COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 4078 Konkoly Observatory Budapest 1 September 1994 HU ISSN 0374 - 0676 NEW PERIOD AND PERIOD CHANGE OF EU HYDRAE The eclipsing binary EU Hya was observed with the photoelectric photometer attached to the 60 cm reflecting telescope in BV bands at Yunnan Observatory during February to March, 1991. HD 74332 and HD 74309 were used as comparison and check stars, respectively. From our observations three primary minimum times were determined, which are listed in Table 1 (the last three minima). We have collected all minimum times which could be found to calculate the new ephemeris formula Min.I.=JD(hel.)2448323.1732+0.77820650d x E (1) +/-27 +/-35 by means of the least squares method. This ephemeris was used in calculating the (O-C)I values in the Table, using these (O-C)I values we derived the O-C diagram displayed in Figure 1. In Figure 1 a systematic trend is seen: the period became shorter continuously. In order to determine the rate of period change, all the minimum times were introduced into a quadratic least squares solution which resulted in: MinI=JD(hel.)2448323.1676+0.77820374dxE-1.99dx10^-10xE2 (2) +/-20 +/-50 +/-32 and the rate of period change: dP/dE=-3.98dx10^-10. With this ephemeris we computed the (O-C)II values in Table 1 which is shown in Figure 2. Comparing Figures 1 and 2 the quadratic ephemeris has smaller deviation than the linear one, this point could also be seen from the sums of weighted square of the deviations: Summa_i W^2_(O-C)I_i = 0.0269, Summa_i W^2_(O-C)II_i = 0.0118 [FIGURE 1] Figure 1. The O-C diagram of the linear ephemeris, the smooth curve represents the quadratic fit. [FIGURE 2] Figure 2. The O-C diagram of the quadratic ephemeris. Table 1. JD(Hel.) E (O-C)I (O-C)II Weight Source 24000000+ 30470.3100 -22941 -0.0278 0.0190 3 K 34126.3360 -18243 -0.0160 0.0054 3 K 35862.4970 -16012 -0.0337 -0.0214 3 B 35876.5250 -15994 -0.0134 -0.0012 3 K 37403.3510 -14032 -0.0286 -0.0226 3 B 37669.5030 -13690 -0.0232 -0.0182 3 B 38321.6660 -12852 0.0028 0.0057 3 B 38449.2850 -12688 -0.0041 -0.0016 1 K 38473.3830 -12657 -0.0305 -0.0280 3 B 38852.3980 -12170 -0.0021 -0.0007 3 B 39507.6400 -11328 -0.0100 -0.0101 3 B 39536.4580 -11291 0.0144 0.0142 3 B 39915.4240 -10804 -0.0062 -0.0072 3 B 40290.5140 -10322 -0.0117 -0.0134 1 D 40319.3130 -10285 -0.0063 -0.0081 1 D 40319.3220 -10285 0.0027 0.0009 1 L 40319.3430 -10285 0.0237 0.0219 3 B 40322.4120 -10281 -0.0202 -0.0219 1 L 40322.4260 -10281 -0.0062 -0.0079 1 D 40326.3350 -10276 0.0118 0.0100 3 B 41410.3680 -8883 0.0031 -0.0001 1 P 42010.3660 -8112 0.0039 0.0002 30 K2 42045.3850 -8067 0.0036 -0.0001 30 K2 42080.4070 -8022 0.0063 0.0026 30 K2 42081.1850 -8021 0.0061 0.0024 30 K2 42838.3850 -7048 0.0112 0.0072 1 P 42866.3990 -7012 0.0098 0.0058 1 P 43161.3330 -6633 0.0035 -0.0004 30 K2 43189.3510 -6597 0.0061 0.0021 1 P 43196.3530 -6588 0.0042 0.0003 30 K2 43197.1330 -6587 0.0060 0.0021 30 K2 48298.2635 -32 -0.0071 -0.0015 30 G 48323.1672 0 -0.0060 -0.0004 30 G 48334.0619 14 -0.0062 -0.0005 30 G K=Kordylewski; B=Busch; D=Diethelm; L=Locher; P=Peter; K2=Kulkarni; G=Gu In all above calculations we assigned weight 1 to visual minimum times, weight 3 to the photographic minimum times and weight 30 to photoelectric minimum times. GU SHENGHONG Yunnan Observatory Academia Sinica Kunming, China References: Busch, H., 1972, IBVS, No. 639 Diethelm, R. and Locher, K., 1969, Orion, 14, 112, 81 Diethelm, R. and Locher, K., 1969, Orion, 14, 113, 109 Kordylewski, K., 1947, Roczn. Astr. Obs. Krakov, 18 Kordylewski, K., 1953, Roczn. Astr. Obs. Krakov, 24 Kordylewski, K., 1958, Roczn. Astr. Obs. Krakov, 29 Kordylewski, K., 1964, IBVS, No. 46 Kulkarni, A. G., 1978, Contrib. Nizamiah Japal-Rangapur Obs., No. 7 Peter, H., 1972, BBSAG Bulletin, No. 3, List 36 Peter, H., 1976, BBSAG Bulletin, No. 26, List 59 Peter, H., 1976, BBSAG Bulletin, No. 27, List 60 Peter, H., 1977, BBSAG Bulletin, No. 32, List 65