A new apsidal motion determination of the eccentric eclipsing binary
V1143 was carried out by J. Burns (USAF), Guinan, and student J.
Marshall. The eclipsing binary V1143 Cyg (HR 7484, HD 185912,
BD+54
2193; 
) consists of a pair of
F5V stars moving in an eccentric orbit (e=0.54) and having an orbital
period of 
. The system is detached with both
components residing well inside their respective Roche lobes. The
orbital and stellar properties of V1143 Cyg are very well determined
from the careful study of Andersen et al.. One of the interesting
aspects of this binary is that its U,V, W space velocity
components, as given by Andersen of +31, -16, -2 km/s are very close to
those of the Hyades cluster (+40, -17, -3). Although the similarity
between the space motions of the binary and the Hyades Moving group
could be a coincidence, it is more likely that V1143 Cyg is a member.
If this is true, then the binary would be coeval with the Hyades, thus
having an age of about 600 Myr. Knowing the age of a binary vastly
increases its importance for testing stellar structure, opacity laws,
and evolution models.
Photoelectric photometry of V1143 Cyg was conducted with the Jenkins
38-cm reflector at Villanova Un. Obs. These observations were
made on the nights of 17 and 19 Oct 1987 UT, using
intermediate-bandpass blue (
Å) and yellow
Å) interference filters. The secondary and
primary minima occurred respectively on these nights. These timings
were combined with the photoelectric eclipse timings already available
up to 1994. Independent linear least squares solutions were made of the
primary and secondary eclipses respectively, yielding periods of
and 
. The period determination from the primary
eclipses is better determined than secondary eclipses because the
primary eclipse has twice as many timings. The analysis of all
available timings yielded an apsidal motion rate of 
yr. This value is nearly identical to
those previously determined. More timings, in particular of secondary
eclipses, are necessary to define the apsidal motion rate more
precisely, so additional photometry will take place during 1997. This
work was supported by NSF grant AST 93-153665 and made use of the SIMBAD
data base, operated at CDS, Strasbourg, Fr.
Beginning in Spring 1995, UBVR photoelectric photometry of
V541 Cyg has been conducted on the Villanova-Fairborn 0.8M APT at Mt.
Hopkins by Guinan, McCook and students J. Maley and J. Marshall. During
1995, differential photometry of the star was obtained on 63 nights.
Nearly complete light curves have been obtained and new eclipse timings
have been made from these data. V541 Cyg is a detached eclipsing binary
consisting of a pair of B9.5 V stars having an eccentric orbit
(e=0.4740) and an orbital period of 
d. Khaliullin was
the first to show that this binary could be an important test case for
General Relativity (GR) because the apsidal motion expected from GR is
significantly larger than the classical apsidal motion arising from the
tidal and rotational distortions of the component stars. Using updated
values for the internal structure constant from Claret & Giménez,
theory predicts a relativistic effect of
yr
/100yr and classical
effects of 
yr
yr.
This result is particularly interesting because in V541 Cyg most of the
apsidal motion is expected to arise from GR.
A new determination of apsidal motion was made using timings
recorded with the APT along with timings reported in the literature.
The analysis yielded an apsidal motion rate of 
yr 
/100yr. This apsidal motion is
nearly the same as one found by M. Wolf. These studies confirm that
V541 Cyg has an observed rate of apsidal motion significantly less than
the theoretically expected apsidal motion. This discrepancy is as
difficult to explain as those found for two other eclipsing binaries, DI
Her and AS Cam. The plan is to continue photometry of the star with the
APT during 1997 to complete the UBVR light curves, in particular,
to cover fully the primary eclipse. Spectroscopic radial velocity
observations of V541 Cyg are currently being conducted by Etzel (SDSU).
Once the light and radial velocity curves are complete, a more thorough
study of this important binary can be made. This study is supported by
NSF grants AST-861362 and AST-9315365 which we gratefully acknowledge.
The reduction and analysis of the IUE observations were supported
by NASA NAG 5-2160. A preliminary report can be found in IBVS 4362.