J/A+A/701/A103ivo://CDS.VizieR/J/A+A/701/A103doi:10.26093/cds/vizier/bc-nx/lbadCDSKovari Zs.Strassmeier K.G.Olah K.Seli B.Henry G.W.Vida K.2026-08-03T06:56:52Z2025-09-04T08:10:35ZCDS support team

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

cds-question@unistra.frlate-type-starsinfrared-photometryvisible-astronomybroad-band-photometryOver the past 40 years the brightness variations of XX Tri, a single line RS Canum Venaticorum (RS CVn)-type binary system with a synchronized K-giant primary, has exceeded one magnit ude in the V band. Although these changes are primarily caused by starspots, an additional activity-related mechanism may also be behind the long-term trend of overall brightness increase. By compiling the most complete photometric data set so far, we attempt to examin e how the nature of seasonal-to-decadal changes can be linked to global magnetis m. To find the long-term activity cycles and their properties a time-frequency anal yser code is used. We divided the entire data set into four consecutive interval s, for which we separately determined the Fourier spectra around the orbital per iod. This is performed with a Fourier-transformation based frequency analyser to ol. The long-term brightening of XX Tri was accompanied by a gradual increase in the effective temperature, which resulted in a blueing shift in the Herzsprung-Russ ell diagram. In the long term, a constant cycle of about 4 years is most strongl y present in the entire data. Besides, we also found a modulation of about 11 ye ars, and a slowly decreasing cycle of about 5.7-5.2 years. From the seasonal datasets we found that the most dominant rotation-related periods are scattered around the orbital period. From this we infer a solar-type surface differential rotation, although the surface shear is significantly smaller than that of the Sun. The 4-year cycle indicates flip-flop-like behavior: during this time, the 2-3 active longitudes usually present on the stellar surface are rearranged. The magnitude-range changes in the long term cannot be interpreted solely as changes in the number and size of spots; the unspotted brightness of XX Tri has also increased over the decades. This should alert users of photometric spot models to reconsider the basic concept of constant unspotted brightness in similar cases.2025A&A...701A.103Khttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/701/A103CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/701/A103https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/701/A103http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/701/A103https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/701/A103https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/701/A103http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/701/A103GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tap2.367228618189496e-19 6.118840631666147e-19OpticalInfrareddefaultJ/A+A/701/A103/skiffV photometry from Skiff & Nations, (1991) private communication in Strassmeier et al. (1997A&AS..125...11S)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintHJDHeliocentric Julian Datedtime.epochdoubledVmagDifferential V magnitudemagphot.mag;arith.difffloatJ/A+A/701/A103/noltheniBVRIc photometry from Nolthenius (1991IBVS.3589....1N)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintHJDHeliocentric Julian Datedtime.epochdoubledBmag? Differential B magnitudemagphot.mag;arith.difffloatnullabledVmagDifferential V magnitudemagphot.mag;arith.difffloatdRmag? Differential R magnitudemagphot.mag;arith.difffloatnullabledIcmagDifferential Ic magnitudemagphot.mag;arith.difffloatJ/A+A/701/A103/konkolyUBV(RI)c photometry from Konkoly ObservatoryrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintHJDHeliocentric Julian Datedtime.epochdoubleUmagU magnitudemagphot.mag;em.opt.UfloatBmagB magnitudemagphot.mag;em.opt.BfloatVmagV magnitudemagphot.mag;em.opt.VfloatRcmagRc magnitudemagphot.mag;em.opt.RfloatIcmagIc magnitudemagphot.mag;em.opt.IfloatJ/A+A/701/A103/hootenV photometry from Hooten & Hall (1990ApJS...74..225H)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintHJDHeliocentric Julian Datedtime.epochdoubledVmagDifferential V magnitudemagphot.mag;arith.difffloatJ/A+A/701/A103/henry_vAPT V photometry from T3, Tennessee State Univ.recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintHJDHeliocentric Julian Datedtime.epochdoubledVmagDifferential V magnitudemagphot.mag;arith.difffloatJ/A+A/701/A103/henry_bAPT B photometry from T3, Tennessee State Univ.recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintHJDHeliocentric Julian Datedtime.epochdoubledBmagDifferential B magnitudemagphot.mag;arith.difffloat