J/A+A/646/A6ivo://CDS.VizieR/J/A+A/646/A6doi:10.26093/cds/vizier.36460006CDSKorhonen H.Roettenbacher R.M.Gu S.Grundahl F.Andersen M.F.,Henry G.W.Jessen-Hansen J.Antoci V.Palle P.L.2021-05-04T13:24:33Z2021-02-01T07:20:49ZCDS support team

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

cds-question@unistra.frlate-type-starsccd-photometryspectroscopyWe aim to study the spot evolution and differential rotation in the magnetically active cool K-type giant star sigma Gem from broadband photometry and continuous spectroscopic observations that span 150 nights. We use high-resolution, high signal-to-noise ratio spectra obtained with the Hertzsprung SONG telescope to reconstruct surface (photospheric) temperature maps with Doppler imaging techniques. The 303 observations span 150 nights and allow for a detailed analysis of the spot evolution and surface differential rotation. The Doppler imaging results are compared to simultaneous broadband photometry from the Tennessee State University T3 0.4m Automated Photometric Telescope. The activity from the stellar chromosphere, which is higher in the stellar atmosphere, is also studied using SONG observations of Balmer Halpha line profiles and correlated with the photospheric activity. The temperature maps obtained during eight consecutive stellar rotations show mainly high-latitude or polar spots, with the main spot concentrations above latitude 45{deg}. The spots concentrate around phase 0.25 near the beginning of our observations and around phase 0.75 towards the end. The photometric observations confirm a small jump in spot phases that occurred in February 2016. The cross-correlation of the temperature maps reveals rather strong solar-like differential rotation, giving a relative surface differential rotation coefficient of alpha=0.10+/-0.02. There is a weak correlation between the locations of starspots and enhanced emission in the chromosphere at some epochs.2021A&A...646A...6Khttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/646/A6CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/A+AS/123/209 : Radial velocity curve of Sigma Gem (Duemmler+ 1997)J/A+A/391/641 : Spectroscopic study of sigma Gem from IUE (Ekmekci+, 2002)J/A+A/562/A107 : {sigma} Gem V-band differential light curve (Kajatkari+, 2014)J/ApJ/807/23 : RS CVn primaries companions. I. sig Gem (Roettenbacher+, 2015)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/646/A6https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/646/A6http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/646/A6https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/646/A6https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/646/A6http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/646/A6GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapdefaultJ/A+A/646/A6/table1Photometric observations of sigma GemrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintDateObserving date (DD-MM-YYYY)time.epochnullableMJDModified Julian Date (MJD-57000)dtime.epochdoublePhaseOrbital phasetime.phasefloatFilter[BV] Johnson Filtermeta.id;instr.filtercharmag-origOriginal differential magnitudemagphot.mag;arith.difffloatmag-ellDifferential magnitude with ellipticity removedmagsrc.ellipticity;arith.difffloatJ/A+A/646/A6/table2Observing log of the spectroscopic observationsMJDModified Julian Date (MJD-57000)dtime.epochdoublerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintObsObserving date (YYYY-MM-DD)stime.epochnullablePhaseOrbital Phasetime.phasefloatSet[1/7] Observing set number (1)meta.number;phys.atmol.numberintSNRSignal-to-noise ratio of the spectrum (2)stat.snrintPhase-combPhase of the combined observations (3)time.phasefloatSNR-combSignal-to-noise ratio of the combined observation (2) (3)obs.param;obsint