S T A N / W F P C 2 - Number 27, August 1997

CONTENTS:

• The 1997 HST Calibration Workshop
• WFPC2 NEWS:
• WFPC2 Supplemental Darks Program
• Anomaly in Header Keywords PA_V3 and ORIENTAT
• WFPC2 Documentation:
• Instrument Science Report: Properties of WFPC2 Bias Frames (WFPC2 ISR 97-04)
• Instrument Science Report: WFPC2 Cycle 7 Calibration Plan (WFPC2 ISR 97-06)
• Instrument Science Report: WFPC2 Electronics Verification (WFPC2 ISR 97-07)
• Instrument Science Report: New Results on Charge Transfer Efficiency and Constraints on Flat-Field Accuracy" (WFPC2 ISR 97-08)
• STSDAS/TABLES 2.0 Release
• RECENT PREPRINTS
• APPENDIX: WFPC2 CONTACTS

The 1997 HST Calibration Workshop with a New Generation of Instruments:

September 22-24, 1997

STScI will host the third HST Calibration Workshop on September 22-24, 1997. Topics include the most recent calibration results for STIS and NICMOS, updates for WFPC2, FOC, and FGS, closure reports for GHRS and FOS, and an advance look at ACS and COS, the newly selected instrument for the 2002 servicing mission.

WFPC2 Supplemental Darks Program:

by Stefano Casertano, Andy Fruchter, Sylvia Baggett, Shireen Gonzaga

We have recently started (July 14, 1997) a program to obtain more frequent dark frames for use in the identification of warm pixels. WFPC2 images contain a significant number of pixels with elevated dark current (``warm'' pixels), the majority of which are temporary: they are generated by particle hits, at a rate of several tens/day/detector, but are ``annealed'' during the monthly decontamination of the camera. Lists of warm pixels with time resolution of about a week are available via the Web, and can be used by the STSDAS task ``warmpix'' to correct and/or flag warm pixels in WFPC2 data. About 90% of all warm pixels can be identified in this way.

The new Supplemental Darks program (7621, 7712, 7713) is designed to provide more frequent, short (1000s) darks to be used primarily for the identification of hot pixels. Shorter darks are used so that observations can fit into almost any occultation period, making automatic scheduling feasible. The program is designed to complement the Standard Darks program (7620), whose longer individual observations are better suited to produce high-quality pipeline darks and superdarks. This program has become possible after the Second Servicing Mission thanks to the larger storage capacity of the Solid State Recorder.

Currently, about 15 darks are taken each week as part of this program. The darks will not be used in standard STScI products, but are available to observers via the Hubble Data Archive.

Anomaly in Header Keywords PA_V3 and ORIENTAT:

by John Baum and Stefano Casertano

In a few cases, the keywords PA_V3 and ORIENTAT in the header of a WFPC2 image have been assigned an incorrect value. This behavior occurs only for the last exposure in an orbit, and only when a large slew of the telescope follows immediately. We have found about 50 occurrences of this anomaly, although there could be a few more.

Users affected by this problem will be informed directly when we complete the identification of these images. Meanwhile, images with this problem can be recognized from the following set of circumstances: several exposures of the same target taken in the same orbit all have the same value of PA_V3, except for the last one which is different (generally by several degrees). The value of PA_V3 can easily be inspected directly from the Hubble Data Archive interface screens, both via the Web interface and in Starview. No other data are affected. A possible fix is to copy the appropriate header parameters (image parameter PA_V3 and group parameter ORIENTAT) from one of the other images in the series.

Thanks to Marcella Carollo and Massimo Stiavelli for alerting us to this problem.

