COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 802 Konkoly Observatory Budapest 1973 June 4 PHOTOELECTRIC OBSERVATIONS OF EV Lac DURING THE 1972, SEPTEMBER 1-15 INTERNATIONAL PATROL Photoelectric observations of EV Lac were carried out at the McDonald Observatory in coincidence with the observation campaign organized by the I.A.U. Working Group on Flare Stars of Comm. 27. The multicolor high speed photometer described by Nather and Warner (1971), fed by a 75 cm cassegrain reflector, was used. This photometer allows to obtain a rapid succession of photon count measurements in four sequential colors by means of an automatically rotating wheel. Four holes are provided in the rotating wheel to locate filters. This system proves to be suitable for good color determination at peak light only for relative slow flares. Moreover, each filter change requires 0.25 sec, so that the effective integration time for each of the four colors is 0.25 sec less than those quoted in Table 1. A standard set of filters matching the UBV system was used: Corning 9863 (U), Corning 5030 + Shott GG13 (B) and Corning 3384 (V). No filters were located in the fourth filter hole. The corresponding photon counts are referred to in this Bulletin as U,B,V and NF. A blue sensitive photomultiplier tube (RCA 8575) was operated cooled at - 75 deg.C. During the 12.4 hours of patrol four flares were observed, two of which were not detectable in V light. In Table 1 the time coverage and in Table 2 the flare characteristics are given. Note that the NF characteristics are comparable with the B ones because of the relative high blue sensitivity of the photomultiplier tube. The accompanying figure shows a plot of the detected photon counts which refers to flares No. 1 and 2. The colors at flare maximum are consistent with those observed by Cristaldi and Rodono (1973) with a synchronous three color photometer. Catania Astrophysical Observatory M. RODONO 95125 Catania Italy May 23, 1973 References: Cristaldi, S., Rodono, M. 1973, Astron.Astrophys.Suppl. (in press). [BIBCODE 1973A&AS...10...47C] Nather, R.E., Warner, B. 1971, Monthly Notices Roy.Astr.Soc. 152, 209. [BIBCODE 1971MNRAS.152..209N ] Table 1 Date Colors Coverage (UT) Total 1972 Integration time (sec) coverage Sep. 5 NF/1, U/1, B/1, V/1 0334-0515,0528-51, 0618-21,0626-0830 251^m 7 NF/1, U/2, B/1, V/1 0454-0746,0755-0806, 0811-29 205 9 NF/1, U/2, B/1, V/1 0436-0639,0653-0711 141 10 NF/1, U/2, B/1, V/1 0417-0532,0536-0647 146 Table 2 (*) Date tmax N (1972 (UT) Light db da (If/Io)max P U-B B-V Sky Sep.) 1 5 06h53m2 U 0.3 2.5 1.96 1.60 -0.86 - clear B 0.3 1.3 0.33 0.19 V - - (not detectable) NF 0.3 0.8 0.26 0.14 2 5 07/02.9 U 3.0 23.0 2.00 11.10 -0.66+0.55 clear B 3.0 23.0 0.41 3.04 V 3.0 23.0 0.16 1.37 NF 3.0 23.0 0.36 2.74 3 9 05:39.7 U 2.1 24.0 0.54 0.42 -1.32 - foggy B 2.1 24.0 0.07 0.06 V - - (not detectable) NF 2.1 24.0 0.07 0.06 4 9 06:04.3 U 0.3 1.5 0.83 0.63 -0.94+0.90 cirrus B 0.3 24.0 0.13 0.12 V 0.3 24.0 0.07 0.05 NF 0.3 24.0 0.14 0.10 (*) For explanation of symbols see IBVS no.525 For multiple flares, the tmax, da, db and (If/Io)max values refers to the highest peak, while the P value includes pre- and post- maximum activity, whatever, during the given flare. [FIGURE 1]