J/A+A/621/A21ivo://CDS.VizieR/J/A+A/621/A21doi:10.26093/cds/vizier.36210021CDSReinhold T.Bell K.J.Kuszlewicz J.Hekker S.Shapiro A.I.2019-01-09T08:21:02Z2018-12-20T09:04:07ZCDS support team

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

cds-question@unistra.frvariable-starsThe study of stellar activity cycles is crucial to understand the underlying dynamo and how it causes magnetic activity signatures such as dark spots and bright faculae. Having knowledge about the dominant source of surface activity might allow us to draw conclusions about the stellar age and magnetic field topology, and to put the solar cycle in context. We investigate the underlying process that causes magnetic activity by studying the appearance of activity signatures in contemporaneous photometric and chromospheric time series. Lomb-Scargle periodograms are used to search for cycle periods present in the photometric and chromospheric time series. To emphasize the signature of the activity cycle we account for rotation-induced scatter in both data sets by fitting a quasi-periodic Gaussian process model to each observing season. After subtracting the rotational variability, cycle amplitudes and the phase difference between the two time series are obtained by fitting both time series simultaneously using the same cycle period. We find cycle periods in 27 of the 30 stars in our sample. The phase difference between the two time series reveals that the variability in fast-rotating active stars is usually in anti-phase, while the variability of slowly rotating inactive stars is in phase. The photometric cycle amplitudes are on average six times larger for the active stars. The phase and amplitude information demonstrates that active stars are dominated by dark spots, whereas less-active stars are dominated by bright faculae. We find the transition from spot to faculae domination to be at the Vaughan-Preston gap, and around a Rossby number equal to one. We conclude that faculae are the dominant ingredient of stellar activity cycles at ages >~2.55Gyr. The data further suggest that the Vaughan-Preston gap cannot explain the previously detected dearth of Kepler rotation periods between 15 and 25 days. Nevertheless, our results led us to propose an explanation for the lack of rotation periods to be due to the non-detection of periodicity caused by the cancelation of dark spots and bright faculae at ~800Myr.2019A&A...621A..21Rhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/621/A21CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/ApJ/457/L99 : 25yr CaII-HK observations of F-K nearby stars (Baliunas+, 1996)J/A+A/393/225 : Starspot cycles of six young solar analogues (Messina+, 2002)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/621/A21https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/621/A21http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/621/A21https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/621/A21https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/621/A21http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/621/A21GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/621/A21/table1 (Basic stellar parameters of the taken from Simbad)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/621/A21/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/621/A21/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/621/A21/table1?GETtext/xml+votable180.050000true5.7157847-12.20943670.0055555555555555566/254 684 1603 4591 5088 5670 7763 8716 8790 8843 9403 11856 12592 13301 16069 17219 17918 23230 24151 24160 26521 27973 28664 30176 30665 30965 31073 32552 40823https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/621/A21?format=asciidefaultJ/A+A/621/A21/table1Basic stellar parameters of the taken from SimbadrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintHDHD numbermeta.id;meta.maincharNameNamemeta.idcharTypeObject type (1)src.classcharSpTypeSpectral type (2)src.spTypecharTeffEffective temperatureKphys.temperature.effectiveintE_TeffError on Teff (upper value)Kstat.error;stat.maxinte_TeffError on Teff (lower value)Kstat.error;phys.temperature.effectiveintloggSurface gravitylog(cm.s**-2)phys.gravityfloatE_loggError on logg (upper value)log(cm.s**-2)stat.error;stat.maxfloate_loggError on logg (lower value)log(cm.s**-2)stat.errorfloat[Fe/H]Metallicityphys.abund.ZfloatE_[Fe/H]Error on [Fe/H] (upper value)stat.error;stat.maxfloate_[Fe/H]Error on [Fe/H] (lower value)stat.error;phys.abund.FefloatRefReferencesmeta.refcharSimbadSimbad column added by the CDSmeta.ref.urlchar_RARight Ascension (J2000) from SIMBAD (not part of the original data)degpos.eq.ra;meta.main_DEDeclination (J2000) from SIMBAD (not part of the original data)degpos.eq.dec;meta.mainJ/A+A/621/A21/tableb1Physical parameters of the samplerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintHDHD numbermeta.id;meta.maincharB-VB-V colour index (1)magphot.color;em.opt.B;em.opt.VfloatlogR'HKActivity index (1)phot.flux;arith.ratiofloatProtRotation period (2)dtime.periodfloatPcyc? Cycle period (3)yrtime.periodfloatnullablee_Pcyc? rms uncertainty on Pcycyrstat.errorfloatnullablePlcp? Possible long period subtracted from the photometric time seriesyrtime.periodfloatnullablePlcc? Possible long periods subtracted from the chromospheric time seriesyrtime.periodfloatnullableAmpp? Amplitude to the photometric time seriesmmagphot.magfloatnullablee_Ampp? rms uncertainty on Amppmmagstat.errorfloatnullableAmpc? Amplitude to the chromospheric time seriesmmagphot.magfloatnullablee_Ampc? rms uncertainty on Ampcmmagstat.errorfloatnullableDphi? Phase difference between the two time seriestime;arith.difffloatnullablee_Dphi? rms uncertainty on Dphistat.errorfloatnullableFlagpPhotometric flag (4)meta.code.errorcharFlagcChromospheric flag (4)meta.code.errorcharchi2p? Photometric time series chi^2^ valuestat.fit.chi2floatnullablechi2c? Chromospheric time series chi^2^ valuestat.fit.chi2floatnullablechi2s? Combined time series chi^2^ valuestat.fit.chi2floatnullable