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WFPC2 STAN

S T A N / W F P C 2 - Number 49, December 2001

CONTENTS:

CYCLE 11 PHASE II ADVISORIES:

Dither Handbook Update V2.0:

An update of "The Dither Handbook" (V2.0; Koekemoer, et al., 2001) is now available. It includes clarified and updated descriptions of how to design dithered observations for Cycle 11, including information on ACS and NICMOS, as well as WFPC2 and STIS. It also includes updated examples of how to reduce and analyze dithered HST observations, including a section on how to combine dithered ACS images using the new PYRAF-based version of drizzle, known as "pydrizzle".

New WFPC2 Exposure Time Calculator:

-J. Biretta

The new WFPC2 Exposure Time Calculator (V4.0) is now available. This version includes calculations of exposure times and/or signal-to-noise ratios for point sources (plus background) using either the traditional "optimal PSF weighting" method or simple aperture photometry in a fixed aperture radius specified by the user.

In addition, the ETC has been upgraded to allow for a more flexible specification of the sky background. There are now three options. The first option uses a rough estimate of "average" or "high" or "low" sky background conditions. The second option estimates the sky background based on the position of the target and (optionally) an estimate for the heliocentric longitude of the target (sun angle). The last option allows the user to explicitly provide a value for the sky background, in magnitudes per square arcsecond.

The WFPC2 Photometric CTE Monitor (ISR 01-09):

-I. Heyer

The Charge Transfer Efficiency of the WFPC2 CCD arrays has been monitored since the instrument's deployment aboard HST in 1993. Since then a significant increase in CTE loss has been observed. We examine photometric data from 28 April 1994 to 11 February 2001. The CTE loss appears to be growing worse in a linear fashion with time. The results from the latest set of observations show that CTE loss has reached a level of 53% in the worst case scenario. More typical observations have ~5% CTE loss (i.e. long exposures using broad band filters).

The adverse effects of the CTE can be minimized by carefully choosing the position of the object on the PC or WFC chips. The recommended positioning for each chip is described in Section 4 of the WFPC2 Instrument Handbook for Cycle 11 (see Table 4.3).

WFPC2 NEWS:

OTFR (On-the-Fly-Reprocessing) - An Update:

-S. Baggett and M. McMaster

In May 2001, OTFR replaced OTFC (On-the-Fly-Calibration). This new system has the advantage of automatically fixing the majority of previous keyword problems (i.e., significantly fewer header fixups are required for OTFR). However, the new system has not been without a few minor glitches. OTFR has trouble with about a dozen WFPC2 images (out of ~115,000 total in the archive); these few images cannot currently be obtained through the normal HST archive interface (these images are internal calibration images and are generally not used by observers). It had also recently been setting the FGSLOCK keyword incorrectly to "unknown" in some images. Fixes for these problems will be in place by mid-January.

NOTE: It is not necessary to run the STSDAS task, UCHCOORD, on OTFR data
      since changes to the WFPC2 plate scale, chip rotations, and shifts
      are automatically incorporated into the new OTFR calibration pipeline.
      In fact, versions of UCHCOORD older than May 2001 may corrupt
      astrometric information if applied to data from the OTFR system.

An Improved Geometric Solution for WFPC2 (ISR 01-10):

-S. Casertano and M. S. Wiggs

We present an improved solution for the geometric distortion in WFPC2, based on multiple observations of a rich stellar field. We also quantify the long-term variation of the relative position of the detectors by tracking the position of the K spots over time. We suggest possible avenues to develop an improved wavelength- and time-dependent geometric solution for WFPC2.

Summary of WFPC2 SM3B Plans (ISR 01-11):

-A. M. Koekemoer, S. Gonzaga, I. Heyer, L. M. Lubin, and V. Kozhurina-Platais

We summarize WFPC2 activities and calibrations planned for Servicing Mission SM3B, currently scheduled for launch in February 2002.

RECENT PREPRINTS:

We draw your attention to these papers, based on WF/PC and WFPC2 data, that will appear in the next few months. This list includes all preprints received by the STScI Library not yet published in the journals. Please remember to include our Library in your preprint distribution list.

KOEKEMOER, A.; GROGIN, N.A.; SCHREIER, E.J.;
GIACCONI, R.; GILLI, R.; KEWLEY, L.; ZIRM, A.;
BERGERON, J.; ROSATI, P.; HASINGER, G.; TOZZI, P.;
MARCONI, A. "HST Imaging in the Chandra Deep Field
South. II. WFPC2 Observations of an X-ray
Flux-Limited Sample from the 1 Msec Chandra
Catalog" ApJ 2-20-02

WALBORN, N.R. "The Pillars of the Second
Generation" Hot Star Wksp 3:
       
FEINSTEIN, C.; MACCHETTO, F.D.; MARTEL, A.R.;
SPARKS, W.B. "Filaments and Ionized Gas in the
Vicinity of 3C 244.1" ApJ 1-20-02

VANZELLA, E.; CRISTIANI, S.; SARACCO, P.; ARNOUTS,
S.; BIANCHI, S.; D'ODORICO, S.; FONTANA, A.;
GIALLONGO, E.; GRAZIAN, A. "Multicolor Observations
of the Hubble Deep Field South" AJ 11-01

APPENDIX: WFPC2 Contacts:

Any questions about the scheduling of your observations should be addressed to your Program Coordinator. Post-Observation questions can be addressed to your Contact Scientist. If you do not know who these persons are, you can find the information on the WWW at: www.stsci.edu/public/propinfo.html.

Analysis, STSDAS or any other questions can also be addressed to help@stsci.edu.

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