SIMBAD references

Absolute dimensions and masses of V541 Cyg (B9.5 V + B9.5 V) have been computed from its first spectroscopic orbit and the excellent light curve published by Khaliullin in 1985. This binary has a long period (15.34 days) and a highly eccentric orbit (e = 0.479), with very small stars relative to their separation. It shows apsidal motion of 0°.60 ± 0°.10 per 100 years, significantly slower than the rate predicted by theory [0°.89±0°.03 (100 yr)^–1 ]. In this system the rate of apsidal motion due to general relativistic effects is 5 times that from the classical Newtonian causes (tidal and rotational distortions of the stars). The discrepancy in the apsidal motion rate is difficult to explain, and is in the same sense as the discrepancies found for two other eclipsing binaries, DI Her and AS Cam, in which the relativistic contributions to apsidal motion are also significant.