6.4.1 Pipeline Mosaics and Default Spectrum Extraction
The post-BCD pipeline data processing fulfills the following requirements: (1) correction for a small spectrum tilt and perform distortion corrections, (2) derive mosaic images for ON, OFF and ON-OFF using the actual pointing information, and (3) a default extraction of a 1-d spectrum from the ON-OFF mosaic.
The basic algorithm of the post-BCD pipeline processing of the SED data is described in the MOSAIC SED User's Guide, available with the MOPEX documentation. It uses the standard area-weighted interpolation in mosaicking. For a pointed observation (or each raster point in a rastermap), two mosaics are generated for the ON and OFF pointings, respectively. A difference mosaic between the ON and OFF mosaics is also derived, from which a sky-subtracted spectrum is extracted by placing a 5-column aperture centered in the column with the largest flux sum between detector rows 2 and 20. Table 6.4 lists some important post-BCD files for the SED mode.
The plain text file ''..._sed.tbl'' (e.g., SPITZER_M2_17169162_1_ A9183226_sed.tbl) follows IPAC table format with a short header showing the position of the target (RA_SOURCE and DEC_SOURCE), the actual columns (i.e., COLUMN_1 to COLUMN_5) in the mosaic for the spectrum extraction, etc. The table itself contains 5 columns, which are (1) detector row number, (2) wavelength in microns, (3) flux density in Jy, (4) flux density uncertainty in Jy, and (5) the aperture correction factor used in deriving columns (3) and (4). Figure 6.6 illustrates such a post-BCD spectrum from an observation of star HD 45348 along with a model-predicted spectrum.
It should be pointed out that the default pipeline spectrum extraction is for your inspection only. You may well need to do your own spectral extraction using the ON-OFF mosaic image.
Figure 6.6: Plot of the post-BCD extracted spectrum (squares) from an observation of the star HD 45348 in MC21 in comparison with a model predicted spectrum (dotted line).
Table 6.4: Some Important Post-BCD Files for MIPS/SED.
*maic.fits, *munc.fits, *mosst.fits
Mosaic difference image and its associated uncertainty and std images.