COMMISSION 27 OF THE I. A. U.
             INFORMATION BULLETIN ON VARIABLE STARS
                          NUMBER 809
      
                                         Konkoly Observatory
                                         Budapest
                                         1973 July 2


     PHOTOELECTRIC OBSERVATIONS OF THE FLARE STAR EV LAC



   Continuous photoelectric monitoring of the flare star EV Lac has
been carried out at the Stephanion Astronomical Station (lambda=-22d49'44"
phi=+37d45'15") during the following periods: 1.) the period August 14-31,
1972, 2.) the period of cooperative optical observations of this star
proposed by the IAU Working Group on Flare Stars i.e. September 1-15,
1972 (Chugainov, IBVS, No. 605, 1971) and 3.) the period September 16-19,
1972, using the 30-inch Cassegrain reflector of the Department of 
Geodetic Astronomy, University of Thessaloniki. Observations have been
made with a Johnson dual channel photoelectric photometer in the B
color of the international UBV system. The telescope and photometer
will be described elsewhere. Here we mention only that the transformation 
of our instrumental ubv system to the international UBV system is
given by the following equations:

                 V = v_0 + 0.018 (b-v)_0 + 1.788,
             (B-V) = 0.814 + 0.930 (b-v)_0,
             (U-B) =-0.951 + 0.864 (u-b)_0.
   The monitoring intervals in UT as well as the total monitoring
time for each night are given in Table 1. Any interruption of more than
one minute has been noted.

   During the 44.2 hours of monitoring time 6 flares were observed
the characteristics of which are given in Table 2. For each flare 
following characteristics (Andrews et. al. IBVS No.326, 1969) are given:
a) the date and universal time of flare maximum, b) the duration before
and after maximum (t_b and t_a respectively) as well as the total duration
of the flare, c) the value of the ratio (I_f-I_0)/I_0 corresponding to
flare maximum, where I_0 is the intensity deflection less sky background
of the quiet star and I_f is the total intensity deflection less sky 
background of the star plus flare, d) the integrated intensity of the flare
over its total duration, including pre-flares, if present, 
P=Integral(I_f-I_0)/I_0 dt,
e) the increase of the apparent magnitude of the star at flare maximum
Deltam(b)= 2.5 log(I_f/I_0), where b is the blue magnitude of the star in our
instrumental system, f the standard deviation of random noise fluctuation 
sigma(mag)= 2.5{log(I_0+sigma)/I_0} and g) the air mass. The light curves of
the observed flares in the b color are shown in Figs. 1-6.


G. ASTERIADIS, L.N. MAVRIDIS and D. STAVRIDIS
Department of Geodetic
Astronomy, University       
of Thessaloniki, Greece.



			        TABLE 1
Date                    Monitoring intervals                     Total
1972                                                           Monitoring
Aug.                                                             Time
14-15   19h36m-19h49m,1954-2013,2017-2031,2032-2037,2137-2159,
        2202-2214,2217-2224,2227-2244,2302-2321,2325-2332,
        2338-2347,2350-2358,2359-0009,0020-0032,0041-0100,                 
        0109-0134,0137-0150.                                     3h51m
15-16   1936-1951,1955-2015,2018-2036,2040-2100,2111-2131,
        2134-2152,2156-2214,2307-2316,2318-2333,2337-2358,
        0001-0021,0024-0041,0051-0110,0114-0131,0134-0201.       4h34m
16-17   1949-2006,2009-2025,2028-2042,2051-2109,2112-2130,
        2133-2148,2258-2323,2337-2353,2356-0015,0018-0037,
        0044-0100,0102-0121,0123-0141,0143-0200.                 4h07m          
17-18   2343-2354,0002-0029,0031-0056,0110-0131,0133-0204.       1h55m
19-20   2135-2155,2156-2202,2204-2227,2338-2357,0000-0028,
        0037-0100,0103-0128,0136-0200.                           2h48m
20-21   2026-2055,2059-2120,2154-2158,2309-2335,2338-2351,
        0002-0032,0035-0104,0115-0138,0141-0200.                 3h14m
21      2045-2111,2115-2142,2150-2157.                           1h
30-31   2257-2321,0025-0053,0057-0114.                           1h09m
31      2019-2036,2038-2048,2051-2123,2129-2156,2200-2229,
        2329-0000.                                               2h26m
Sept.
                                                              
1       0004-0033,0042-0110,0113-0142,0149-0238.                 2h15m
6-7     1952-2026,2034-2042,2049-2115,2118-2158,2219-2226,
        2336-0003.						 2h22m
8-9     2114-2139,2141-2154,2157-2227,2231-2256,2320-2333,
        2345-0012.						 2h13m
9-10    2206-2231,2233-2309,2312-2346,2349-0001,0012-0112.       2h47m
11-12   2221-2246,2248-2326,2327-2339,2343-0008,0010-0144,
        0147-0157.                                               3h24m
12-13   2229-2250,2254-2347,2352-0027,0028-0105,0109-0120,
        0123-0135,0138-0152,0155-0208.                           3h16m
16      2210-2317.                                               1h07m
18-19   2350-0023,0025-0043,0054-0113,0115-0151.                 1h46m
						        Total    44h 14m



                                TABLE 2
                  Characteristics of the flares observed
Flare   Date        U.T.    t_b   t_a   Duration   (I_f-I_0)/I_0   P   Deltam  sigma   Air
No.
        1972      maximum   min.   min.   min.       maximum      min.   mag    mag.   mass
        Aug.
1       14       22h33m8    1.3    4.5   5.8        0.21         0.35   0.21   0.01   1.03
2       16       20h31m5    0.6    0.4   1.0        0.15         0.06   0.16   0.02   1.21
3       16       23h15m8    0.4    4.3   4.7        0.79         0.57   0.63   0.01   1.02
4       19       23h48m8    0.3    0.5   0.8        0.11         0.05   0.11   0.01   1.01
        Sept.
5       11       23h57m4    0.4    8.7   9.1        0.90         2.14   0.70   0.01   1.10
6       19       01h04m4    0.2    2.8   3.0        0.29         0.21   0.28   0.01   1.34


                           [FIGURE 1]