Superoutbursts of Z Chameleontis. Detection of the Hot Spot

Eclipse light curves of Z Cha collected during its superoutbursts are decomposed into the disk eclipse and spot eclipse components. It is found that the presence (or absence) of the hot spot and all its parameters depend on the phase φb of the beat period (related to the orbital and superhump periods). At beat phases 0.40<φb<0.60 the "standard" hot spot is present, the analysis of its parameters shows that (a) the mass transfer rate is strongly enhanced and (b) the radius of the disk is roughly equal to the tidal radius. No hot spot can be detected during eclipses located close to the superhump (beat phases 0.80<φb<0.35). The spot observed at intermediate beat phases (φb≈0.35 and φb≈0.75) shows peculiarities which are interpreted as being due to the stream overflow. Rediscussion of system parameters, based on the mass ratio obtained from the analysis of the spot eclipses during quiescence (Smak 1996) and K2 from Wade and Horne (1988), gives: M1=0.93±0.10 Msolar, M2=0.186±0.030 Msolar, q=0.20±0.01 and i=80°.2±0°.3.