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Fig. 6.11. A portion of a PFUEI spectroscopic CCD image. The figure is 5.5 arcmin on a side with east at the top and north to the left. Note the zeroth-order (point-like) images for each spectrum that appear about one spectral length to their west. The large star-like object near the top middle of the frame is a saturated zeroth-order image from an object whose spectrum is off the top of the image. The zeroth-order images are at the positions of the sources as seen in a direct image and are used in the PFUEI data reduction to set the wavelength scale. The arrow points to the C IV 1550Â line in a redshifted 19.5 magnitude quasar. From Schmidt & Gunn (1986).

aligned with the scan direction to avoid spectral clipping at the CCD edges. No attempt is made to flux calibrate the data but initial wavelength calibration is accomplished by identification of known spectral lines detectable in stars.

Slitless spectroscopy is a wonderful tool for obtaining spectra of many objects simultaneously and to very faint limits. The simplistic nature of the

Fig. 6.12. A 1000 x 4000 pixel section of a QUEST CCD drift scan obtained with the use of an objective prism. The dispersion is parallel to the scan direction and each spectrum is 200-400 pixels in extent. Examples of some extracted spectra are shown on the right. From Sabby, Coppi, & Oemler (1998).

Fig. 6.12. A 1000 x 4000 pixel section of a QUEST CCD drift scan obtained with the use of an objective prism. The dispersion is parallel to the scan direction and each spectrum is 200-400 pixels in extent. Examples of some extracted spectra are shown on the right. From Sabby, Coppi, & Oemler (1998).

technique makes for an ease of use given that a direct imaging CCD camera is available. The addition of slitless spectroscopy with large-format CCDs and CCD drift scanning go even further, allowing spectroscopic identification of many thousands of objects with little additional effort beyond the direct imaging already in place. Slitless spectroscopy promises to be an evolving CCD application, yet to have reached its peak potential.

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