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Title: 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 (22h 24m < {alpha}{sub J2000} < 04h 08m, -1.27{sup o} < {delta}{sub J2000} < +1.27{sup o}, {approx} 290 deg{sup 2}), 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 {approx}5 years). In each photometric bandpass we compute various low-order lightcurve statistics such as root-mean-square scatter (rms), {chi}{sup 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 confirmmore » 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 {approx}2 million low-redshift quasars, and will discover at least 50 million variable stars.« less

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »; ; ; ; ; ; ; ; ; ; ; ; « less
Publication Date:
Research Org.:
COLLABORATION - U.Washington
Sponsoring Org.:
USDOE Director. Office of Science. High EnergyPhysics
OSTI Identifier:
928596
Report Number(s):
LBNL-63511
Journal ID: ISSN 0004-6256; ANJOAA; R&D Project: PBARY1; BnR: KA1503020; TRN: US0803239
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal; Journal Volume: 134; Related Information: Journal Publication Date: 2007
Country of Publication:
United States
Language:
English
Subject:
72; ASYMMETRY; COLOR; DISTRIBUTION; EQUATOR; PERFORMANCE; QUASARS; SKY; STARS; STATISTICS; TELESCOPES; VARIABLE STARS

Citation Formats

Sesar, Branimir, Ivezic, Zeljko, Lupton, Robert, Juric, Mario, Gunn, James, Knapp, Gillian, De Lee, Nathan, Smith, J. 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, and Vanden Berk, Daniel. Exploring the Variable Sky with the Sloan Digital Sky Survey. United States: N. p., 2007. Web. doi:10.1086/521819.
Sesar, Branimir, Ivezic, Zeljko, Lupton, Robert, Juric, Mario, Gunn, James, Knapp, Gillian, De Lee, Nathan, Smith, J. 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. Exploring the Variable Sky with the Sloan Digital Sky Survey. United States. doi:10.1086/521819.
Sesar, Branimir, Ivezic, Zeljko, Lupton, Robert, Juric, Mario, Gunn, James, Knapp, Gillian, De Lee, Nathan, Smith, J. 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, and Vanden Berk, Daniel. Sun . "Exploring the Variable Sky with the Sloan Digital Sky Survey". United States. doi:10.1086/521819. https://www.osti.gov/servlets/purl/928596.
@article{osti_928596,
title = {Exploring the Variable Sky with the Sloan Digital Sky Survey},
author = {Sesar, Branimir and Ivezic, Zeljko and Lupton, Robert and Juric, Mario and Gunn, James and Knapp, Gillian and De Lee, Nathan and Smith, J. Allyn and Miknaitis,Gajus and Lin, Huan and Tucker, Douglas and Doi, Mamoru and Tanaka, Masayuki and Fukugita, Masataka and Holtzman, Jon and Kent, Steve and Yanny, Brian and Schlegel,David and Finkbeiner, Douglas and Padmanabhan, Nikhil and Rockosi, Constance and Bond, Nicholas and Lee, Brian and Stoughton, Chris and Jester, Sebastian and Harris,Hugh and Harding, Paul and Brinkmann, Jon and Schneider, Donald and York, Donald and Richmond, Michael and Vanden Berk, Daniel},
abstractNote = {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 < {alpha}{sub J2000} < 04h 08m, -1.27{sup o} < {delta}{sub J2000} < +1.27{sup o}, {approx} 290 deg{sup 2}), 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 {approx}5 years). In each photometric bandpass we compute various low-order lightcurve statistics such as root-mean-square scatter (rms), {chi}{sup 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 {approx}2 million low-redshift quasars, and will discover at least 50 million variable stars.},
doi = {10.1086/521819},
journal = {Astronomical Journal},
number = ,
volume = 134,
place = {United States},
year = {Sun Apr 01 00:00:00 EDT 2007},
month = {Sun Apr 01 00:00:00 EDT 2007}
}
  • 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 < {alpha}{sub J2000} < 04h 08m, -1.27 < {delta}{sub J2000} < +1.27, {approx}290 deg{sup 2} ), 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 {approx}5 years). In each photometric bandpass we compute various low-ordermore » lightcurve statistics such as root-mean-square scatter (rms), {chi}{sup 2} 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 ux-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 {approx}2 million low-redshift quasars, and will discover at least 50 million variable stars.« less
  • We describe photometric recalibration of data obtained by the asteroid survey LINEAR. Although LINEAR was designed for astrometric discovery of moving objects, the data set described here contains over 5 billion photometric measurements for about 25 million objects, mostly stars. We use Sloan Digital Sky Survey (SDSS) data from the overlapping {approx}10,000 deg{sup 2} of sky to recalibrate LINEAR photometry and achieve errors of 0.03 mag for sources not limited by photon statistics with errors of 0.2 mag at r {approx} 18. With its 200 observations per object on average, LINEAR data provide time domain information for the brightest fourmore » magnitudes of the SDSS survey. At the same time, LINEAR extends the deepest similar wide-area variability survey, the Northern Sky Variability Survey, by 3 mag. We briefly discuss the properties of about 7000 visually confirmed periodic variables, dominated by roughly equal fractions of RR Lyrae stars and eclipsing binary stars, and analyze their distribution in optical and infrared color-color diagrams. The LINEAR data set is publicly available from the SkyDOT Web site.« less
