S T A N / W F P C 2 - Number 38, November 1999
- WFPC2 NEWS:
- HST entered Zero Gyro Safemode
- WFPC2 and the upcoming Servicing Mission
- WFPC2 Group Plans for FY2000
- WFPC2 AAS poster abstract
- CTE paper to be published
- Bug in warmpix task for the latest release of STSDAS (v2.1)
- SCIENCE OBSERVATIONS DURING ORBITAL VERIFICATION
- RECENT PREPRINTS
- APPENDIX: WFPC2 CONTACTS
HST entered Zero Gyro Safemode:
by D. Taylor
HST entered Zero Gyro Safemode at 8:30 AM Eastern Standard Time on Saturday 13 November 1999 (day 317 13:29:39 UT). This mode was entered when the flight software detected a large increase in the motor current for gyro 1. Entry into safemode appears to have been nominal. An attempt to recover the gyro was not successful. At this time, all HST observing has been suspended until completion of HST Servicing Mission 3A, scheduled for early December, when all of the gyros on HST will be replaced. Observations lost due to this safemode will be reviewed and replanned if possible following SM3A. Program Coordinators will contact PIs regarding any observations that need changes in order to be rescheduled.
WFPC2 and the upcoming Servicing Mission:
by S. Casertano
The upcoming Servicing Mission 3A, slated to launch in early December, will be followed by an Orbital Verification phase (SMOV3A), lasting about 40 days, to ensure that the instruments remain in good working efficiency and that they are properly calibrated. WFPC2 activities will follow the plan successfully implemented for the Second Servicing Mission in early 1997, after which WFPC2 fully recovered its photometric throughput and PSF properties with minimal disruption to the science program. The main elements of this plan are:
- Release of HST from the orbiter will be followed by a twelve-day Bright Earth Avoidance (BEA) period. Ultraviolet radiation reflected off the Earth's surface could cause polymerization of molecular contaminants before they have a chance to evaporate; therefore the telescope will be pointed nearly parallel to the Earth limb, so that Earth shine will not strike directly the internal optics, including the WFPC2 Pick-Off Mirror. The telescope will be limited to very small slews during the BEA period. - WFPC2 will be cooled to its operating temperature of -88C following a two-step procedure. Since deposition of contaminants on the cold internal WFPC2 optics is accelerated after a Servicing Mission, the camera heads will be first cooled to -55C for 48 hours, then warmed up to +22C for a day. The camera will be cooled down to -88C only if the contamination rate, measured at -55C, is safe. - UV contamination will be closely monitored for the first two weeks of operation at -88C, and decontaminations will be done every two weeks - more frequently if needed. - In order to limit contact with the rest of HST interior, decontaminations will follow a special procedure in which the WFPC2 shutter remains closed with a filter in place. Parallel science will not be allowed during the first month of science operations. - Special calibrations will be carried out to verify that the photometric throughput, PSF properties, focus, flat fields, and dark current of WFPC2 remain well calibrated.
Science observations with WFPC2 will be resumed 15 days after the release of HST, and the Orbital Verification phase will end 25 days later.
More detailed information on the WFPC2 plans can be found in WFPC2 ISR 99-03. Details on specific WFPC2 proposals, numbered 8491 through 8498, can be found on the PRESTO web pages at: http://presto.stsci.edu/public/propinfo.html.
WFPC2 Group Plans for FY2000:
by J. Biretta
A key activity during October was developing the WFPC2 Group Plan for FY2000. We are glad to welcome three new scientist to the group: Adam Riess, Anton Koekemoer, and Al Schultz; and Chris O'Dea who has returned from sabbatical. This added manpower increases the group from 3 scientists to 7 scientists, and should allow several new initiatives during the coming year. Many of these will have benefits for STIS, ACS, WF3 as well as WFPC2 users:
- Augment "drizzling" software to better handle multi-detector images; update Drizzling Cookbook. - Create new software for modeling and subtracting PSFs in STSDAS. - CTE studies (study physics using dark frames; photometric impact on extended targets; preflash tests; continue monitoring impact on stellar observations). - Create a "Photometry Cookbook". - Support on-the-fly data reprocessing from POD files.
