J/A+A/695/A114ivo://CDS.VizieR/J/A+A/695/A114doi:10.26093/cds/vizier.36950114CDSRathour R.S.Smolec R.Hajdu G.Ziolkowska O.Hocde V.Soszynski I.,Udalski A.Karczmarek P.2025-07-30T20:01:14Z2025-07-25T09:21:07ZCDS support team

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

cds-question@unistra.frmagellanic-cloudsvariable-starsvisible-astronomyClassical Cepheids are not only excellent standard candles, but also invaluable tools to test stellar evolution and pulsation theories. Rates of their pulsation period change, quantified usually through O-C diagrams, can be confronted with predictions of stellar evolution theory. On the other hand, period changes on much shorter time scales (~10^2^-10^4^ days), attributed to non-evolutionary effects are often detected and lack detailed explanation. We aim to provide a systematic and quantitative description of irregular or non-linear period changes in Cepheids. Such a study is crucial for a complete understanding of period changes in Cepheids and is key to decoupling the evolutionary aspects from the non-evolutionary ones. We analysed part of the OGLE data for classical Cepheids in the Magellanic Clouds (MCs; from both Large Magellanic Cloud, LMC, and the Small Magellanic Cloud, SMC) using the modified Hertzsprung O-C technique. A sample of 3658 stars, with the best quality data and void of additional low-amplitude periodicities (e.g. due to non-radial pulsations), that could impact the results, was selected for analysis. Based on O-C shapes, stars were classified into three categories: no period change (class 1), linear period change (class 2), and irregular change (class 3). The Eddington-Plakidis test, wavelet analysis, Stetson index, and instantaneous period method were used to characterise class 3 candidates. We also investigated the correlation between the irregular period change in Cepheids and their metallicity environment In our investigation, 33.5+/-0.7% of analysed stars show irregular period changes. Considering the pulsation mode, irregular period changes were detected in 16.5+/-0.7% of the analysed fundamental mode stars and in 68.1+/-1.2% of the first overtone stars. The amplitude of variability in the O-C diagrams increases with the pulsation period, and at a given pulsation period, it is larger for first overtone stars. While the increase is linear for first overtone stars, for fundamental mode stars it becomes steeper as the pulsation period increases. Time scales of the observed variability range from a few hundred to a few thousand days. Irregular period changes are a ubiquitous property of classical Cepheids and may impact the derivation of secular, evolutionary period change rates; hence their quantitative characterisation is essential. The nature of these changes is still unknown. Our research provides observational constraints on their modelling. The markedly higher frequency of irregular period variations in first overtone Cepheids is a key observation that must be accounted for by the models.2025A&A...695A.114Rhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/695/A114CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/AcA/65/297 : OGLE4 LMC and SMC Cepheids (Soszynski+, 2015)J/A+A/686/A268 : New binary systems in Magellanic Clouds (Rathour+, 2024)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/695/A114https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/695/A114http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/695/A114https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/695/A114https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/695/A114http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/695/A114GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/695/A114/table2 (List of class 1 Cepheid candidates)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/695/A114/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/695/A114/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/695/A114/table2?GETtext/xml+votable180.050000true72.7604581-69.91366610.005555555555555556Cone search capability for table J/A+A/695/A114/table3 (List of class 2 Cepheid candidates)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/695/A114/table3?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/695/A114/table3?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/695/A114/table3?GETtext/xml+votable180.050000true80.00657-70.85183750.005555555555555556Cone search capability for table J/A+A/695/A114/table4 (List of class 3 Cepheid candidates)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/695/A114/table4?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/695/A114/table4?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/695/A114/table4?GETtext/xml+votable180.050000true86.3645133-70.42345030.0055555555555555564/2068 5/8263 8268-8269 8280 8323-8324 8326 8329 6/33045-33047 33049 33051 33080-33081 33083-33084 33104-33106 33124-33126 33128-33129 33287 33291 33313 33315 33321 33328-33330 37416 37504 37506 37514 37536 37538https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/695/A114?format=asciiOpticaldefaultJ/A+A/695/A114/table2List of class 1 Cepheid candidatesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMode[F 1O] Pulsation modemeta.code;src.varcharNameOGLE name (OGLE-LMC-CEP-NNNN or OGLE-SMC-CEP-NNNN)meta.id;meta.maincharPpulPulsation perioddtime.perioddoubleSimbadSimbad 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/695/A114/table3List of class 2 Cepheid candidatesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMode[F 1O] Pulsation modemeta.code;src.varcharNameOGLE name (OGLE-LMC-CEP-NNNN or OGLE-SMC-CEP-NNNN)meta.id;meta.maincharPpulPulsation perioddtime.perioddoubledP/dtPeriod change rated/Myrarith.rate;time.perioddoublee_dP/dtPeriod change rate errord/Myrstat.errorfloatSimbadSimbad 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/695/A114/table4List of class 3 Cepheid candidatesSimbadSimbad column added by the CDSmeta.ref.urlcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMode[F 1O] Pulsation modemeta.code;src.varcharNameOGLE name (OGLE-LMC-CEP-NNNN or OGLE-SMC-CEP-NNNN)meta.id;meta.maincharPpulPulsation perioddtime.perioddoubleepsilon? Period fluctuation parameter epsilon from E-P teststat.fit.paramdoublenullablePerDomDominant variability period from Wavelet methoddsrc.varintAmpDom? Dominant amplitude from Wavelet methodsrc.var.amplitudedoublenullableLindexStetson L indexmeta.codedoublesigmaStandard deviation for instantaneous period values calculated at O-C points, from instantaneous period methodstat.stdevdoubleDeltaPDifference between the maximum and minimum instantaneous period, Delta_P_, from instantaneous period methodtime.perioddouble_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.main