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Session 41 - Visible & UV Telescopes.
Display session, Thursday, January 08
The WFPC2 CCDs onboard the Hubble Space Telescope (HST) undersample the PSF delivered to them by the optics. On the three WF chips, the width of a pixel equals the FWHM of the PSF in the near-infrared, and greatly exceeds it in the blue. The image quality can be improved by combining sub-pixel dithered images. If the dithers are particularly well-placed, the pixels from each image can simply be interlaced on a finer grid. But in practice, imperfect offsets and the geometric distortion can make interlacing impossible.
To combine the dithered images of the Hubble Deep Field, a new technique known as variable-pixel linear reconstruction, or ``drizzling'', was created. The IRAF/STSDAS task DRIZZLE and the other tasks in the DITHER package were created to help HST users reconstruct dithered WFPC2 images, and remove cosmic rays from singly-dithered images. We now demonstrate the use of these tasks with typical images from the HST archive.
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Program listing for Thursday