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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– ~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– 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)

• 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)

• 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

• 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

• A major strength of the WFC3/IR channel is that Broad Filters and GRISMS are intended to be Zodiacal background limited

• 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• 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, Editor-

in-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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