TV3 Science Team Cast of “Characters”

TIPS May 22, 2008 1H. Bushouse


TV3 Science TeamCast of “Characters”

• Instrument Scientists:–Sylvia Baggett

–Howard Bond

–Tom Brown

–Howard Bushouse

–Susana Deustua

–Linda Dressel

–George Hartig

–Bob Hill (GSFC)

–Randy Kimble (GSFC)

–John MacKenty

–Andre’ Martel

–Peter McCullough

–Larry Petro

–Steven Rinehart (GSFC)

• QuickLook Operators:–Elizabeth Barker–Misty Cracraft–Bryan Hilbert–Sherrie Holfeltz–Diane Karakla–Jessica Kim–Kevin Lindsay–Doug Long–Ray Lucas–Jennifer Mack–Helen McLaughlin–Cheryl Pavlovsky–Brittany Shaw–Ed Smith–Megan Sosey–Alex Viana

• WFC3 Operations:–Tom Wheeler


High-Level Statistics

• Total of 743 hours (31 days) on Science Calibration activities– Initial ambient calibrations: Feb. 20 – 29

– Vacuum calibrations: Mar. 4 – Apr. 16

– Final ambient calibrations: Apr. 18 – 21

• 188 hours (8 days) spent on unplanned investigations– UVIS window droplets

– IR FPA persistence

– IR bias jumps (“banding”)

– UVIS PSF short-term stability (shutter-induced jitter)

– UVIS electronic crosstalk linearity

• 555 hours (23 days) spent on original 20-day Science Calibration plan activities (15% overrun)

• ~ 265 SMS runs; 10,605 exposures; ~25 lbs of M&M’s


Objectives Met

• Calibrate all WFC3 science modes Obtain all data necessary to support on-orbit science operations and data

calibration using UVIS-1’ and IR-4 detectors UVIS & IR detector calibrations: bias, dark, flat field, read noise, gain,

linearity, full-well, fringing, … System-level calibrations: system, filter, & grism throughputs

• Verify system-level performance Optical alignment, image quality, photometric stability, scattered light,

internal cal system performance Effects of input voltage and thermal cycling on calibrations Verify instrument performance model (Exposure Time Calculators)

• CEI spec and lien verifications, where possible


Accomplishments

• All tests in original 20-day calibration plan accomplished

• No tests or calibrations deferred to SMOV


Sci Cal Tests Completed

Servicing Mission Aliveness/Functional Test

UVIS & IR Optical Alignment

UVIS & IR Science Monitors

IR Darks (read noise)

IR Background Levels vs. Filter

IR FPA Gain

IR FPA Linearity (full-well)

IR Optical Performance (Encircled Energy)

IR Throughput

IR Filter Blue Leaks

IR External & Internal Flat Fields

IR Flat Field Stability

IR Grism Narrowband Flat Fields

IR Grism Flux Calibration (throughput)

IR Grism Dispersion & Spectral Trace

IR FPA Edge and Baffle Scattered Light

IR Photometric Stability

IR Electronic Crosstalk

IR Bias/Dark vs. Orbit Cycling

IR Rate Dependent QE

IR Intrapixel Sensitivity

IR Persistence

UVIS Bias (read noise)

UVIS Darks

UVIS CCD Gain

UVIS Linearity (full-well)

UVIS Optical Performance (Encircled Energy)

UVIS System Throughput

UVIS Filter Throughput

UVIS CCD Red Cutoff

UVIS Filter Red Leaks

UVIS External & Internal Flat Fields


Sci Cal Tests Completed (2)

UVIS Flat Field Stability

UVIS Grism Narrowband Flat Fields

UVIS Grism Flux Calibration (throughput)

UVIS Grism Dispersion & Spectral Trace

UVIS CCD Fringing

UVIS Glint

UVIS Electronic Crosstalk

UVIS Filter Wedge

UVIS CTE EPER Flat Fields

Unplanned tests:

IR Bias Jump Monitor

UVIS Window Droplet Investigations

UVIS PSF Stability (shutter-induced jitter)

