APSIDAL MOTION OF THE ECLIPSING BINARY AS CAMELOPARDALIS: DISCREPANCY RESOLVED

Abstract

We present a spectroscopic study of the eclipsing binary system AS Camelopardalis, the first such study based on phase-resolved CCD echelle spectra. Via a spectral disentangling analysis we measure the minimum masses of the stars to be M{sub A}sin {sup 3} i = 3.213 {+-} 0.032 M{sub sun} and M{sub B}sin {sup 3} i = 2.323 {+-} 0.032 M{sub sun}, their effective temperatures to be T{sub eff}(A) = 12, 840 {+-} 120 K and T{sub eff}(B) = 10, 580 {+-} 240 K, and their projected rotational velocities to be v{sub A}sin i{sub A} = 14.5 {+-} 0.1 km s{sup -1} and v{sub B}sin i{sub B} {<=} 4.6 {+-} 0.1 km s{sup -1}. These projected rotational velocities appear to be much lower than the synchronous values. We show that measurements of the apsidal motion of the system suffer from a degeneracy between orbital eccentricity and apsidal motion rate. We use our spectroscopically measured e = 0.164 {+-} 0.004 to break this degeneracy and measure {omega}-dot{sub obs} = 0{sup 0}.133{+-}0{sup 0}.010 yr{sup -1}. Subtracting the relativistic contribution of {omega}-dot{sub GR} = 0{sup 0}.0963{+-}0{sup 0}0002 yr{sup -1} yields the contribution due to tidal torques: {omega}-dot{sub cl} = 0{sup 0}.037{+-}0{sup 0}.010 yr{sup -1}. This value is much smaller than the rate predicted by stellar theory, 0.{sup 0}40-0.{sup 0}87 yr{sup -1}. We interpret this as a misalignment between the orbital axis of the close binary and the rotational axes of its component stars, which also explains their apparently low rotational velocities. The observed and predicted apsidal motion rates could be brought into agreement if the stars were rotating three times faster than synchronous about axes perpendicular to the orbital axis. Measurement of the Rossiter-McLaughlin effect can be used to confirm this interpretation.