COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1172 Konkoly Observatory Budapest 1976 September 6 ON THE LIGHT CURVE AND PERIOD OF V743 Cen During test runs of the newly installed double beam photometer at the 50 cm ESO photometric telescope the delta Scuti- or RR_S-star V743 Cen was continuously monitored on the nights April 18/19 and 19/20, 1976 in U,B,V. The photometer is identical to the Hoher List Observatory instrument, which was described by Geyer and Hoffmann (Mitt.Astron.Gesellschaft No. 35, 209, 1974; Astron.& Astrophys. 38, 359, 1975). The photometer allows the simultaneous photometric observations of the variable and a comparison star within the field of the telescope with fairly high time resolution. Data acquisition and preliminary on-line reductions are done with a HP 2100 computer system. On each night four consecutive cycles of the stars have been covered with an average of about 70 individual observations per cycle and colour. The photometric accuracy is about +-0.003m in all colours. As was already noticed by Kwan-Yu Chen (I.B.V.S. No. 142, 1966) and C.R. Chambliss (Mon.Not.R.astr.Soc. 138, 437, 1968) the amplitudes of the B-light curves are quite small, and are less than 0.3m, which is conform with the present observations. Yet the amplitude variations are much larger, and also the shape variations of the light curve from one cycle to the next are much more pronounced than was anticipated by Chambliss. Both the maximum and minimum brightness, as well as the average brightness vary about 0.05 magnitudes. The following amplitude variations have been observed: A_V from 0.135m to 0.188m; A_B from 0.192m to 0.272m, and A_U from 0.180m to 0.248m. In general these light curve changes resemble more the well known Blazko- effect than a beat period phenomenon. The maxima times of the U-,B-, V-light curve cycles were derived by using Pogson's method. Since there no colour dependent lag in the maxima times was found, the mean time instants for the three colours are given in the Table below. They are accurate to at least +-0.0007d. Also listed are the maxima of Chen as given by Chambliss, those of Chambliss himself and by D.H.P. Jones (Mem.R.Astr.Soc. 72, 101, 1969). Since the period is so short, and about 9 years have elapsed between the latter observations and the previous ones it was not possible to establish the epoch number from the light elements given by Jones. Therefore the following linear light elements have been obtained with a least square solution and a "period finding program" written for a HP 9820 computer, assuming that no period change exceeding more than 6% of the period has taken place: Max.= J.D.hel.2439243.6436+0.102254d E. The period seems to be constant within +-5*10^-6 days. The "noise" of the cycle length of the 1976 observations is +-1.92%. This explains the difficulties of Chambliss to reconcile his and Chen's observations. Chambliss has classified V743 Cen as a delta Scuti star on account of its small light curve amplitude. The strong Blazko-effect as well as the period noise makes us believe to see in it an RR_S type star. Table Maxima of V743 Cen Observer Maxima J.D.hel. E O-C 2400000+ Chen 39243.6433 0 -0.0003d " 39243.7455 1 - .0003 " 39243.8520 2 .0039 " 39244.5642 9 .0004 " 39244.6660 10 - .0001 " 39244.7687 11 .0003 " 39244.8765 12 .0059 Jones 39594.474 3431 - .0042 " 39603.380 3518 .0056 Chambliss 39634.1525 3819 - .0004 " 39635.0740 3828 .0008 " 39636.0968 3838 .0010 " 39637.9335 3856 - .0028 " 39638.1368 3858 - .0041 " 39638.9520 3866 - .0069 Geyer/Vogt 42886.8633 35629 - .0006 " " 42887.6844 35637 .0025 " " 42887.7859 35638 .0017 " " 42887.8878 35639 .0014 " " 42888.6000 35646 - .0022 " " 42888.7014 35647 - .0031 " " 42888.8073 35648 .0006 " " 42888.9100 35649 .0010 Acknowledgement: The computations were performed on a HP 9820 calculator of the Deutsche Forschungsgemeinschaft (grant Schm. 167/12). The observations have been collected at the European Southern Observatory, La Silla, Chile. E.H. GEYER N. VOGT Astron. Institute der European Southern Universitat Bonn Observatory Observatorium Hoher List