The WF4 anomaly is characterized by low or zero bias levels, faint horizontal streaks, and low photometric counts (reduced gain) on the WF4 detector. In an effort to mitigate these effects, the temperature of the WFPC2 electronics has been reduced three times since January 2006. Each temperature reduction has temporarily restored the WF4 bias and gain to near-normal (pre-anomaly) levels with no significant degradation of instrument performance. As the underlying electronics failure progresses, additional temperature adjustments will be necessary.

We have used the new GSC-II to significantly improve the absolute astrometric accuracy of a large number of ACS datasets from the first years of ACS operations, reducing the initial levels of uncertainty (typically 1 2”, or more in some cases) to an accuracy of about 0.1 0.3”. There are typically enough GSC-II objects in the field of view of the ACS/WFC detectors to enable a robust solution to be determined by identifying the GSC-II objects and comparing their measured positions with those in the GSC-II. The resulting set of improved header coordinates are accurate enough to permit immediate multi-band comparisons between data from HST and other space-based and ground-based facilities, as well as a range of wavebands including X-ray, mid-IR, and radio data. The Institute has also begun planning to extend this work by including it in the automatic processing pipeline for ACS and eventually perhaps also for other HST instruments.

Photometric monitoring observations of a white dwarf standard (GRW+70D5824) have been used to update the contamination rates for WFPC2 UV filters. Observations from April 1994 through May 2002 were used in the analysis. In general, the contamination rates have declined by roughly 50% for most of the filters during this period. Leastsquares fits have been made to the data to allow observers to remove the effects of contamination in their WFPC2 observations.

We present narrow-band images of sixty-four 3CR radio sources observed in lines of [OII] 3727 Å, [OIII] 5007 Å, and Hα using the WFPC2 camera on-board HST. The images reveal a wide variety of emission lime morphologies, from compact nuclear regions to large-scale emission knots, filaments, and spiral-like structures. Many objects give evidence of ionization cones. In general we find a close correspondence between the emission-line and radio axes; most are aligned within 40 degrees. There is also evidence for a positive correlation between radio luminosity and the spatial extent of the emission-line region. Properties of interesting individual objects are discussed.

This report describes in detail the WFPC2 observations used to maintain and improve the quality of WFPC2 calibrations during Cycle 8 and their status as of May 2001. The results from servicing mission 3a (December 1999) have been reported separately.

This report presents the details of the WFPC2 Cycle 9 calibration plans. The proposal suite is aimed at maintaining the calibration accuracy of WFPC2 via monitoring programs , as well as continuing some previous proposals into Cycle 9 and performing several new tests. The standard monitoring programs will be continued (e.g., decontaminations, photometric and astrometric monitors, darks, biases, internal flats, and earthflats). In addition, the CTE monitor, PSF and photometric checks will be performed. Three new programs are planned as well: a red leak check, a verification of the wavelength stability of the narrowband and linear ramp filters, and a CTE calibration. The CTE calibration, in conjunction with WIYN groundbased observations (if approved), will permit a direct verification of the absolute photometric calibration of WFPC2 in observations that may be affected by CTE, providing a more robust determination of the zero point for many WFPC2 observations.

We find evidence for the presence of a population of numerous binaries with comparably bright components (C binaries) among Hipparcos F stars that are flagged in the Hipparcos catalog as single. We propose a criterion that identifies such binaries. The criterion is based on comparison of absolute magnitude M-v obtained from the Hipparcos parallax and Johnson V magnitude with absolute magnitude derived from the dereddened uvby luminosity index c(o), M-co. For photometrically unresolved binaries, M-v must be brighter because it represents the integrated flux of a binary system, while M-co is determined by the integrated spectrum and is thus close to the absolute magnitude of the primary. We have conducted a series of tests that have revealed the presence of C binaries among Hipparcos "single" F stars and confirmed that the proposed criterion is quite effective at identifying these stars. The C binary candidates have been found to be, on average, older than the candidates comprising single stars and binaries with disparate components (D binaries).

