COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                        Number 3070



                                             Konkoly Observatory
                                             Budapest
                                             19 August 1987

                                             HU ISSN 0374-0676


   TIME OF MINIMUM DETERMINATION OF THE ECLIPSING BINARY V1143 CYGNI


   V1143 Cygni is a bright (Vmax = +5.86) eclipsing binary consisting of a
pair of F5V stars moving in an eccentric orbit (e=0.54) with an orbital period
of 7.64 days. The orbital and stellar properties of this system have been
accurately determined by Andersen et al. (1987) who find that the stars are
close to the ZAMS with an age of about 2 x 10^9 years. In addition, independent,
recent determinations of the apsidal motion of V1143 Cyg have been made by
Khaliullin (1983) and by Gimenez and Margrave (1985). The results of these
studies yield an average value for the observed apsidal motion of omega_dot_obs=3.45+/-
0.14 deg/100 yr. This is somewhat smaller than the result of the combined theoretical
classical and relativistic contributions to apsidal motion of omega_dot_c1+gr=
4.25+/-0.72 deg/100 yr. determined by Andersen et al. As first noted by Koch
(1977), V1143 Cyg could be an important system for studying general relativity
because the relativistic contribution to apsidal motion (omega_dot gr = 1.86 deg/100 yr)
is nearly equal to the Newtonian contribution (omega_dot cl = 2.39 deg/100 yr). The
classical or Newtonian contribution to apsidal motion arises from the deviations
of the figures of the stars from spherical symmetry, caused by tidal and 
rotational effects which depend on the fractional radii, masses, rotation rates,
and the internal mass distribution of the stars.
   Photoelectric photometry of V1143 Cyg was conducted with the 51 cm telescope
of Biruni Observatory at Shiraz University, Shiraz, Iran. The observations 
were made on 10 June 1977 UT using blue (b) and yellow (y) filters which
are matched closely to the Stromgren uvby system. The data were reduced using
the software developed at Villanova University. Details of the instrumentation
and data reduction are given by Guinan et al. (1979). Differential magnitudes
were computed in the sense variable minus comparison star in which HD 186239
(V= +7.4; A5V) served as the comparison star. Extinction corrections were
applied from the atmospheric extinction coefficients determined from the 
observations of the comparison star, and the local standard times were converted
to heliocentric Julian data (HJD).


                             [FIGURE 1]

 Figure 1: The differential Stromgren yellow (y) and blue (b) observations
           of primary eclipse of  V1143 Cyg.


   The blue and yellow light observations of primary eclipse appear in
Figure 1, plotted versus heliocentric Julian Date. A determination of the
time of mid-eclipse was made for both light curves using a computer code
developed by one of us (SMC). The algorithm involves a computer graphics
version of the familiar "tracing-paper" method. The reduced photometric data
is first plotted on the screen as observed. This data is then plotted again,
reversed in the time coordinate. This second plot can be moved, as a unit,
relative to the first curve. When the second plot is positioned such that the
curves appear superimposed, the minimum occurs at the same point on the
normal and reversed graphs.     This best fit method gives extremely
precise determinations, as can be seen by the errors given. The time of primary
eclipse is:

      T(min1)=HJD 2443305.3943 +/- 0.0004.

   Using the ephemeris of Andersen et al., the (O-C) of this determination
is +0.00003d. More photoelectric timings of primary and secondary eclipses
of V1143 Cyg are currently being attempted. A further refinement of the system's
apsidal motion should be possible with these new timings.



  EDWARD F. GUINAN     PATRICIA T. BOYD
  SAYED-IRAJ NAJAFI    SEAN M. CARROLL
  FARID ZAMANI-NOOR    Department of Astronomy
  Biruni Observatory   and Astrophysics
  Shiraz University    Villanova University
  Shiraz, Iran         Villanova, PA 19085





References:
Andersen, J., Garcia, J.M., Gimenez, A., and Nordstrom, B. 1987.
   Astron. Astrophys., 174, 107. [BIBCODE 1987A&A...174..107A ]
Gimenez, A. and Margrave, T. E. 1985. Astron. J. 90, 358. [BIBCODE 1985AJ.....90..358G ]
Guinan, E. F., Dorren, J.D., Siah, M.J. and Koch, R.H. 1979.
   Astrophys. J. 229, 296. [BIBCODE 1979ApJ...229..296G ]
Khaliullin, Kh. F. 1983. Astron. Tsirk., No. 1262. [BIBCODE 1983ATsir1262....1K ]
Koch, R. H. 1977. Astron. J. 82, 653. [BIBCODE 1977AJ.....82..653K ]