Wide Field Camera 3
TIPS
18 September 2014
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WFC3 Inserted in SM4 (2009)
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WFC3 Summary
• WFC3 is operating nominally
– Photometric zero points (including UV) stable to ~1% since 2009
– Astrometric calibration is stable (dominated by HST OTA “breathing”)
– UVIS CCD Detectors CTE declining as expected with radiation damage and
mitigation/correction methods have improved considerably
– IR Detector shows essentially zero evolution of its performance in flight
– 5 year life requirement surpassed this summer!!
• Kudos to GSFC, Ball Aerospace, e2v, Teledyne, etc…..
• Thanks to Kailash for helping with the refreshments this morning!
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Past Year Highlights
• Improved understanding of UVIS CTE and IR Persistence
– Sink pixels in CCDs; GOs are 2/3 using Post-Flash in Cy22
– IR Persistence depends upon many factors! Model available <5 days
• UVIS Initiative  2 Chip Photometric solution (this fall)
– Includes improved UV flats; better darks
• IR Background variations  He 1.0830 mm line; zodi
– F105W and F110W: often can schedule around dusk/dawn
– G102 and G141: two component background model
• Spatial Scan observations have “gone mainstream”
– Exoplanets & Cepheid parallax distances (25 micro arc seconds)
• System improvements: CRDS, Side-Switch SMOV, QL
• User Support: Contact Scientist identification of bad actors
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Future Initiatives (1)
• PSF Library
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~10^7 stars “reasonably isolated” with “reasonable S/N” in F606W
Will expand to entire set of WFC3 observations
First application: improve focus monitoring from ~2 mm to <1mm
Exploring methods for making this usefully available
• Astrometric improvements
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Initial requirement: 4 mas (0.1 pixels) for AstroDrizzle
WFC3 very stable internally due to thermal control of optical bench
Inclusion of photolithographic mask offsets (2013)  2 mas
Inclusion of filter induced mid-spatial frequencies  1 mas
• Done for ~10 UVIS filters with sufficient Omega Cen data
• Expanding to remaining filters over Cycles 22-23
– How to best exploit GAIA?
• All Guide Stars and many (most?) frames to <1mas absolute!
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Future Initiatives (2)
• Better instrument calibration/understanding
– Time correction for UVIS zero points (<0.3 percent per year)
• This affects visible (not UV or IR); WHY??
– Continued exploration of infrared detector persistence
• Improved model for predicted images (but will hit limits)
• Repeated observations of bright objects noise floor?
– Very high precision astrometric calibrations for spatial scans
• Advanced GRISM data reduction algorithms/software
– Tools to handle observations at multiple roll angles
– Modeling approach to extract fainter sources and understand errors
– Highly synergistic with JWST and WFIRST-AFTA needs
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WFC3 Team (1)
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Jay Anderson – CTE Mitigation
Sylvia Baggett – Detectors Lead
Matthew Bourque – Detector Calibrations, PSF DB & QL
Ariel Bowers – Flats, WWW & QL S/W Lead
Gabe Brammer – IR Grisms and Backgrounds
Susana Deustua – Photometry Lead
Linda Dressel – User Support Lead & Image Analysis
Mike Dulude – IR Darks, Earth Flats, QL
Meredith Durbin – new RIA
Mike Fall – GAIA Astrometry
Kati Gosmeyer –Photometry & QL
Heather Gunning – Detector, CRDS & QL Ops Lead
Harish Khandrika – new RIA
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WFC3 Team (2)
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Knox Long – IR Detector Persistence
Jen Mack -- Flat Fields
Peter McCullough – Spatial Scans for Exoplanets & CSM
Kai Noeske – Photometry & CTE
Nor Pirzkal – IR Grisms and Backgrounds
Vera Platais -- Astrometry
Adam Riess – Spatial Scans for Astrometry/Precision Photometry
Elena Sabbi – Calibration Lead & Deputy Team Lead
Kailash Sahu – Photometry & PSF DB Lead
Dave Taylor -- Systems
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Departures
• Tomas Dahlen
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Mike Dulude  HLA
Derek Hammer Industry
Bryan Hilbert  JWST
Kai Noeske  MPIA
Alex Viana Industry
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Engineering
• Analysis of Channel Select Mechanism
– Two unexplained issues related to this critical mechanism
• Two episodes of particle contamination on CSM mirror (2009 and 2012)
• Handful of mirror mis-positions (~0.3 to 0.5 motor steps; typical is <0.1
steps)
– Coincidence?? Working hypothesis: failure of epoxy staking holding
pin in motor shaft
– Response:
• reduce CSM usage via changes to ops rules and calibration program
• tools for manage usage constructed
• Careful monitoring
• Cause of small visible CCD throughput decline – new study
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CSM Position and Blob Count
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Reduction in CSM Moves
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Infrared Background Variation
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A major strength of the WFC3/IR channel is that Broad Filters
and GRISMS are intended to be Zodiacal background limited
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Nominal Backgrounds: 0.5 to 1.0 e-/s/pixel
• HOWEVER: sometimes brighter (up to 3 to 5e-/s) and non-uniform
backgrounds are observed
• Particularly problematic for deep Grism surveys
• Causes now well understood
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Pointing traversing central part of zodiacal cloud
• i<80°sun angle near ecliptic plane
• Long dwells near bright earth limb (i.e. CVZ or near CVZ situations).
• Inclusion of He I 10830Å line within the passbands of G102,
G141, F105W, F110W
• Careful scheduling required for faint observations – consult
STScI
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Sections From Two GRISM Observations
(background level & structure varies)
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He I 10830A Line
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Background function of Day/Night
Location with He Line
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Minimal Effect without He Line
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Spectroscopic Confirmation
• Dust particles on in-focus IR
channel select mirror provide
“negative” spectrum
• He I 10830 line present when
background is high in both
Grisms.
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Invitation to Publish
• New SPIE Journal
• Mark Clampin, Editorin-Chief
• JATIS publishes peer-reviewed
papers reporting on original
research in the development,
testing, and application of
telescopes, instrumentation,
techniques, and systems for
ground- and space-based
astronomy.
• JWM is Associate-Editor
covering space instruments
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