COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2841 Konkoly Observatory Budapest 27 December 1985 HU ISSN 0374 - 0676 SOME COMMENTS ON THE MINIMA OF THE RS CVn TYPE ECLIPSING BINARIES CQ Aur, RU Cnc, VV Mon AND SZ Psc In recent years a considerable effort has been made to describe in the most comprehensive way the features of the photometric wave-like distortions shown by the RS CVn type binaries. However, there are some problems that, on the contrary, have received less attention; among them we should like to quote the effects produced by the migrating wave on the epochs of minimum light (changes in the slopes of ascending and descending branches) and on the levels at the bottoms of primary and secondary minima (related to size and position of the perturbed regions). In this work we report on some results obtained from the extensive V photometry carried out at the Astronomical Observatory of Torino in the interval 1975-1984 on the systems CQ Aur, RU Cnc, VV Mon and SZ Psc. CQ Aurigae (P= 10.62d) Most of the epochs of primary minimum (Kurotschkin, 1940) seem to be quite uncertain; therefore, in order to minimize the large scatter shown by them, we assumed, as representative of the oldest epochs, the mean value as deduced by Kurotschkin (1940), i.e. JD 2429558.78. More recently, timings were determined by O'Connell (1978) (JD 2440000.281) and by us (JD 2443814.05 +-0.01 and JD 2445396.850 +-0.004). The weighted period as derived from these four epochs is P=10.62251d +- 0.00004. We suggest that the following ephemeris: Min.I(Hel.) = 2443814.05 +10.62251d E can be used to predict future epochs of minimum light with a good reliability. From our photometry, spread over the interval 1978-1985, we infer no appreciable variations in the luminosity level at the bottom of the secondary minimum; on the contrary, an increase larger than the experimental error (up to about 0.1 mag).occurs near phase 0.0 (when only the cooler active component is visible) at the epochs 1978.02 and 1980.96. RU Cancri (P= 10.17d) The oldest photographic and visual estimates can be found in Hall and Kreiner (1980). We are able to add the epochs: JD 2441775.856+-0.001 (as derived from the data kindly sent to us by Dr. D.M. Popper (see also Popper and Dumont, 1977)) and JD 2445356.713+-0.001 from our own photometry. Both linear and parabolic fits to the (O-C)'s have been calculated; the best agreement has been found using the following light elements: Min.I (Hel.)= 2422650.7152 + 10.17298843d.E - 2.25 10^-8.E^2 +-0.0024 +- 0.00000005 +-0.05 No clear evidence can be drawn about the bottoms of primary and secondary minima even if a quite large spread (up to about 0.06 mag) suggests possible variations in the luminosity levels. Assuming an inclination i= 90deg, the durations of the eclipse (0d894+-0.020) and of the totality (0.314d+-0.016) allow to determine the fractional radii of the components, R_S=0.089+0.006 and R_L=0.186+0.010. VV Monocerotis (P = 6.05d) For this binary the ephemeris found by Scaltriti (1979) proved to be satisfactory also for the new epoch JD 2444189.440+-0.003. A weighted linear least squares fit led to: Min.I (Hel.) = 2442834.110 + 6.050592d E +-0.010 +-0.000006 As far as the luminosity levels at the bottoms of minima are concerned, the same conclusions drawn for RU Cnc are valid in the case of VV Mon. SZ Piscium (P= 3.97d) As pointed out in Catalano et al. (1978) and Hall and Kreiner (1980), this system shows one of the largest amplitudes in the O-C curve (up to about 0.6) among the eclipsing binaries. In Table I we collected all the epochs we could find in the literature. In order to minimize the uncertainty in the older determinations of Jensch (1934) and Gaposchkin (1943, 1952), we have constructed normal minima wherever some epochs a few cycles apart were present. The (O-C)1 values calculated by means of the linear ephemeris by Catalano et al. (1978) (see