II/362ivo://CDS.VizieR/II/362CDSSergison D.J.Naylor T.Littlefair S.P.Bell C.P.M.Williams C.D.H.2020-01-10T12:08:06Z2020-01-09T15:24:36ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.fropen-star-clustersyoung-stellar-objectsvisible-astronomysloan-photometryWe present an i-band photometric study of over 800 young stellar objects in the OB association Cep OB3b, which samples timescales from 1 minute to ten years. Using structure functions we show that on all timescales (tau) there is a monotonic decrease in variability from Class I to Class II through the transition disc (TD) systems to Class III, i.e. the more evolved systems are less variable. The Class Is show an approximately power-law increase (tau^0.8^) in variability from timescales of a few minutes to ten years. The Class II, TDs and Class III systems show a qualitatively different behaviour with most showing a power-law increase in variability to a timescale corresponding to the rotational period of the star, with little additional variability beyond that timescale. However, about a third of the Class IIs show lower overall variability, but their variability is still increasing at 10 years. This behaviour can be explained if all Class IIs have two primary components to their variability. The first is an underlying roughly power-law variability spectrum, which evidence from the infrared suggests is driven by accretion rate changes. The second component is an approximately sinusoidal and results from the rotation of the star. We suggest that the systems with dominant longer-timescale variability have a smaller rotational modulation either because they are seen at low inclinations or have more complex magnetic field geometries. We derive a new way of calculating structure functions for large simulated datasets (the "fast structure function"), based on fast Fourier transforms.2020MNRAS.491.5035Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/II/362CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/MNRAS/403/545 : Young stars in Cepheus OB3b (Littlefair+, 2010)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=II/362https://vizier.iucaa.in/viz-bin/VizieR-2?-source=II/362http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=II/362https://vizier.cds.unistra.fr/viz-bin/votable?-source=II/362https://vizier.iucaa.in/viz-bin/votable?-source=II/362http://vizieridia.saao.ac.za/viz-bin/votable?-source=II/362GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table II/362/stars (List of studied stars)https://vizier.cds.unistra.fr/viz-bin/conesearch/II/362/stars?https://vizier.iucaa.in/viz-bin/conesearch/II/362/stars?http://vizieridia.saao.ac.za/viz-bin/conesearch/II/362/stars?GETtext/xml+votable180.050000true344.3119958362.431736110.005555555555555556Cone search capability for table II/362/tableb (Cep OB3b object properties and lightcurve summary statistics)https://vizier.cds.unistra.fr/viz-bin/conesearch/II/362/tableb?https://vizier.iucaa.in/viz-bin/conesearch/II/362/tableb?http://vizieridia.saao.ac.za/viz-bin/conesearch/II/362/tableb?GETtext/xml+votable180.050000true344.1421583334662.9462555556827040.0055555555555555566/15682 15683 15689https://cdsarc.cds.unistra.fr/viz-bin/moc/II/362?format=asciiOpticaldefaultII/362/starsList of studied starsCCD[1/4] The CCD the star was observed withmeta.id.part;meta.mainintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintL2010Display the data of Littlefair et al., 2010, Cat. J/MNRAS/403/545meta.ref.urlcharStarIDStar identifier within the CDD number (G1)meta.id.part;meta.mainintRAJ2000Right ascension (J2000)pos.eq.ra;meta.mainindexedDEJ2000Declination (J2000)pos.eq.dec;meta.mainLCShow the light curvemeta.ref.urlcharlcdataDisplay the light curve data from tableameta.ref.urlcharII/362/tablebCep OB3b object properties and lightcurve summary statisticsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintCCD[1/4] The CCD the star was observed withmeta.id.part;meta.mainintStarIDStar identifier number within CCD (G1)meta.id.part;meta.mainintimagClean? Clean