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Abstract. Results of photoelectric observations of TT Ari during the 1985-1994 interval are presented. Observations were carried out at the Rozhen and Belogradchik observatories as part of our programme for the study of anti-dwarf novae. The long-term light curve in the standard UBV system is constructed and peculiarities of the long-term behaviour of the star in this time interval are discussed. 21 moments of maxima and 14 moments of minima are added to the list of known maxima and minima of 3.2-hour modulations. The period of 3.2-hour modulations during the 1987/1988, 1989/1990 and 1990/1991 seasons is determined. In our 29 observing runs we searched for 20-min quasi-periodic variations, which were detected in 25 of them. Our results show that in 1989, the 20-min modulation mean period reached a local maximum of 19.45 min and declined afterwards. The mean brightness variability analysis during the aforementioned seasons confirmed the reliability of the 3. d 8 period suspected by Semeniuk et al. (1987).

Abstract.We present an analysis of CCD photometric observations of the eclipsing novalike cataclysmic variable DW UMa obtained in two different luminosity states: high and intermediate. The star presents eclipses with very different depth: ∼1.2 mag in the high and ∼3.4 mag in the intermediate state. Eclipse mapping reveals that this difference is almost entirely due to the changes in the accretion disc radius: from ∼0.5R L 1 in the intermediate state to ∼0.75R L 1 in the high state (R L 1 is the distance from the white dwarf to the first Lagrangian point). In the intermediate state, the entire disc is eclipsed while in the high state, its outer part remains visible. We also find that the central intensity of the disc is nearly the same in the two luminosity states and that it is the increase of the disc radius that is responsible for the final rise from the 1999/2000 low state. We find that the intensity profile of the disc is rather flat and suggest a possible explanation. We also discuss the effect of using a more realistic limb-darkening law on the disc temperatures inferred from eclipse mapping experiments. Periodogram analysis of the high state data reveals "positive superhumps" with a period of 0.

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Abstract. An analysis of spectral and photometric observations of the novalike TT Ari obtained in the interval 1999-2001 is presented. The photometry in November 1999 shows "positive superhumps" with a period of 0.d 14815 and full amplitude 0.13-0.14 mag. The emission lines equivalent widths are also modulated with the "positive superhumps" period, as its value in the interval from August 2000 to January 2001 is 0.d 148815. The analysis shows that the flux in the emission lines vary in anti-phase with the continuum. It is found that Hα asymmetry is modulated with the expected precessional period of 1.d 81715 supporting the precession accretion disc model for the "positive superhumps" observed in TT Ari. An expansion of the TT Ari accretion disc due to a mass transfer rate reduction is proposed as a possible mechanism for the appearance of the "positive superhumps". The Hα profile shows a weak, blue-shifted absorption, whose strength is modulated with the orbital period of the system. The Hα Doppler tomogram reveals the presence of an asymmetric source of emission in the accretion disc. Eclipse of this emission source by the outflowing wind is the most likely explanation of the phase dependent Hα P-cygni profile. The He i λ6678 tomogram shows a strong asymmetric emission source located at the back side of the disc. The asymmetric emission sources in Hα and He i λ6678 tomograms are thus located on the opposite sides of the system mass center. The emission of the secondary is detected in He i λ6678 Doppler tomogram, which allows us to secure the absolute phasing of the radial velocities. We derive a new orbital ephemeris of TT Ari by analysis of all availible high state radial velocities.