COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1379 Konkoly Observatory Budapest 1978 January 9 TIMES OF MINIMA OF ECLIPSING VARIABLES This bulletin lists times of minima determined at this observatory in 1973, 1974, 1975 and 1976. The equipment was the same as used for the minima listed by us in IBVS 844, 1973. However, in 1974 the d.c. output of the photometer was replaced by a photon counter designed and built by J.R. Stilborn, and all subsequent observations have been obtained with this new system. The computer programme for reduction by the method of Kwee and van Woerden (BAN 12, 327, 1956) was modified by one of us (D.J. B.) to use the digital output data directly and to calculate and print out magnitude differences in the process of determining the times of minima. The ephemerides used to calculate O-C were the same as those used in IBVS 844 for the stars 44i Boo, VW Cep, MR Cyg, AI Dra, Z Her, RX Her, U Oph, and U Sge. Ephemerides for the other stars are given in Table 2. Some remarks on individual systems follow the tables. Table 1. Observed Times of Minima. Star H.J.D. E O-C Observer (2,440,000+) (days) OO Aql 2986.8086+-0.0003 4200 +-0.0130 S 44i Boo 1900.7444+-0.0005 12648 +-0.0131 B 2196.8176+-0.0004 13753.5 +-0.0176 S 2218.7782+-0.0005 13835.5 +-0.0175 B 2228.8212+-0.0003 13873 +-0.0174 B 2635.7667+-0.0006 15392.5 +-0.0191 B 2947.7702+-0.0008 16557.5 +-0.0189 R Table 1. Observed Times of Minima, (Cont.) Star H.J.D. E O-C Observer (2,440,000+) (days) ZZ Boo 2551.8384+-0.0004 798.5 +0.0116 S RZ Cas 2266.8220+-0.0001 10367 +0.0030 B 3001.8946+-0.0002 10982 -0.0014 B 3019.8240+-0.0004 10997 -0.0008 B TV Cas 1919.8125+-0.0004 5016 -0.0049 S VW Cep 1895.8309+-0.0004 9095 +0.0098 B 2198.7773+-0.0007 10183.5 +0.0116 S 2256.8019+-0.0002 10392 +0.0078 S 2268.7702+-0.0002 10435 +0.0086 S 2269.7467+-0.0006 10438.5 +0.0110 B 2290.7587+-0.0006 10514 +0.0103 B 2290.8973+-0.0005 10514.5 +0.0098 B 2557.8039+-0.0003 11473.5 +0.0135 B 2563.7854+-0.0003 11495 +0.0113 B 2977.7824+-0.0003 12982.5 +0.0166: R XX Cep 1894.7619+-0.0016 152 -0.0003 S 2289.7776+-0.0007 321 +0.0107 S MR Cyg 2252.8221+-0.0005 5281 +0.0007 B 2273.7832+-0.0013 5293.5 -0.0012 B AI Dra 1881.8234+-0.0002 3618 +0.0005 B 1890.8109+-0.0010 3625.5 -0.0031 B 2255.8543+-0.0007 3930 +0.0011 S 2270.8314+-0.0012 3942.5 -0.0070: B Z Her 2217.8226+-0.0005 7296 -0.0030 B RX Her 2259.7932+-0.0006 5554.5 +0.0005 S 2267.7942+-0.0004 5559 -0.0020: B 2564.8175+-0.0004 5726 -0.0003 S 3031.6935+-0.0004 5988.5 +0.0006 B TX Her 2226.7781+-0.0003 5778 +0.0002 B 2262.8256+-0.0005 5795.5 +0.0011 S 2570.7668+-0.0004 5945 +0.0008 A 2985.8213+-0.0007 6146.5 +0.0039 R AK Her 2596.8128+-0.0003 9644.5 +0.0016 S AR Lac 2287.8275+-0.0003 1468 -0.0014 B 2288.8215+-0.0007 1468.5 +0.0010 B CM Lac 1893.7814+-0.0003 9265 -0.0003 B 1905.8139+-0.0006 9272.5 -0.0030 B 2636.7537+-0.0002 9728 -0.0001 B 2989.7850+-0.0004 9948 -0.0009 R U Oph 2942.8337+-0.0003 20665.5 -0.0029 B V566 Oph 2215.8078+-0.0002 927.5 -0.0003 B 2216.8320+-0.0003 930 -0.0002 Bl 2241.8201+-0.0003 991 -0.0005 S 