COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3069 Konkoly Observatory Budapest 17 August 1987 HU ISSN 0374 - 0676 FLARES ON AD Leo IN 1973 AND 1983 Since 1968,undergraduate students at the University of Delaware have participated in our continuing program of flare-star monitoring with the 24-inch cassegrain at Mt. Cuba Observatory. Except for the possible slow deterioration of equipment, supervising professor, and atmospheric conditions, the instrumental system has remained the same since IBVS 329. Previously unreported are 21.5 hours of ultraviolet photoelectric monitoring of AD Leonis by a special-project class during January, 1973. To this we have added 5.9 hours of observations in the spring of 1983. To facilitate comparisons, we present both seasons in this combined report. The distribution of times is given in Table II in which gaps greater than one minute are explicitly shown. Differential measures of the ultraviolet magnitude of AD Leo with respect to the comparison star were made at times of supposed quiescence. From Table III it may be noted that AD Leo averaged 0.07 mag brighter in 1983 than in 1973; however, as might be expected for so active a flare star, this difference is not statistically significant. Standard deviations in 1973 and 1983, respectively, were 0.05 mag (25 points) and 0.08 mag (13 points). In March-April 1982 (IBVS 2426) 17 measures also showed AD Leo brighter than in 1973; the average then being 0.11 mag (0.07 s.d.) brighter. That the signal-to-noise ratio in 1973 is notably better than in 1983 is due largely to a dark-moon run of excellent weather in January 1973. Less time is now available for such work at the Mt. Cuba telescope; and, consequently, some of the 1983 monitoring was done on lower quality nights. Concern that the system had deteriorated during the decade was relieved by noting that on the two nights when AD Leo was briefly monitored through the same Johnson U filter in 1971 (IBVS 597), the signal-to-noise ratios were as low (5.5 to 8.7) as in 1983. [FIGURE 1a] Fig. 1. Flares in January, 1973. See Table I. The upper plots for flares 1 and 2 are tracings from the original photometer chart to show the interpolated reference levels for the background sky and the comparison star as well as the noise (pen response ~< 1 s) present in the unsmoothed signal. The smoothed plots are in a standardized form as described in the text. [FIGURE 1b] Fig. 1. cont'd. Flares of AD Leo observed in January, 1973. Table I. Ultraviolet Flares of AD Leonis* No. Date UT max tb ta Delta P Air JD yr mo da h m min min mag min Mass 244 0000+ 1 1973 1 11 09:10.6 0.3 17. 