WFPC2 Documentation:

by C.P.O'Dea, S.Gonzaga, M.McMaster, I.Heyer, J.C.Hsu, S.Baggett, K.Rudloff

We report on the basic on-orbit characteristics of the biases and the overscan region, and also discuss the superbiases. We then investigate the jumps in the bias level, and present the procedure for creation of the current set of pipeline superbiases.

by S.Casertano and the WFPC2 Group

This report describes in detail the WFPC2 observations planned to maintain and improve the quality of WFPC2 calibrations during Cycle 7. The total spacecraft time we plan to use for such observations is 76 pointed orbits, and ~3000 occultation periods, the latter being used for internal observations and Earth flats.

by M. Stiavelli and M. Mutchler

The results of calibration proposal 6924 aimed at verifying the linearity of WFPC2 for various exposure times and operating modes are described and analyzed. For count rates exceeding 0.5DN/s, WFPC2 appears to be linear to better than 0.5%. Results at very low count levels are less conclusive given the low signal-to-noise.

by B. Whitmore and I. Heyer

The primary new results based on observations from calibration proposal 6195 are:

1) A set of new formulae has been developed to correct for CTE loss,
   with dependencies on the X and Y positions, the background counts, and
   the brightness of the star. The use of this formula reduces the
   observational scatter in this particular dataset from 4-7% to 2-3%,
   depending on the filter. 

2) A small correction is required to normalize results from aperture
   photometry on the three WF chips. This normalization can be understood
   as the product of different aperture corrections (i.e., variations in
   the PSF) and different gain ratios for the three chips. 

3) The uncertainties in aperture photometry of point sources due to
   flat-fields are less than (probably considerably less than) 1.5% across
   the chip and 0.6% chip-to-chip. 

STSDAS/TABLES 2.0 Release:

by Rick White & Perry Greenfield

We are pleased to announce the availability of the beta release of TABLES and STSDAS, versions 2.0. This version includes new tasks for accessing NICMOS and STIS datasets along with a number of tools for manipulating these and other data stored in FITS image extension format.

This beta release is "load and go" for Sun SPARCstations running SunOS 4.1.3 or Solaris 2.5 with the IRAF 2.11 beta release, which means it has already been compiled for execution under these versions of the Sun operating systems. Once the tar file has been read, you can use the package. Please note that IRAF 2.11 is REQUIRED to run STSDAS/TABLES 2.0. They will NOT run correctly under 2.10.

The final (non-beta) release of STSDAS/TABLES 2.0 is expected on about September 7th. The exact timing depends on the release by NOAO of the final version of IRAF 2.11 (which should be available any day now.).

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.

CLOSE, L.M.; RODDIER, F.; HORA, J.L.; GRAVES, J.E.;
NORTHCOTT, M.; RODDIER, C.; HOFFMANN, W.F.; DAYAL, A.;
FAZIO, G.G.; DEUTSCH, L.K. "Adaptive optics infrared
imaging-polarimetry and optical HST imaging of Hubble's
variable nebula (R Mon/NGC 2261): a close look at a very
young active Herbig Ae/Be star"  ApJ accepted
 
BOSH, A.S.; RIVKIN, A.S.; PERCIVAL, J.W.; TAYLOR, M.; VAN
CITTERS, G.W. "Saturn ring-plane crossing, May 1995: pole
precession and ring thickness"  Icarus accepted
 
HILKER, M.; BOMANS, D.J.; INFANTE, L.; KISSLER-PATIG, M.
"NGC 1427A: an LMC type galaxy in the Fornax cluster"  A&A
 
JANNUZI, B.T.; YANNY, B.; IMPEY, C. "HST imaging of the
host galaxies of three X-ray selected BL Lacertae objects"
ApJ 11-20-97
 
DOHM-PALMER, R.C.; SKILLMAN, E.D.; SAHA, A.; TOLSTOY, E.;
MATEO, M.; GALLAGHER, J.; HOESSEL, J.; CHIOSE, C.; DUFOUR,
R.J. "Recent star formation history of the dwarf irregular
galaxy Sextans A from HST observations"
 
REIPURTH, B.; HARTIGAN, P.; HEATHCOTE, S.; MORSE, J.A.;
BALLY, J. "Hubble Space Telescope images of the HH 111 jet"
 
SURACE, J.A.; SANDERS, D.B.; VACCA, W.D.; VEILLEUX, S.;
MAZZARELLA, J.M. "HST/WFPC2 observations of warm
ultraluminous infrared galaxies"  ApJ accepted

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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