COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                       Number 3016


                                        Konkoly Observatory
                                        Budapest
                                        23 April 1987

                                        HU ISSN 0374-0676

    
     PHOTOELECTRIC OBSERVATIONS OF THE FLARE STAR EV LAC IN 1983

 Photoelectric monitoring of the flare star EV Lac has been carried out at
the Stephanion Observatory during the year 1983 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-colour of the international UBV system.
  The telescope and photometer used have been described elsewhere (Mavridis
et al. 1982). The transformation of our instrumental ubv system to the 
international UBV system is given by the following equations:


           a) For the period August 2-21, 1983:

              V = v0 + 2.910 + 0.037 (b-v)0,
              B-V= 0.444 + 1.093 (b-v)0

           b) For the period October 3-5, 1983:

              V = v0 + 2.645 + 0.171(b-v)0 ,
             B-V = 0.487 + 0.972(b-v)0 .

  The monitoring intervals in UT as well as the total monitoring time for
each night are given in Table I. Any interruption of more than one minute has
been noted.
  During the 31.33 hours of monitoring time three flares were observed, the
characteristics of which are given in Table II. In this table following 
characteristics (Andrews et al. 1969) are given: a) the date and universal time of
flare maximum, b) the duration before and after the maximum (tb and ta, 
respectively), as well as the total duration of the flare, c) the value of the ratio
(If-I0)/I0 corresponding to flare maximum, where I0 is the intensity deflection
less sky background of the quiet star and If is the total intensity deflection


                               Table   I

Date             Monitoring Intervals (U.T.)                Total monitoring
1983                                                        Time
August
           h m        h m            h m   h m   h m    h m
2-3       2038     - 2106           2132- 2201  2206 - 2240
          2304     - 2333,          2337- 0009,             2h  32m
3-4       2120     - 2140,          2144- 2211, 2314 - 2344,
          2349     - 0026.                                  1   54
4         2231     - 2301,          2305- 2334.             0   59
9         2201     - 2234,          2237- 2311.             1   07
10        2238     - 2311,          2314- 2350.             1   09
11        2212     - 2244,          2248- 2319.             1   03
12-13     2129     - 2232,          2252- 2324,  2326  - 2341,
          2348     - 0012.                                  2   14
13        2033     - 2108,          2111- 2141,  2158  - 2230,
          2233     - 2320.                                  2   24 
16-17     2305     - 2334,          2338- 0019.             1   10
17        2153     - 2222,          2227- 2237,  2240  - 2301,  1  00
18-19     2042     - 2111,          2115- 2147,  2207  - 2244,
          2248     - 2317,          0010- 0110.             3   07
19-20     2236     - 2313,          2317- 2353,  0002  - 0045,
          0103     - 0147,                                  2   40
20-21     2208     - 2237,          2242- 2311,  2315  - 2344,
          0007     - 0038,          0042- 0100.            2   16
October
3         1839     - 1909,          1912- 1945,  1948  - 2017,
          2033     - 2059,          2102- 2137,             2   33
4         1833     - 1900,          1902- 1931,  1934  - 2007,
          2022     - 2053,          2055- 2128,             2   33
5         1828     - 1903,          1906- 1934,  1936  - 2005,
          2021     - 2058,          2100- 2130,             2   39


                                                 Total     31h 20m

               Table II
Characteristics of the flares observed
                                 
Flare   Date   UT tb              ta     Duration
No      1983   max min            min    min
        Oct.
1       3      21h15m71  0m36     1.00   1.36
2       5      18 30.05  0.52     5.30   5.82
3       5      20 27.97  0.32     0.44   0.76

(If-I0)/I0      P      Deltam   sigma   Air
max             min     mag     mag     mass

0.20            0.09    0.20    0.02    1.02
0.44            1.00    0.40    0.03    1.08
0.21            0.08    0.21    0.02    1.01

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 =
(If-I0)/I_0dt, e) the increase of the apparent magnitude of the star at
flare maximum delta m(b) = 2.5 log(If/I0), where b is the blue magnitude of the
star in the instrumental system, f) the standard deviation of random noise
fluctuation sigma(mag) = 2.5 log(I0+sigma)/I0 during the quiet-state phase 
immediately preceding of the flare and g) the air mass at flare maximum.
The light curves of the observed flares in the b colour are shown in Fig. 1-3.


                             [FIGURE 1]
                             [FIGURE 2]
                             [FIGURE 3]


S. AVGOLOUPIS                   L.N. MAVRIDIS

Department of Astronomy         Department of Geodetic
University of Thessaloniki      Astronomy
                                University of Thessaloniki
                                

P. VARVOGLIS
Department of Mathematics
University of Thrace


References:

Andreas, A.D, Chugainov, P.P., Gershberg, R.E., and Oskanian, V.S.:1969,
  Inf. Bull. Var. Stars No. 326,
Mavridis, L.N., Asteriadis, G.A., and Mahmoud, F.M,: 1982, in Compendium
  in Astronomy (ed by E.G. Mariollopoulos, P.S. Theocaris, and
  L.N. Mavridis) D. Reidel Publishing Company, Dordrecht,
  Holland, p. 253. [BIBCODE 1982coas.conf..253M ]