We present a spectroscopic study of the eclipsing binary system AS Camelopardalis , the first such study based on phase-resolved CCD échelle spectra .
Via a spectral disentangling analysis we measure the minimum masses of the stars to be M _ { A } \sin ^ { 3 } i = 3.213 \pm 0.007 { M } _ { \odot } and M _ { B } \sin ^ { 3 } i = 2.323 \pm 0.006 { M } _ { \odot } , their effective temperatures to be T _ { eff } ( { A } ) = 12 840 \pm 120 K and T _ { eff } ( { B } ) = 10 580 \pm 240 K , and their projected rotational velocities to be v _ { A } \sin { i _ { A } } = 14.5 \pm 0.1 km s ^ { -1 } and v _ { B } \sin { i _ { B } } \leqslant 4.6 \pm 0.1 km s ^ { -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 \pm 0.001 to break this degeneracy and measure \dot { \omega } _ { obs } = 0.133 \pm 0.010 ^ { \circ } yr ^ { -1 } .
Subtracting the relativistic contribution of \dot { \omega } _ { GR } = 0.0963 \pm 0.0002 ^ { \circ } yr ^ { -1 } yields the contribution due to tidal torques : \dot { \omega } _ { cl } = 0.037 \pm 0.010 ^ { \circ } yr ^ { -1 } .
This value is much smaller than the rate predicted by stellar theory , 0.40–0.87 ^ { \circ } yr ^ { -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 .