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_A sin^3 i = 3.213 +/- 0.007 M_sun and M_B sin^3 i = 2.323 +/- 0.006 M_sun, their effective temperatures to be T_eff(A) = 12840 +/- 120 K and T_eff(B) = 10580 +/- 240 K, and their projected rotational velocities to be v_A sin i_A = 14.5 +/- 0.1 km/s and v_B sin i_B = 4.6 +/- 0.1 km/s. 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 +/- 0.001 to break this degeneracy and measure (d omega_obs / dt) = 0.133 +/- 0.010 deg/yr. Subtracting the relativistic contribution of (d omega_GR / dt) = 0.0963 +/- 0.0002 deg/yr yields the contribution due to tidal torques: (d omega_cl / dt) = 0.037 +/- 0.010 deg/yr. This value is much smaller than the rate predicted by stellar theory, 0.40--0.87 deg/yr. 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.

Submitted to ApJL on 9 Feb 2011

References in corpus (7)

• The spin axes orbital alignment of both stars within the eclipsing binary system V1143Cyg using the Rossiter-McLaughlin effect
• The Banana Project. III. Spin-orbit Alignment in the Long-period Eclipsing Binary NY Cephei
• Absolute dimensions of eclipsing binaries. XXIV. The Be star system DW Carinae, a member of the open cluster Collinder 228
• Chemical evolution of high-mass stars in close binaries. I. The eclipsing binary V453 Cygni
• Constrained fitting of disentangled binary spectra: application to V615 Per in the open cluster h Persei
• Tidal and rotational effects in the perturbations of hierarchical triple stellar systems. II. Eccentric systems - the case of AS Camelopardalis
• The Exotic Eclipsing Nucleus of the Ring Planetary Nebula SuWt2

Cited by in corpus (10)

• Eclipse Timing Variation Analyses of Eccentric Binaries with Close Tertiaries in the Kepler field
• The BANANA project. V. Misaligned and precessing stellar rotation axes in CV Velorum
• Physical properties of the eclipsing Delta Sct star KIC 10661783
• Absolute dimensions of detached eclipsing binaries. III. The metallic-lined system YZ Cassiopeiae
• Apsidal motions of 90 eccentric binary systems in the Small Magellanic Cloud
• THE BANANA PROJECT. VI. Close double stars are well aligned with noticeable exceptions; results from an ensemble study using apsidal motion and Rossiter-McLaughlin measurements
• Apsidal motion and physical parameters in the eclipsing system V490 Sct
• The Measurement of Dynamic Tidal Contribution to Apsidal Motion in Heartbeat Star KIC 4544587
• The evolution of the eccentricity in the eclipsing binary system AS Camelopardalis
• Quantitative spectroscopy of close binary stars