Apsidal motion of the eclipsing binary as Camelopardalis: discrepancy resolved

Pavlovski, Krešimir and Southworth, J. and Kolbas, Vladimir (2011) Apsidal motion of the eclipsing binary as Camelopardalis: discrepancy resolved. Astrophysical Journal Letters, 734 (2). L29-1-L29-6. ISSN 2041-8205

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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 Asin 3 i = 3.213 ± 0.032 M ☉ and M Bsin 3 i = 2.323 ± 0.032 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 Asin i A = 14.5 ± 0.1 km s–1 and v Bsin 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 ± 0.004 to break this degeneracy and measure $\dot{\omega }_{\rm {obs}}=0\fdg 133 \pm 0\fdg 010$ yr–1. Subtracting the relativistic contribution of $\dot{\omega }_{\rm {GR}}=0\mbox{$.\!\!^\circ $}0963\,{\pm}\, 0\mbox{$.\!\!^\circ $}0002$ yr–1 yields the contribution due to tidal torques: $\dot{\omega }_{\rm {cl}}=0\mbox{$.\!\!^\circ $}037\,{\pm}\, 0\mbox{$.\!\!^\circ $}010$ yr–1. This value is much smaller than the rate predicted by stellar theory, 0fdg40-0fdg87 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.

Item Type: Article
Keywords: binaries: eclipsing, binaries: spectroscopic, stars: early-type, stars: rotation
Date: 26 May 2011
Subjects: NATURAL SCIENCES > Physics > Astronomy and Astrophysics
Additional Information: © 2016. The American Astronomical Society. Received 2011 February 9, accepted for publication 2011 May 12. Published 2011 May 26.
Divisions: Faculty of Science > Department of Physics
Publisher: IOP Publishing
Depositing User: Krešimir Pavlovski
Date Deposited: 26 Mar 2017 14:28
Last Modified: 26 Mar 2017 14:31
URI: http://digre.pmf.unizg.hr/id/eprint/4137

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