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Hubble Space Telescope
WFPC2 STAN

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| STScI Analysis Newsletter (STAN)
| WFPC2
| 20 April 2007
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CONTENTS:

1.  New WFPC2 Phase II Observation Strategy Web Page

2.  Recent Progress on the WF4 CCD Anomaly

3.  WFPC2 Calibration Plans for Cycle 16

4.  Updated Dark Reference Files for 2006 - 2007

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1.  New WFPC2 Phase II Observation Strategy Web Page

We have created a new web page with advice about WFPC2
Phase II Proposal strategies.  At the moment it primarily
covers dithering, CTE, and the WF4 CCD anomaly.  We may
add other topics depending on the range of questions we
receive from proposers in the upcoming weeks.  The page
is available at:
http://www.stsci.edu/hst/wfpc2/wfpc2_phase2.html

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2.  Recent Progress on the WF4 CCD Anomaly

During Dec. 2006 - Feb. 2007 the bias levels in the WF4
CCD were again heading towards zero, and an increased
possibility of blank images.  On 27 March 2007, the
operating temperature of the WFPC2 electronics was
lowered by 1 deg C, and WF4 was again returned
to near-normal operation.

This is the third successful temperature reduction we have
performed (others being in Jan. and Feb. 2006), and we
have yet to see any serious negative side effects of the
temperature reductions.  This gives us some confidence
that we can keep the WF4 CCD alive until Servicng Mission 4.

A side effect of the temperature reductions is that the
relative positions of the four CCDs in the HST focal plane
move by about 0.01 arcsecond for each of these 1 deg C
reductions.  This may have some small effect on projects
needing accurate chip-to-chip astrometry.  We plan to
calibrate these astrometric changes later in the year
and update the CCD offset table.

Details of these temperature reductions can be found in
a new Instrument Science Report "Temperature Reductions
to Mitigate the WF4 Anomaly" available at:
http://www-int.stsci.edu/instruments/wfpc2/Wfpc2_isr/wfpc2_isr0701.pdf

For most observers, the primary impact of the WF4 anomaly
will be low photometric counts in the WF4 CCD during
periods of low bias values.  Work is underway to
incorporate photometric corrections in the WFPC2
calibration pipeline later in 2007.  Until then,
correction equations and scripts are available and can
be manually applied to the data.  These corrections are
accurate to about +/-2%. Please contact help@stsci.edu
for more information.

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3.  WFPC2 Calibration Plans for Cycle 16

The current WFPC2 plans for Cycle 15+16 and instrument
closeout were created in the fall of 2006.  These are
available at
http://www.stsci.edu/hst/wfpc2/analysis/WFPC2_cyc1516_cal_plan_final.pdf

In view of the increased utilization of WFPC2, we will
likely revise and expand these plans in the coming months.
One likely change is an increased effort to calibrate
CTE effects for extended targets.  Observations of an
Abell cluster and part of the HDF field are planned to
study CTE effects.  These new data would be compared with
previous observations of the fields.

We would like to hear from any observer who feels some
specific calibration should be added or augmented in our
planning.

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4.  Updated Dark Reference Files for 2006 - 2007

We have generated new WFPC2 dark calibration reference
files for the period 19 June 2006 to 26 Feb. 2007.
Observers with data within this period, and wishing to
utilize the new files, should re-retrieve their data from
the HST archive; the new retrieval will automatically be
processed with these new reference files. These will give
improved removal of hot and warm pixels.

After February 2007 we have been making new dark
reference files within 30 days of new science observations,
and plan to continue this throughout Cycle 16.

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| Visit the ACS and WFPC2 websites for more news:
| ACS:   http://www.stsci.edu/hst/acs
| WFPC2: http://www.stsci.edu/hst/wfpc2
| Need help? http://www.stsci.edu/hst/acs/help.html
| or send your questions to the Help Desk: help@stsci.edu
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| Previous ACS and WFPC2 STANs are archived at:
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| The Space Telescope Science Institute is operated by the
| Association of Universities for Research in Astronomy,
| Inc., under NASA contract NAS5-26555.
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