Instrument Science Report 2009-07:
Red Leak Characterization for the WFPC2 UV Filters
P. L. Lim, M. Chiaberge, J. Biretta, and D. Di Nino
December 18, 2009
We characterize the red leaks for all eight WFPC2 UV filters (F122M, F160BW, F170W, F185W, F218W, F250W, F300W, and F336W). We crossed each UV filter with three broad band optical filters (F450W, F606W, and F814W) in order to isolate different spectral regions in the red leak. We observed 15 Mon, an O7Ve-type star, using five different pointings to position the star at different locations on three WFPC2 chips (PC1, WF2, and WF3) to study possible filter inhomogeneities. We also observed g Gem, a K4III-type star, with WF3 as a follow-up to further study selected filters. Our results for F160BW, F170W, F300W, and F336W show good agreement (within 20%) between the observed off-band count rates and those predicted by SYNPHOT. Filters F185W, F218W, and F255W showed significant discrepancies between the observed and predicted values (20% to 250%); we derived new throughput curves for these filters, and delivered them to CDBS. The F122M filter shows evidence for a long-term throughput decline and will require additional studies beyond the scope of this report.
The Complete Paper (PDF 2.9 MB) is available.