DSS Photometric Calibrations

DSS Photometric Calibrations

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Photometric calibrations for the three primary photographic surveys which make up the Digitized Sky Survey (DSS) have been completed. These initial calibrations consist of a single lookup table for each survey and are good to about 0.5 magnitudes.

The photometric calibrations are available in FITS file binary tables, one FITS file for each of the three photographic surveys. The three FITS files are bundled in the compressed tar file dss_calibrations.tar.Z. Survey specific information about the calibrations may be accessed at POSS-E for the northern POSS-E (XE) plates, SERC-J for the southern SERC-J (S) plates, and SERC-V for the southern Galactic plane SERC-V (XV) plates. The calibration for the SERC-V plates may be used with the two Magellanic Cloud plates, XX001 and XX002. There is not yet a calibration available for the M31 plate, XX005.

Each calibration lookup table specifies a function of log₁₀(Integrated Signal) vs. Magnitude derived from measurements of stars in The Guide Star Photometric Catalog.I. (GSPC-I)¹. The integrated signal is the sum of counts above a threshold value of 500 counts above the sky background. The sky background is computed individually for each GSPC-I star by taking the mode of the pixel counts in a 512² pixel area around the star. Sample Header is a copy of the header of the POSS-E calibration FITS file which illustrates the organization of the calibration binary tables.

These calibration FITS files are designed to work with GetImage 2.0, the program used for extracting images from the DSS. See GetImage for information about using the calibration FITS files with GetImage.

¹The Guide Star Photometric Catalog.I. (Lasker, B. M., Sturch, C. R., et al. 1988, Astrophys. J. Suppl., 68, 1.) consists of a sequence of 6 to 10 stars at the center of each plate in the DSS.