COMMISSION 27 OF THE I.A.U. INFORMATION BULLETIN ON VARIABLE STARS Number 3259 Konkoly Observatory Budapest 8 November 1988 HU ISSN 0374 - 0676 RS Boo. THE PECULIARITIES OF BLAZHKO EFFECT MANIFESTATION The variability of RS Boo was discovered by Flemming (Pickering, 1907). Oosterhoff published a detailed investigation on the basis of 2418 photographic observations obtained in Leiden wherein he showed that the pulsation period and the star's light curve shape varied with a secondary period equal to 537 days. Kanyo (1980) confirmed the presence of the secondary period as long as 533 days and supposed a shorter secondary period Pi approx. 58 - 62 days on the basis of photoelectric observations made at Konkoly Observatory between 1971 and 1979. We carried out investigations of secondary periodicities in RS Boo using a more extensive material. We had at our disposal 192 moments of RS Boo maximum light (interval J.D. 2417668 - 2444842) published in the literature, as well as 112 moments of maximum light (interval J.D.2437790- 2446654) determined from the photometric observations made by G.A. Lange and the author (the depository of Odessa Astronomical Observatory). The analysis of all the observational material showed that the pulsation period and the light curve shape of RS Boo changed with secondary periods Pi_1= 531.9 and Pi_2= 47.7 days. The periodicity with Pi_1 and Pi_2 retained throughout all the period of the observation of RS Boo. The following plots are given in Figure 1: a) the average curves )-C and DeltaV(m) for Pi_1 = 530.2d(observations by Kanyo, J.D.2442443- 2444008). The phases phi were calculated by the formula: Max_O-B = 2443249+ 530.2d n (1) b) The average curve O'-C' for Pi_2 = 47.7d (observations made by the author, J.D.2441770- 2441923). The phases were calculated by the formula: Max_O-A = 2434207.9 + 47.70d N (2) The series of observations of RS Boo at our disposal enabled us to carry out investigations of non-stability of the pulsation period P, that of the periods Pi_1 and Pi_2 as well as the variations in the amplitude of the Blazhko effect with Pi_1 and Pi_2 from cycle to cycle. Table I Max_O-B n O-B Ampl_O-B 2419823 0d 0d 0d015 26233 12 27 0.019 28363 16 30 0.022 30475 20 14 0.014 33124 25 4 0.015 34169 27 -15 0.015 37925 34 17: 0.025 39531 37 28 0.023 41128 40 29 0.025 42718 43 23 0.020 43249 44 22 0.017 45371 48 17 0.015 [FIGURE 1] [FIGURE 2] To solve this problem, the average curves for cycles Pi_1 and Pi_2 were constructed. From the seasonal average curves the deviations of the moments of maximum O-B were determined for the cycle Pi_1 and those of moments of maximum O-A for the cycle Pi_2 as well as the amplitude of Blazhko effect Ampl_O-B and Ampl_O-A respectively. The values obtained are given in Tables I and II wherein the successive columns contain the following data: the moment of maximum O-B (the moment of maximum )-A); the number of the epoch n (the number of the epoch N); the residual O-B (the residual O-A); Ampl_O-B (Ampl_O-A). Table II Max_O-A N O-A Ampl_O-A 2417863.2 -343 16d4 0d009 24610.3 -201 - 9.9 0.016 26413.6 -163 -19.2 0.020 27036.2 -150 -16.7 0.016 30429.9 - 79 - 9.7 0.014 34207.9 0 0.0 0.012 37027.4 59 5.2 0.021 39655.5 114 9.8 0.017 41751.9 158 7.4 0.016 41828.9 160 -11.0 0.011 42201.7 168 -19.8 0.010 42393.2 172 -19.I 0.011 42780.3 180 -13.6 0.013 43259.5 190 -11.4 0.007 43549.2 196 - 7.9 0.011 43759.5 200 11.6 0.010 44530.5 216 19.4 0.013 45490.2: 236 25.1: 0.008 The residuals O-B were calculated with respect to the elements: Max = 2419823+ 531.9d * n (3) while the residuals O-A were calculated with respect to the elements (2). In Figure 2 there are given: a) the O-D residuals for the period of pulsation of RS Boo calculated using the formula: Max.hel. J.D.= 2441770.486+ 0.37733657d E (Zessewitsch, 1986); b) the O-A residuals calculated by the formula (2); c) the O-B residuals calculated by the formula (3); d) the plot Ampl_O-B; e) the plot Ampl_O-A. The analysis of Figure 2 shows that the pulsation period is increasing monotonously. The presence of two periods of Blazhko effect (Pi_1 = 531d.9 and Pi_2= 47.7) is a characteristic peculiarity of RS Boo pulsation. The variations of, the O-A residuals and those of O-B residuals do not show any ordinary pattern of mirror image of the trend seen in the O-D residuals. However, the residuals O-A and O-B have a similar to each other character of variations, these change cyclically and in antiphase. A characteristic cycle duration is 36 years. The variations of Ampl_O-A and Ampl_O-B proceed with an analogous cycle but in synphase. The absence of apparent relation between the nonstability of the pulsation period P and the character of amplitude instability and the periods Pi_1 and Pi_2 of Blazhko effect shows that in the case of RS Boo we observe a multiparametrical manifestation of the Blazhko effect. B.N. FIRMANYUK Odessa Astronomical Observatory Odessa, U.S.S.R. References: Kanyo, S. 1980, Inf. Bull. Var. Stars, No. 1832. Oosterhoff, P.T. 1946, B.A.N., 10, 101. [BIBCODE 1946BAN....10..101O ] Pickering, E.C. 1907, Astr. Nachr., 174, 101. [BIBCODE 1907AN....174..101P ] Zessewitsch, W.P. 1986, SAC-58, 127.