COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3606 Konkoly Observatory Budapest 20 May 1991 HU ISSN 0374 - 0676 A FURTHER PROOF ON THE BINARY MODEL OF HD 94033 HD 94033 was discovered by Przybylski and Bessell (1979) as a dwarf Cepheid with a pulsation period of 86 min. We have observed 23 times of light maximum with the 60cm reflector at Xinglong station of Beijing Observatory from 1981 to 1991. Additionally, we collected 67 times of light maximum from the literature (Hobart et al., 1985; McNamara, 1985; McNamara et al., 1985). Combined with the 90 data, we have done some analysis of the period and noticed that the O-C values exhibit regular variation with a long period of about 9 years. New data provided here enable the periodicity to be repeated twice, and the analysis indicates that the growth rate of pulsation period is bigger than that in the literature (Yang Xiabing et al., 1985). Table I gives the heliocentric epochs of maximum of HD 94033. Column 2 is the cycle number of each maximum, column 3 and 4 are the residual values computed with the parabolic equation and the binary model respectively. After a least squares fit for all the times of maximum by following equation, T_max = T_0 + P_0E + 0.5 beta E^2 and substracting this parabola, we get Figure 1 showing how O-Cs vary with cycle number E. It is very clear that the new observation supports the hypothesis of binary model suggested by Jiang Shiyang (1986). According to the light travel time effect in binary model, we use another (as following) formula to fit the times of maximum again. T_max = T_0 + P_0E + 0.5 beta E^2 + A sin phi + D cos phi + C where phi = 2 pi f (T-tau) + e sin phi a sin i A = ------- sqrt(1-e^2) cos omega c a sin i B = ------- sin omega c Table I. Time of light maximum for HD99033 T max E (O-C)p (O-C) T max E (O-C)p (O-C) HJD2440000.+ day day HJD2440000.+ day day 2516.1585 0 0.0027 -0.0001 5751.7243 54369 0.0044 0.0003 2517.9439 30 0.0029 0.0000 5769.7564 54672 0.0046 0.0005 2518.0034 31 0.0028 0.0001 5769.8158 54673 0.0045 0.0006 2518.1223 33 0.0027 0.0001 5769.8750 54674 0.0041 0.0002 2541.9266 433 0.0025 0.0000 5770.6479 54687 0.0034 -0.0005 2541.9859 434 0.0024 -0.0002 5770.7077 54688 0.0037 -0.0005 2542.0448 435 0.0017 -0.0009 5770.7674 54689 0.0039 0.0001 2542.1044 436 0.0019 -0.0006 5776.7185 54789 0.0038 -0.0003 2542.8787 449 0.0025 -0.0000 5777.6699 54805 0.0031 -0.0008 2542.9382 450 0.0025 0.0000 5777.7303 54806 0.0039 0.0002 2542.9973 451 0.0021 -0.0004 5782.6699 54889 0.0041 0.0003 2543.8903 466 0.0024 0.0000 5782.7294 54890 0.0041 0.0003 2544.0094 468 0.0025 -0.0001 5782.7890 54891 0.0042 0.0004 2545.9137 500 0.0025 0.0001 5782.8485 54892 0.0042 0.0004 2545.9729 501 0.0021 -0.0003 5783.6812 54906 0.0037 -0.0002 2562.9930 787 0.0021 -0.0003 5783.7410 54907 0.0040 0.0003 2755.2111 4017 -0.0006 -0.0006 5783.8000 54908 0.0035 -0.0006 2846.9767 5559 -0.0010 0.0003 5784.6935 54923 0.0043 0.0003 2847.0958 5561 -0.0009 0.0005 5784.7527 54924 0.0040 0.0004 2847.1550 5562 -0.0012 0.0000 5784.8125 54925 0.0043 0.0004 2890.0628 6283 -0.0009 0.0008 5792.6660 55057 0.0023 -0.0014 2890.9553 6298 -0.0011 