UV Quantum Yield Measurements

UVIS CCD Amplifier “smearing” check


UVIS CCD Characteristics

• Read noise: 3.0–3.3 e- rms• Dark current: <1 e-/pix/hour• Full-well: 70-85k e-

• All consistent with TV1 results using detector with same CCD chips


UVIS Flat Fields

F275W

F555W

F814W

15% structure

7% structure59 of 66 filters have total of 120ke- in flats (0.3%)7 (all narrow quads) have 40-80ke- (0.4-0.5%)


IR FPA Characteristics

• Read noise in a CDS difference image: ~22 e-/pix rms– Averages down to ~14 e- over 16 samples

Dark current: ~0.05 e-/pix/sec

• Linearity: 5% at ~72k e-

– Hard saturation at ~84k e-


IR Flat Fields

“Death Star” “Wagon Wheel”35-40% structure

>200k e- in all IR flats (~0.2%)


Orbital Cycling

• Vary thermal environment and WFC3 input voltage to simulate orbital cycles

• Check IR FPA temperature and bias stability

Temp stable to ~0.6 K


Open Issues/Studies

• UVIS “bowtie” feature

• UVIS shutter-induced image jitter

• IR image persistence

• Launch on Side 1 or 2?– Intermittent IR bias jumps seen on Side 1

– UVIS shutter jitter somewhat worse on Side 2


UVIS “Bowtie”

• Regions of enhanced brightness occasionally seen in darks and flats

• Example here is at strongest level yet seen (5% UV flatfield enhancement in the bowtie and in the location of two alignment spots)

• Typical levels are much less (0.5-1%)


Bowtie Investigation

• Physical mechanism not understood; there appears to be both a persistence and a QE hysteresis phenomenon at work

• Physical morphology is suggestive of a charging effect (electrical field “pincushion” morphology)

• The DCL has never seen this behavior in testing of e2v devices, yet it has been seen with UVIS-1, UVIS-2, and UVIS-1’ in WFC3

• Science team is surveying all biases, darks, and flats from T/V-1, TV-2, and TV-3 to identify all examples and search for trends, correlations

• Seems to occur most often in images taken in ambient (CCD’s warmer than flight), or soon after detector cooldown, but not always

• The clear CCD-level symmetry naturally suggests a CCD-level cause – no upstream sources (optics, stray light, CASTLE illumination) know anything about the split focal plane

• The problem does not arise in the readout electronics (not present in the overscan; readout wouldn’t know about alignment spots)


UVIS Shutter-Induced Image Jitter

• Series of short (1 sec) exposures shows lower peak pixel fraction and larger PSF width in alternating images, while total flux is constant

• Phase of alternating behavior correlates with phase of the 2-blade shutter mechanism

• For exposures >5-10s, no significant effects are seen


Effects Are Strongest In Short Exposures and Small Apertures

• Theory: motion of shutter induces mechanical jitter in the instrument that slightly blurs short exposures; the element most likely affected is the UVM1 mirror (<1 arcsec of rotation of that optic is required to produce the effects observed)

• Possible changes to shutter operations (starting position, encoder feedback, etc) under investigation

EE (diameter in arcsec)


IR Image Persistence

• Initial test using 0.5x-100x full-well sources showed negative persistence (essentially negative dark current); never seen in DCL tests

• Severe over-illumination had occurred due to ground test equipment

• Reran with modified techniques, which showed normal positive persistence, and was (as expected) very low for the sub-full-well exposures

• Target brightness constraint for IR channel could result, though the strong preference is to avoid this; perhaps at least an alert to observers as to the potential effects of very bright objects in their target fields


IR Bias Jumps: Gone but not forgotten

• Low-level bias shift (~2.5DN) was seen intermittently only in lower left quadrant of readout; effect is tracked by the reference pixels in those rows

• Only seen with Side 1 electronics

• Initial rate of occurrence: ~4.5% of all reads

• After March 19: zero in >3000 reads


Results & Remaining Work

• ISR 2008-05 “IR Channel Blue Leaks”, T. Brown

• ISR 2008-06 “IR Channel Baffle Scatter”, T. Brown

• ISR 2008-07 “UVIS Channel Glints”, T. Brown

• ISR 2008-08 “UVIS Filtered Throughput”, T. Brown

• ISR 2008-09 “IR Channel Throughput”, T. Brown

Finish TV3 analysis and delivery of calibration reference files by end of July

Documents

TV3 Science Team Cast of “Characters”