COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3118 Konkoly Observatory Budapest 9 December 1987 HU ISSN 0374-0676 NEW MINIMA TIMES AND LIGHT ELEMENTS FOR SIGMA AQUILAE In 1986, I chose the small-amplitude eclipsing binary Sigma Aquilae (HR 7474) to test the capabilities of a new photometer. It was soon apparent that minima were occurring almost 2.5 hours later than predicted by the light elements in the General Catalogue of Variable Stars (Kholopov et al., 1985, citing Wylie, 1922). Observations were therefore continued to determine accurate times of primary and secondary eclipses. During the 1986 and 1987 seasons, 162 mean differential magnitudes in V of the Johnson system were obtained with an Optec SSP-3 solid-state photometer and 20-cm reflector, using Upsilon Aquilae (HR 7519) as the comparison star. The following normal times of minima were determined by the tracing paper method from each season's light curve: TABLE I HJD 244+ Min. I/II O-C (a) O-C (b) 6728.6292 I +0d100 -0d0009 +/-10 6729.6086 II +0.105 +0.0034 +/-15 7027.0196 I +0.101 -0.0015 +/-12 7027.9978 II +0.104 +0.0016 +/-16 (a) GCVS elements, Min. I = HJD 242 2486.797 + 1.95026d E (b) New light elements, below. [FIGURE 1] FIGURE 1. The light curve of Sigma Aquilae. The phases are calculated according to the light elements of Wylie (1922). Each point represents the mean of three or four differential measures. A literature search failed to find any photoelectric times of minima published since Wylie (1922). However, one unpublished timing of primary eclipse by D. Engelkemeir (17 pe measures in 1961) is recorded on card 4 of the Sigma Aquilae file, Eclipsing Binary Card Catalogue, University of Florida (Wood, 1987): Min. I = HJD 243 7589.669. Engelkemeir's timing differs by only 0.004d from a constant period between Wylie's epoch and the new times of minima reported here. Assuming, on this evidence, that the period has indeed been constant, the six available times of eclipses were used to derive improved light elements by least-squares linear regression: Min. I = HJD 242 2486.7955 + 1.95026827d E The standard deviation of a single timing from these elements is +/-0.0027d. Monet (1980) reports a spectroscopic period of 1.950271d, much closer to the improved photometric value than Wylie's period. The observations are plotted in the accompanying figure. Based on Upsilon Aquilae's magnitude, 5.91 V, in The Bright Star Catalogue (Hoffleit and Jaschek, 1982), Sigma's magnitude at maximum is 5.17 V. The V amplitude is 0.18 (Min. I) and 0.16 (Min. II). Surprisingly, no modern photoelectric light curve of Sigma Aquilae has been published. Hill et al. (1976) report 57 three-color measures, but almost no observations were made in the deep phases of eclipse. I am therefore continuing observation of Sigma Aquilae to provide light curves with complete phase coverage in B and V. DAVID B. WILLIAMS 9270-A Racquetball Way Indianapolis, Indiana 46260 USA References: Hill, G., Hilditch, R. W., and Pfannenschmidt, E. L., 1976, Publications of the Dominion Astrophysical Observatory, Victoria, 15, 1. [BIBCODE 1976PDAO...15....1H ] Hoffleit, D., and Jaschek, C., 1982, The Bright Star Catalogue, Yale University Observatory, New Haven. [BIBCODE 1982bscf.book.....H ] Kholopov, P. N., Samus, N. N., Frolov, M. S., Goranskij, V. P., Gorynya, N. A., Kireeva, N. N., Kukarkina, N. P., Kurochkin, N. E., Medvedeva, G. I., Perova, N. B., Shugarov, S. Yu., 1985, General Catalogue of Variable Stars, 4th edition, Nauka Publishing House, Moscow. Monet, D. G., 1980, Astrophys. J. 237, 513. [BIBCODE 1980ApJ...237..513M ] Wood, F. B., 1987, private communication. Wylie, C. C., 1922, Astrophys. J. 56, 232. [BIBCODE 1922ApJ....56..232W ]