10.5.6 ACS Aperture Coordinate System

ACS is located off-axis in the focal plane of HST. This article shows how the detector reference frame compares to HST's U2, U3 reference frame.

Format definitions

Boldface type indicates the name of an APT parameter or a value for a parameter.

(red star) Black text indicates an important note.

Magenta text indicates available but unsupported parameters (requires prior approval from STScI).

Red text indicates restricted parameters (for STScI use only).

Brown text indicates text file parameters.

Items in brackets - <value> - are required values.

Items in square brackets - [<value>] - are optional.

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Figure 10.1: ACS Coordinate System shows how the POS-TARG coordinates, X and Y, are related to the U2,U3 and detector Axis1 and Axis2 directions. The Y axis is parallel to Axis2. The X axis is normal to Y but differs from the Axis1 direction by about 5°. This diagram correctly shows the WFC and SBC orientations, but it does not represent their relative sizes or positions.

Figure 10.1: ACS Coordinate System

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