We will also continue work towards resolving many of the long-standing issues and areas where we feel calibration could be further improved. These are in addition to the usual monitoring and support activities:
- Improve photometry in LRF filters. - Improve polarimetric calibration. - Improve transforms between photometric systems. - Time-dependence of flat fields. - Improvements to UV flats.
WFPC2 AAS Poster Abstract:
by I. Heyer, J. Biretta, S. Baggett, S. Casertano, C. O'Dea, A. Schultz, S. Gonzaga, M. McMaster, M. S. Wiggs, A. Koekemoer, A. Riess (to be presented as a poster paper at the January 2000 AAS in Atlanta):
We review the status of the Wide-Field Planetary Camera II (WFPC2) onboard the Hubble Space Telescope as well as recent enhancements to calibration and analysis methods. The instrument continues to perform extremely well after ~70000 images. Low level effects such as CTE and dark current continue to increase with long-term radiation exposure, but still affect only a minority of observations; work continues to characterize and monitor these effects. The long-term photometric stability appears to be excellent, with most filters showing changes of a few percent or less. Recent work shows that aperture photometry for small apertures (1-2 pixel radius) will be affected at the 5% to 10% level by target position in the field-of-view due to small focus variations. A new "on-the-fly calibration" feature of the HST archive allows instant re-calibration of WFPC2 data with the latest reference files; this should be a great benefit to both new observers and archival WFPC2 users. Recent results on polarization calibration, CTE, and other topics are discussed.
CTE Paper to be Published:
by B. Whitmore, I. Heyer, S. Casertano
Observations of Omega Cen have been used to characterize the Charge Transfer Efficiency (CTE) of the Wide Field and Planetary Camera 2 (WFPC2) onboard the Hubble Space Telescope. A set of formulae has been developed to correct aperture photometry for CTE loss with dependencies on the X and Y positions, the background counts, the brightness of the star, and the time of the observation. The observations indicate that for very faint stars on a very faint background, the CTE loss from the top to the bottom of a chip has increased from about 3% shortly after the cool-down of WFPC2 (April 23, 1994) to roughly 40% in February 1999. In general, typical WFPC2 exposures are much longer than these short calibration images, resulting in higher background which significantly reduces the CTE loss and minimizes the CTE problem for most science exposures.
(Bibliography entry: "Charge-Transfer Efficiency of WFPC2", Bradley Whitmore, Inge Heyer, Stefano Casertano, 1999, PASP, 111, 1559)
Bug in WARMPIX Task for the Latest Release of STSDAS (v2.1):
by S. Gonzaga and J.C. Hsu
There is a bug in the current STSDAS version (2.1) of warmpix. One of the new enhancements of STSDAS 2.1 was for the TABLES interface to support text tables with column names and attributes. Unfortunately, the warmpix code was not updated to handle this change.
A workaround is available. In the case where fits and STSDAS warmpix tables are used, the warmpix task converts these formats into an ascii table before crashing. This temporary table is named using random characters and can be easily identified in the working directory. The user simply has to edit this file to remove comments in the first few lines, these comments are preceded by hash marks (#). Then, run warmpix again using this edited text table. If the user downloads ascii warmpix tables from the WFPC2 website, all he or she needs to do is edit these comments out before running warmpix.
A patch for this bug in warmpix will be available in the near future, and we apologize for any inconvenience it has caused.
Science Observations during Orbital Verification:
During the forthcoming HST servicing mission, SM3A, which is currently scheduled for December 11, we will carry out a recommissioning program of the HST observatory called Servicing Mission Orbital Verification (SMOV). During the early phases of this program the HST will be restricted to point away from the Earth at a region of space called the Bright Earth Avoidance region (BEA) for approximately 12 days. This procedure ensures we do not reduce permanently the reflectivity of the WFPC2 pickoff mirror, as UV light reflected by the Earth's surface might polymerize contaminants accumulated during the servicing mission and prevent their evaporation. During that time the WFPC2 will not be useable for scientific observations and operations with the STIS MAMAs will not be allowed for safety reasons. Normal science operations will therefore not be possible during that period of time.
However it is possible to use the STIS CCD and the FGS to carry out some observations during the BEA period and we have decided to craft a science observing program to take advantage of this restricted observing opportunity, on a non interference basis with the SMOV activities. The program, which is currently being finalized, will consist of simple observations with the STIS CCD which can be carried out during an orbit. As the location of the BEA on the sky changes daily the program has to be flexible enough to allow for new targets to be chosen every time that there is a change of launch date or a delay in the related SMOV activities.
