Exploring the variable sky with the Sloan Digital Sky Survey
Date
2007-12Author
Sesar, Branimir
Ivezic, Zeljko
Lupton, Robert
Juric, Mario
Gunn, James
Knapp, Gillian
De Lee, Nathan
Smith, Allyn
Miknaitis, Gajus
Lin, Huan
Tucker, Douglas
Doi, Mamoru
Tanaka, Masayuki
Fukugita, Masataka
Holtzman, Jon
Kent, Steve
Yanny, Brian
Schlegel, David
Finkbeiner, Douglas
Padmanabhan, Nikhil
Rockosi, Constance
Bond, Nicholas
Lee, Brian
Stoughton, Chris
Jester, Sebastian
Harris, Hugh
Harding, Paul
Brinkmann, Jon
Schneider, Donald
York, Donald
Richmond, Michael
Vanden Berk, Daniel
Metadata
Show full item recordAbstract
We quantify the variability of faint unresolved optical sources using a catalog
based on multiple SDSS imaging observations. The catalog covers SDSS Stripe
82, which lies along the celestial equator in the Southern Galactic Hemisphere
(22h 24m < J2000 < 04h 08m, −1.27◦ < J2000 < +1.27◦, ∼ 290 deg2), and
contains 58 million photometric observations in the SDSS ugriz system for 1.4
million unresolved sources that were observed at least 4 times in each of the
gri bands (with a median of 10 observations obtained over ∼5 years). In each
photometric bandpass we compute various low-order lightcurve statistics such as
root-mean-square scatter (rms), 2 per degree of freedom, skewness, minimum
and maximum magnitude, and use them to select and study variable sources.
We find that 2% of unresolved optical sources brighter than g = 20.5 appear
variable at the 0.05 mag level (rms) simultaneously in the g and r bands. The
majority (2/3) of these variable sources are low-redshift (< 2) quasars, although
they represent only 2% of all sources in the adopted flux-limited sample. We
find that at least 90% of quasars are variable at the 0.03 mag level (rms) and
confirm that variability is as good a method for finding low-redshift quasars as
is the UV excess color selection (at high Galactic latitudes). We analyze the
distribution of lightcurve skewness for quasars and find that is centered on zero.
We find that about 1/4 of the variable stars are RR Lyrae stars, and that only
0.5% of stars from the main stellar locus are variable at the 0.05 mag level. The
distribution of lightcurve skewness in the g − r vs. u − g color-color diagram
on the main stellar locus is found to be bimodal (with one mode consistent with
Algol-like behavior). Using over six hundred RR Lyrae stars, we demonstrate rich
halo substructure out to distances of 100 kpc. We extrapolate these results to
expected performance by the Large Synoptic Survey Telescope and estimate that
it will obtain well-sampled 2% accurate, multi-color lightcurves for ∼ 2 million
low-redshift quasars, and will discover at least 50 million variable stars.