COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                      Number 1148

                                Konkoly Observatory
                                Budapest
                                1976 July 5



         ON THE SECONDARY MINIMUM OF theta1 Ori A



  Photoelectric observations of theta1 Ori A were obtained on 21 March
1975, starting at 0332 UT. This is within the time predicted for
the secondary minimum (W.A. Feibelman 1975).
Eight UBV observations obtained with the 1 meter Ritchey-Chretien
telescope at the Flagstaff Station of the Naval Observatory failed
to show a decrease in light from normal.
  A 13.39" aperture was used, theta1 Ori D was monitored as a comparison 
star, sky readings were taken 15" west of A in the nebulosity,
and observations were terminated by clouds. As can be seen below,
where the observations are grouped in three means, differential
photometry was not needed to demonstrate that the light did not
vary by more than the error of each mean.

     JDH          theta      V           B-V         U-B       n
   2440000.0+

   2858.6465    195.559  6.72+-0.03  0.03+-0.00  -1.00+-0.02   3
   2858.6569    195.578  6.74+-0.04  0.03+-0.01  -1.00+-0.01   3
   2858.6694    195.601  6.73+-0.04  0.03+-0.02  -0.99+-0.02   2

  The values of theta were computed using the light elements below
which were derived from data by E. Lohsen (1975a, 1976b) and K.Aa.
Strand (1975).
           T_0 = 244 1966.826 +- 196.297 E.
            
  Feibelman predicted the secondary minimum to extend to theta=196deg.
The above observations do not support this, but do confirm visual
observations reported by Lohsen (1976b).


                          R.L. WALKER

                          Naval Observatory
                          Flagstaff Station
                          Flagstaff, Arizona, U.S.A.

References:
W.A. Feibelman, 1975, IBVS No. 1070
E. Lohsen, 1975a, IBVS No. 988
E. Lohsen, 1976b, IBVS No. 1129
K.Aa. Strand 1975, IBVS No. 1025