0.94 2.26 1.11 1693.88236 2 1973 1 11 09:35.8 0.4 1.2 0.12 0.09 1.14 1693.89986 3 1973 1 11 10:25.3 0.1 1.5 0.15 0.12 1.26 1693.93424 4 1973 1 12 05:36.5 0.2 0.8 0.24 0.17 1.23 1694.73389 5 1973 1 12 05:55.6 0.4 7 0.55 1.16 1.18 1694.74694 6 1973 1 12 06:18.1 0.2 3.5 0.55 0.33 1.14 1694.76257 7 1973 1 12 07:37.7 0.9 2.5 0.24 0.28 1.06 1694.81785 8 1973 1 12 07:54.4 0.7 21 >1.56: >7.7: 1.06 1694.82944 9 1973 1 12 10:09.9 1.4 33 1.68 10.0 1.22 1694.92354 10 1973 1 13 06:41.4 0.3 4 0.24 0.09 1.10 1695.77275 11 1973 1 13 08:37.3 0.9 9 0.44 0.71 1.08 1695.85931 12 1973 1 13 09:27.7: 0.3: 1: 0.13 0.05 1.14 1695.8942 13 1973 1 30 04:56.3: 0.2: 4 0.22 0.28 1.16 1712.7058 14 1983 3 17 03:50.5 3.5 20+ 1.34 15.6+ 1.06 5410.66007 15 1983 3 17 05:44.6 1.6 6.4 0.32 2.20 1.18 5410.73931 16 1983 3 17 06:05.3 0.5 23 ? >2.3 12 ? 1.34 5410.75368 17 1983 5 10 05:27.5 0.2: - >3 >20 ? 2.79 5464.72743 * where tb and ta are the durations before and after maximum, Delta m is the change in magnitude of AD Leo (quiescent to maximum), P is the equivalent duration of the flare. Flares that we observed are numbered in Table I. Examples of the light curves for both major and uncertain flares are provided in the figures, on which flares are identified by their numbers in Table I. Breaks in the light curves are moments when the background sky and/or comparison star were measured. In a few cases, shown by a fragmented line, the break was caused by a passing cloud (see Flares 15 & 16). [FIGURE 2] Fig. 2. AD Leonis flares observed in 1983. See Table I and the caption to Fig. 1. Tracings of all the flares were digitized and plotted in units of the flux of the comparison star. This provides a coordinate reference that is more consistent than the quiescent level of AD Leo, which varies with background activity over the visible hemisphere of the flare star. Also, this plot facilitates estimating when a flare has ended. Note that the ordinate of these graphs may be converted to astronomical magnitudes by taking its logarithm and multiplying by 2.5. For convenient general comparison with Table III, a magnitude scale has been added on the right hand side of the flare-8 figure. Because this analysis suppresses high frequencies, we have included in Figure 1 faithful reproductions of the original chart recordings for flares 1 and 2. Here may be seen the full photometric noise down to the instrumental time constant of approximately 1 second as well as any potentially real stellar flashes. A peak-to-peak measure of this higher frequency noise has been made near each flare, translated to the relative flux units and included as a vertical "error bar" on the graphs. These represent approximately six standard deviations of the high frequency noise as tabulated in the signal-to-noise ratio in Table III. The astrophysical importance of the rotation periods of dMe stars has been pointed out by Marcy, Lindsay, and Wilson (1987). Photometric determinations based on the star's