Light-Curve and Period Changes in the W UMa-Type System TY Bootis

摘要

AdetailedstudyoftheperiodandthelightcurveoftheeclipsingbinaryTYBootisispresented.Basedonastudyofthe$$(mathrm{O}-mathrm{C})$$curve,wehavefoundthattwoperiodicalvariationssuperimposeonacontinuousincrease($$dP/dt=6.283 imes10^{-8},mathrm{d},mathrm{yr}^{-1}$$)initsperiod.Wecomparedlightcurvesobtainedbyothergroups,andfoundthatthelightcurveofthesystemhaschangedconsiderably.Weanalyzedthephysicalmechanismsthatunderliethevariationintheperiodandlightcurveofthesystem,andobtainedsomenewconclusions.Thecontinuousincreaseofitsorbitalperiodisprobablycausedbymasstransferfromthesecondarytotheprimary,ratherthananexpansionoftheprimaryduetoitsdynamicalinstability.Also,thetwoperiodicalcomponentsareprobablycausedbytwodifferentphysicalmechanisms,i.e.,thelight-timeeffectisoneofthepossiblemechanisms,whichmightcauseaperiodicalcomponentwithalongertimescale(31.5a€‰yr),andthemagneticactivitycycleistheotherone,whichmightunderlietheotherperiodicalcomponentwithashortertimescale(11.76a€‰yr).Thelong-termvariationinthelightcurveofthesystemislikelytobecausedbyadecreaseinthelightleveloftheprimaryduetostarspot(s)ontheprimaryoranexpansionoftheprimary.Finally,thetrendsintheevolutionofthesystemarediscussedaccordingtoatheoryofWUMasystems.