COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2743 Konkoly Observatory Budapest 10 June 1985 HU ISSN 0374 - 0676 BV PHOTOMETRY AND PERIOD VARIATION OF GO CYGNI The variability of GO Cyg (=HD 196628 = BD + 34deg4095) was discovered photographically by Schneller (1928). The star was classified as a short- period eclipsing binary by Kukarkin (1929). The first light elements were given by Szczyrbak (1932) considering the system to be of Algol type as follows: Min.I = JD Hel. 2426509.467 + 0.717767d.E. (1) The visual observations made by Kukarkin (1932) from 1929 to 1931 showed a beta Lyrae type variation. From the visual and photographic observations, several authors have found contradictory results about the shape of the light curve and the eccentricity of the orbit (see Ovenden, 1954). The only published spectrographic observation of the system was made by Pearce (1933). The complete two-colour photoelectric photometry of the star was made by Ovenden (1954), and Mannino (1963) who also analyzed their light curves. The period variation of the system was discussed by Purgathofer and Prochazka (1967) collecting all of the published minima in the literature. Using the recent photoelectric times of primary minima, they gave the following linear light elements: Min.I = JD Hel. 2433930.40561 + 0.71776382d.E. (2) Assuming a parabolic O-C variation for all minima they also suggested the following quadratic light elements: Min.I = JD Hel. 2433930.40614 + 0.71776314d.E + 0.108.10^-9d.E^2. (3) The system was observed photoelectrically at the Ege University Observatory on eight nights during the summer of 1984. The observations were made in yellow and blue colours using a 48 cm Cassegrain telescope and a photoelectric photometer equipped with an unrefrigerated photomultiplier tube EMI 9781A and Johnson's standard B, V filters. A total of 398 individual points were obtained in each colour. BD + 35deg4180 was used as the comparison and BD + 34deg4098 as the check star. No evidence for the variability of the comparison star was found. The extinction coefficients determined night by night were applied in the correction for differential extinction. During the observations three primary and two secondary minimum times were obtained. These minima are given in Table I together with all of the other published ones. Table I. Times of minima of GO Cygni. JD Hel. Min Method B (O-C)1 (O-C)2 Ref. 2425556.99 I pg -11666 0.02 0.00 1 864.905 I vis -11237 0.011 -0.009 2 26112.539 I vis -10892 0.017 -0.002 3 120.424 I pg -10881 0.007 -0.013 4 509.467 I vis -10339 0.022 0.009 5 540.327 I vis -10296 0.018 0.000 2 711.145 I vis -10058 0.008 -0.009 6 957.355 I vis -9715 0.025 0.009 7 27058.553 I vis -9574 0.018 0.003 8 140.3745 I pg -9460 0.0146 -0.0007 8 325.561 I vis -9202 0.018 0.003 8 330.589 I pg -9195 0.022 0.007 9 417.433 I vis -9074 0.016 0.002 8 28035.431 I vis -8213 0.020 0.007 10 398.612 I vis -7707 0.012 0.001 11 418.708 I vis -7679 0.011 0.000 11 797.688 I vis -7151 0.011 0.002 11 807.744 I vis -7137 0.019 0.009 11 823.529 I vis -7115 0.013 0.003 11 838.604 I vis -7094 0.015 0.005 11 33111.4392 I pe -1141 0.0021 0.0010 12 483.9573 I pe -622 0.0008 0.0000 13 496.8783 I pe -604 0.0020 0.0013 14 539.944 I pg -544 0.002 0.001 15 861.499 I pe -96 -0.001 -0.002 16 930.40600 I pe 0 0.00039 0.00000 17 34309.38563 I pe 528 0.00072 0.00057 17 516.818 I pe 817 -0.001 -0.001 18 606.53982 I pe 942 0.00069 0.00068 17 923.786 I pg 1384 -0.005 -0.005 19 36782.442 II pe 3973.5 0.002 0.002 20 37106.5092 I pe(V) 4425 -0.0013 -0.0017 20 106.5116 I pe(B) 4425 0.0011 0.0007 20 147.42258 I pe 4482 -0.00047 -0.00085 21 189.41700 II pe 4540.5 0.00477 0.00436 21 882.4140 I pe 5506 0.0008 -0.0002 20 887.4377 I pe 5513 0.0002 -0.0009 20 888.516 II pe 5514.5 0.002 0.001 20 910.4056 I pe 5545 -0.0009 -0.0014 20 45866.4836 II pe(B,V) 16629.5 0.0245 0.0014 22 874.376 II pe(B,V) 16640.5 0.022 -0.002 22 954.4082 I pe(B,V) 16752 0.0231 -0.0005 22 972.3535 I pe(V) 16777 0.0243 0.0006 22 972.3528 I pe(B) 16777 0.0236 -0.0001 22 982.4010 I pe(B,V) 16791 0.0231 -0.0006 22 References to Table I 1. Schneller, H.: 1928, Astron.Nachr. 