S T A N / W F P C 2 - Number 35, April 1999

CONTENTS:

• WFPC2 NEWS:
• Internal Flat Field Monitoring II: Stability of the Lamps, Flat Fields, and Gain Ratios
• Cycle 8 Calibration Plan
• Minor Keyword Changes due to new OPUS Software
• Filter Workshop in July for Wide Field Camera #3
• RECENT PREPRINTS
• APPENDIX: WFPC2 CONTACTS

Internal Flat Field Monitoring II: Stability of the Lamps, Flat Fields, and Gain Ratios:

by C. O'Dea, M. Mutchler, and M. S. Wiggs

We have compared the on-orbit behavior of the VISFLAT and INTFLAT lamps and the "flat fields" that they produce over the period from early 1994 to early 1998. We find:

1) The VISFLAT lamps continue to degrade in intensity at the expected rate. The loss is less in the blue due to the Welch-Allyn Bulb becoming hotter.

2) One (or more) INTFLAT lamps have increased output slightly (the net change is ~1.3% in 4 years). On timescales of ~6-35 s, the output of the Carley bulbs is relatively constant.

3) The relative gain ratios of the electronics are stable in WF2 and WF4, though there is a steady 0.3% drift in the WF3 gain ratio, and a jump in PC gain ratio of 0.7% in February 1997 (second servicing mission).

4) The pixel-to-pixel response of the chips is very stable. There are variations in the flat fields (donuts and blemishes) not due to the chips but due to dust on optical surfaces either moving or appearing. New flat field reference files are being generated to correct these features. There are changes in the large-scale structure of the INTFLAT fields with time probably related to varying lamp brightness. The effects of contamination (location of "worms") are stable with time.

Overall, the results from the VISFLATs and INTFLATs are in good agreement. If the VISFLAT lamps become unusable, the INTFLAT lamps would provide useful diagnostics of all properties except possibly for the stability of the flat fields on large scales which is affected by the variations in the Carley bulbs.

WFPC2 Cycle 8 Calibration Plan:

by S. Baggett, S. Casertano, J. Biretta, S. Gonzaga, and the WFPC2 Group

Calibration plans for Cycle 8 are being finalized and as always, observers are welcome to suggest new calibrations or comment on the existing plans, send Email to help@stsci.edu.

As in the past, part of the program consists of routine monitors and decontamination (decon) procedures. The decons will continue to be performed on a monthly basis, to remove the UV contaminants and anneal hot pixels. The monitoring programs will be used to track the health and performance of the cameras via internal exposures (biases, darks, flats, kspots), Earth flats, and external exposures (imaging of standard stars and fields, e.g., in UV throughput, CTE, and astrometric monitors).

The remaining proposals planned for Cycle 8 will be used to improve the existing WFPC2 calibration in certain key areas, continue investigations of the CTE effect, and address specific user concerns from previous cycles. The proposals include a verification of the photometric zeropoints, a spot-check of the PSF characterization, a test of the stability of the polarization calibration, and a check of the linear ramp filters. In addition, the plan includes data to improve the UV flatfielding, a confirmation of the UV plate scale, and a check of the photometric zeropoints for BVRI using very red stars. Finally, a program to observe an appropriate galaxy cluster is being implemented, to measure the effect of CTE on small, extended targets, and a "noiseless" preflash proposal is being prepared, to test whether preflashing exposures will reduce the CTE and/or long vs short effects.

Planning is also underway for health and safety monitoring, as well as calibration verification, during and following the up-coming Service Mission 3a which is nominally scheduled for October 1999. The Servicing Mission plans will be posted and announced at a later date.

Minor Keyword Changes due to New OPUS Software:

by D. Swade, C. Heller, L. Sherbert, M. McMaster, and S. Baggett

In response to diminishing support for the VMS/VAX platform, both within STScI and by third-party software, the OPUS pipelines were ported to the ALPHA/VMS platform. The new version of the OPUS software was installed in the pipeline April 05, 1999. The data processing steps remain the same and the changes should be transparent to most WFPC2 users. There are, however, some minor header keyword changes which can be summarized as follows.

All Headers:

 - FITS standard TELESCOP keyword added.
 - DATE, FILETYPE, INSTRUME, EQUINOX in new location in header.