Table I) are plotted in Figure 1. Quadratic fits to this trend were calculated by Hall and Kreiner (1980) and Tunca (1984); however, unacceptable deviations (up to about 0.13) suggest different approximations to the observed (O-C)'s; we find that the curve (O-C) = 0.4d*sin((360deg/7200)(E+ 4000)) (1) represent quite well the (O-C)1 values; the (O-C)2's listed in Table I have Table I. Times of minimum of SZ Psc JD(Hel.) E (O-C)1 (O-C)2 Source 2425576.836 -4219 -0.119 -0.022 Jensch(1934) 25854.410 4149 -0.157 -0.084 Jensch(1934) 26262.943 4046 -0.107 -0.070 Jensch(1934) 27036.365 3851 -0.030 +0.042 Jensch(1934) 27409.322 3757 +0.135 +0.072 Jensch(1934) 28000.255 3608 +0.155 +0.040 Gaposchkin(1943) 29935.858 3120 +0.415 +0.154 Gaposchkin(1952) 35741.819 1656 +0.348 +0.003 Jakate et al.(1976) 36114.574 -1562 +0.311 -0.018 Jakate et al.(1976) 42308.767 0 -0.179 -0.038 Jakate et al.(1976) 43117.822 + 204 -0.161 +0.043 From Eaton (1977) 43498.502 300 -0.204 +0.028 Catalano et al.(1978) 43815.707 380 -0.268 -0.014 From Hall and Kreiner(1980) 43823.674 382 -0.233 +0.021 Present paper 44069.544 444 -0.247 +0.024 Tunca(1984) 44073.51 445 -0.25 +0.03 From Tumer et al.(1980) 44184.529 473 -0.272 +0.006 Present paper 44573.16 571 -0.30 +0.01 Present paper 2444827.005 + 635 -0.266 +0.049 Tunca(1984) [FIGURE 1] Figure 1. O-C values of SZ PSC been calculated taking into account the contribution of formula (1); the resulting period of the cycle is about 78 years, which is longer than the estimation reported by Ahn (1982) (66 years). It is clear that only determinations of future epochs can prove the longterm validity of the new ephemeris. In fact, we may notice that the last epoch in Table I gives (O-C)2= 0.049, a quite large value for a photoelectric timing; moreover, the periodicity of formula (1) might imply : i) a light-time effect in a triple system, that would require a very massive third body (M>50Msun); a similar phenomenon seems to be present in the RS CVn type system SV Cam (Cellino et al., 1985), ii) an apsidal motion in an orbit with e=~0.15, far larger than found by Jakate et al. (1976) from a spectroscopic orbit solution (e=~0.04). Perhaps we are witnessing just a long-term cyclic variation similar to those characterizing other RS CVn and W UMa type binaries. Eventually, we notice that the epochs with E >-1656 can also be fitted by a linear least squares approximation, leading to the ephemeris: Min.I (Hel.) = 2442308.817 + 3.9655847d E +-0.007 +-0.0000096 F. SCALTRITI, M. BUSSO and A. CELLINO Osservatorio Astronomico de Torino Strada Osservatorio 20 I-10025 Pino Torinese (Torino) - Italia References: Ahn, Y.S., 1982, Publ. Korean Nat. Astron. Obs., 5, 25. Catalano, S., Frisina, A., Rodono, M., and Scaltriti, F., 1978, Inf. Bull. Var. Stars, No. 1427. Cellino, A., Scaltriti, F., and Busso, M., 1985, Astron. Astrophys., 144, 315. [BIBCODE 1985A&A...144..315C ] Eaton, J.A., 1977, Inf. Bull. Var. Stars, No. 1297. Gaposchkin, S., 1943, Harvard Annals, 113, No. 2. [BIBCODE 1953AnHar.113...67G ] Gaposchkin, S., 1952, Harvard Annals, 118, No. 6. [BIBCODE 1952AnHar.118...41G ] Hall, D.S., and Kreiner, J.M., 1980, Acta Astron., 30, 387. [BIBCODE 1980AcA....30..387H ] Jakate, S., Bakos, G.A., Fernie, J.D., and Heard, J.F., 1976, Astron. J., 81, 250. [BIBCODE 1976AJ.....81..250J ] Jensch, A., 1934, Astron. Nachr., 252, 393. [BIBCODE 1934AN....252..393J ] Kurotschkin, N.E., 1940, Variable Stars, 8, 362. O'Connell, D.J.K., 1978, Ric. Astr. Spec. Vaticana, 8, No.30. [BIBCODE 1978RA......8..556O ] Popper, D.M., and Dumont, P.J., 1977, Astron. J., 82, 216. [BIBCODE 1977AJ.....82..216P ] Scaltriti, F., 1979, Astron. Astrophys. Suppl. Ser. 35, 291. [BIBCODE 1979A&AS...35..291S ] Tumer, O., Kurutac, M., Tunca, Z., Evren, S., Ertan, A.Y., and Ibanoglu, C., 1980, Inf. Bull. Var. Stars, No. 1741. Tunca, Z. 1984, Astrophys. Space Sci., 105, 23. [BIBCODE 1984Ap&SS.105...23T ]