Measurements of the inelastic scattering of 210 MeV {sup 6}Li ions from {sup 12}C, {sup 28}Si, and {sup 58}Ni have been made. Differential cross sections leading to the first excited (2{sup +}) states of the target nuclei were obtained. The angular distributions for {sup 12}C (6.8{degree}--60.6{degree}), {sup 28}Si (4.9{degree}--45.9{degree}), and {sup 58}Ni (7.2{degree}--48.3{degree}) are similar in shape to those for elastic scattering, with diffractive oscillations at forward angles followed by smooth exponential falloff, characteristic of refractive nuclear scattering, at the larger angles. Distorted-wave Born approximation calculations provide good fits to the data when unique {sup 6}Li optical-model potentials, derived from elastic scattering data, are used. Calculations with discrete ambiguous potentials deviate from the data at large angles. Coupled-channels calculations reproduce both the elastic and inelastic scattering data without significant changes in the unique potentials. The deformation lengths, {beta}{sub 2}R, derived from the analyses are compared with results of previous measurements. The deduced quadrupole moments, {ital q}{sub 20}, are in excellent agreement with those obtained from electromagnetic measurements.

Angular distributions of the differential cross sections for the elastic scattering of 210 MeV /sup 6/Li from /sup 12/C (3/sup 0/--61/sup 0/) and /sup 58/Ni (3/sup 0/--48/sup 0/) have been measured. The cross sections exhibit diffractive oscillations at small angles and exponential falloff characteristic of nuclear rainbow scattering at large angles. The data beyond the rainbow angle make it possible to obtain unique optical model potentials for the /sup 6/Li+nucleus interaction, thus eliminating the discrete ambiguities inherent in the lower-energy studies. By truncating the angular distributions, data up to the rainbow angle could be fitted with several discrete ambiguous potentials. Extrapolation of the unique potentials to lower energies provides an energy dependence of the real potential volume integral given by J/sub R//6A = J/sub R//sup 0//6A-..beta.. lnE/sub lab/ with J/sub R//sup 0//6Aapprox. =800 +- 30 MeV fm/sup 3/ and ..beta..approx. =100 MeV fm/sup 3/, a result which is essentially consistent with proton elastic scattering.

As part of the WFPC2 close-out calibrations, we have revised the SYNPHOT throughput curves for the linear ramp filters using on-orbit photometry of a standard white dwarf, EGGR-102 (GRW +70 5824). Comparison of the new on-orbit data and previous groundbased calibrations show differences up to ~20%. The accuracy of the new throughput table is expected to be ~2% at most wavelengths, though as noted herein, some wavelengths with limited or no on-orbit data will have poorer accuracy. The new ramp filter throughput file has been delivered to CDBS and will be used in reprocessing the WFPC2 archive.

We derive a detailed calibration for WFPC2 polarization data which is accurate to about 1.5%. We begin by computing polarizer flats, and show how they are applied to data. A physical model for the polarization effects of the WFPC2 optics is then created using Mueller matrices. This model includes corrections for the instrumental polarization (diattenuation and phase retardance) of the pick-off mirror, as well as the high cross-polarization transmission of the polarizer filter. We compare this model against on-orbit observations of polarization calibrators, and show it predicts relative counts in the different polarizer / aperture settings to 1.5% RMS accuracy. We then show how this model can be used to calibrate GO data, and present two WWW tools which allow observers to easily calibrate their data. Detailed examples are given illustrating the calibration and display of WFPC2 polarization data. In closing we describe future plans and possible improvements. Instrument Science Report WFPC2 97-11

The WF4 anomaly is characterized by low or zero bias levels, faint horizontal streaks, and low photometric counts (reduced gain) on the WF4 detector. In an effort to mitigate these effects, the temperature of the WFPC2 electronics has been reduced three times since January 2006. Each temperature reduction has temporarily restored the WF4 bias and gain to near-normal (pre-anomaly) levels with no significant degradation of instrument performance. As the underlying electronics failure progresses, additional temperature adjustments will be necessary.