Instrument Science Report 98-03:

WFPC2 Long-Term Photometric Stability

S. Baggett and S. Gonzaga

October 21, 1998

Abstract:

We examine the WFPC2 stellar photometric monitoring data obtained over the last four years. The new analysis shows that, for bright targets, (1) the long-term photometric throughput continues to be quite stable: fluctuations are ~2% or less peak-to-peak over 4 years in filters longwards of and including F336W, (2) the UV throughput has gradually evolved, that is, the clean count rates (immediately after the decons) have increased over the 4 years in some filters, e.g., F160BW by ~12% in the PC, and F170W by ~9%, while decreasing slightly in others, e.g., F255W by ~3% and, (3) the contamination growth rates have slowed slightly for the UV filters, e.g., ~1% per day to 0.5% per day in F160BW on the PC. The small discontinuity around Feb. 1995 is discussed. These results are being used to update the WFPC2 time-dependent photometric calibration within SYNPHOT.

The complete paper is available, PDF (0.55 MB) and Post Script (1.2 MB).