COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3161 Konkoly Observatory Budapest 22 March 1988 HU ISSN 0374-0676 PHOTOELECTRIC EPHEMERIS OF THE EARLY-TYPE ECLIPSING BINARY V593 CENTAURI The variability of the eleventh magnitude eclipsing binary V593 Cen (CoD -61d 3721, CPD -61d 3558) was first announced by Shapley and Swope (1940). Van Gent (1948) classified this star as a W UMa-type eclipsing binary and obtained the following ephemeris on the basis of his 19 photographic times of minima. Min I = J.D.hel 2427621.2693 + 0.7553542d E (1) +/-0.0024 +/-0.0000028 E New photoelectric observations of V 593 Cen were carried out with the 154 cm, reflector at the Bosque Alegre Astrophysical Station of the National University of Cordoba (Argentina) during observational seasons from 1984 until 1987. The f/21 Cassegrain reflector was equipped with a conventional design photometer; a 1P21 photomultiplier refrigerated with dry ice and a standard UBV set of filters were used. The measurements were made differentially with respect to the comparison star HD115071, whose spectral type is B1. All the UBV observations have been corrected for first and second order differential extinction. A total of 1165 individual observations in each band which completely cover the light curve were obtained and a preliminary photoelectric analysis of the system was realized (Lapasset et al., 1987). The location of the variable at maximum light in the color-color diagram is consistent with an unreddened main sequence star of spectral type B5. So V593 Cen is a new member of the early- type contact binary group. In this note we present 18 times of minimum determined by means of the bisection-of-chords procedure. A linear least squares solution using our photoelectric data yields the following updated ephemeris: Min I = J.D. hel 2445815.56344 + 0.75535990d E (2) +/-0.00017 +/-0.00000018 The photoelectric minima, the epoch numbers and O-C residuals calculated from the ephemeris given in equation (3) are listed in Table I. As Van Gent (1948) noticed the choice of the primary minimum is somewhat arbitrary because the minima differ only by a few hundredths of a magnitude. Table I Photoelectric times of minimum light of V593 Centauri Min JD Hel. E O-C 2440000.+ I 5815.5634 0.0 -0.00004 I 5815.5639 0.0 0.00046 I 5815.5648 0.0 0.00136 I 6170.5820 470.0 -0.00059 I 6170.5815 470.0 -0.00109 I 6170.5814 470.0 -0.00119 II 6582.6319 1015.5 0.00048 II 6582.6313 1015.5 -0.00012 II 6582.6312 1015.5 -0.00022 II 6613.6019 1056.5 0.00072 II 6613.6017 1056.5 0.00052 II 6613.6002 1056.5 -0.00098 I 6615.4894 1059.0 -0.00018 I 6615.4896 1059.0 -0.00002 I 6615.4899 1059.0 -0.00032 II 6887.7981 1419.5 -0.00127 II 6887.7968 1419.5 -0.00002 II 6887.7961 1419.5 -0.00076 Spectroscopic observations of this system will be carried out in the coming observing season. These observations together with the photoelectric ones will allow us to obtain a simultaneous solution of radial velocity and UBV light curves (Wilson, 1979, Van Hamme and Wilson, 1985). We wish to express our thanks to J. Laborde, J.R. Puerta and J. Ahumada for their assistance during the observations. This work was partially supported by the Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) of Argentina. E. LAPASSET, J.J. CLARIA, M. GOMEZ Observatorio Astronomico Universidad Nacional de Cordoba Laprida 854, 5000 Cordoba Argentina References: Lapasset, E., Gomez, M., and Claria, J.J., 1987, Boletin de la Asociacion Argentina de Astronomia, No. 33, in press. [BIBCODE 1987BAAA...33..301L ] Shapley, H., and Swope, H.H., 1940, Annals of the Harvard College, Vol. 90, No. 5, p. 177. [BIBCODE 1940AnHar..90..177S ] Van Gent H., 1948, Bulletin of the Astronomical Institutes of Netherlands, Vol 10, p. 382. [BIBCODE 1948BAN....10..382V ] Van Hamme, W. and Wilson, E.R., 1985, Astron. and Astrophys., 152, 25. [BIBCODE 1985A&A...152...25V ] Wilson, E.R., 1979, Astrophys. J., 234, 1054. [BIBCODE 1979ApJ...234.1054W ]