COMMISSIONS 27 AND 42 OF THE IAU 
          INFORMATION BULLETIN ON VARIABLE STARS 
                      Number 3746 
 
                                       Konkoly Observatory 
                                       Budapest 
                                       9 July 1992 
 
                                       HU ISSN 0374 - 0676 
 
 
 
 
   THE POSSIBLE ECLIPSES IN THE T TAURI SPECTROSCOPIC 
             BINARY SYSTEM GW ORIONIS 
 
 
 
  Mathieu et al. (1991) discovered that the classical T Tauri star 
GW Ori is a spectroscopic binary with an orbital period of 242 
days. Besides, they described the properties of GW Ori including the 
spectral energy distribution in the near- and far-infrared regions. 
The mass function is f(M)=0.026 M and the orbital amplitude is 
K=4.7+/-0.3 km/s. Bouvier and Bertout (1989) detected the rotation 
modulation period P=3.25 days and the axial velocity vsini = 43.0+/-2.5 
km/s for GW Ori. The view angle i_0 between the rotation axis and the 
line of sight was computed by Bouvier and Bertout (1989) using these 
two quantities as well as the stellar radius. The latter was 
calculated from the bolometric luminosity and the effective 
temperature of the star (R=8.5R_sun, L=110L_sun, T_e=5660 degK, 
i_0=15deg +/- 1deg). Mathieu et al. (1991) found the inclination angle of the 
spectroscopic orbital plane to be 15deg<i<60deg and assumed a primary 
mass of M_1=2.5M_sun and the secondary mass 0.31<M_2<1.27M_sun. Neither 
value of the inclination angle (i_0, i) permits an eclipse observation 
in GW Ori binary system. 
 
  At the same time we have detected several Algol-like light fadings 
close to spectroscopic phase 0.00 on the photoelectric light curve. 
 
  Our observations of GW Ori have been carried out since 1987 at the 
Mt. Maidanak using 0.6-m and 0.5-m reflectors with identical UBVR 
pulse-counting photometers. Limits of light variations, average 
colours, number of observations and intervals of phases calculated 
according to Mathieu et al. (1991) are listed in Table I. Maidanak 
UBVR-photometry is stored in Tashkent Astronomical Institute Bank 
Data: (Shevchenko V.S., Astronomical Institute of Acad. Sci.  RUz., 
Astronomicheskaya str. 33, Tashkent, 700052 CIS (S.U.)), and are 
available. 
 
  The folded light curves of GW Ori based on Maidanak photoelectric 
observations, Bouvier and Bertout's observations end some other ones 
are shown in Figure 1. Our phase values obtained at Maidanak are very 
close to those of Mathieu et al. (1991), (T_0=2447909 and 
T_0=2447903, respectively). Algol-like fadings are distinguished near 
phase 0.00 in spite of significant irregular light variations. There 
are sufficiently complete observations of two Algol-like minima in 1988 
and 1990. They are shown in Figure 2. It is most probable that minima 
of 1988 and 1990 occurred due to occultation of the T Tauri star GW 
Ori by a circumstellar formation surrounding the secondary component. 
This provides an inclination angle of the orbital plane 80deg<i<90deg and 
the secondary mass M_2<0.25M_sun. 
 
 
                                Table I. UBVR data 
 
Year      Epoch      Phase       N        V         <U-B>   <B-V>   <V-R> 
       2440000 +                       max-min 
1987    7031-7133   0.37-0.79   38   9.815-10.058   0.324   0.977    0.955 
1988    7392-7549   0.86-0.51   69   9.867-10.310   0.205   1.001    0.967 
1989    7767-7887   0.41-0.91   51   9.848-10.026   0.307   1.018    0.950 
1990    8135-8279   0.93-0.53   58   9.860-10.119   0.339   1.003    0.946 
1991    8489-8589   0.39-0.81   52   9.759- 9.970   0.298   0.982    0.923 
 
 
                            [FIGURE 1]

          Figure 1. The folded light curve of GW Ori in V-band 
 
 
  To search for a short-period component in the light variability, our 
observations made in 1987-1991 were analysed by method of digital 
spectral analysis (Berdnikov et al., 1991; Grankin et al., 1991). 
But no significant period shorter than 100d was revealed by this 
analysis, though the light curves outside eclipses contain waves of 
different duration. Two power spectra are shown in Figure 3 as a 
sample. At the same time less reliable periods 1.5<P_0<10 days may 
be revealed in shorter intervals (< 20 days). So, a similar period 
3.0<P_0<3.8 days was confirmed by Bouvier and Bertout's (1989) data 
covering an interval of 13 days. 


                           [FIGURE 2]

            Figure 2. The 1988 and 1990 minima of GW Ori

                           [FIGURE 3]

 Figure 3. Samples of power spectra for GW Ori. The dashed lime 
 indicates 80% confidence interval. The period in the 3-4 day interval 
 (arrows) is absent.

 
  The circumstellar formation around the low mass secondary component 
seems to consist of dust and molecular gases having a dimension of 
(10-50) x 10^8 km. The masses of the secondary stellar body and its 
circumstellar formation can be comparable. 
 
  We suppose that the next eclipse will take place on 10 September 
1992 near zero phase. 
 
 
 
       V.S. SHEVCHENKO, K.N. GRANKIN, M.A. IBRAGIMOV, S.Yu. MELNIKOV 
               Tashkent Astronomical Institute, Uzbekistan, CIS 
 
 
References: 
 
Berdnikov, L.N., Grankin, K.N., Chernyshev, A.V. et al.: 1991, Pisma 
  v Astron. Zh., 17,1, 50.  [BIBCODE 1991PAZh...17...50B ]
Bouvier, J., Bertout, C.: 1989, Astron. and Astrophys., 211, 99.  [BIBCODE 1989A&A...211...99B ]
Grankin, K.N., Ibragimov, M.A., Melnikov, S.Yu. et al.: 1991, 
  IBVS, No. 3627. 
Mathieu, R.D., Adams, F.J., Latham, D.W.: 1991, Astron. J., 101, 
  2184.  [BIBCODE 1991AJ....101.2184M ]