2248.7844+-0.0002 1008 -0.0002 S 2265.7848+-0.0003 1049.5 -0.0001 S 2572.8131+-0.0004 1799 -0.0012 A 2581.8262+-0.0002 1821 -0.0003 B 2614.8044+-0.0012 1901.5 +0.0011 B 2938.8340+-0.0003 2692.5 +0.0013 S 2987.7861+-0.0003 2712 +0.0009 R Table 1. Observed Times of Minima, (Cont.) Star H.J.D. E O-C Observer (2440,000+) (days) U Sge 2207.8447+-0.0001 7418 +0.0023 B 2633.8033+-0.0002 7544 +0.0030 B Observers: A= S.B. Alers B= D.J. Barlow Bl= B.W. Baldwin R= J. Regan S= C.D. Scarfe Table 2. Ephemerides Star H.J.D. Period References (2,400,000+) OO Aql 40858.291 0.5067868 Herczeg IBVS 699,1972 ZZ Boo 38565.9192 4.991744 McNamara et al.PASP 83,192,1971 RZ Cas 29875.6902 1.1952473 Herczeg & Frieboes-Conde, A.&Ap. 30, 259, 1974 TV Cas 32827.7665 1.81260983 Frieboes-Conde & Herczeg, A.&Ap. Supp. 12, 1, 1973 XX Cep 41539.4917 2.3373059 Battistini et al.,IBVS 1325, 1977 TX Her 30326.2006 2.05980915 Vetesnik & Papousek, BAC 24, 57, 1978 AK Her 38531.4318 0.42152309 Kurutac & Ibanoglu, IBVS 369, 1969 AR Lac 37376.4979 1.9831955 present work +-5 +-10 CM Lac 27026.3159 1.6046914 Alexander, A.J. 63, 108, 1958 V566 Oph 41835.8617 0.40964569 present work +-3 +-25 Notes on individual systems: 1. OO Aql The trend of recent is to later times than predicted by the ephemeris of Herczeg. 2. ZZ Boo An increase of the period since the observations of McNamara et al. is indicated. 3. RZ Cas Our data and those of Surkova (IBVS 1335, 1977), and Pohl and Kizilirmak (IBVS 1358, 1977) indicate a new change in the period since the observations of Chambliss (PASP 88, 22, 1976). 4. TV Cas Recent minima, including those of Tremko and Bakos (BAC 28, 41, 1977), Grauer et al.(A.J. 82, 740, 1977) and Pohl and Kizilirmak (IBVS 1163, 1976, and IBVS 1358, 1977) leave undecided the question of the nature of the period changes, ie. abrupt as proposed by Grauer et al., sinusoidal as suggested by Frieboes- Conde and Herczeg (A.&.Ap.Supp. 12, 1, 1973), or possibly steady. 5. XX Cep Our data and those of Pohl and Kizilirmak (IBVS 1358, 1977), support the suggestion of Battistini et al. (IBVS 1325, 1977), that an increase in the period may have occurred a few years ago. 6. AR Lac A new ephemeris has been calculated by least-squares from the present minima and those listed in IBVS 201, 456, 817, 873 and 937 and in.A.A. 27, 93, 1977. 7. U Oph Three additional minima are listed by Batten and Scarfe (Revista Mexicana de A. y Ap. 1978, in press). 5.V566 Oph A new ephemeris has been calculated by least-squares using the present minima and those since 1972 given in IBVS 844, 937, and 1053 by Bookmyer (PASP 88, 473, 1976) and by Dawson and Narayanaswamy (PASP 89, 47 1977). The ephemerides given in both of these latter papers give substantial O-C's for the most recent minima. The present ephemeris fits the 1972-76 data nearly as well as that of Bookmyer (A.J. 74, 1197, 1969) fitted the pre-1969 data. The minima in the interval 1969-71 while the period was changing show a very large scatter. C.D. SCARFE and D.J. BARLOW University of Victoria Observatory Victoria, B.C. Canada