XO-3行星系统中的自旋轨道错位？
Misaligned spin-orbit in the XO-3 planetary system?
摘要：
凌日系外行星XO-3b是一颗引人注目的行星，它的质量很大，轨道偏心。这些不寻常的特征使得测试它的轨道平面是否平行于其宿主恒星的赤道变得有趣，因为它被观察到其他过境行星。我们进行了径向速度测量XO-3与SOPHIE摄谱仪在1.93米望远镜的上普罗旺斯天文台在行星过境，并在其他轨道阶段。这使我们能够观察到罗西特-麦克劳克林效应，并结合对凌日光变曲线的新分析，改进行星的参数。凌日期间径向速度异常的不寻常形状为近似横向的罗斯特-麦克劳克林效应提供了线索。行星轨道轴和恒星旋转轴之间的天空投影角应该是lambda = 70 +/- 15度，以与我们的观测相一致。这表明，一些靠近的行星可能是由于行星和/或恒星之间的引力相互作用，而不是由于与吸积盘相互作用而迁移。这一令人惊讶的结果需要额外的观测来证实，特别是在低气团的情况下，以完全排除信号是由于系统效应造成的可能性。
英文摘要：
The transiting extrasolar planet XO-3b is remarkable, with a high mass and eccentric orbit. The unusual characteristics make it interesting to test whether its orbital plane is parallel to the equator of its host star, as it is observed for other transiting planets. We performed radial velocity measurements of XO-3 with the SOPHIE spectrograph at the 1.93-m telescope of Haute-Provence Observatory during a planetary transit, and at other orbital phases. This allowed us to observe the Rossiter-McLaughlin effect and, together with a new analysis of the transit light curve, to refine the parameters of the planet. The unusual shape of the radial velocity anomaly during the transit provides a hint for a nearly transverse Rossiter-McLaughlin effect. The sky-projected angle between the planetary orbital axis and the stellar rotation axis should be lambda = 70 +/- 15 degrees to be compatible with our observations. This suggests that some close-in planets might result from gravitational interaction between planets and/or stars rather than migration due to interaction with the accretion disk. This surprising result requires confirmation by additional observations, especially at lower airmass, to fully exclude the possibility that the signal is due to systematic effects.
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