COMMISSIONS 27 AND 42 OF THE IAU
            INFORMATION BULLETIN ON VARIABLE STARS
                        Number 3925

                                              Konkoly Observatory
                                              Budapest
                                              18 August 1993

                                              HU ISSN 0374 - 0676

                 RED FLARES AT THE PRIMARY MINIMA
                OF THE ECLIPSING BINARY FF ORIONIS


  The eclipsing variable FF Ori (=HD 288053=49.1929, m=10.2-11 pg, Sp=A1) was
discovered by Hoffmeister (1929). After that, the star was observed only visually and
photographically. The binary is situated in the region of the OB association Ori I.
  Our UBVR photoelectric observations were made with 60cm telescope on Mt. Maidanak 
(Uzbekistan) in 1990/92. The star BD+2d1008 (V=10.44m, U-B=10.14m, B-V=0.67m,
V-R=0.38m) was used as a comparison one. 106 in U, 176 in B, 179 in V and 174 in R
measurements for the binary were made. The principal photometric characteristics of the
light curves are presented in Table 1.
           

                       Table 1
                    V     U-B  B-V   V-R
            -------------------------------
            Max   11.23 -0.11 +0.15 +0.18
            MinI  12.13 -0.05 +0.23 +0.25
            MinII 11.32 -0.14 +0.13 +0.14
            -------------------------------
   
   The amplitude of the primary minimum shows the most depth in U (1.02m) and the
least one in R (0.82m). Both minima have the equal durations of 0.145p. They do not show
flat bottoms. According to Kordylewski's (1948) ephemeris the phase of the primary
minimum is moved by 0.0103p+-0.0002p. On the base of the known times of minima listed
in Table 2 we calculated the improved light elements of FF Ori using the method of least
squares:

             Min I=JDH 2448916.658 + 1.8105251d x E
                           +-0.003 +-0.0000004

  This ephemeris was used to calculate the O-C values in Table 2.
  The UBVR-curves are shown in Figure 1. The first three curves are typical for 
Algols, but the R-curve has a distortion after the primary minimum. We have reinspected
carefully all our measurements of both the variable and the comparison star but not any
mistake has been found. The phases of the curve were obtained on JD 2448556 (one point)
and on JD 2448918 (8 points). 52 measurements of the binary were made on the second
night and 44 of them did not show any anomalies. The bottom of the R-curve is plotted
in detail in Figure 2 where the normal curve is drawn by the solid line. The distortion
was 0^p.014 or 36 minutes long and it got the peak of approximately 0.10m R. This peak
brightness is considered to be due to the contribution of some third light equivalent to
a star of 14.6m R. We have calculated Delta R=R_nor - R_obs where R_nor is the brightness of the
binary on its normal curve and Robs is that observed. Plotted in Figure 3 are Delta R values
as a function of phase. It is seen from the Figure that the graph of the distortion resembles

                            [FIGURE 1]

    Figure 1.   The light curves of FF Ori.

                            [FIGURE 2]

    Figure 2.   The R-curve bottom. (The distortion's points
            are denoted by empty symbols.)

                            [FIGURE 3]

        Figure 3.   The light curve of the distortion.



                   Table 2.

J.D.            E            O-C
2400000+                            Reference
----------------------------------------------------------------
25890.40      -12717       +0.0011d Schneller, 1938
30693.727     -10064       +0.0049  Whitney, 1948
31497.600     -9621        +0.0048     "
31772.793     -9469        -0.0020     "
32216.367     -9224        -0.0067  Kordylewski, 1948
42833.289     -3360        -0.0041  Kreiner, Mistecka, 1980
47553.335      -753        +0.0028  Danielkiewicz-Krosniak, 1990
48916.6576        0        -0.0008  Present paper
----------------------------------------------------------------

that of flares on the UV Cet type stars.  We suppose these flares to occur on a cool
secondary the spectrum of which we estimated to be K0. It is well known, however, that
the flares of UV Cet stars reach the peak amplitude at short wavelengths.  The flares
observed do not show this important feature of these stars. The fact that only red flares
(perhaps, regular) occur on FF Ori is difficult to understand.


                          M. M. ZAKIROV
                          Ulugh Beg Astronomical Institute
                          Astronomicheskaya, 33, Tashkent
                          700052, Uzbekistan


References

Danielkiewicz-Krosniak, E.: 1990, Rocznik Astron., No. 62, 92
Hoffmeister, C.: 1929, Astron. Nachr., 236, No. 5655, 233 [BIBCODE 1929AN....236..233H ]
Kordylewski, K.: 1948, Rocznik Astron., No. 19, 76
Kreiner J., Mistecka, A.: 1980, Astron. Nachr., 301, H. 6, 327 [BIBCODE 1980AN....301..327K ]
Schneller, H.: 1938, Klein. Veroff. Sternw. Berlin-Babelsberg, No. 20, 3
Whitney, B. S.: 1948, Astron. J., 53, No. 1,13 [BIBCODE 1947AJ.....53...13W ]