  • We present details of the construction and characterization of the coaddition of the Sloan Digital Sky Survey (SDSS) Stripe 82 ugriz imaging data. This survey consists of 275 deg{sup 2} of repeated scanning by the SDSS camera over –50° ≤ α ≤ 60° and –1.°25 ≤ δ ≤ +1.°25 centered on the Celestial Equator. Each piece of sky has ∼20 runs contributing and thus reaches ∼2 mag fainter than the SDSS single pass data, i.e., to r ∼ 23.5 for galaxies. We discuss the image processing of the coaddition, the modeling of the point-spread function (PSF), the calibration, and themore » production of standard SDSS catalogs. The data have an r-band median seeing of 1.''1 and are calibrated to ≤1%. Star color-color, number counts, and PSF size versus modeled size plots show that the modeling of the PSF is good enough for precision five-band photometry. Structure in the PSF model versus magnitude plot indicates minor PSF modeling errors, leading to misclassification of stars as galaxies, as verified using VVDS spectroscopy. There are a variety of uses for this wide-angle deep imaging data, including galactic structure, photometric redshift computation, cluster finding and cross wavelength measurements, weak lensing cluster mass calibrations, and cosmic shear measurements.« less
  • We report the first results of a study of variable point sources identified using multi-color timeseries photometry from Sloan Digital Sky Survey (SDSS) Stripe 82, including data from the SDSS-II Supernova Survey, over a span of nearly 10 years (1998-2007). We construct a light-curve catalog of 221,842 point sources in the R.A. 0-4 hr half of Stripe 82, limited to r = 22.0 mag, that have at least 10 detections in the ugriz bands and color errors < 0.2 mag. These sources are then classified by color and by cross matching them to existing SDSS catalogs of interesting objects. Inhomogeneousmore » ensemble differential photometry techniques are used to greatly improve our sensitivity to variability and reduce contamination by sources that appear variable due to large photometric noise or systematic effects caused by non-uniform photometric conditions throughout the survey. We use robust variable identification methods to extract 6520 variable candidates from this data set, resulting in an overall variable fraction of {approx}2.9% at the level of {approx}0.05 mag variability. Despite the sparse and uneven time sampling of the light-curve data, we discover 143 periodic variables in total. Due to period ambiguity caused by relatively poor phase coverage, we identify a smaller final set of 101 periodic variables with well-determined periods and light curves. Among these are 55 RR Lyrae, 30 eclipsing binary candidates, and 16 high-amplitude Delta Scuti variables. In addition to these objects, we also identify a sample of 2704 variable quasars matched to the SDSS Quasar Catalog, which make up a large fraction of our variable candidates. An additional 2403 quasar candidates are tentatively identified and selected by their non-stellar colors and variability. A sample of 11,328 point sources that appear to be nonvariable given the limits of our variability sensitivity is also briefly discussed. Finally, we describe several interesting objects discovered among our eclipsing binary candidates, and illustrate the use of our publicly available light-curve catalog by tracing Galaxy halo substructure with our small sample of RR Lyrae variables.« less
  • The ROSAT All-Sky Survey (RASS) was the first imaging X-ray survey of the entire sky. Combining the RASS Bright and Faint Source Catalogs yields an average of about three X-ray sources per square degree. However, while X-ray source counterparts are known to range from distant quasars to nearby M dwarfs, the RASS data alone are often insufficient to determine the nature of an X-ray source. As a result, large-scale follow-up programs are required to construct samples of known X-ray emitters. We use optical data produced by the Sloan Digital Sky Survey (SDSS) to identify 709 stellar X-ray emitters cataloged inmore » the RASS and falling within the SDSS Data Release 1 footprint. Most of these are bright stars with coronal X-ray emission unsuitable for SDSS spectroscopy, which is designed for fainter objects (g > 15 [mag]). Instead, we use SDSS photometry, correlations with the Two Micron All Sky Survey and other catalogs, and spectroscopy from the Apache Point Observatory 3.5 m telescope to identify these stellar X-ray counterparts. Our sample of 707 X-ray-emitting F, G, K, and M stars is one of the largest X-ray-selected samples of such stars. We derive distances to these stars using photometric parallax relations appropriate for dwarfs on the main sequence, and use these distances to calculate L{sub X} . We also identify a previously unknown cataclysmic variable (CV) as a RASS counterpart. Separately, we use correlations of the RASS and the SDSS spectroscopic catalogs of CVs and white dwarfs (WDs) to study the properties of these rarer X-ray-emitting stars. We examine the relationship between (f{sub X} /f{sub g} ) and the equivalent width of the H{beta} emission line for 46 X-ray-emitting CVs and discuss tentative classifications for a subset based on these quantities. We identify 17 new X-ray-emitting DA (hydrogen) WDs, of which three are newly identified WDs. We report on follow-up observations of three candidate cool X-ray-emitting WDs (one DA and two DB (helium) WDs); we have not confirmed X-ray emission from these WDs.« less