COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2865 Konkoly Observatory Budapest 14 February 1986 HU ISSN 0374 - 0676 A PHOTOELECTRIC LIGHT CURVE AND PERIOD STUDY FOR CZ Aqr CZ Aqr is a relatively neglected short-period eclipsing binary of the Algol type in the southern sky. Its magnitude range has been given variously as 9.5m - 11.0m (Hoffmeister 1933) and 11.10m - 12.03m (Payne-Gaposchkin 1953). Its spectral type is A5 (Payne-Gaposchkin 1953) and Table I gives its coordinates. The variability of the system was discovered by Hoffmeister back in 1932. The most recent determination of the period, 0.8627540d by Gaposchkin (1953), is not recent at all. No previous photoelectric photometry of CZ Aqr has been published, but there are three light curves in the literature: one photographic (Gaposchkin 1953) and two visual (Tsesevich 1953, Szafraniec 1970). Also, one previous period study has been published, by Szafraniec (1970), but there has been no solution of the light curve. Photoelectric observations were made at the Mt. John University Observatory in New Zealand in 1984 on the nights of September 1, 3, and 6 (UT). A pulse-counting photometer was used with filters selected to match the UBV photometric system. The telescope was a 0.6-meter Optical Craftsmen reflector. Each observation required a 20-second integration time, and three successive integrations were averaged for one measurement. The comparison star was BD -16deg6271, the coordinates of which are given in Table I. The results include approximately 90 measurements in each bandpass. The differential magnitudes were reduced to the UBV system, using a program written by C. R. Chambliss, and have been sent to the I.A.U. Commission 27 Archive of Unpublished Observations of Variable Stars (Breger 1985) where they are available as file no. 152. There was one complete run through minimum light, and the entire light curve in blue is plotted in Figure 1. A time of mid eclipse, for which there was no obvious indication of a flat bottom, was determined graphically from the light curve. A mean from the three bandpasses was JD(hel.) - 2,445,945.056, uncertain by approximately one minute. Table I Coordinates Star BD a (1984) d (1984) CZ Aqr -16deg6270 23h21m33s -16deg01.1 Comp. -16deg6271 23 21 37 -16deg04.0 Check -16deg6266 23 20 27 -16deg02.0 Table II Times of Primary Minimum for CZ Aqr JD (hel.) E O-C Type Observer 2420773.36 -17392 0.00852 pg Soloviev 20786.34 -17377 .04722 pg " 25506.46 -11906 .04196 pg Hoffmeister 25512.45 -11899 -.00732 pg " 25864.46 -11491 -.00081 pg " 25883.47 -11469 .02861 pg " 25909.33 -11439 .00600 pg " 26242.37 -11053 .02309 pg Soloviev 26267.36 -11024 -.00677 pg Hoffmeister 26625.38 -10609 -.02954 pg " 26651.30 -10579 .00785 pg " 27413.972 -9695 .00562 pg Kanda & Kanamori 30003.117 -6694 .02690 pg Gaposchkin 30969.370 -5574 -.00420 v Tsesevich 30976.269 -5566 -.00723 v " 31001.288 -5537 -.00808 v " 32823.422 -3425 -.00981 v Szafraniec 33514.487 -2624 -.01049 v " 33539.513 -2595 -.00434 v " 33872.528 -2209 -.01226 v " 34576.541 -1393 -.00624 v " 35011.366 -889 -.00908 v " 35401.333 -437 -.00674 v " 35721.416 -66 -.00534 v Tsesevich 35778.357 0 -.00608 v Szafraniec 43371.472 8801 .01398 v Locher 2445945.056 11784 0.00382 pe Bruton [FIGURE 1] Figure 1 The light curve of CZ Aqr, where the ordinate is differential magnitude in the blue bandpass and the abscissa is orbital phase. [FIGURE 2] Figure 2 The O-C residuals from Table 2 plotted against E. The curve represents the best quadratic fit to the data, as explained in the text. An analysis of O-C residuals shows that the period may be changing. Table II tabulates all available times of primary minimum: those appearing in Szafraniec (1970), one determined by Locher (1977), and the recent one determined in this paper. The O-C residuals have been computed with the ephemeris JD (hel.) = 2,435,778.3631 + 0.86275366d*E, (1) which is the best linear fit to those residuals using weights of 20, 3, and 1 for the photoelectric, visual, and photographic times, respectively. Figure 2 shows the contents of Table II plotted with O-C as the ordinate and E as the abscissa. The solid curve in that figure represents the best quadratic fit using the same weights. When the corrections -0.007485d (constant term) -3.12 x 10^-8 (first power term) +1.164 x 10^-10 (second power term) are made to the linear ephemeris in equation (1), the result is JD (hel.) = 2,435,778.3536 + 0.86275363d E + 1.164d x 10^-10*E^2. (2) The correlation coefficient in this fit was 0.61. While it would seem at this point that the system's period is probably increasing in some fashion, the quadratic solution above is only a tentative approximation. More data, in the form of photoelectric times, are needed. The author wishes to thank Dr. Edwin E. Budding, Dr. Carlson R. Chambliss, Dr. Douglas S. Hall, Dr. John Hearnshaw, and Dr. Richard L. Walker. JAMES R. BRUTON Dyer Observatory Vanderbilt University Nashville, Tennessee 37235 U.S.A. References: Breger, M. 1985, P.A.S.P. 97, 85. [BIBCODE 1985PASP...97...85B ] Gaposchkin, S. 1953, Harvard Ann. 113, no. 2, 69. [BIBCODE 1953AnHar.113...67G ] Hoffmeister, C. 1933, Astr. Nachr. 247, no. 5919, 286. [BIBCODE 1933AN....247..281H ] Locher, K. 1977, B.B.S.A.G. no. 34. [BIBCODE 1977BBSAG..34....1A ] Payne-Gaposchkin, C. 1953, Harvard Ann. 115, no. 10, 121. Szafraniec, R. 1970, Acta Astr. 20, 29. [BIBCODE 1970AcA....20...25S ] Tsesevich, W. 1953, Odessa Isvestia 4, 56. [DATAFILE 3]