COMMISSION 27 OF THE I. A. U.
             INFORMATION BULLETIN ON VARIABLE STARS
                          Number 3491

                                             Konkoly Observatory
                                             Budapest
                                             17 July 1990

                                             HU ISSN 0374 - 0676


     NEW PHOTOELECTRIC OBSERVATIONS OF THE ECLIPSING BINARY FO Vir

   The light variation of FO Vir star was discovered by Jackisch (1972).
It was initially thought to be an RRc type variable star with a period of
less than one day (Jackisch 1972, Poretti 1977 and Eggen 1983). It is also
a member of visual binary J2091. Recently Schmidt and Fernie (1984), Antonello,
Mantegazza and Poretti (1984) found independently its period being
0.775567 days. Mochnacki et al. (1986) disclosed that FO Vir is a precontact
binary. The A7V primary component very nearly fills its Roche lobe.
   The UBV photoelectric observations of FO Vir were made in March and May
1986, and in March 1987, H-beta-w and H-beta-n were observed in April 1988 using
the 60 cm reflector equipped with a photoelectric photometer at Beijing 
Observatory. HR 5037 and HR 5059 were chosen as the comparison star and check
star respectively.
   The UBV light curves of FO Vir (Figure 1) show that the amplitude 
increases with the decreasing wavelength, about 0.88 magnitude in U band, 
about 0.56 magnitude in B band and 0.52 magnitude in V band.
   The U-B and B-V color index curves (Figure 2) show that there is an 
obvious dip near the minimum, especially in U-B curves.
   The light minimum time of FO Vir and the O-C values are as follows:
           Minimum time                     E               O-C (days)
   JD(hel) 2446863.3214 (I)               1833              -0.0039
                   +/-5
   JD(hel) 2446565.1126 (II)              1448.5            -0.0072
                   +/-4
The O-C values of light minimum are calculated according to the ephemeris
which was given by Mochnacki et al. (1986). They noted the individual data
imply changes in the shape of the V light curves at different epochs at the
level of several hundredths of a magnitude.
   In order to test the short-time-scale light fluctuation of FO Vir, we
analysed all our data using autoregressive (AR) power spectral and harmonic
analysis method for FO Vir. We did not find any short-time-scale light variation,
the amplitude of which is larger than the observed error (+/-0.01 mag.).


                                [FIGURE 1]

             Figure 1. The UBV Light Curves of FO Vir

                                [FIGURE 2]

       Figure 2. The Color Index D(B-V) and D(U-B) Curves of FO Vir



                         LIU XUEFU and FANG YONGGEN
                         Dept. of Astronomy
                         Beijing Normal University, China

                         JIA GUISHAN
                         Beijing Planetarium, China

References:
Antonello, E., Mantegazza, L., Poretti, E.: 1984, IBVS No. 2567.
Eggen, O.J.: 1983, Astron.J., 88, 361. [BIBCODE 1983AJ.....88..361E ]
Jackisch, G.: 1972, Astron.Nach., 249, 1. [BIBCODE 1972AN....294....1J ]
Mochnacki, S.W., Fernie, J.D., Lyons, R., Schmidt, F.H., Gray, R.O.: 1986,
     Astron.J., 91, 1221. [BIBCODE 1986AJ.....91.1221M ]
Poretti, E.: 1977, IBVS No. 1336.
Schmidt, F.H., Fernie, J.D.: 1984, IBVS No. 2527.