0.0007 5793.2037 55066 0.0044 0.0005 2891.9664 6315 -0.0016 0.0000 5793.2629 55067 0.0041 0.0001 2929.9939 6954 -0.0017 0.0004 5793.6792 55074 0.0038 0.0000 2958.9161 7440 -0.0019 0.0005 5795.0488 55097 0.0047 0.0009 3601.6931 18241 -0.0094 0.0009 5795.1073 55098 0.0037 -0.0000 3604.6688 18291 -0.0043 0.0009 5795.1670 55099 0.0038 0.0000 4664.2720 36096 0.0021 0.0004 5795.6431 55107 0.0038 0.0000 4690.0997 36530 0.0019 -0.0001 5796.0606 55114 0.0047 0.0009 4690.1593 36531 0.0020 -0.0000 5796.1194 55115 0.0040 0.0005 4691.1109 36547 0.0014 -0.0006 5796.1793 55116 0.0044 0.0006 4691.1705 36548 0.0015 -0.0005 5798.6785 55158 0.0041 0.0006 5383.2904 48178 0.0051 -0.0001 5800.6422 55191 0.0040 0.0001 5384.1834 48193 0.0055 0.0003 5808.6168 55325 0.0041 0.0003 5384.2430 48194 0.0056 0.0003 5808.6761 55326 0.0038 0.0004 5748.7479 54319 0.0036 -0.0004 5808.7358 56327 0.0040 0.0004 5748.8081 54320 0.0043 0.0001 5854.4989 56096 0.0029 -0.0002 5748.8671 54321 0.0038 -0.0003 5856.4620 56129 0.0021 -0.0012 5748.9278 54322 0.0049 0.0007 6153.0652 61113 0.0006 0.0006 5748.9861 54323 0.0037 -0.0002 6153.1298 61114 0.0007 0.0012 5749.9861 59336 0.0048 0.0006 6501.2014 66963 -0.0049 -0.0012 5749.8199 54337 0.0044 0.0002 6503.1650 66996 -0.0052 -0.0012 5749.8795 54338 0.0045 0.0002 6503.2248 66997 -0.0049 -0.0011 5749.9387 54339 0.0041 -0.0002 6889.1548 73482 -0.0067 -0.0013 5750.9503 54356 0.0041 -0.0002 8398.1510 97998 0.0047 -0.0012 [FIGURE 1] a sin i C= - ------- e sin omega c where phi, f, tau, e, c, a sin i, omega are the eccentric anomaly, orbital frequency, time of periastron passage, eccentricity, velocity of light, projected semimajor axis and longitude of the periastron passage in the plane of the orbit respectively. The least squares fit yields the following pulsational and orbital elements of HD 94033. T_o = H.J.D. 2442516.15576 +- 0.0003 P_o = 0.059511036 +- 0.00000017 day beta = (2.92+-0.18) x 10^-12 f = 0.0002956 +- 0.0000036 /day; or: P_b = 33829.5 +- 41.2 day a sin i=(1.43+-0.17)*10^8km=0.95+-0.11 A.U. e = 0.2 tau = H.J.D. 2442708.4 omega=175deg The solid line constructed in Figure 1 was determined by the above 8 factors. Here, we would like to make some explanation. From Figure I we can see that e is relatively small, and it is difficult to determine omega, tau exactly with fewer data, we can only regard the above 3 values as reference. The further proof about binary model on HD 94033 needs more photometry, and a better method is to obtain spectral information. LIU YANYING, JIANG SHIYANG Beijing Astronomical Observatory Chinese Academy of Sciences CAO MING Shanxi Astronomical Observatory Chinese Academy of Sciences References: Hobart, M.A. et al.: 1985, Rev. Mex. Astron. Astrofis., 11, 19. [BIBCODE 1985RMxAA..11...19H ] Jiang Shiyang: 1986, Ke Xue Tong Bao, 21, 1642. McNamara, D.H.: 1985, P.A.S.P., 97, 715. [BIBCODE 1985PASP...97..715M ] McNamara, D.H. et al.: 1985, P.A.S.P., 97, 322. [BIBCODE 1985PASP...97..322M ] Przybylski, A., Bessell, M.S.: 1979, M.N.R.A.S., 189, 377. [BIBCODE 1979MNRAS.189..377P ] Yang Xiabing et al.: 1985, Acta Astrophysica Sinica, 5, 192. [BIBCODE 1985AcApS...5..192Y ]