TT Arietis: 40 yr of photometry

ABSTRACT In an effort to characterize variations on the time-scale of hours and smaller during the high and low states of the nova-like variable TT Ari, light curves taken over the course of more than 40 yr are analysed. It is found that the well-known negative superhump observed during the high state persists until the present day at an average period of 0.132 95 d, which is slightly variable from year to year and exhibits substantial amplitude changes. The beat period between superhump and orbital period is also seen. Quasi-periodic oscillations occur at a preferred quasi-period of 18–25 min and undergo a systematic frequency evolution during a night. The available data permit for the first time a detailed investigation of the low state that is highly structured on time-scales of tens of days. On hourly time-scales, the light curve exhibits strong variations that are mostly irregular. However, during an interval of several days at the start of the low state, coherent 1.2 mag oscillations with a period of 8.90 h are seen. During the deep low state, quiet phases and strong (1.5–3 mag), highly structured flares alternate in irregular intervals of roughly 1 d. The quiet phases are modulated on the orbital period of TT Ari, suggesting reflection of the light of the primary component off the secondary. This is the first time that the orbital period is seen in photometric data.

X-Ray Observations of VY Scl-Type Nova-Like Binaries in the High and Low State

Four VY Scl-type nova-like systems were observed in X-rays both during the low and the high optical states. They are BZ Cam, MV Lyr, TT Ari, and V794 Aql. Using archival ROSAT, <em>Swift</em> and <em>SUZAKU</em> observations we found that the X-ray flux for BZ Cam is higher during the low state, but there is no supersoft X-ray source (SSS) that would indicate the thermonuclear burning predicted in a previous article. The X-ray flux is lower by a factor 2–10 in the low than the high state in other systems, and does not reflect the drop in <em>˙M</em> inferred from optical and UV data. The best fit model for the X-ray spectra is a collisionally ionized plasma model. The X-ray flux may originate in a shocked wind or in accretion onto polar caps in intermediate polar systems that continues even during the low state.