Space Telescope Science Institute   7.7.5 HRC Apertures  7.8 Specifying Orientation on the Sky

7.7.6 SBC Apertures


The SBC aperture is 1024 pixels square. There are no overscan pixels to consider. The x and y scales are 0.034 and 0.030 arcseconds/pixel leading to a coverage on the sky of 35 by 31 arcseconds. The reference point has been moved to (512,400) to place targets further from a bad anode which disables several rows of the detector near y = 600. As with the CCDs we maintain an SBC-FIX aperture which will always have position (512,512). MAMA detectors slowly lose efficiency with each exposure, therefore the SBC reference point may be shifted again if the chosen position shows this effect to a measurable degree.

The (512,512) reference point falls near to the same position in (V2,V3) as the HRC, namely (205, 470), and the x and y axis angles are -85.4º and -0.9º.

Use of either prism PR110L or PR130L requires use of aperture SBC and results in a reference point of [425,400] to optimally center the target coordinates with respect to vignetting on the right side of the field and to avoid a set of bad rows at 599 to 605.

Although the SBC direct imaging and prism apertures have the same name in APT, they are actually distinct, and HST executes a small angle maneuver between observations of a given target with them, to compensate for the positional deflection by the prisms. One consequence is that the Special Requirement SAME POS AS cannot be used among mixed direct and prism exposures, as always with different apertures.


Table 7.9: SBC aperture parameters
APT Aperture
Name
Active area
Extent
(arcsec)
Reference
pixel
Reference
V2,V3
(arcsec)
x-axis angle
y-axis angle
SBC
1024 × 1024
34 × 31
(512, 400)
(205, 467)
-85.4
-1.0
SBC-FIX
1024 × 1024
34 × 31
(512, 512)
(205, 470)
-85.4
-1.0
SBC-PRISM1
1024 × 1024
28 × 31
(425, 400)
(203, 467)
-85.4
-1.0
1SBC-PRISM is automatically created by commanding software when spectral elements PR110L and PR130L, and aperture SBC, are selected in APT.

 7.7.5 HRC Apertures  7.8 Specifying Orientation on the Sky
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