New UV Filters Improve Ghost Performance and Increase Sensitivity

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f218w - new

f225w - new

f275w - new

f300x - new


Point-Like Filter Ghosts (e.g. F606W)

F606W replacement – nearly ghost-free


Improved F606W and Stromgren Filters Ready for Installation

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f410m - orig

f467m - new

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f621m - orig

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f621m - orig


UVIS Crosstalk Solution In Hand

• Electronic crosstalk observed from quadrant to quadrant of 4-amp readout

• Analogous to ACS “extended source” crosstalk, but stronger (5-10e)

• Source traced to A/D conversion of pixel n while sampling pixel n+1

• Eliminate by speeding up A/D conversion and fitting it into pixel period away from sampling (<0.1e remains)

• Validated on non-flight elect.


IR FPA Radiation Effect

• WFC3 radiation testing revealed a radiation-induced background effect in the IR focal plane arrays

• Diffuse background produced, in addition to localized “hits”

• Followup testing in May 2004 identified the source as luminescence in the thick CdZnTe substrate on which the HgCdTe detectors are grown

Radiation-induced

background morphology

800 nm flat-field

morphology


Estimating On-Orbit Impact

• Extrapolation to flight situation is very difficult without full understanding of the microphysics of the phenomenon

• But making our best estimate, we predict

~0.25 electrons/pixel/second in orbit from the radiation effect

• Significant compared with other backgrounds, potentially leading to significant impact on IR channel sensitivity

• Estimate is very uncertain, but not a risk we want to take

• Fortunately, solution exists: substrate-removed detectors are now available! Fabrication of new IR arrays for WFC3 is underway


Insignificant Background Seen In Substrate-Removed Detector

• The diffuse radiation-induced background is reduced to undetectable levels when the substrate is removed

• Scales to negligible background for the on-orbit case

Substrate On Substrate Off


Dramatic QE Improvement with Substrate Removal

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)

FPA 64

FPA 102

FPA 104

FPA 105

FPA 106

FPA 114

QE For Devices With High and Flat QE


Dramatic QE Improvement with Substrate Removal (2)

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FPA 64

FPA 107

FPA 110

FPA 112

FPA 113

FPA 115

QE For Devices With Sloped QE


Cumulative Dark Distributions

T=150K

Dark Current For Devices With High and Flat QE


Cumulative Dark Distributions

Dark Current For Devices With Sloped QE

T=150K


FPA114 Cumulative Dark vs. Temperature


Survey Speed Metric (Speed x FOV) for Candidate IR Detectors

Detector

CDS

noise

Mean dark at 145K F110W F160W F126N

FPA64 24 0.04 (100%) 12.5 9.1 11.7

FPA112 24 0.09 (100%) 15.6 7.7 12.4

FPA104 33 0.14 (90%) 28.7 10.4 18.2

FPA105 28 0.10 (90%)

26.6 10.0 20.6

Potential FPA

20 0.04 (100%)

Flat 90% QE

31.4 12.5 36.1


Discovery Efficiency with Improved Filters and IR Detector

Curves connect values at central wavelengths of available broadband filters – instruments’ spectral coverage is wider


WFC3 SM4 FlowShuttle Launch

4/21-6/15/05

5/25/06– 12/1/06

Pre-IR Detector Instrument

Level Testing (Includes T/V

test #1)

Delivery to HST I&T

3/15/07

Pre Component Removal Activities

4/26– 11/03/05Optical Filter Fab

and Test

Build Flight IR1 Detector Assy

2/15/05 – 11/15/06

7/25/05 - 3/22/06

SOFA Rework at GSFC/Moog/Ball

Fab and test new IR FPA

4/26 – 2/7/06

Component Removal(SOFA, GCHP, Cal Source, IR Grism

LVPS boards, DEB board, SOFA Relay

Box)

6/16-7/22/05

IR Grism Rework

6/17 – 11/25/05

7/25 – 11/23/05

Electrical Mod/ Fix

Change out Lamps on Cal Source & Test

9/9-11/15/05

Heat PipeFab and Test

4/25/05 -5/5/06

Instrument Level Testing (EMI/EMC & T/V test #2)

12/29/06– 3/14/07 12/2/06 – 12/28/06Flight IR 1 installation

and final instrument closeout

10/5/05 – 5/24/06

Component Reassembly

HST Cal Conf -- Oct 27, 2005 Calibration Status and Results for Wide Field Camera 3 – R....

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