Beam Extraction

Once the beam positions have been located, the beams can be extracted. First, an extraction window width is calculated based on the position and number of beams in the spectral image. This window is used for all beams. If there are two beams, then the half-width of the window is half the beam separation. If there are three, then the half-width of the window is half the distance between the positive beam and the first negative beam. Otherwise, the half-width is 50 pixels.

UISTdiffers from this in that if either the HK or KL grisms are used, the half-width of the extraction window is 10 pixels.

For each beam, an optimal extraction profile (Horne, 1989) is then determined over the extraction window. If requested (i.e. if a standard star is reduced), this optimal extraction profile is filed with the calibration system.

The beams are then optimally extracted using the appropriate profile.
[_EXTRACT_ALL_BEAMS_]