Furthermore we have approved a Director Discretionary Time program, PI Nelan, to use the FGS on a non interference basis with the SMOV activities, and with no proprietary time.
We must emphasize that while we will do our best to execute part of the program, the targets observed and the actual amount of data obtained will depend on the date of launch and on the successful execution of the scheduled SMOV activities which will have priority at all times.
Immediately after the end of these observations we will carry out a few Early Release Observations to demonstrate the success of the Servicing Mission and we will also resume the regular GO program. We are therefore requesting that potential users of the STIS CCD or FGS data do not use the data for Public Relations purposes until the ERO data has been released and the related PR activities have been completed.
Duccio Macchetto Associate Director Science Programs
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.
Casertano, S.; Gonzaga, S.; Biretta, J. "Summary of WFPC2 SM3a Plans" WFPC2 ISR 99-03 BRANDNER, W.; GREBEL, E.K.; CHU, Y-H.; DOTTORI, H.; BRANDL, B.; RICHLING, S.; YORKE, H.W.; POINTS, S.D.; ZINNECKER, H. "HST/WFPC2 and VLT/ISAAC Observations of PROPLYDS in the Giant HII Region NGC 3603" AJ 1/00 DA COSTA, G.S.; ARMANDROFF, T.E.; CALDWELL, N.; SEITZER, P. "The Dwarf Spheroidal Companions to M31: WFPC2 Observations of Andromeda II" AJ accepted COLE, A.A.; TOLSTOY, E.; GALLAGHER, J.S. III; HOESSEL, J.; MOULD, J.R.; HOLTZMAN, J.A.; SAHA, A.; BALLESTER, G.E.; BURROWS, C.J.; CLARKE, J.T.; CRISP, D.; GRIFFITHS, R.E.; GRILLMAIR, C.J.; HESTER, J.J.; KRIST, J.E.; MEADOWS, V.; SCOWEN, P.A.; STAPELFELDT, K.R.; TRAUGER, J.T.; WATSON, A.M.; WESTPHAL, J.R. "Stellar Populations at the Center of IC 1613" AJ accepted GREBEL, E.K.; CHU, Y-H. "Hubble Space Telescope Photometry of the Hodge 301: an `Old' Star Cluster in 30 Doradus" AJ 2/00 LORENZ, R.D.; LEMMON, M.T.; SMITH, P.H. "Seasonal Change on Titan Observed with the Hubble Space Telescope WFPC-2" Icarus accepted MARTEL, A.R.; BAUM, S.A.; SPARKS, W.B.; BIRETTA, J.A.; VERDOES KLEIJN, G.; TURNER, N.J. "The Nuclear Dust Disks of Five Nearby 3CR Elliptical Galaxies" Life Cycles of Radio Galaxies ZHANG, Q.; FALL, S.M. "The Mass Function of Young Star Clusters in the `Antennae' Galaxies" ApJ 12-20-99 KARACHENTSEV, I.D.; SHARINA, M.E.; GREBEL, E.K.; DOLPHIN, A.E.; GEISLER, D.; GUHATHAKURTA, P.; HODGE, P.W.; KARACHENTSEVA, V.E.; SARAJEDINI, A.; SEITZER, P. "The Dwarf Spheroidal Galaxy DDO 44: Stellar Populations and Distance" A&A accepted SCHROEDER, D.J.; GOLIMOWSKI, D.A.; BRUKARDT, R.A.; BURROWS, C.J.; CALDWELL, J.J.; FASTIE, W.G.; FORD, H.C.; HESMAN, B.; KLETSKIN, I.; KRIST, J.E.; ROYLE, P.; ZUBROWSKI, R.A. "A Search for Faint Companions to Nearby Stars Using the Wide Field and Planetary Camera 2" AJ 2/00 ROMANIELLO, M.; SALARIS, M.; CASSISI, S.; PANAGIA, N. "HST Observations of the LMC Field Around SN 1987A: Distance Determination with Red Clump and Tip of the Red Giant Branch Stars" ApJ accepted astro-ph/9910082 WHITMORE, B.; HEYER, I.; CASERTANO, S. "Charge Transfer Efficiency of the Wide Field and Planetary Camera 2" PASP 12-99
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.
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