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23.3 Working with Two Dimensional Extracted Spectra

Sensitivity Units and Conversions

Your two dimensional extracted spectrum (_sx2, or _x2d file) has units of erg cm-2 sec-1 Å-1 arcsec-2. The conversion from counts to surface brightness (I) is calculated by the pipeline as:

where

23.3.1 Wavelength and Spatial Information

Two-dimensionally extracted spectra have been wavelength calibrated and rectified to a linear wavelength scale. Tasks such as splot can work directly on the _sx2.fits and _x2d files and can read the wavelength header information which is stored in the standard FITS CD-matrix keywords. Alternatively you can use these keywords directly to determine the wavelength or distance along the slit at any pixel as:

where (x) is the wavelength at any given x pixel, and s(y) is the distance along the slit from slit center for any given y pixel, in units of degrees.



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1 To keep from degrading the spectral purity Npix ¥m must be less than W.

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