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Between 1969 and 1993 a number of UBVR light curves of the long-period W Ser-type interacting binary RX Cas (P orb = 32.328 days) were obtained at Tallinn Observatory. The results of earlier observations, the interpretation of the light curves as well as the investigation of the nature of invisible primary component, intrinsic variability and its period (P intr = 516.06 days) were summarized by Kalv (and also discussed by Martynov). In recent years, new solutions of the radial velocity curves as well as of the synthetic light curves of RX Cas have been obtained. This enables the physical parameters of the components to be determined more accurately and the rate of mass exchange between the components and the initial parameters of the progenitor to be estimated with better precision.RX Cas belongs to a small group of W Ser-type binaries which according to our current knowledge are caught in a state of high-rate mass loss and mass transfer. The other beststudied members of the W Ser group are SX Cas, W Crucis, V367 Cygni, β Lyrae and W Ser itself. A common feature for this group is the presence of rich ultraviolet emission line spectra coming from higher ionization levels than can be expected from the effective temperatures of the stellar components.The early stage of studies of RX Cas was summarized by Dmitri Yakovlevich Martynov [1, 2] who was the first to propose the quantitative model of RX Cas and to study in detail the effect of apsidal motion in this system, estimating the total period of apsidal motion as = 29 000 ± 4 000 years. Kalv [3] found a reliable period P = 516.06 days of the intrinsic variability in RX Cas. Additional UBVR light curves of RX Cas were obtained at Tallinn Observatory in the observational period following the publication by Kalv [3] of the comprehensive analysis of the data consisting of the earlier observations obtained between 1969 and 1979 (see also [4,5]). New R light curves [6] are shown in figure 1. The orbital phases were calculated with a value for the orbital period of P = 32.327 39 days. In figure 2, the O − C diagram is shown covering the total period of photoelectric photometry of RX Cas at Tallinn Observatory. Note that our orbital period is slightly longer than the value of P = 32.3238 days given by Kreiner et al. [7] but the trend (secular lengthening of the period) is the same. From the value dP /P ≈ 10 −7

We report main results of the analysis of UBVR light curves of the long-period eclipsing binary BM Cas obtained between 1967 and 1996 in Tallinn observatory. The orbital period variations, evolutionary stage, peculiarities of the light curves and colour variations are discussed.

New results of UBVR photometry of the long-period eclipsing binary BM Cas obtained at Tallinn Observatory between 1979 and 1996 are discussed.We report some results of UBVR photometry of the long-period eclipsing binary BM Cas (P orb = 197. d 275) conducted between 1979 and 1996 at Tallinn Observatory. diagram is caused basically by pronounced intrinsic variability seen in all colours ( Figure 1). Sporadic displacements of the primary minimum epochs from the predicted ephemerides amounting to 0.02P orb have been observed. The observed (B − V ) changes in both minima of the light curve are consistent with the presence of a hot region located between the components. A similar pattern was found for another long-period eclipsing binary, UU Cnc (Kalv and Oja, unpublished).To our knowledge, no satisfactory solution of the light curves of BM Cas exists. The existing estimates of the masses and the radii of the components range between M 1 = 1.7 M , M 2 = 7.3 M , R 1 = 74 R , R 2 = 18 R (Barwig, 1976) and Kalv, 1980). The colour excess for BM Cas is 1. m 0, and probably the binary, located slightly below the Perseus arm, belongs to Association III of Cassiopeia. Assuming A v = 3.2 E B−V and d = 2.5 kpc, Kalv (1980) finds for the primary component M V = −5. m 7.A close resemblance between the observed parameters of BM Cas and those of h&χ Per, namely the distance to the object (2.5 kpc) and the mean radial velocity −43 km s −1 has been noted by several authors. BM Cas could be an example of a system at the common envelope stage. Available observational data do not contradict this idea. The mechanism responsible for a putative hot region between the components could be the "drag luminosity" as the secondary spirals towards the primary component (Iben and Livio, 1993).

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