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Session 45 - Eclipsing Binaries.
Display session, Thursday, January 08
Exhibit Hall,

[45.10] Physical Properties of the Apsidal Motion Binary System V541 Cygni

N. H. Volgenau (SDSU/U. Maryland), P. B. Etzel (SDSU)

V541 Cygni, an eclipsing system with a period of 15.34 days, provides an important test of relativistic apsidal motion. The system's high orbital eccentricity (e = 0.47) and well-detached components (r_1 = 0.044,\: r_2 = 0.042) cause the relativistic contribution to the apsidal motion to dominate the classical contribution. Previous studies of its theoretical apsidal motion suffered from uncertain estimates of the masses of the components; these estimates relied upon color calibrations of photometric data. For this investigation, the masses were determined from solutions to radial velocity curves. Eighty-two spectra, covering the entire phase cycle, were obtained during the 1995 and 1996 observing seasons using the 1-meter Prairie telescope at Mount Laguna Observatory. The solutions to the radial velocity curves assembled from these spectra reveal masses of 2.41\pm0.02Mødot and 2.16\pm0.03Mødot for the primary and secondary stars, respectively. These masses are slightly lower than previous estimates, yet they are still apposite to the stars' A0 spectral types. In addition, a new analysis of the original photoelectric observations was undertaken using the NDE code. The resultant light curve solution indicates that the primary star has evolved ahead of its companion. The primary star is slightly larger and cooler than the secondary star.

The newly-determined orbital and physical elements of the system allowed the theoretical rate of apsidal motion to be calculated. The total apsidal rate of the system is 0.00826\pm0.00013 degrees/year, and the relativistic contribution is almost nine times greater than the classical contribution. The discrepancy of this result with the observed apsidal rates reported in recent studies by other authors is discussed.

This research was supported by NSF grant AST-9417035.

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