COMMISSION 27 OF THE I.A.U. INFORMATION BULLETIN ON VARIABLE STARS Number 3270 Konkoly Observatory Budapest 1 December 1988 HU ISSN 0374 - 0676 AD LEO: FLARE ACTIVITY IN 1988 AD Leonis continued its ultraviolet activity this season although none of the seven flares that we observed within our 16.4 hours of sampling were particularly dramatic. All of these flares occurred during the 9.5 hours of the first five nights. As in the past, the 0.6-m telescope at Mt. Cuba, an EMI 62565 photomultiplier, and a Johnson U filter were used for the observations. Data analysis and plotting of the light curves was performed following the procedure described in IBVS 3069 (Herr & Opie, 1987). All figures are plotted to the same vertical scale in units of the flux of the comparison star. Outside of the recognized flares AD Leo averaged 2.7 times brighter than the comparison star. However, on February 17 this level remained higher as may be seen in Table 3 and in the figures for the flares (Nos. 3 and 4) on that night. Table 1. Flares of AD Leo No. 1988 UT max t_b t_a Delta_m P Air JD min min mag min Mass 2440000+ 1 Jan 24 04:55.3 0.3 3.3 0.26 0.50 1.22 7184.7051 2 Jan 24 05:20?* ? 5 >0.28? 1.3? 1.16 7184.7222 3 Feb 17 02:06.6 0.6 4.4 0.66 0.71 1.52 7208.5872 4** Feb 17 03:32.6? 1? 16 ? 0.52? 3? 1.19 7208.6476 5 Apr 10 03:09.2 0.5 4.8 0.45 0.92 1.09 7261.3614 6 Apr 10 04:04.5 0.5 2.5 0.44 0.55 1.18 7261.6698 7 Apr 14 03:00.0 0.4 7.4 0.53 0.90 1.10 7265.6250 * Maximum probably occurred between 5:18.6 UT, when we moved to measure sky, and 5:21, when we returned to find an elevated, declining signal. ** Peak of Flare 4 may have been missed. Times, including estimated minutes before and after the maximum, and the magnitude change were measured directly from the original charts. P is the flare's equivalent duration (in minutes of quiescent flux). Table 2. Monitoring Coverage in 1988 Date U.T. in hours and minutes Jan. 24 4:16.0-4:21.3, 4:30.1-4:41.6, 4:43.4-5:02.5, 5:06.6-5:18.6, 5:21.0-5:36.1, 5:41.6-5:56.9. Feb. 17 1:29.7-1:38.0, 1:39.7-1:51.7, 1:54.5-2:10.1, 2:12.6-2:25.0, 2:26.4-2:38.6, 2:41.9-2:57.4, 2:59.5-3:13.0, 3:17.2-3:30.7, 3;32.0-3:46.1, 3:48.5-4:03.9, 4:05.2-4:19.1, 4:21.1-4:37.9, 4:39.2-4:58.2, 5:00.2-5:14.1, 5:15.4-5:33.7, 5:34.8-6:06.0. Apr. 6 1:56.3-2:04.2, 2:05.4-2:18.8, 2:20.9-2:39.8, 2:41.6-2:51.9, 3:05.3-3:17.7, 3:19.8-3:34.5, 3:36.7-3:56.6, 3:58.7-4:15.9, 4:18.1-4:29.5. Apr. 10 3:02.0-3:16.6, 3:18.0-3:21.4, 3:22.8-3:33.0, 3:42.8-3:55.1, 3:58.3-4:11.7, 4:15.2-4:28.5, 4:31.0-4:42.2, 4:45.0-4:55.4. Apr. 14 2:30.4-2:33.0, 2:55.4-3:07.6, 3:11.6-3:23.7, 3:26.8-3:32.0. Apr. 27 1:20.9-1:35.9, 1:38.4-1:40.3, 1:52.0-2:02.8, 2:05.1-2:17.4, 2:20.3-2:39.0. May 8 1:40.3-1:52.1, 1:54.1-2:08.0, 2:09.1-2:24.5, 2:26.4-2:40.1, 2:42.1-2:57.8, 2:59.7-3:13.0, 3:18.1-3:20.0, 3:22.3-3:38.0, 3:40.1-3:56.0, 3:58.3-4:11.0. May 9 1:27.8-1:31.0, 1:33.3-1:40.1, 1:42.5-1:58.5, 2:00.6-2:16.0, 2:17.8-2:32.0, 2:34.4-2:50.0, 2:52.2-3:07.0, 3:09.0-3:22.0, 3:26.8-3:40.6, 3:42.4-3:55.7, 3:58.1-4:10.2. May 15 2:17.8-2:32.0, 2:35.0-2:49.0, 2:51.2-3:07.0, 3:09.2-3:24.0, 3:26.3-3:39.0, 3:41.1-3:56.0. [FIGURE 1] [FIGURE 2] Figure 1. Light curves of the seven flares (see Table 1) normalized to the same scale (1 = UV flux of the comparison star). Vertical error bars indicate the peak-to-peak higher frequency noise (to 1 Hz) present in the original signal. Table 3 Ultraviolet magnitude differences between the comparison star and AD Leo during quiescence. Signal/noise is estimated from the chart pen excursions (response to 1 Hz) within a four- minute interval. Date Time JD m_c-m_v I_0/sigma Air 1988 hr min 2440000+ Mass Jan.24 4h48m 7184.7000 1.14 8.6 1.24 5 34 7184.7319 1.03 8.1 1.14 Feb.17 1 57 7208.5183 1.27 7.8 1.58 3 21 7208.6396 1.24 8.6 1.22 4 53 7208.7034 1.21 11.1 1.08 Apr.6 2 34 7257.6069 1.09 9.7 1.06 3 22 7257.6403 1.18 9.3 1.09 Apr.10 3 05 7261.6285 1.12 12.3 1.09 4 01 7261.6674 1.08 11.2 1.17 4 39 7261.6938 1.16 11.1 1.27 Apr.14 2 57.4 7265.6232 1.10 11.4 1.10 3 20 7265.6389 1.06 11.5 1.13 Apr.27 1 29 7278.5618 0.99 4.8 1.07 2 35 7278.6076 1.01 4.5 1.14 May 8 2 03 7289.5854 1.20 7.6 1.16 3 03 7289.6271 1.13 7.3 1.32 3 49 7289.6590 1.10 5.9 1.53 May 9 1 56 7290.5806 1.05 8.7 1.15 3 00 7290.6250 0.92 7.7 1.32 4 02 7290.6681 1.12 6.0 1.64 May 15 2 41 7296.6118 0.85 6.1 1.34 3 37 7296.6507 0.92 6.6 1.63 After Flare 4, AD Leo remained even brighter for some minutes with evidence of continued activity. This may be contrasted to Flares 5-7 in similar time intervals following their peaks. We are pleased to thank Francis Marlon Caputo and Alicia Cuesta for contributions to this project and the Mt. Cuba Observatory for permitting us to use the 0.6-m telescope. RICHARD B. HERR University of Delaware DARRYL H. CHARACHE Newark, DE 19716, U.S.A. Reference: Herr, R.B., end Opie, D.B., 1987, Inf. Bull. Var. Stars, No. 3069.