COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3367 Konkoly Observatory Budapest 18 August 1989 HU ISSN 0374 - 0676 MICROVARIABILITY OF RX CAS RX Cas is a strongly interacting close binary system with an orbital period of 32.33d and spectral type A2-5e + K0 II-III. Photometric monitoring observations were carried out between January 7 and February 12, 1986 with a one-channel WBVR photoelectric photometer attached to the 48-cm telescope of the Tien-Shan High Altitude Observatory of the Sternberg Astronomical Institute (Khaliullin et al., 1985). The observations were processed by a standard scheme: background - comparison star - variable - comparison star - background. The comparison star was BD +67d248 and check star - HD 6210. The integration time in each filter was 10-40 sec. It depends on both the filter and the orbital phase. Thus, the records from each filter were repeated every 1-2 minutes. The duration of each observational series and the number of records were changed in order to eliminate its influence on the periodogram analysis. Observing nights with high transparency and stability of seeing were chosen for the analysis. Khaliullin et al.'s (1985) method was used for primary processing of the data. The observational data in the W filter are listed in Table I. Table I JD 2446400+ Delta T N Phi Sigma_int Sigma_Delta T P>90% P>80% 49 .112 21 .31 .012 .013 49min 50 .151 133 .34 .016 .022 40min 51 .158 137 .37 .016 .026 95min 52 .132 115 .40 .015 .026 53 .094 79 .43 .012 .024 62 .162 117 .71 .012 .023 42min 64 .208 103 .77 .010 .017 65 .101 55 .81 .010 .017 86min 67 .100 37 .86 .020 .020 29min Column JD contains the date, column Delta T - the interval of observation, column psi - the orbital phase, column sigma_int - internal error of one observation, sigma_DeltaT=sigma/ is the relative variation over the entire time interval. The analysis was carried out by Deeming's (1975) method. Frequencies in the interval 1-100 cycles/day were searched for. In Figure 1 the periodograms of JD 2446450 and 2446462 in filter W are shown. They are the only ones that show peaks with a significance of more than 90%. On some periodograms of other observations different variations with periods of 20-90 minutes can be supposed. All of them are listed in the last two columns of Table I where "p>90%" contains the period in minutes corresponding to the peaks on the periodogram with a significance of 90-95%, and "p>80%" - the respective periods with a significance 80-90%. The study of the comparison star does not show peaks with a significance of more than 20%. [FIGURE 1] [FIGURE 2] The values of the periods are: JD 2446450 P_1=0.0278+-0.0023d JD 2446462 P_2=0.0294+-0.0023d They coincide in phases and the following elements can be used: T_min=JD 2446450.1534+0.0292d*N +-30 +-25 The average curve of brightness computed with these elements for the data of the two nights is shown in Figure 2. The amplitude of the variation is approximately 0.04m. Microvariability in the other filters (B, V, R) is not yet suspected. It is interesting to mention that the dates JD 2446450 and 2446462 coincide with maxima of the 11.007d period (Todorova and Khruzina, 1989), i.e. when the line of sight crosses the supposed active areas on the accretion disc. These active areas are likely to be "spots" or zones of shock waves originated from a superposition of non-radial variations. Before these phases and after them toward to the minima of the 11 period the observed variations vanish. To adopt or reject the hypothesis of a non-uniform distribution of the brightness on the surface of the accretion disc (Todorova and Khruzina, 1989) more observations are necessary. P. N. TODOROVA T. S. KHRUZINA National Astronomical Sternberg Astronomical Observatory - Rozhen Institute, Bulgarian Academy of Science 117234, Moscov P. O. B. 136, 4700 Smolyan U.S.S.R. BULGARIA References: Deeming, T. 1975, Astrophysics and Space Science, 36, 137. [BIBCODE 1975Ap&SS..36..137D ] Khaliullin, Kh., Mironov, A. and Moshkalyov, V. 1985, Astrophys. and Space Sci., 111, 291. [BIBCODE 1985Ap&SS.111..291K ] Todorova, P. and Khruzina, T. 1989, Pisma v Astr. Zhu., 15, 524. [BIBCODE 1989PAZh...15..524T ]