i-band magnitude from Bell et al. (2013A&A...551L...7B)magphot.mag;em.opt.Idoublenullablei-ZClean? Clean i-Z colour from Bell et al. (2013A&A...551L...7B)magphot.color;em.opt.I;em.opt.IdoublenullableNptsNumber of good lightcurve points (2)meta.numberintAH68? Half the magnitude range covering 68 percent of observations for good low-cadence datapointsmagphot.mag;em.opt.IdoublenullablemagMed? Median magnitude for good low-cadence datapointsmagphot.mag;em.opt.IdoublenullablemagMean? Mean magnitude for good low-cadence datapointsmagphot.magdoublenullablerchi2? Reduced chi-squared about weighted mean of good datapointsstat.fit.chi2doublenullableuncMeanMean uncertainty for all unflagged datapointsmagstat.errordoublemagMed2004? Median magnitude from 2004 data for unflagged datapointsmagphot.mag;em.opt.IdoublenullablemagMed2005? Median magnitude from 2005 data for unflagged datapointsmagphot.mag;em.opt.IdoublenullablemagMed2007? Median magnitude from 2007 data for unflagged datapointsmagphot.mag;em.opt.IdoublenullablemagMed2013Median magnitude from 2013 data for unflagged datapointsmagphot.mag;em.opt.IdoubleClClass (I, II, TD, III or LPS)meta.code.classcharPer? Period from Littlefair et al. (2010, Cat. J/MNRAS/403/545)dtime.periodfloatnullableR-HaClean? Clean R-Halpha colour from Littlefair et al. (2010, Cat. J/MNRAS/403/545)magphot.color;em.opt.R;em.line.HalphafloatnullableRAJ2000Right ascension (J2000.0) from Littlefair et al. (2010, Cat. J/MNRAS/403/545)degpos.eq.ra;meta.mainindexedDEJ2000Declination (J2000.0) from Littlefair et al. (2010, J/MNRAS/403/545)degpos.eq.dec;meta.mainindexedII/362/tablecCep OB3b low cadence structure functions for 6845 starsb_SLPS16th percentile LPS SF at median flux MedFluxmeta.notedoublerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTauTimescale in daysdtime.scaledoubleSnettStructure function (SF) after removal of photon and instrument noisestat.fit.paramdoublee_SUncertainty in S and Snettstat.errordoubleSStructure function (SF) including photon and instrument noisestat.fit.paramdoubleSLPSMean local photometric standard (LPS) structure function (SF) at median flux MedFluxstat.fit.paramdoubleB_SLPS84th percentile LPS SF at median flux MedFluxmeta.notedoubleCCD[1/4] The CCD the star was observed withmeta.id.part;meta.mainintStarIDStar identifier number within CCD (G1)meta.id.part;meta.mainintMedFluxMedian fluxphot.flux.density;em.opt.IdoubleClClass (I, II, TD, III or LPS)meta.code.classcharFLAG[OO OU] Set to OU if SNett<e_S, else OOmeta.code.errorcharII/362/tabledCep OB3b high cadence structure functions for 6850 starsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTauTimescale in daysdtime.scaledoubleSnettStructure function (SF) after removal of photon and instrument noisestat.fit.paramdoublee_SUncertainty in S and Snettstat.errordoubleSStructure function (SF) including photon and instrument noisestat.fit.paramdoubleb_SLPS16th percentile LPS SF at median flux MedFluxmeta.notedoubleSLPSMean local photometric standard (LPS) structure function (SF) at median flux MedFluxstat.fit.paramdoubleB_SLPS84th percentile LPS SF at median flux MedFluxmeta.notedoubleCCD[1/4] The CCD the star was observed withmeta.id.part;meta.mainintStarIDStar identifier number within CCD (G1)meta.id.part;meta.mainintMedFluxMedian fluxphot.flux.density;em.opt.IdoubleClClass (I, II, TD, III or LPS)meta.code.classcharFLAG[OO OU] Set to OU if SNett<e_S, else OOmeta.code.errorcharII/362/tableaCep OB3b lightcurves for the 41883 starsimagSloan i-band magnitudemagphot.mag;em.opt.IdoubleRunINT run numbermeta.idintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintCCD[1/4] The CCD the star was observed withmeta.id.part;meta.mainintStarIDStar identifier within the CDD number (G1)meta.id.part;meta.mainintBJDMid exposure (BJD-2450000)dtime.epochdoublee_imagUncertainty in imagmagstat.error;phot.mag;em.opt.IdoubleQual[BCEFGHILNORS] Quality flag (2)meta.code.qualcharNegFlux[false/true ] Set true if flux is negativemeta.codechar