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 CCDéchelle 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 ⊙ and M B sin 3 i = 2.323±0.006 M ⊙ , their effective temperatures to be T eff (A) = 12 840 ± 120 K and T eff (B) = 10 580 ± 240 K, and their projected rotational velocities to be v A sin i A = 14.5 ± 0.1 km s −1 and v B sin i B 4.6 ± 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±0.001 to break this degeneracy and measureω obs = 0.133 ± 0.010 • yr −1 . Subtracting the relativistic contribution oḟ ω GR = 0.0963 ± 0.0002 • yr −1 yields the contribution due to tidal torques:ω cl = 0.037 ± 0.010 • yr −1 . This value is much smaller than the rate predicted by stellar theory, 0.40-0.87 • 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.

Analysis of Spin-Orbit Misalignment in the Eclipsing Binary Di Herculis

“…Then, if this quadrupoleinduced precession is fast enough it can easily alter the full rate of apsidal precession and even make it smaller thanω GR as in the case of DI Her. Somewhat less extreme version of this idea has recently been applied to another eclipsing binary AS Camelopardalis (Pavlovski et al 2011), which also exhibits relatively slow rate of apsidal precession.…”

The Banana Project. V. Misaligned and Precessing Stellar Rotation Axes in Cv Velorum

“…Precession would also produce small changes in the orbital inclination, and therefore changes in any eclipse signals. Misalignment also influences the rate of apsidal precession, as predicted by Shakura (1985) for the case of DI Her and confirmed by Albrecht et al (2009), and as is suspected to be the case for AS Cam (Pavlovski et al 2011).…”

Chemical History of Algol and its Components

“…However, Algol has persistently lacked extensive high-precision photometric and spectroscopic observations. Therefore, in 2006 we started a newÉchelle spectroscopic programme to observe Algol (Pavlovski et al 2010). Over 80 high-resolution and high-S/NÉchelle spectra were secured in two observing runs with FIES at the Nordic Optical Telescope on La Palma, Spain.…”

“…Spectral disentangling has been performed on these data as described in Pavlovski et al (2010). Algol is a hierarchical triple system with a third component in a wide orbit of period 640 d. The contribution of the third component to the total light of the system is uncertain (Richards et al 1988), but is significantly larger than that of the sub-giant component in the inner semidetached binary.…”