235, 85. 2. Kukarkin, B.W.: 1932, VS 4, 1, 19. 3. Beyer, M.: 1936, Astron.Nachr. 258, 273. 4. Iwanowska, W. and Dziewulski, W.: 1932, Wilno Bull. 13, 30. 5. Szczyrbak, S.: 1932, SAC 10, 44. 6. Kordylewski, K.: 1933, AAc 2, 48. 7. Warmbier, E.: 1938, AAc 3, 95. 8, Dziewulski, W.: 1936, Wilno Bull. Tome II, 6. 9. Liau, S.P.: 1935, Publ. Lyon 1, Fasc. 13. 10. Micaika, G.R.: 1939, BZ 21, 78. 11. Pierce, N.L.: 1939, Astron.J. 48, 113. 12. Piotrowski, S.L. and Strzalkowski, A.: 1951, AA 4, 129 13. Szafraniec, R.: 1962, AA 12, 181. 14. Popper, D.M.: 1957, Astrophys.J.Suppl. III, 107. 15, Kaho, S.: 1952, Tokyo Astr.Bull. Ser. II, No. 49. 16. Ovenden, M.W.: 1954, MN 114, 569. 17, Kwee, K.K.: 1958, BAN 14, 131. 18. Fitch, W.S.: 1964, Astron.J. 69, 316. 19. Koch, J.C. and Koch, R.N.: 1962, Astron.J. 67, 462. 20. Mannino, G.: 1963, Publ. Bologna 8, No. 15. 21, Purgathofer, A. and Widorn, Th.: 1964, Mitt.Univ.-Sternw.Wien 12, 31. 22. This paper. [FIGURE 1] Figure 1: O-C diagram of GO Cygni. The dots, circles, plusses and crosses denote photoelectric MinI, photoelectric MinII, photographic and visual MinI, respectively. The dashed line represents the computed parabola. The (O-C)1 residuals in the table were computed using Equation (2) and plotted in Figure 1 versus E. As it is seen from the figure, the distribution of the (O-C)1 residuals seems to be a parabola. Using the two photographic and 23 photoelectric times of minima obtained after JD 2433000, the new quadratic light elements, Min.I = JD Hel. 2433930.4060 + 0.71776331d.E + 0.113.10^(-9)d E^2 (4) +/-5 +/-22 +/-12 have been derived by the least squares method. The (O-C)2 values in the table are the differences between observations and calculations with these new light elements. Although the old visual and photographic observations are not taken into account in the computations because of their large scattering, they fit well to the parabolic curve. The parabolic curve has a minimum at about JD 2435600 (E ~= 2300) and after this epoch the period is increasing. The increase in the period of the system is found to be about 0.99+/-0.11 second per century. [FIGURE 2] Figure 2: The light and colour curves of GO Cygni. The light and colour curves of GO Cygni are shown in Figure 2 where the phases have been calculated with the following linear light elements: Min.I = JD Hel. 2445865.4056 + 0.71776707d.E. These light elements have been obtained from the Equation (4) reducing the epoch and the period to June 13, 1984 and may be used in the near future. The shape of the light curve is typical of beta Lyrae type. There is no asymmetry in the minima and no displacement in the secondary minimum, and the maxima are equal. The amplitudes are about 0.600mag and 0.580mag at the primary, 0.230mag and 0.240mag at the secondary minimum in the blue and yellow light, respectively. The system is slightly redder at the primary and bluer at the secondary minimum which is consistent with the spectral types of the components given by Pearce (1933). C. SEZER, O. GULMEN and N. GUDUR Ege University Observatory Campus P. K. 21 Bornova, Izmir- Turkey References: Kukarkin, B.W.: 1929, N.N.V.S., 2, 26. Kukarkin, B.W.: 1932, ibid 4, 19 Mannino, G.: 1953, Publ.Univ.Bologna, Vol. 8, No. 15. Ovenden, M.W.: 1954, Monthly Notices Roy. Astron.Soc., 114, 569. [BIBCODE 1954MNRAS.114..569O ] Pearce, J.A.: 1933, J.R. Astron.Soc.Canada 27, 62. [BIBCODE 1933JRASC..27...62P ] Purgathofer, A. and Prochazka, F.: 1967, Mitt.Univ.-Sternw.Wien, 13, 151. Schneller, H.: 1928, Astron.Nachr. 235, 85. [BIBCODE 1929AN....235...85S ] Szczyrbak, S.: 1932, S.A.C., 10, 44