Exploring the Variable Sky with the Sloan Digital Sky Survey

By B. Sesar, Željko Ivezic´, Robert Lupton, Mario Juric, J. Gunn, G. Knapp, Nathan De Lee, J. A. Smith, G. Miknaitis, Huan Lin and 22 more. 2007

296 citations recorded by the source corpus.

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 < αJ2000.0 < 04h08m, -1.27° < δJ2000.0 < +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, χ2 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). Using over 600 RR Lyrae stars, we demonstrate rich halo substructure out to distances of 100 kpc. We extrapolate these results to the expected performance by the Large Synoptic Survey Telescope and estimate that it will obtain well-sampled, 2% accurate, multicolor light curves for ∼2 million low-redshift quasars and discover at least 50 million variable stars.

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Citations in the corpus

ON THE SHOULDERS OF GIANTS: PROPERTIES OF THE STELLAR HALO AND THE MILKY WAY MASS DISTRIBUTION (2014, background): “The outer-most,r & 100 kpc, region of the halo is diffuse and highly structured (Sesar et al. 2007; Sharma et al. 2011b).”
Substructure revealed by RR Lyraes in SDSS Stripe 82 (2009, background): “Sesar et al. (2007) label these regions as white dwarfs (Region 1, red), low-redshift quasars (Region 2, orange), M dwarf/white dwarf binaries (Region 3, green), RR Lyraes (Region 4,cyan), main stellar locus (Region 5, blue) and high-redshift quasars (Region 6, purple). g < 19 g < 20.5 g <…”
LIGHT CURVE TEMPLATES AND GALACTIC DISTRIBUTION OF RR LYRAE STARS FROM SLOAN DIGITAL SKY SURVEY STRIPE 82 (2009, methodology): “…and relatively clean samples of RR Lyrae stars can be selected using single-epoch colors (Ivezić et al. 2005), and if multi-epoch data exist, using variability (Ivezić et al. 2000; QUEST, Vivas et al. 2001; Sesar et al. 2007, De Lee 2008; SEKBO, Keller et al. 2008; LONEOS-I, Miceli et al. 2008).”
IS QUASAR OPTICAL VARIABILITY A DAMPED RANDOM WALK? (2012, background): “…of individual quasars found in a heterogeneous sample, OGLE (Optical Gravitational Lensing Experiment, Udalski et al. 1997) and SDSS Stripe 82 (S82, Sesar et al. 2007), respectively, and that the parameters τ and σ are correlated with the physical properties of the quasar (rest wavelength,…”
PERIODOGRAMS FOR MULTIBAND ASTRONOMICAL TIME SERIES (2015, background): “Stripe 82 is a three hundred square degree equatorial region of the sky which was repeatedly imaged through multiple band-passes during phase II of the Sloan Digital Sky Survey (SDSS II, see Sesar et al. 2007).”
The Accretion Origin of the Milky Way’s Stellar Halo (2007, background): “…to expand the coverag of the Milky Way’s stellar halo, probing to larger halo radii where models predict that halo substructure should be easier to discern (see, e.g., the prominent substructures discovered by Sesar et al. 2007 using RR Lyrae stars in the multiply-imaged ‘Stripe 82’ of the SDSS).”
QUANTIFYING QUASAR VARIABILITY AS PART OF A GENERAL APPROACH TO CLASSIFYING CONTINUOUSLY VARYING SOURCES (2009, methodology): “Sesar et al. (2007) found that essentially all quasars vary at some level on long timescales, with 90% of Sloan Digital Sky Survey (SDSS) quasars having rms variability 0.03 mag on a six year timescale.”
COMPARING SINGLE-EPOCH VIRIAL BLACK HOLE MASS ESTIMATORS FOR LUMINOUS QUASARS (2012, background): “This absolute flux calibration neglects the continuum variability between the 2MASS and (spectroscopic) SDSS epochs, which is typically at the level of∼ 0.1 mag for average SDSS quasars (e.g., Sesar et al. 2007; MacLeod et al. 2011).”
OPTICAL DISCOVERY OF PROBABLE STELLAR TIDAL DISRUPTION FLARES (2010, methodology): “Selecting flares in SDSS observations The ∼ 300 deg2 Sloan Digital Sky Survey (SDSS; York et al. 2000) multi-epoch imaging data Stripe 82 (Sesar et al. 2007; Bramich et al. 2008; Frieman et al. 2008; Abazajian et al. 2009) was the starting point of our search.”
MODELING THE TIME VARIABILITY OF SDSS STRIPE 82 QUASARS AS A DAMPED RANDOM WALK (2010, methodology): “Because some observations were obtained in non-photometric conditions, improved calibration techniques have been applied to SDSS S82 data by Ivezić et al. (2007) and Sesar et al. (2007), and we use their results.”
THE CATALINA SURVEYS PERIODIC VARIABLE STAR CATALOG (2014, methodology): “Deeper searches for variability, in much smaller fields, have been carried out by QUEST (Vivas et al. 2004), LONEOS (Miceli et al. 2008), MOTESS-GNAT-1 (MG1, Krauss et al. 2007), Kepler (Matijevic et al. 2012) and SDSS Stripe-82 (Sesar et al. 2007, Bhatti et al. 2010, Becker et al. 2011).”
PROBING THE OUTER GALACTIC HALO WITH RR LYRAE FROM THE CATALINA SURVEYS (2012, background): “An overdensity in Pisces was reported by Sesar et al. (2007) and confirmed by Kollmeier et al. (2009).”
The Milky Way Tomography with SDSS. II. Stellar Metallicity (2008, methodology): “3 and the photometric errors in the g − r color (the median value is 0.025 mag, and 0.03 mag at g = 19.5; these values, computed by the photometric pipeline, are reliable, as discussed in detail by Sesar et al. 2007).”
A systematic search for changing-look quasars in SDSS (2015, background): “(SDSS; e.g., Vanden Berk et al. 2004; Wilhite et al. 2005; Sesar et al. 2007; Schmidt et al. 2010; Butler & Bloom 2011; MacLeod et al. 2012) and more recently Pan-STARRS1 (PS1; Morganson et al. 2014, 2015; Simm et al. 2015).”
THE SDSS-III BARYON OSCILLATION SPECTROSCOPIC SURVEY: THE QUASAR LUMINOSITY FUNCTION FROM DATA RELEASE NINE (2012, background): “…two reasons: (i) the improved photometry of the deeper data better defines the stellar locus (Ivezić et al. 2007) and (ii) quasars can be selected based on their variability (Sesar et al. 2007; Bramich et al. 2008; Schmidt et al. 2010; MacLeod et al. 2011; Palanque-Delabrouille et al. 2011, 2012).”
MAPPING THE STELLAR STRUCTURE OF THE MILKY WAY THICK DISK AND HALO USING SEGUE PHOTOMETRY (2009, background): “…and photometric measurements for all detected objects (Lupton, Gunn, & Szalay 1999; Stoughton et al. 2002; Smith et al. 2002; Pier et al. 2003; Ivezić et al. 2004; Tucker et al. 2006), reaching a photometric accuracy of 2% down to g ≃22.5 and r ≃22 (Ivezić et al. 2004; Sesar et al. 2007).”