COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1703 Konkoly Observatory Budapest 1979 November 8 LIGHT ELEMENTS OF V 757 Cen The variability of V757 Cen=SAO 204919=HD 120734=CoD-36d8903=CPD-36d6160 was discovered by Bond (PASP 82, 489, 1065, 1970) on Curtiss-Schmidt objective prism plates. From photoelectric observations in the "y" Stromgren filter Bond, in the same article, derived a period P=0.3432d, an amplitude Delta y=0.4m, the magnitude at maximum V=8.3m, and confirmed the W UMa type of the star as indicated ed by the spectra. This variable was listed by Kukarkin et al. (2nd Suppl. GCVS, 1974) and kept as current program by M. de Groot (IAU, Comm. 42, 1973). In this note we present times of minimum light obtained from about 1000 photoelectric observations in the UBV system made between March and August 1979 at the Bosque Alegre Station of Cordoba Observatory with the 154 cm reflecting telescope, and at El Leoncito Station of Felix Aguilar Observatory (San Juan, Argentine) with the 76 cm Perrine reflecting telescope. Table I Times of minima JD hel.2440000+ V B U 3940.80745(09) 3940.80938(07) 3940.80774(18) 3970.83333(14) 3970.83340(11) 3970.83536(23) 3973.75011(07) 3973.74914(04) 3973.74863(07) 4024.54094(20) 4024.54095(03) 4024.54101(14) 4025.74068(15) 4025.74100(06) 4025.74043(05) 4027.62836(13) 4027.62837(14) 4027.62845(14) 4031.74757(13) 4031.74580(16) 4031.74574(15) 4033.46211(33) 4033.46325(08) 4033.46127(23) 4033.63356(08) 4033.63336(25) 4033.63310(13) 4069.49467(09) 4069.49513(11) 4069.49396(18) 4069.66343(22) 4069.66170(30) 4069.66108(20) Individual minima are listed in Table I. The standard errors are given in parenthesis; they were determined from the light curves on each pass-band. A least squares linear ephemeris using the mean values of the minima in the UBV bands, gives Min I = JD hel. 2444024.53970d +0.3431629d*E +-.00030 +-.0000034 Table II Times of maxima JD hel. 2440000+ V B U 3973.83800(28) 3973.83683(41) 3973.83539(08) 4025.65636(15) 4025.65618(11) 4025.65448(15) 4033.54585(31) 4033.54580(13) 4033.54700(13) 4069.57990(21) 4069.57975(17) 4069.57690(16) Also in Table II are listed four times of maximum light which were handled in a similar way as the minima. The corresponding ephemeris is Min I = JD hel. 2444024.53893d +0.3431609d*E +-.00046 +-.0000051 Table III Mean times of maxima and minima JD hel. w cycles (O-C) 2440000+ 0653.760 1 -4822.50 -0.0008 0654.788 1 -4819.50 .0007 0656.676 1 -4814.00 .0002 3940.80819(60) 1 4756.00 - .0019 3970.83403(67) 1 4843.50 - .0005 3973.74929(43) 1 4852.00 .0012 3973.83674(75) 1 4852.25 - .0004 4024.54097(02) 4 5000.00 - .0014 4025.65567(60) 1 5003.25 - .0008 4025.74070(16) 2 5003.50 - .0001 4027.62839(03) 3 5009.00 - .0003 4031.74637(60) 1 5021.00 - .0003 4033.46221(57) 1 5026.00 - .0003 4033.54622(39) 2 5026.25 .0015 4033.63334(13) 2 5026.50 .0002 4069.49459(34) 1 5131.00 .0001 4069.57885(98) 1 5131.25 .0017 4069.66207(70) 1 5131.50 .0042 Since both solutions are in close agreement within the errors we constructed a new one including the minima and the maxima: Min I = JD hel. 2444024.53953d +0.3431622d*E +-.00025 +-.0000028 Finally, the ephemeris representing these seasonal minima and those of the discovery, derived from the observations supplied by Bond (private communication, 1971) gives the values Min I = JD hel. 2442308.69312d +0.34316929d*E +-.00106 +-.00000021 In Table III are listed the epochs, their standard errors, the assigned weights, the cycles and the residuals (O-C) of the last ephemeris. We see that the secondary minimum is centered at phase 0.5. An inspection of the light curves (not given in the text) indicates that V757 Cen is an A-type W UMa system, exhibiting a flat secondary minimum of about 15 minutes, a primary minimum of amplitude 0.47m in V and the light in the maximum preceding the Min I slightly exceeding the other. Differential colours are almost constant throughout the period. MIGUEL A. CERRUTI Fellow of the CONICET at the Instituto de Astronomia y Fisica del Espacio (IAFE) C.C. 67 Suc. 28 1428 Capital Federal Argentina [DATAFILE 4]