D0H:

 - STDCFFP keyword is now populated correctly (fill pattern '0x5569').
 - For internal images, default values for ORIENTAT & CRPIXn have changed.

SHH:

 - UTCO1 is now unsigned 32 bit integer instead of signed 32 bit integer.
 - CALIBRAT, TRK_TYPE, PAR_CORR values have changed but retain same
   meaning (e.g., CALIBRAT is now T or F instead of Y or N).
 - 33 keywords added for use with interactive target images.

The next software upgrade, planned for the end of May, will add two new keywords to the WFPC2 shh headers:

  FLTSWVER=       flight software version number                    C08
  OPUS_VER=       OPUS software system version number               C18

As always, if you have any questions or problems with your WFPC2 data, please contact us at help@stsci.edu.

Filter Workshop in July for Wide Field Camera 3:

The Wide Field Camera #3 (WFC3), a radial bay instrument replacement for the Wide Field Planetary Camera #2, is slated for rendezvous with the Hubble Space Telescope in 2003. The design of WFC3 is a well-integrated composite of new technologies, cost-saving recycling of original WFPC1 parts (housing and filter assembly), and enhancements of existing ACS and NICMOS design features. The WFC3 will have an independent near-UV and visible light chain (called UVIS) which includes a wide field 4kx4k (two 2kx4k) CCD camera with blue sensitivity (2000A - 10000A) and a 48-element filter wheel (the WFPC1 SOFA - filter assembly). The STScI and the WFC3 Science Oversight Committee are hosting a one-day WFC3 Filter Workshop at the Space Telescope Science Institute on July 14, 1999 where we hope to collect the advice and recommendations of the community concerning the filter selection. We are taking this opportunity to alert the community of the workshop and encourage all that are interested in participating to visit the WFC3 website for further details.

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.

GILLILAND, R.L.; NUGENT, P.E.; PHILLIPS, M.M.  "High
Redshift Supernovae in the Hubble Deep Field"  ApJ 8-10-99

KISSLER-PATIG, M.; ASHMAN, K.M.; ZEPF, S.E.; FREEMAN, K.C.
"HST Imaging of Globular Clusters in the Edge-on Spiral
Galaxies NGC 4565 and NGC 5907"  AJ accepted

MCLURE, R.J.; KUKULA, M.J.; DUNLOP, J.S.; BAUM, S.A.;
O'DEA, C.P.; HUGHES, D.H.  "A Comparative HST Imaging Study
of the Host Galaxies of Radio-Quiet Quasars, Radio-Loud
Quasars and Radio Galaxies: Paper I"  MNRAS accepted

MIGHELL, K.J.; BURKE, C.J.  "WFPC2 Observations of the Ursa
Minor Dwarf Spheroidal Galaxy"  AJ accepted

MIRANDA, L.F.; GUERRERO, M.A.; TORRELLES, J.M.
"Multi-wavelength Imaging and Long-Slit Spectroscopy of the
Planetary Nebula NGC 6884: the Discovery of a Fast
Precessing, Bipolar Collimated Outflow"  AJ accepted

KRIST, J.E.; STAPELFELDT, K.R.; BURROWS, C.J.; HESTER,
J.J.; WATSON, A.M.; BALLESTER, G.E.; CLARKE, J.T.; CRISP,
D.; EVANS, R.W.; GALLAGHER, J.S. III; GRIFFITHS, R.E.;
HOESSEL, J.G.; HOLTZMAN, J.A.; MOULD, J.R.; SCOWEN, P.A.;
TRAUGER, J.T.  "Hubble Space Telescope WFPC2 Imaging of XZ
Tauri: Time Evolution of a Herbig-Haro Bowshock"  ApJ accepted,

FELTZING, S.; GILMORE, G.; WYSE, R.F.G.  "The Faint Optical
Stellar Luminosity Function in the Ursa Minor Dwarf
Spheroidal Galaxy"  ApJ accepted

PERLMAN, E.S.; BIRETTA, J.A.; ZHOU, F.; SPARKS, W.B.;
MACCHETTO, F.D.  "Optical and Radio Polarimetry of the M87
Jet at 0.2" Resolution"  AJ 5-99

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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