COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3999 Konkoly Observatory Budapest 24 February 1994 HU ISSN 0374 - 0676 AN IMPROVED PERIOD FOR DU LEONIS The 9th-magnitude eclipsing variable DU Leonis (BD +26d1996, HD 84207, SAO 80992) was discovered by Kaiser (1990). The system has a G0 spectrum and two nearly equal minima 0.7 magnitude deep. An approximate period of 1.3742 days was found by Williams et al. (1990). The official designation DU Leonis was assigned in the 71st Name List (Kazarovets et al., 1993). Popper (1993) reported preliminary results from radial velocity measures in a program to determine accurate masses for G-K main sequence stars. I have examined DU Leo on almost 700 Harvard patrol plates from the intervals 1899- 1953 and 1968-1989. Table I lists 40 times when DU Leo was estimated to be at or very near minimum light. Due to long exposure times and accidental errors of estimation, the uncertainty in the photographic minima is about 0.03 day. I have also obtained additional R-band photoelectric observations, using the same equipment described previously (Williams et al., 1990). From this data, one new time of minimum is included in the Table. The photoelectric observations were affected by low signal to noise ratio, and the estimated uncertainty of the minimum is +-0.002 day. Table I -------------------------------------------------------------------------------- HJD Min. O-C HJD Min. O-C HJD Min. O-C -------------------------------------------------------------------------------- 2414973.835 pg I -0.003 22042.603 pg I -0.041 28919.778 pg II +0.028 15169.618" II -0.042 22382.729" II -0.025 29988.880 " II +0.014 15711.801" I +0.025 22422.627" II +0.021 31146.630 " I +0.014 16519.785" I -0.011 22729.745" I +0.009 44376.596 " II +0.018 16939.626" II +0.017 22782.650" II +0.008 45812.574 " II -0.027 16961.587" II.-0.009 24905.783" II +0.026 45823.586 " II -0.008 17171.852" II +0.005 25603.863" II +0.020 46139.663 " II +0.006 17321.659" II +0.026 25954.905" I -0.042 46519.592 " I -0.027 20111.936" I +0.022 26016.775" I -0.010 46846.676 " I +0.001 20131.853" II +0.013 26069.674" II -0.017 47208.782 " II +0.010 20246.595" I +0.011 26447.563" II -0.029 47511.799 " I +0.019 20575.715" II +0.013 28139.918" I +0.018 47537.884 " I -0.005 21010.609" I -0.022 28221.661" II -0.003 48348.658 pe I 0.000 21251.783" II -0.017 28550.773" I -0.009 -------------------------------------------------------------------------------- I have also used a photoelectric timing of minimum published by Diethelm (1991), HJD 2448362.401 +-0.003, in the calculation of improved light elements. Entering all 42 times into a least squares solution with weight 1 for photographic data and 10 for photoelectric, the following improved light elements were derived: Min I=HJD 2448348.658 + 1.37418454d * E ( 1 ) +-.002 +-6 The O-C residuals in Table I were calculated from this ephemeris. The period has been constant. Scatter in the photoelectric data (Figure 1 ) prevents a precise determination of the small difference in depth between the two minima. But in the R-band the primary minimum appears to be no more than 0.03 magnitude deeper than the secondary minimum; the estimated amplitudes are 0.73 and 0.70 magnitude, respectively. [FIGURE 1] Figure 1. R-band photoelectric light curve of DU Leo. I am grateful to Dr. Martha Hazen for use of the Harvard plates. David B. WILLIAMS 9270-A Racquetball Way Indianapolis, IN 46260 USA References: Kaiser, D. H.: 1990, Inform. Bull. Var. Stars, No. 3480 Kazarovets, E. V., Samus, N. N., and Goranskij, V. P.: 1993, Inform. Bull. Var. Stars, No. 3840 Diethelm, R.: 1991, in BBSAG Bull., No. 97 Popper, D. M.: 1993, Astrophys. J., 404, L67 [BIBCODE 1993ApJ...404L..67P ] Williams, D. B., Baldwin, M. E., and Kaiser, D. H.: 1990, Inform. Bull. Var. Stars, No. 3514