Instrument Science Report WFPC2 96-01:
Internal Flat Field Monitoring
M. Stiavelli and S. Baggett
The study of internal WFPC2 flat fields and their temporal behaviour allows for the monitoring of a number of instrumental features, including ADC performance, stability of gain ratios, and flat fielding stability.
The aim of this report is to give an overview of the monitoring of these vari ous aspects. Most of the results presented are derived from two cycle 5 calibrat ion proposals (ID 6189 and 6190), although we have also made use of frames from Cycle 4 proposals (ID 5561, 5655, 5764).
The visible cal-channel calibration system (VISFLAT mode) is based upon two C arley bulbs operating at about 2060 K and one Welch Allyn bulb operating at 2550 K. The Carley bulbs were used previously in WF/PC-1 and have been reliable. Since less was known about the reliability of the Welch Allyn (hereafter WA) bulbs, a back up bulb was provided. The backup bulb is not currently in use but it is ac tivated in the event the primary bulb fails. In order to obtain the desired flat and smooth spectrum, the light from these lamps was filtered through a combinat ion of BG 38 and BG 24 glass windows. A different set of bulbs of the Carley typ e are also used for illuminating the shutter blades and obtaininig INTFLATs.
We will address the results obtained from VISFLATs and INTFLATs separately.