Spectroscopic and Photometric Observations of a Z Cam-Type Dwarf Nova, AT Cancri, in Standstill

摘要

Weperformedquasi-simultaneousspectroscopicandphotometricobservationsofaZCamstar,ATCnc,instandstillin1997February.V-bandtime-resolvedphotometrymarginallyrevealedsmall-amplitude(a??0.01mag)oscillationswithperiodcandidatesof0.132d,0.124d,0.142d,and0.249d.Low-resolutionspectrashowBalmerlinesinemissionandabsorption,andNaDabsorption.Fromtheradial-velocityvariationofH?±,wededucedthesystemparameters:theorbitalperiod=0.2011(?±0.0006)d,thesemi-amplitude=80(?±4)kmsa?’1,thesystemicvelocity=11(?±3)kmsa?’1,theprimarymass=0.9(?±0.5)Ma??.ThephaseofthevelocityvariationofH?±isveryclosetothatofNaD.Therearetwopossibilities:theH?±emissionlineradiated(a)fromthesecondarystar,or(b)fromtheaccretiondisk.Theinclinationisestimatedtobe17?°(?±5?°)and36?°(?±12?°)basedontherespectivepossibilities.Dopplermapdrawnunderpossibility(a)revealedonabroadlyextendedcomponentinthe(a?’Vx,a?’Vy)region.IntheDopplermapdrawnunderthepossibility(b),thepeakexistsontheirradiatedsideoftheDopplerpositionofthesecondaryandthe(+Vx,+Vy)region.WediscoveredanabsorptioncomponentinthebluewingatH?±.ThePCygprofileappearedduringalimitedperiodinitsorbitalphase,whichisinterpretedtobecausedbytransientmassejectionepisodes.