Study of Superoutbursts and Superhumps in SU UMa Stars by the Kepler Light Curves of V344Lyrae and V1504 Cygni

摘要

Wehavestudiedtheshort-cadenceKeplerpubliclightcurvesoftwoSUUMastars,V344LyrandV1504Cyg,extendingoveraperiodofmorethantwoyearsbyusingpowerspectralanalysis.WedeterminedtheorbitalperiodofV344LyrtobePorb=0.087903(1)d.WealsoreanalyzedthefrequencyvariationofthenegativesuperhumpinacompletesupercycleofV1504CygwithadditionaldataoftheOa€“Cdiagram,confirmingthatitscharacteristicvariationisinaccordancewiththethermal-tidalinstabilitymodel.Wepresentanewtwo-dimensionalperiodanalysisbasedonanewmethodofaleastabsoluteshrinkageandselectionoperator(Lasso).Thenewmethodgivesverysharppeaksinthepowerspectra,anditisveryusefulforstudyingthefrequencyvariationincataclysmicvariablestars.Wehaveanalyzedsimultaneousfrequencyvariationsofthepositiveandnegativesuperhumps.Iftheyareappropriatelyconverted,itisfoundthattheyvaryinunison,indicatingthattheyrepresentadisk-radiusvariation.Wehavealsostudiedthefrequency(orperiod)variationsofpositivesuperhumpsduringsuperoutbursts.Thesevariationscanbeunderstoodinaqualitativewaybycombiningthedisk-radiusvariationandthevariationofpressureeffectsduringasuperoutburst.Asuddenexcitationofoscillationwithafrequencyrangeneartothenegativesuperhump(whichwecalla€?impulsivenegativesuperhumpa€?)wasobservedinthedescendingbranchofseveraloutburstsofV344Lyr.Theseeventsseemtohaveoccurredjustpriortothenextsuperoutburst,andtoactasaa€?leada€?oftheimpendingsuperoutburst.