WFPC2 Instrument Handbook for Cycle 10

Cycle 4 Calibration Plan

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The primary goal of the Cycle 4 calibration plan was to provide an instrument calibration for Cycle 4 GO and GTO science programs as well as monitor internal health, photometric and optical stability of the instrument. This report briefly summarizes the WFPC2 calibration proposals as they were implemented during Cycle 4. Table 8.3 outlines the proposal contents as well as the approximate frequency of execution while the following section presents more details of the justification and intent for each proposal.

Table 8.3: Summary of Cycle 4 Calibration Plans

ID	Title	Frequency	notes
Internals
5568	Decontaminations	1 x month	internals plus decon itself
5560	Internal Monitor 1.	2 x week	intflats, biases, kspots
5561 5655	Internal Monitor 2. - Flats	~2 x month	darks, visflats. UVflats suspended after June 12; one set of uvflats run as a test (Oct. 1994)
5562	Internal Monitor 3. - Darks	5 per week	serials=ON taken in 5561/5655
5569 5764	Internal Flats	once	intflats & visflats, in variety of filters
6140	Ramps: Internals & Earthcals	once	internals to aid in LRF calibration
Photometry
5563	Photometric Monitor - UV Std.	2 x month	GRW+70d5824, std.filters. Clocks OFF except Dec. 1994, 1994 (ON).
5565 5663	Photometric Monitor - Fields	2 x month	Usually NGC5139. Clocks OFF except Dec. 1994 (ON).
5629	Photometric Monitor - Four Chip Std.	1 x week	GRW+70d5824; 4 CCDs, F170W
5572	Photometric Filter Calibration	run twice during Cycle 4	GRW+70d5824 in all filters used by GO/GTOs during cycle 4; NGC5139 done in subset of broadbands.
5646	CTE Dither Test	run once	Omega Cen, nine 40 sec images in F555W, offset in 15" steps
5659	CTE Dither Test - Part 2	run once	same as 5646 but in F439W, F814W
5564	Photometric Calibration: 4-CCD	to be run once	GRW+70d5824, in 4 CCDs, standard broadband filters
Earth Flats
5570	Earth flats - Large Set	~ 40 per week	200 Earthflats in each of four filters: F375N, F502N, F656N and F953N
5571	Earth flats - Small Set	~14-20 per week	20 Earthflats in each of ~20 filters
Other
5643	Partially Rotated Filters	done once	GRW+70d5824 & visflats, FQUVN, FQCH4N and partial rotations
5632	Preflash Test	done twice	Omega Cen in broadband filters; includes preflash done with intflat; replaced 5565 during Apr. 1994
5778	Lyman Alpha Throughput Check	do twice	target: BD+75D325
5573	Ramp Calibration
5574	Polarization Calibration	done once	G191B2B, BD+64D106, RMon, NGC 4147, and visflats
Placeholders/Contingency (no plans to execute, may not be run at all)
5627	Photometric Monitor 1a: Std. in UV		Not needed.
5628	Photometric Monitor 1b: Std. in Vis.		Not needed.
5645	Optimum Preflash Test		Not needed.
5648	Charge Transfer Test		Withdrawn.
5566 5567	UV Campaign Photometry UV Campaign Flats		Not needed; no UV campaigns run
5575	Dither Test		Not needed.

Internal Monitors

These proposals monitor the instrument's health throughout the cycle, including the stability of the cameras, their signal chain electronics, and the internal optical alignment of the WFPC2. The internal flat fields are intended as delta-flats, in order to monitor the stability for the main photometric filter set as well as provide data for the generation of high S/N flat fields. The darks are required not only for the generation of darks for the pipeline but also for tracking the evolution of hot pixels and mapping low-level CCD defects such as traps.

The internal visflats obtained in most of the visible WFPC2 filters will be used with the thermal vacuum test flat fields and the Earth flats to generate "superflats"; the intflats are obtained as a backup for the visflats (for example, if the cal-channel should fail).

Photometric Monitors

These proposals provide a regular monitor of the instrument's QE stability from the FUV to the near-IR, allow tracking of the UV throughput decline due to contaminant buildup, and provide observational PSFs. The standard star observations provide a baseline for the standard field photometry and allow updates to SYNPHOT. The standard field measurements will allow calibration of the filter sets' color terms, as well as enabling a mapping of the geometric distortions across the field of view. The four CCD photometry program provides the relative CCD-to-CCD sensitivities for the filter set and allows the regular PC1/WF3 standard star photometry to be applied to WF2 and WF4.

Earth flats

These are divided into two proposals: the first to obtain a large number of Earth cals (observations of the bright Earth) in just four filters and the second to obtain a small set of Earth cals in a larger number of (primarily narrowband) filters. The superflats generated from the first proposal's data map the OTA illumination pattern and are combined with the thermal vacuum test data flats (and possibly cal-channel flat fields) to provide a set of flat fields which remove both the OTA illumination pattern and the pixel-to-pixel response of the cameras. The images from the second proposal will also help determine the OTA illumination pattern, but used in conjunction with the Earth superflats (and cal-channel flats), will provide delta corrections to the superflats applicable to the narrow- and medium- band filters.