COMMISSIONS 27 AND 42 OF THE IAU 
          INFORMATION BULLETIN ON VARIABLE STARS 
                      Number 3794 
 
                                    Konkoly Observatory 
                                    Budapest 
                                    26 October 1992 
 
                                    HU ISSN 0374 - 0676 
 
 
      FLARE STARS IN THE PRAESEPE CLUSTER REGION 
 
 
Examination of photographic material of the Praesepe cluster 
region from Tonantzintla Schmidt plates, covering the 
interval 1976-80 allowed us to find two new flare stars and 
9 flare-ups of known stars. The total observational time is 
about 102 hours. In Table 1 in first column we continue the 
Tonantzintla numbering of the Praesepe flare stars, then the 
equatorial coordinates, ultraviolet magnitude at minimum, 
the amplitude of flare event, the date of flare are given 
respectively. 
 
                          Table 1 
           New flare stars in the Praesepe region 
 
Ton  alpha(1950)   delta(1950)    U       DeltaU    Date of flare 
25      8h39.3m      20d51'       15.6     0.6      14 March 1978 
26         44.1      20 46       >17      >3.5      13 March 1978 
 
In Table 2 data on repeated flare-ups of known flare stars 
which are non-members or probable non-members are given. In 
the first column the Praesepe Flare Star Catalogue number is 
given (Tsvetkova et al. 1991). 

                        Table 2 
        Repeated flares in the Praesepe region 
 
PFSC  TON     U    DeltaU  Date of flare 
 
3*     12   13.9    3.5    16 March 1977 
3      12   13.9    3.0    22 March 1977 
3      12   13.9    2.0    13 March 1978 
3**    12   13.9    2.0    16 April 1980 
4      13   15.8    0.5    10 March 1978 
4      13   15.8    1.9    01 April 1978 
11     15   16.5    2.0    19 March 1980 
53     23   17.0    0.8    04 March 1978 
 
* Three images (15m X 3) before the fast flare-up were 
about 0.5 mag brighter than normal minimum. Star can be 
variable at minimum light. 
 
** This flare-up was slow, rise time was longer than 30 
minutes and total time of flare is 2h15m. 
 
During 102 hours of observations only two new flare stars 
were found. From among 57 known flare stars of the Praesepe 
catalogue only 48 can be considered as members of the 
cluster. The total expected number of flare stars in the 
Praesepe cluster according to Ambartsumian's method 
(Ambartsumian et al., 1970) is about 160. 
 
The mean period of flare-ups of cluster flare stars is about 
2000 hours. It confirms once more, that the Praesepe 
cluster is poor of flare stars and with the age of the 
cluster, the mean frequency of flare-ups increases. 

 
G. GONZALEZ                          E. PARSAMIAN 
C. ESCAMILLA                         Byurakan Observatory, Armenia 
Instituto Nacional de Astrofisica,   Instituto Nacional de Astrofisica, 
Optica y Electronica,                Optica y Electronica, 
Tonantzintla, Mexico                 Tonantzintla, Mexico 
 
 
References: 
 
Ambartsumian V. A., Mirzoyan L. V., Parsamian E. S., 
  Chavushian O. S., Erastova L. K., 1970, Astrofizika, 6, 7  [BIBCODE 1970Afz.....6....7A ]
Tsvetkova K. P., Tsvetkov M. K., Jankovics I., 1991, 
  Catalogue of Flare Stars in the Praesepe Region, Sofia