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WFPC2 STAN

S T A N / W F P C 2 - Number 16, June 1996

CONTENTS:

New Version of crrej for STSDAS:

by A. Fruchter

With the release of STSDAS 1.3.5 in July a new version of the cosmic-ray removal task, hst_calib.wfpc.crrej, will become available to users. CRREJ has been given a number of new capabilities that have already found application in the processing of the Hubble Deep Field. CRREJ now allows the user to specify a different scale noise for the PC and WF chips (The scale noise is an error estimate proportional to the value of the pixel. Its use can prevent small shifts in position between images from causing stars to be masked.) The new CRREJ also properly handles images of varying exposure length, can fit and remove a background sky level, and can update or create cosmic ray masks for the individual input images. The output image of the new CRREJ has an effective exposure time of the sum of the input images; therefore, in regions where no cosmic rays have been found, the output image will be equal to the sum of the inputs, less any sky that has been removed. In contrast, the previous version of CRREJ assumed all input images had the same exposure time and averaged the images. This previous version of CRREJ will still be available to users of STSDAS under the new task name MKDARK.

Update of FQCH4N* and FQUVN* Tables in SYNPHOT:

by S. Baggett and K. Noll

Based on observations of a spectrophotometric standard, we have identified improvements which can be made to the current filter throughputs for the methane and UV [OII] quad filters. The corresponding tables in the SYNPHOT package (see note below) have been updated to bring SYNPHOT into better agreement with these observations. This update affects only the filter curves for the 6193 A and 8929 A methane quad filters (apertures fqch4n33, fqch4n15, fqch4p15, and fqch4w3) and the UV quad filters (apertures wf2, wf3, wf4, and fquvn33).

The adjustments consisted of scaling the filter throughputs down (by 3-15% for all except FQCH4P15, which was scaled down by 30%) and fixing an incorrect path (FQUVN33). Note that the throughputs for the unrotated methane quad used with WF2 or WF4 (mean wavelengths 5433 and 7274) were not changed; these will be updated when additional calibration data becomes available.

The new tables are available for ftp retrieval; changes will take effect in the routine pipeline the last week of June 1996. Observers with data taken prior to this date and using the header keywords (PHOTFLAM, PHOTZPT, etc.) for calibrating their observations will want to retrieve the new versions and re-run SYNPHOT for their image obsmodes. As a reminder, there is a SYNPHOT Readme file available via ftp from the WFPC2 SYNPHOT tables directory.

The Readme file offers a brief history of all changes to the wfpc2-related SYNPHOT tables as well as information on how to retrieve, install, and use the tables. As reported in STAN at the time, the last update to SYNPHOT was July 1995 and affected all observation modes.

Note: The SYNPHOT package in STSDAS has three primary uses: 1) to provide photometric calibration information, which is inserted by the calibration software into image headers: (keywords photflam, photbw, etc), 2) to estimate exposure times for HST observations and, 3) to use synthetic photometry to calibrate observations.

New WFPC2 Documentation:

Instrument Science Report 96-04: Effects of Contamination on WFPC2 Photometry

by B. Whitmore, I. Heyer, and S. Baggett

Abstract:

Photometric monitoring observations are examined to determine the effect of contamination on WFPC2 photometry. New contamination rates are determined using observations of both a white dwarf standard (GRW+70D5824) and a globular cluster (Omega Cen = NGC 5139). Evidence for a long term increase in throughput with time has been found on the PC1 for F160BW and F170W filter observations. This, and other supporting evidence from the thermal vacuum tests and on-orbit observations, suggest that a long-lived contaminant is present in the PC1 which is slowly dissipating. In addition, corrections to the relative zeropoints for the different chips are determined for the F160BW, F170W, and F218W filters.

Paper copies of the report may be requested by sending email to help@stsci.edu.

Data Analyst Position Available at STScI:

The Space Telescope Science Institute anticipates several openings for Data Analysts. Data Analysts in the Science Support Division help General Observers and Archive Researchers analyze HST data, work with Instrument Scientists in calibrating the HST instruments, and work with STScI staff on grant-supported research projects. These research projects span a range of size scales from comets and planets to the large scale structure of the universe and a range of wavelengths from radio to X-ray astronomy. Applicants should possess a B.S. degree in astronomy or physics, or equivalent; experience with astronomical research; familiarity with scientific computing; expertise in data analysis; knowledge of IRAF, IDL or other software packages for astronomical data analysis; and programming ability. Additional mathematical, statistical, and computer skills are desirable. Candidates should have the ability to work with a minimum of direction, enjoy research and possess skills to develop excellent working relationships. Candidates should send a letter with current curriculum vitae and the names of three references to:

		Human Resources Manager
		Space Telescope Science Institute
		3700 San Martin Dr.	
		Baltimore, MD 21218

Women and minorities are strongly urged to apply. AAE/EOE.

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.

FERRARESE, L.; FORD, H.C.; JAFFE, W.  "Evidence for a
massive black hole in the active galaxy NGC 4261 from
Hubble Space Telescope images and spectra"  ApJ accepted.

FORBES, D.A.  "Globular cluster luminosity functions and
the Hubble constant from WFPC2 imaging: the giant
elliptical NGC 4365"  AJ.

KUDRITZKI, R.-P.; LENNON, D.J.; HASER, S.M.; PULS, J.;
PAULDRACH, A.W.A.; VENN, K.  "Hot luminous stars in nearby
galaxies"  Sci. with the HST 2.

MCNAMARA, B.R.; WISE, M.; SARAZIN, C.L.; JANNUZI, B.T.;
ELSTON, R.  "Optical structure in the Abell 1795 cluster
central galaxy: evidence for stripping and deflection of
radio jets"  ApJ accepted.

SEITZ, C.; KNEIB, J.-P.; SCHNEIDER, P.; SEITZ, S.  "The
mass distribution of CL0939+4713 obtained from a `weak'
lensing analysis of a WFPC2 image"  A&A.

SILBERMANN, N.A.; HARDING, P.; MADORE, B.F.; KENNICUTT,
R.C.; SAHA, A.; STETSON, P.B.; FREEDMAN, W.L.; MOULD, J.R.;
GRAHAM, J.A.; HILL, R.; TURNER, A.; BESSOLIN, F.;
FERRARESE, L.; FORD, H.; HOESSEL, J.G.; HAN, M.S.; HUCHRA,
J.; HUGHES, S.M.; ILLINGWORTH, G.D.; PHELPS, R.; SAKAI, S.
"The HST key project on the extragalactic distance scale.
VI. The Cepheids in NGC 925"  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.

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

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