COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1617 Konkoly Observatory Budapest 1979 June 1 ON THE DECREASING PERIOD AND ASYMMETRIC LIGHT CURVE OF RT SCULPTORIS RT Scl is a southern EB-type eclipsing binary whose light curve has been studied fairly regularly since the turn of the century. An asymmetry is present in all light curves, which manifests itself in the different heights of the maxima and the shape of the secondary minimum. It is therefore interesting to study the stability of the period in order to decide on the presence and strength of mass flow between the components. A new study of the period is also important because recent visual minimum determinations suggest very large period changes. We present here a new UBV light curve, obtained with the ESO 50 cm telescope in 1977, and new photographic minima, derived from plates of the Bamberg sky patrol for the years 1964 to 1972. [FIGURE 1] Fig. 1. U B V light curves of RT Scl, relative to CoD -26d 193 (CPD -26d 49) The new light curves, as compared with the photoelectric light curves of Cillie and Lindsay (1958), and Clausen and Gronbech (1977), show no obvious change in the asymmetric disturbance (Fig. 1). A detailed analysis will be published later. All available minimum times are collected in Table 1. A new linear ephemeris, derived from the existing photoelectric observations, yields J.D.hel. (primary minimum) = 2 443 450.6370 + 0.51156208 * E +/-0.0007 +/-.00000007 Table 1. minimum times of RT Scl J.D.hel. E (O-C)_1 (O-C)_2 type source (2400000+) 11736.1140 -61995 -0.2319 -0.0019 pg Pickering/Whiteside (1908) 23761.5806 -38488 -0.0551 +0.0073 pg Dugan (1928) 24116.6056 -37794 -0.0542 +0.0048 pg " 24147.2980 -37734 -0.0555 +0.0032 pg Schilt (1925) 34222.5660 -18038 -0.0026 -0.0047 pe Cillie and Lindsay (1958) 34991.4463 -16536 -0.0002 -0.0040 pe " 35014.4661 -16491 -0.0006 -0.0045 pe " 35030.3257 -16460 +0.0005 -0.0034 pe " 35031.3501 -16458 +0.0018 -0.0021 pe " 38621.5180 - 9440 +0.0270 +0.0204 pg Bamberg 38641.4470 - 9401 +0.0051 -0.0015 pg " 38701.3030 - 9284 +0.0084 +0.0018 pg " 38721.2650 - 9245 +0.0194 +0.0129 pg " 38722.2650 - 9243 -0.0037 -0.0103 pg " 40469.7610 - 5827 -0.0038 -0.0083 pg " 40509.6570 - 5749 -0.0096 -0.0141 pg " 40555.2860 - 5660 +0.0904 vis Diethelm and Locher (1970) 40572.0620 - 5627 -0.0152 -0.0195 pg Bamberg 41580.4620 - 3656 +0.0960 vis Locher (1972) 41623.3901 - 3572 +0.0529 vis " 41624.4160 - 3570 +0.0556 vis " 41987.5718 - 2860 +0.0024 +0.0013 pe Clausen and Gronbech (1976) 41989.6177 - 2856 +0.0020 +0.0010 pe " 42415.2470 - 2024 +0.0117 vis Locher (1975) 42417.3020 - 2020 +0.0204 vis " 43143.2150 - 601 +0.0268 vis Locher (1977) 43450.6352 0 -0.0018 +0.0020 pe this paper [FIGURE 2] Fig. 2. O-C diagram of RT Scl. The quadratic ephemeris is also indicated. Open circles represent photographic, filled circles photoelectric, and dots visual minima. The O-C diagram is shown in Fig. 2. It is noted that the visual minima deviate strongly, especially the early ones, while nearly simultaneous photographic minima confirm the period variation obtained from the photoelectric data. Thus it must be stated that at least the early visual minimum times must be grossly in error. The O-C diagram thus does not show dramatic irregularities of the period, but merely a continuous decrease of the length of the period. A thorough period study, taking into account also the early observations, was published by Cillie and Lindsay (1958). They proposed the introduction of a quadratic term into the ephemeris to represent the minimum times between 1891 and 1954. The photoelectric minimum times obtained between 1952 and 1977 are also not well represented by a linear ephemeris. Thus we have introduced a new quadratic term. Surprisingly it differs only by about 10% from the one derived from the early minima. We propose therefore that a general quadratic term really exists which is determined from all observed minimum times of good quality (with proper weighting): J. P.hel. (prim. min. ) = 2 443 450.6332 + (0. 51156012 - 9. 04 * 10^-11 E ) E +/-.0037 +/-.00000034 +/-.53 This ephemeris might be suited to describe future minimum times with some confidence. It should be noted that this ephemeris cannot describe the "fine structure" of period variations, which are certainly superimposed on the general trend, but are difficult to determine because of the scarcity of data of high precision. We only want to draw attention to this star whose period, like that of SV Cen, is continuously decreasing in a roughly predictable way. Acknowledgements. Observations were collected at the European Southern Observatory, La Silla, Chile. We thank Professor J. Rahe, Bamberg, for his invitation to use the Remeis Observatory plate collection, and for his hospitality. M.T.K. also thanks the Alexander von Humboldt - Stiftung, Bonn- Bad Godesberg, for financial support of his work. H. W. DUERBECK and M. T. KARIMIE Observatorium Hoher List der Universitats-Sternwarte Bonn D - 5568 Daun Federal Republic of Germany References: Cillie, G.G., Lindsay, E.M., Mon. Not. R. astr. Soc. 118, 585 (1958) [BIBCODE 1958MNRAS.118..585C ] Clausen, J.V., Gronbech, B., Astr. Astrophys. Suppl. Ser. 28, 389 (1977) [BIBCODE 1977A&AS...28..389C ] Diethelm, R., Locher, K., Orion 28, 22 (1970) [BIBCODE 1970Orion..28...21D ] Dugan, R.S., Princeton Univ. Obs. Contr. 8 (1928) [BIBCODE 1928CoPri...8....1D ] Locher, K., BBSAG 5 (1972) Locher, K., BBSAG 6 (1973) Locher, K., BBSAG 20 (1975) Pickering, E.C., Whiteside, I., Harvard Circ. 139 (1908) [BIBCODE 1908HarCi.139....1W ] Schilt, F., Bull. astr. Inst. Netherl. 3, 63 (1925) [BIBCODE 1925BAN.....3...63S ]