MEMORANDUM
TO:
Distribution
DATE:
February 21, 2002
SUBJECT:
Questions and Answers from the 21 February 2002 TIPS Meeting
SISD Perspective
Presenter – Harry Ferguson
No questions.
Cycle 11 Update and Cycle 12 Plans
Presenter – David Soderblom
Q: Is there any change to the SM3b launch date?
A: There is no change.
WFPC2 Status
Presenter – Anton Koekemoer
Q: Will the Dither Working Group work on a release of the meta-drizzle tool and make it available to the
user community?
A: The Dither Working Group plans to discuss the specifications for future drizzle software, and metadrizzle is on the discussion list.
Comment: The issue and information regarding the study of the WFPC2 filter wheel rotation anomaly
have been disseminated to the WFC3 community.
Q: Could other shifting anomalies, such as the jitter shifting, be caused by the filter wheel rotation
anomaly?
A: It is possible, and we will need to investigate this further.
ACS Flat Fields
Presenter – Ralph Bohlin
Q: Why would the structures seen on the ACS WFC flat fields go across from one chip to the other?
A: The two detector chips were split from the same whole chip and were matched back, and so one would
expect to see flat field structures to cross from one chip to the other.
Q: What are the other faint circular structures seen on the flats?
A: Those are dust particles on the window, and the magnitudes of those are less than 1%, which will not be
of significant impact.
Q: How reproducible are the flat fields and are there significant variations?
A: The flat fields are highly reproducible, and variations are less than 1%.
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Q: Regarding the filter shift problem, one would expect the linear ramp filters to be more problematic.
Have flat fields been taken for those filters?
A: No, as long as the dust contamination is not larger than expected, we do not anticipate any problem with
the flats. Actual science data might have problems, though.
Q: Given that the data from the resolver can determine the filter wheel’s offset, could we implement a fix
in the calibration pipeline?
A: It is possible, but there is no current plan to pursue this.
WFC3 Status (Detectors)
Presenter – Massimo Robberto
Q: What is the implication of the measured persistence value for the IR detectors?
A: The measured persistence is simply the dark current as measured 96 minutes after the illumination, and
it does not provide insights to cosmic-ray persistence issues.
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