nonuniform surface brightness require analyzing a large number of samples because of the inherent variability. Pettersen, Coleman, and Evans (1984) report that Sandmann deduced a rotation period of 2.7 days from starspot modulation of AD Leo. Our UV data is not sufficient to confirm or negate this result, although, on the four consecutive days at the beginning of the 1973 run, such a period is possible if the amplitude at that time was less than 0.03 mag. Quiescent ultraviolet flux, as indicated by the magnitude differences in Table III, averages 2.77 times that of the comparison star. This may be compared directly to the levels portrayed in the figures. Table II. AD Leo Flare Monitoring: Coverage in 1973 & 1983. Date U.T. in hours and minutes 1973 Jan.10 9:53.9- 9:58.1, 10:02.1-10:15.1, 10:17.4-10:32.5, 10:36.4-10:49.0, 10:51.2-10:58.7. Jan.11 8:57.8- 8:58.8, 9:00.7- 9:09.0, 9:10.2- 9:26.9, 9:28.2- 9:45.0, 9:47.7- 9:59.5, 10:00.6-10:13.8, 10:15.6-10:29.0, 10:32.5-10:44.0, 10:46.0-10:49.5, 10:51.9-10:55.0. Jan.12 5:11.6- 5:13.7, 5:16.9- 5:20.8, 5:23.8- 5:30.2, 5:31.8- 5:38.8, 5:40.2- 5:46.9, 5:48.9- 6:10.5, 6:13.7- 6:49.8, 6:51.2- 7:07.4, 7:08.8- 7:24.9, 7:26.2- 8:11.8, 8:13.2- 8:23.9, 8:25.2- 8:26.7, 8:29.0- 8:30.0, 8:31.8- 8:37.0, 8:38.3- 9:00.7, 9:02.2- 9:13.7, 9:15.1- 9:28.5, 9:30.2- 9:38.6, 9:42.5-10:24.1, 10:25.3-10:40.6, 10:42.5-11:00.0. Jan.13 3:10.4- 3:19.1, 3:25.2- 3:36.9, 3:38.2- 3:59.4, 3:55.8- 4:02.2, 4:03.1- 4:10.8, 4:12.6- 4:15.4, 4:16.5- 4:30.4, 4:33.5- 4:48.9, 4:50.7- 4:59.7, 5:59.8- 5:56.3, 6:02.1- 6:19.6, 6:15.2- 6:22.0, 6:23.6- 6:38.0, 6:39.5- 6:43.6, 6:49.8- 6:49.0, 6:51.2- 6:56.8, 6:58.9- 7:11.1, 7:12.5- 7:39.0, 7:35.5- 7:51.0, 7:51.9- 7:59.4, 8:11.2- 8:21.7, 8:22.8- 8:25.9, 8:28.1- 8:44.8, 8:46.7- 9:03.0, 9:09.2- 9:28.6, 9:30.4-10:02.9, 10:04.2-10:18.6, 10:19.8-10:34.4, 10:36.3-10:42.0. Jan.26 4:32.5- 4:35.1, 4:37.1- 4:43.8, 4:46.0- 4:57.6, 4:58.8- 5:21.2, 5:23.6- 5:39.2, 5:40.9- 6:02.1, 6:03.6- 6:12.0, 6:14.3- 6:31.9, 6:34.0- 6:51.0. Jan.30 1:57.4- 1:59.4, 2:03.7- 2:11.0, 2:12.8- 2:17.4, 2:20.7- 2:33.9, 2:35.9- 2:46.7, 2:49.5- 3:01.8, 3:07.8- 3:23.8, 3:29.2- 3:44.4, 3:47.6- 3:58.2, 4:00.6- 4:01.9, 4:05.8- 4:22.6, 4:25.0- 4:42.0, 4:47.2- 5:01.8, 5:04.1- 5:08.3, 6:05.6- 6:21.0, 6:23.9- 6:37.4, 6:38.5- 6:53.0, 7:02.6- 7:19.2, 7:21.2- 7:38.0, 7:40.5- 7:56.6, 7:58.0- 8:16.2, 8:19.1- 8:26.2, 8:27.0- 8:35.0, 8:36.6- 8:51.7, 8:54.2- 9:08.8, 9:10.5- 9:27.0, 9:29.6- 9:44.4, 9:47.0-10:02.9, 10:05.2-10:22.6. 