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We report on optical high-dispersion spectroscopic monitoring observations of the Be/X-ray binary A0535+26/V725 Tau, carried out from 2005 November to 2009 March. The main aim of these monitoring observations is to study spectral variabilities in the Be disc, on both the short (a week or so) and long (more than hundreds of days) time-scales, by taking long-term frequent observations. Our four-year spectroscopic observations indicate that the V/R ratio, i.e. the relative intensity of the violet (V) peak with respect to the red (R) one, of the double-peaked Hα line profile varies with a period of 500 d. The Hβ line profile also varies in phase with the Hα profile. With these observations covering two full cycles of the V/R variability, we reconstruct the two-dimensional structure of the Be disc by applying the Doppler tomography method to the Hα and Hβ emission-line profiles, using a rigidly rotating frame with the V/R variability period. The resulting disc structure reveals non-axisymmetric features, which can be explained by a one-armed perturbation in the Be disc. It is the first time that an eccentric disc structure is directly detected by using a method other than the interferometric one. [ABSTRACT FROM AUTHOR]

The highlights of the recent study of variable stars of different types are discussed. We present some results (out of more than 500 papers) and plans for the further studies within bi- or multi-lateral observational campaigns. Special attention is paid to the polarimetric and photometric monitoring of polars, intermediate polars, superhumpers in dwarf novae and nova-like systems, symbiotic variables, pulsating semi-regular and Mira-type stars and other long-periodic variables, new suspected variables from the Hipparcos-Tycho space observatory and other surveys. To study multi-periodic and aperiodic variability superimposed onto long-term trends, an expert system for time series analysis is briefly referred. [ABSTRACT FROM AUTHOR]

We report on time-resolved photometry carried out during the 1995 short outburst and the 1997 long outburst in the eclipsing dwarf nova DV UMa. The revised orbital period is 0.0858526172 (67) d. We detected gigantic superhumps with an amplitude of ∼0.6 mag in the mid-phase of the 1997 outburst, revealing the SU UMa nature of DV UMa. The superhump period is 0.0887 (4) d. The superhumps became less clear during the late phase of the superoutburst, and we found two possible periods of 0.0885 (15) and 0.0764 (15). During both outbursts, the eclipse was wide and shallow near the maximum, and then became narrower and deeper, which is qualitatively well explained by the current disc instability theory. [ABSTRACT FROM AUTHOR]

We observed the unique helium cataclysmic variable CR Boo (=PG 1346+082) extensively, using CCD and visual photometry, during the period 1995–1998. The observation revealed the existence of a quasi-periodic alternation of bright and faint states with a period of 46.3 d. During the faint states, the system shows short outbursts with a characteristic recurrence period of 4–8 d. The 1490-s signal, which has been considered as superhumps, almost disappeared during the short outburst on 1998 January 2. The overall patterns of outbursts and the appearance of the superhump signal are remarkably similar to those of hydrogen-rich ER UMa stars. We propose CR Boo as a member of a class of ‘helium’ counterparts of ER UMa stars. [ABSTRACT FROM AUTHOR]

We are developing two new systems of a high-speed CCD camera, and an automated monitor telescope. This camera using a frame transfer-type CCD that enables us to take images each 27.3 msec at the highest speed. We wish to investigate accretion and eruption phenomena around compact stars by optical light. The system we have developed for automated monitoring of X-ray binaries and cataclysmic variables consists of a 30-cm reflector, a CCD camera, and a computer. It is a cheap system, but can monitor more than 150 systems each night. It will reveal long-term light curves of programmed stars of those transient systems, and catch sudden outbursts/decays. We will be able to start follow-up observations to clarify the mechanism of these activities as early as possible. We here report the current status of these projects, the target physics, and the future development. [ABSTRACT FROM PUBLISHER]

We have kept optical monitoring of a peculiar black hole X-ray binary, V4641 Sgr. Based on our observations, we show that its unprecedented activity can be divided into 5 phases. In this paper, we report their observational properties. [ABSTRACT FROM PUBLISHER]