Exploring the Variable Sky with the Sloan Digital Sky Survey
Abstract
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 (22h24m < J2000:0 < 04h08m, 1:27 < J2000:0 < 1:27 , 290 deg2), and contains 34 million photometric observations in the SDSS ugriz system for 748,084 unresolved sources at high Galactic latitudes (b < 20 ) that were observed at least four times in each of the ugri bands (with a median of 10 observations obtained over 6 yr). In each photometric bandpass we compute various low-order light-curve statistics, such as rms scatter, 2 per degree of freedom, skewness, and 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 (at high Galactic latitudes). The majority (2 out of 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 the UV excess color selection (at high Galactic latitudes).We analyze the distribution of light-curve skewness for quasars and find that it is centered on zero. We find that about one-fourth 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 light-curve skewness in the g - r versus u - g color-color diagram on the main stellar locus is found to be bimodal (with one mode consistent with Algol-like behavior).
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 2007
- Accession Number
- ADA474991
Entities
People
- Branimir Sesar
- Gajus Miknaitis
- Gillian R. Knapp
- Huan Lin
- J. A. Smith
- James E. Gunn
- Mario Juric
- Nathan De Lee
- Robert H. Lupton
- Zeljko Ivezic
Organizations
- United States Naval Observatory Flagstaff Station