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arXiv 1104.2179astro-ph.SR
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食双星AS Camelopardalis的拱点运动:矛盾解决

Apsidal motion of the eclipsing binary AS Camelopardalis: discrepancy resolved

K. Pavlovski, J. Southworth, V. Kolbas

摘要:

我们提出了一个光谱研究的食双星系统AS Camelopardalis,第一个这样的研究的基础上相位分辨CCD阶梯光栅光谱。通过光谱解缠分析,我们测得这些恒星的最小质量分别为M_A sin^3 i = 3.213 +/- 0.007 M_sun和M_B sin^3 i = 2.323 +/- 0.006 M_sun,它们的有效温度分别为T_eff(A)= 12840 +/- 120 K和T_eff(B)= 10580 +/- 240 K,它们的投影自转速度分别为v_A sini_A = 14.5 ± 0.1 km/s和v_B sini_B = 4.6 ± 0.1 km/s。这些预计的旋转速度似乎比同步值低得多。我们发现,测量的拱点运动的系统遭受从轨道偏心率和拱点运动速率之间的简并。我们使用光谱测量的e = 0.164 +/- 0.001来打破这种简并,并测量(d omega_obs / dt)= 0.133 +/- 0.010 deg/yr。减去相对论贡献(d omega_GR / dt)= 0.0963 +/- 0.0002 deg/yr得到潮汐力矩的贡献:(d omega_cl / dt)= 0.037 +/- 0.010 deg/yr。这个值比恒星理论预测的0.40- 0.87度/年的速率小得多。我们将其解释为近距离双星的轨道轴与其组成恒星的旋转轴之间的不对准,这也解释了它们明显的低旋转速度。如果恒星围绕垂直于轨道轴的轴旋转的速度比同步速度快三倍,那么观测到的拱点运动速率和预测的拱点运动速率就可以达成一致。测量Rossiter-McLaughlin效应可以用来证实这一解释。

英文摘要:

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.

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