MEMORANDUM
TO:
Distribution
DATE:
July 18, 2002
SUBJECT:
Questions and Answers from the 18 July 2002 TIPS Meeting
CADC/ECF WFPC2 Associations
Presenter – Dave Schade
Q: Do the associations span across different visits? Do the association span across different proposals?
A: The associations do not span across different proposals, but they do span across visits with the same roll
angle.
Q: Will the number of associations increase significantly if they span different proposals?
A: We do not know, but we expect the number to be small.
Q: Are the data currently available publicly? What is the current means to access the data?
A: The data do exist but not in a public form. CADC can arrange for immediately access to available data
on a case-by-case basis, and we are working with the STScI archive to make the data available publicly.
Q: What is the assessment of the quality of the current data? What fraction of the data is being considered
as problematic? How do you measure the quality of the data?
A: The assessment of data quality spans across the entire reduction process, which includes source
detection problems. Data towards the blue side seem to have more problems. Problematic data constitute
only a few percent of the entire dataset. An empirical parameter set, which includes filters used, exposure
time, etc., was used to provide quantitative measures to assess the quality of the data.
Status of PyDrizzle Software
Presenter – Warren Hack
Q: Does PyDrizzle refine shifts with delta-associations and rotation as well?
A: Yes, rotation is part of it.
Q: Does PyDrizzle give shifts in pixels?
A: In PyDrizzle, shifts are given in RA and Dec.
Q: Does OTFR result in PyDrizzle products?
A: Yes, but only the default parameters will be used for the process.
Q: When should we run PyDrizzle externally beyond the standard pipeline calibration?
A: Some examples of situation where one would want to run PyDrizzle externally include deep
observations and observations with different dither patterns.
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Q: Are there plans to implement other techniques, such as cross-correlations, to improve on the shifts?
A: We are not clear at this point as to what specific techniques will be incorporated into the current
pipeline. We might need to implement a set of different techniques for different situations, or to develop a
specific toolsets. The group will continue to investigate the options.
Q: Is there a plan to develop a completely automated PyDrizzle pipeline?
A: We do have a plan but without a schedule.
GSC2 Status and Implementation Plans
Presenter – Brian McLean
Q: Is there a need to improve on the astrometric calibration for GSC II when other more current surveys,
such as UCAC, can provide much better astrometry?
A: There are two aspects to be considered. One is the astrometric accuracy for post-observational analysis.
The other is the accuracy needed for operational use. GSC II provides better coverage and better positions
for the faint end. For example, UCAC will be complete only down to 16th magnitude, whereas GSC II will
cover down to 21st magnitude.
Q: Will GSC II satisfy NGST requirements?
A: Studies have indicated that NGST will require 1 arc-sec accuracy. GSC II will certainly satisfy this
requirement.
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