FLS-SDSS Version Information

These data are assembled, calibrated, mosaiced, and arranged by a set of IDL (6.0) and C code in four CVS modules at Princeton and NYU. The current version of the downloadable data is:
• version 1_0_2

The current version was created with the following tag versions of the following CVS modules:

module name	CVS tag	location
sirtf	v1_0_2	NYU
photoop	v1_1_3	Princeton
idlspec2d	v4_10_7	Princeton
idlutils	v4_10_8	Princeton

FLS-SDSS Image Mosaic Properties

• 5-band ugriz visual image mosaics composed of hundreds of SDSS drift-scan fields
• sets of four 1.75 deg × 1.25 deg mosaics, north-up
• each mosaic is 15912×11364
• 0.396 arcsec × 0.396 arcsec square pixels (at fiducial point RA=259.5 deg, Dec=59.5 deg J2000)
• correct, FITS-compliant WCS astrometry headers
• the four mosaics “snap together” into one immense (31824×22728) mosaic with no overlaps or edge distortion issues
• calibrated in intensity units of [nMgy (0.396 arcsec)^-2], where 1 nMgy (“nano maggie”) in flux is equivalent to 22.5 mag (AB system)

NB: If a source in one of the mosaics is measured to have total flux N in nMgy, its magnitude m is then

m = [22.5 mag] - 2.5 log₁₀ N .

The above files are unwieldy, so we have made some lower-resolution, single-field mosaics with the following properties:

• same 5 bands
• individual 3.5 deg × 2.5 deg mosaics, north-up
• each mosaic is 10608×7576
• 1.188 arcsec × 1.188 arcsec square pixels (at fiducial point RA=259.5 deg, Dec=59.5 deg J2000)
• correct, FITS-compliant WCS astrometry headers
• calibrated in intensity units of [nMgy (1.188 arcsec)^-2]

NB: Unlike the high resolution images, these lower-resolution images are not band-limited and should be used with caution.

There are some defects in these mosaics, which need to be worked out, worked around, or avoided by scientific users:

• sky noise variance is not constant but varies inversely with the number of overlapping SDSS fields (1 or 2 for most of the image area); in particular there are diagonal “stripes” of low noise in the images where SDSS camera columns overlap
• sky background level is not exactly zero everywhere; use local sky estimation when photometering sources
• bright stars are saturated and have bleed trails
• the PSF is variable across the fields
• filter reflections in the SDSS cameras cause bright stars to show nearby flares in sky brightness
• some cosmic rays have slipped through
• small CCD readout defects near extremely bright sources
• many bright single-band satellite trails

FLS-SDSS Spectroscopy

We have also assembled all SDSS spectroscopy in the FLS region into a pair of FITS files:
• one FITS file containing all of the SST FLS region SDSS spectra and their observational uncertainties on a common wavelength grid, with common calibration
• one FITS binary table file containing the positions of the spectroscopic sources and all of the parameters derived from the SDSS spectra by the Princeton pipelines

Essentially everything a user needs to know about the format and contents of these files, including calibration, is available at the SDSS Data Release 7 Specta page.

SDSS Photometric Catalog

Data