COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1174 Konkoly Observatory Budapest 1976 September 7 EVIDENCE FOR A PERIOD CHANGE IN THE ECLIPSING BINARY RY Gem * Two epochs of minimum light of the eclipsing binary RY Gem were determined during winter of 1975-76 by means of a series of observations carried out with the 45 cm reflector of the Astronomical Observatory of Torino. We used a photoelectric photometer equipped with a photomultiplier EMI 6256 S and a V filter. All the times of minimum light we could find in the literature are collected in Table 1. The epoch No.11 was evaluated by the authors using the time of end of totality, given by McKellar (1951) with an uncertainty of 0.007d, and the duration of totality (5.26h) was estimated from our primary minimum. Assuming the linear ephemeris: 1) Min_I (Hel.) =2427483.642 + 9.300706d E we derived the (O-C)_1 (see Table 1) of all the listed epochs of primary minimum. These residuals are plotted in Figure 1. It is seen at once that this representation is not satisfactory; it seems more advantageous to consider the epochs before and after about E=+600 separately. A linear ephemeris suggests itself for each group (from now on "labelled" A and B for E<+600 and E>+600, respectively). In the analysis normal minima were used; two of them, nos. 4 and 5 (see Table 2), were given by Lause (1936) but the minima nos. 2, 3,7,8 were calculated by the writers. The weights were assigned inversely proportional to the square of the estimated error. A least- square treatment for the two groups has led to the formulae: A) Min_I(Hel.) = 2427827.7580 + 9.300876d E +-. 14 +-. 6 B) Min_I(Hel.) = 2442792.5190 + 9.300526d E +-. 3 * During the draft of this note, we read in Acta Astronomica (1976, 26, 109) that a similar study had been made by D.S. Hall and T. Stuhlinger. The conclusions about a period change and the deduced periods are in excellent agreement with ours. The period seems to have undergone a rather drastic change even if a large observational error in the epoch No. 11 of Table 1 could conceal a rapid but continuous change in a short time interval. Table 1 Individual observed minima of RY Gem No. J.D. Hel. E (O-C)_1 Observer 1 2418015.32 -1018 -0.20 Blazko 2 23800.484 - 396 -0.078 Beyer 3 24628.262 - 307 -0.063 Beyer 4 27483.642 0 0.000 Lause 5 27827.744 + 37 -0.024 Lause 6 27874.265 + 42 -0.007 Lause 7 27883.563 + 43 -0.009 Lause 8 28106.772 + 67 -0.017 Lause 9 28209.090 + 78 -0.007 Lause 10 28246.300 + 82 0.000 Lause 11 32245.67 + 512 +0.07 McKellar 12 38681.700 +1204 -0.008 Kumsiashvili 13 38700.285 +1206 -0.008 Kumsiashvili 14 38737.485 +1210 -0.011 Kumsiashvili 15 38765.385 +1213 -0.013 Kumsiashvili 16 39416.385 +1283 -0.063 Kumsiashvili 17 39593.100 +1302 -0.061 Kumsiashvili 18 39769.900 +1321 +0.025 Kumsiashvili 19 39779.150 +1322 -0.025 Kumsiashvili 20 42792.521 +1646 -0.083 Present work 21 42820.419 +1649 -0.087 Present work Table 2 Normal minima of RY Gem No. J.D. Hel. W E_A (O-C)_A Observer 1 2418015.32+-0.02 0.5 -1055 -0.014 Blazko 2 23800.484+-0.010 1 - 433 +0.005 Beyer 3 24628.262+-0.010 1 - 344 +0.005 Beyer 4 A 27827.7615+-0.0041 6 0 +0.004 Lause 5 28209.0912+-0.0034 8 + 41 -0.003 Lause 6 32245.67+-0.01 1 + 475 -0.004 McKellar E_B (O-C)_B 7 2438700.288+-0.008 2 - 440 0.000 Kumsiashvili 8 B 39593.131+-0.038 0.1 - 344 -0.007 Kumsiashvili 9 42792.519+-0.003 11 0 0.000 Present work Table 2 summarizes the obtained results. The columns give: the normal minima with their estimated errors, the weights, the number of cycles EA and EB elapsed from the epochs nos.4 and 9, respectively, the (O-C)_A and (O-C)_B relative to the ephemeris A) and B),the observer. [FIGURE 1] Figure 1 - (O-C)'s of the observed epochs of primary minimum of RY Gem according to the ephemeris 1) (see text). M. CERRUTI-SOLA, L. LORENZI and F. SCALTRITI Osservatorio Astronomico di Torino 10025 Pino Torinese, Italia. References: Beyer, M. 1928 Astron. Nachr., 234, 85 [BIBCODE 1928AN....234...85B ] Blazko, S. 1908 Astron. Nachr., 178, 164 [BIBCODE 1908AN....178..163B ] Kumsiashvili, M.I. 1968 Astron.Circ.Acad.Sci.USSR, No. 499, 4 [BIBCODE 1969ATsir.499....4K ] Lause, F. 1936 Astron. Nachr. 260, 289 [BIBCODE 1936AN....260..289L ] McKellar, A. 1951 Publ.Dom.Astroph.Obs.Victoria D.C., 8, 235 [BIBCODE 1949PDAO....8..235M ]