1983 Feb.22 4:43.5- 9:49.0, 9:51.8- 9:58.0, 5:00.9- 5:06.1, 5:12.2- 5:16.0. Mar.3 3:09.0- 3:08.0, 3:12.8- 3:20.6, 3:27.0- 3:34.0, 3:42.2- 3:50.0, 3:54.0- 3:59.0, 4:02.8- 4:09.6, 4:15.8- 4:23.0, 4:27.6- 4:35.0, 4:38.1- 4:44.8, 4:46.0- 4:54.1, 4:56.6- 5:02.5. Mar.17 2:55.1- 3:01.0, 3:05.2- 3:10.6, 3:12.1- 3:17.6, 3:19.7- 3:27.9, 3:29.4- 3:35.6, 3:38.7- 3:45.0, 3:46.3- 3:51.1, 3:52.6- 3:57.8, 4:00.0- 4:10.3, 4:32.0- 4:39.0, 4:41.2- 4:50.0, 4:53.4- 4:59.6, 5:02.2- 5:10.1, 5:12.6- 5:20.8, 5:22.4- 5:30.0, 5:31.8- 5:39.6, 5:41.5- 5:52, 5:55.4- 6:14.9, 6:16.0- 6:23.2, 6:25.0- 6:31.0. Mar.24 5:34.6- 5:43.0, 5:45.5- 5:52.6, 5:55.9- 6:04.3, 6:06.6- 6:15.8, 6:21.5- 6:32.0, 6:36.1- 6:48.2, 6:50.5- 7:00.8. May 10 5:05.0- 5:12.9, 5:15.5- 5:29.0, 5:27.3- 5:40.0, 5:42.8-5:51. Table III. Ultraviolet magnitude differences between the comparison star and AD Leo during moments of apparent quiescence, and estimates of the unsmoothed signal/noise for AD Leo. Date Time JD mc-mv I0/sigma Air hr min 2440000+ Mass 1973 Jan.10 10 33 1692.9396 1.04 13.0 1.27 Jan.11 9 00 1693.8750 1.08 - 1.09 " 9 47 1693.9076 1.07 17.1 1.16 " 10 31 1693.9382 1.10 - 1.27 " 10 51 1693.9521 1.08 14.3 1.34 Jan.12 5 48 1694.7417 1.12 11.5 1.20 " 7 08 1694.7972 1.10 14.1 1.08 " 9 30 1694.8958 1.06 13.4 1.14 " 10 41 1694.9451 1.10 11 1.32 Jan.13 4 31 1695.6882 1.25 6.9 1.46 " 6 50 1695.7847 1.08 15.9 1.09 " 8 28 1695.8528 1.07 15.6 1.07 " 9 29 1695.8951 1.10 15.9 1.14 Jan.26 4 36 1708.6917 1.16 - 1.24 " 4 45 1708.6979 1.14 14.2 1.22 " 5 22 1708.7236 1.01 14.8 1.14 " 6 03 1708.7521 1.07 - 1.09 " 6 33 1708.7729 1.03 16.0 1.07 Jan.30 2 18 1712.5958 1.08 9 1.97 " 3 28 1712.6444 1.00 11.7 1.44 " 4 44 1712.6972 1.02 14.6 1.18 " 6 22 1712.7653 1.03 16.5 1.07 " 7 39 1712.8188 1.06 16.3 1.09 " 8 53 1712.8701 1.05 15.6 1.21 " 10 03 1712.9188 1.15 14.5 1.46 1983 Feb.22 4 55 5387.7049 1.09 4.0 1.07 Mar. 3 3 47 5396.6576 1.11 6.4 1.08 " 4 19 5396.6799 1.15 6.1 1.07 " 4 42 5396.6958 1.16 5.8 1.06 Mar.17 3 43 5410.6549 1.22 9.2 1.06 " 4 57 5410.7062 1.23 7.2 1.10 " 5 07 5410.7132 1.05 7.5 1.12 " 5 18 5410.7208 1.11 8.8 1.13 " 5 37 5410.7340 1.18 7.4 1.17 " 6 21 5410.7646 1.32 7.7 1.28 Mar.24 6 00 5417.7500 1.16 4.3 1.31 " 6 41 5417.7785 1.16 4.7 1.49 May 10 5 20 5464.7222 1.02 5.6 2.62 Many students participated in obtaining and analyzing this data. Particularly valuable were the contributions by John Cambridge, Tony Nicastro, Mike Simmons, and Jeff Frank. Thanks are also due to the trustees of Mt. Cuba Astronomical Observatory for providing telescope time to the University faculty and students for more than twenty years. RICHARD B. HERR DAVID B. OPIE Dept. of Physics & Astronomy University of Delaware Newark, Delaware 19716 U.S.A. References: Herr, R.B., and Brcich, J.A., 1969, Inf. Bull. Var. Stars, No. 329. Herr, R.B., 1971, Inf. Bull. Var. Stars, No. 597. Herr, R.B., and Frank, J.D., 1983, Inf. Bull. Var. Stars, No. 2426. Marcy, G.W., Lindsay, V., and Wilson, K., 1987, Publ. Astron. Soc. Pac., 99, 490. [BIBCODE 1987PASP...99..490M ] Pettersen, B.R., Coleman, L.A., and Evans, D.S., 1984, Astrophys. J. Suppl. Ser., 54, 375. [BIBCODE 1984ApJS...54..375P ]