COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2076

                                  Konkoly Observatory
                                  Budapest
                                  1982 January 26

                                  HU ISSN 0374-0676





      PHOTOELECTRIC PHOTOMETRY OF Theta^1 ORIONIS A = V1016 Ori


   With the Dyer Observatory 24-inch Seyfert reflector in the winter of
1979-80 (between JD 2444191.7 and 2444320.6) we obtained differential 
magnitudes of the eclipsing binary Theta^1 Ori A with respect to the comparison
star Theta^2 Ori B: 21 in V, 15 in B, and 10 in U. These observations have
been sent to the I.A.U. Commission 27 archive for unpublished observations
of variable stars (Breger 1979), where they are available as file no. 88.
Further details are given by Sowell (1981).
   The comparison star was the same one used by Hall and Garrison (1969)
and Arnold and Hall (1976) in their photometry of BM Ori, the other eclipsing 
binary in the Trapezium. The diaphragm, 11 arcseconds in diameter,
included the light of Theta^1 Ori E, the faint companion star about 4 arcseconds
away. The sky offset for the variable was taken always at a point in the
Orion Nebula 18 arcseconds due south of the variable.
   Only on the first night were observations taken anywhere inside primary 
eclipse; they covered part of the rising branch around fourth contact.
Comparing those observations with the V light curve of primary eclipse
shown in figure 3.3/1 of Lohsen (1978), we determined

         JD(hel.) = 2444191.552 +- 0.005d

for a time of mid primary eclipse.

   Our remaining observations plotted with the ephemeris

         JD(hel.) = 2443144.600 + 65.43233d E

of Baldwin and Mattei (1977) showed no trace of secondary eclipse. According
to the elements e = 0.662 +- 0.041 and omega = 188.2d +- 5.6d given by Lohsen
(1978) in his solution of his radial velocity curve, secondary eclipse 
(conjunction with the primary star behind) should occur at orbital phase 0.114P,
surprisingly close to primary eclipse and not at all midway between successive 
primary eclipses. Unfortunately there was a gap in our observations 
between 0.05P and 0.29P, so we can say nothing about the existence of
or depth of any secondary eclipse. It has yet to be detected photometrically 
but should be looked for in the right place.


                                
                 JAMES R. SOWELL *
                 DOUGLAS S. HALL

                 Dyer Observatory
                 Vanderbilt University
                 Nashville, Tennessee 37235
                 U.S.A.





References:
Arnold, C. N. and Hall, D. S. 1976, Acta Astr. 26, 91. [BIBCODE 1976AcA....26...91A ]
Baldwin, M. E. and Mattei, J. A. 1977, J.R.A.S.C. 71, 475. [BIBCODE 1977JRASC..71..475B ]
Breger, M. 1979, I.B.V.S. No. 1659.
Hall, D. S. and Garrison, L. M. 1969, P.A.S.P. 81, 771. [BIBCODE 1969PASP...81..771H ]
Lohsen, E. 1978, Ph.D. thesis, University of Hamburg.
Sowell, J. R. 1981, M.S. thesis, Vanderbilt University.





* now at the Department of Astronomy, University of Michigan, Ann Arbor,
  Michigan 48109, U.S.A.


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