J/ApJ/835/25ivo://CDS.VizieR/J/ApJ/835/25doi:10.26093/cds/vizier.18350025CDSEgeland R.Soon W.Baliunas S.Hall J.C.Pevtsov A.A.Bertello L.2017-09-04T07:53:31Z2017-08-31T14:20:08ZCDS support team

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

cds-question@unistra.frthe-sunThe most commonly used index of stellar magnetic activity is the instrumental flux scale of singly ionized calcium H & K line core emission, S, developed by the Mount Wilson Observatory (MWO) HK Project, or the derivative index R'_HK_. Accurately placing the Sun on the S scale is important for comparing solar activity to that of the Sun-like stars. We present previously unpublished measurements of the reflected sunlight from the Moon using the second-generation MWO HK photometer during solar cycle 23 and determine cycle minimum S_23,min_=0.1634+/-0.0008, amplitude {Delta}S_23_=0.0143+/-0.0012, and mean <S_23_>=0.1701+/-0.0005. By establishing a proxy relationship with the closely related National Solar Observatory Sacramento Peak calcium K emission index, itself well correlated with the Kodaikanal Observatory plage index, we extend the MWO S time series to cover cycles 15-24 and find on average <S_min_>=0.1621+/-0.0008, <{Delta}S_cyc_>=0.0145+/-0.0012, <S_cyc_>=0.1694+/-0.0005. Our measurements represent an improvement over previous estimates that relied on stellar measurements or solar proxies with non-overlapping time series. We find good agreement from these results with measurements by the Solar-Stellar Spectrograph at Lowell Observatory, an independently calibrated instrument, which gives us additional confidence that we have accurately placed the Sun on the S-index flux scale.2017ApJ...835...25Ehttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/835/25CatalogResearchIsServedByTAP VizieR generic servicerelated-toIII/159 : Ca II H and K Measurements Made at MWO (Duncan+ 1991)J/ApJ/416/787 : Mount Wilson Crv Metallicity index (Soon+ 1993)J/ApJ/457/L99 : 25yr CaII-HK obs. of F-K nearby stars (Baliunas+, 1996)J/PASP/108/313 : Empirical stellar flux scales (Hall 1996)J/ApJ/687/1264 : Age estimation for solar-type dwarfs (Mamajek+, 2008)J/AJ/138/312 : Activity of bright solar analogs (Hall+, 2009)J/ApJ/812/12 : S-index and Stroemgren LC of HD30495 (Egeland+, 2015)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/835/25https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/835/25http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/835/25https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/835/25https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/835/25http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/835/25GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapdefaultJ/ApJ/835/25/table4Calibrated solar S-index time seriesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJDJulian Date; JD-2400000dtime.epochdoubleOrgSK[0.08/0.2] Orignal S or K indexspect.indexdoubleCalS[0.1/0.2] Calibrated S indexspect.indexdoubleInstInstrument used (1)instr.setupchar