Wide Field and Planetary Camera 2 Instrument Handbook for Cycle 12
The WFPC2 camera configuration and filter set require a substantial number of apertures for full utilization of its capabilities. All possible aperture and filter combinations are given in Table 3.14.
Each camera has an associated 'optimum' aperture close to the geometric center of its field-of-view (FOV). These positions have been adjusted to reflect CCD performance following SMOV and to allow for pyramid vignetting. The aperture designations are WF2, WF3, WF4, and PC1 for the individual cameras and WFALL for the three-WFC combination. WFALL is located close to the apex in WF3 (see Figure 3.11). Observers are expected to place small or unresolved targets on these apertures. Note that normally all four CCDs are read out even if a specific CCD is selected with an aperture. This is discussed in Section 2.8. The positions of these apertures may be updated if bad pixels, etc., appear on the CCDs.
In cases where the observer does not want to use the current 'optimum' centers, a complimentary set of apertures has been implemented specifically for this purpose. These locations remain fixed and correspond roughly to the geometric center of each camera's field-of-view. They are designated WF2-FIX, WF3-FIX, WF4-FIX, PC1-FIX, and WFALL-FIX. Observers are expected to place extended targets on these apertures.
An additional set of aperture names have been defined for use with the WFPC2 filters which require partial rotations. The characteristics and uses of these filters are discussed earlier in this chapter. In the nominal filter position, the three WFC segments of the [OII], Methane and Polarizer quad filters can be selected with an aperture for each camera corresponding to the optimum or geometric camera centers. The partially rotated quad filters, which generally fall into more than one camera, have been assigned apertures in the camera which provides the largest clear aperture. The pixel coordinates of these apertures will be reviewed on a regular basis to reflect changes in CCD and filter cosmetics. There are no analogous fixed apertures for the partially rotated filter configurations. The aperture name is generally the same as the (rotated) filter name. For the Wood's filters, the nominal filter position is used for the PC1 FOV only, while the rotated filter position is used for WFC observations. The linear ramp filters are unique because the ultimate location of the target will be determined from the central wavelength specified, and therefore only the generic aperture name LRF is required.
Occasionally the V2-V3 coordinates of the WFPC2 apertures are updated to correct slow drifts of the HST focal plane relative to the spacecraft (V1, V2, V3) system. Table 3.15 shows this history. The V2-V3 coordinates prior to 1996 day 127 for any aperture can be derived by setting (V22,V32) to the values in Table 3.14, and then computing the earlier coordinates. The V2-V3 coordinates after 1997 day 335 can also be computed in a similar maneuver.
Table 3.14: Aperture Definitions. The pixel coordinate system uses pixel numbers (row, column) for the CCD in use. See Figure 3.11 or Figure 1.1 for the definition of the V2-V3 coordinate system. Aperture Name Filter Name CCD Location CCD Pixel Coordinates1 X Y V2 V3 PC1 PC Optimum center PC WF2 WF2 Optimum center WF2 WF3 WF3 Optimum center WF3 4362 424.5b WF4 WF4 Optimum center WF4 WFALL WF3 Optimum near apex 1333 149c PC1-FIX PC Fixed center PC WF2-FIX WF2 Fixed center WF2 WF3-FIX WF3 Fixed center WF3 WF4-FIX WF4 Fixed center WF4 WFALL-FIX WF3 Fixed near apex 133c 149c FQUVN33 FQUVN33 WF2 Optimum for FOV POLQN33 POLQN33 WF2 Optimum for FOV POLQN18 POLQN18 WF2 Optimum for FOV 3804 200d POLQP15P POLQP15 PC Optimum for FOV POLQP15W POLQP15 WF2 Optimum for FOV FQCH4NW2 FQCH4N WF2 Optimum for FOV FQCH4NW3 FQCH4N WF3 Optimum for FOV FQCH4NW4 FQCH4N WF4 Optimum for FOV FQCH4N33 FQCH4N33 WF2 Optimum for FOV FQCH4N15 FQCH4N15 PC Optimum for FOV FQCH4P15 FQCH4P15 PC Optimum for FOV F160BN15 F160BN15 WF3 Optimum for FOV
1V2-V3 coordinates in effect 1996 day 127 (May 6) to 1997 day 335 (December 1). CCD pixel positions unchanged.
2CCD pixel position in effect after 1994 day 101 (April 11).
3WFALL and WFALL-FIX "meta-chip" coordinates are (903,904).
4CCD pixel position in effect after 1995 day 86 (March 27).
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