The SDSS-I Stripe 82 Variable Source Catalog


Summary

The catalog lists positions, ugriz photometry (median magnitudes), and various low-order lightcurve statistics for 13,051 candidate variable sources from the SDSS Stripe 82 (20h 24m < R.A. < 04h 08m, -1.27 deg < Dec < +1.27 deg, ~290 deg2). Median magnitudes and low-order lightcurve statistics were calculated from SDSS-I Stripe 82 observations obtained in the period from September 1998 to December, 2004. Details about the construction of the catalog are described in Sesar et al. 2007 (AJ, 134, 2236, also astro-ph/07040655). A quick selection summary is:
  1. unresolved source in imaging data
  2. processing flags BRIGHT, SATUR, BLENDED, or EDGE are not set
  3. at least 4 observations in each of ugri bands
  4. brighter than g= 20.5
  5. candidate variable (sigma > 0.05 mag and chi2 > 3 in the g and r bands, see below)

The Catalog Format

The catalog data file is in text (ascii) format, with one line per star, and each line lists (in this order):
  1. RA Dec: the J2000 mean position in decimal degrees
  2. Ar: the Schlegel, Finkbeiner & Davis (1998) ISM extinction value in the r band; extinction in other bands can be computed as [Rv=3.1]: Am = Cm*Ar, with Cm=(1.873, 1.377, 0.758, 0.537) for m=(ugiz)
  3. and then in each band (ugriz, in this order):
          (Nobs mmed mmu msig mrms mchi2 mmax mrunmax mmin mrunmin mskew mskewErr mkurt mkurtErr), which are: 
          the total number of observations in this band
          the median magnitude 
          the mean magnitude
          the standard error for the mean (1.25 larger for the median)
          the root-mean-square scatter
          chi2 per degree of freedom (computed using the mean magnitude)
          the brightest magnitude
          the SDSS run ID of the brightest magnitude
          the faintest magnitude
          the SDSS run ID of the faintest magnitude
          the lightcurve skewness (calculated using the small sample skewness equation)
          the lightcurve skewness error
          the lightcurve kurtosis (calculated using the small sample kurtosis equation)
          the lightcurve kurtosis error
    

Intrinsic variability (sigma) is computed for each source in each band as

sigma = sqrt(rms2-xi2) for rms > xi (-99.99 otherwise),

where the median photometric error, as a function of magnitude, is

xi = a + b*m + c*m2 + d*m3 + e*m4

where m is the median dereddened magnitude of a source (this should really be done with uncorrected magnitudes, but quantitative differences are tiny) and (a,b,c,d,e) coefficients are
(6.27336, -1.60114, 0.153714, -0.00656245, 0.000105148) for the u band
(2.13439, -0.540752, 0.0517104, -0.00219396, 3.48404e-05) for the g band
(2.48331, -0.631346, 0.0605023, -0.002575, 4.10636e-05) for the r band
(3.60719, -0.940377, 0.0919942, -0.00398576, 6.4533e-05) for the i band
(8.06484, -2.16079, 0.217055, -0.00967042, 0.000161274) for the z band

SM macro for reading the catalog file

For SM users, we provide an SM macro for reading the catalog file.

Referencing

This work was supported by the NSF grant AST-0707901. The reference entry for this catalog is Sesar, B., Ivezic, Z., Lupton, R. H. et al., 2007, Astronomical Journal, 134, 2236 (also astro-ph/0704.0655). In addition, we would greatly appreciate if you add the standard SDSS acknowledgement to your paper:

Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS Web Site is http://www.sdss.org/.

The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington.

Thank you very much,

   
   Branimir Sesar (1)
   Zeljko Ivezic (1)
   and the SDSS Collaboration

(1) University of Washington

Please send us your question, comments or suggestions.


Version 1.0 from May 8, 2007