Co-orbital exoplanets from close-period candidates: the TOI-178 case
Co-orbital exoplanets from close-period candidates: the TOI-178 case
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来自近周期候选者的共轨道系外行星：TOI-178 案例
DOI：
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发表时间：
2019
影响因子：
6.5
通讯作者：
J. Schneider
中科院分区：
文献类型：
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作者：
A. Leleu;J. Lillo;M. Sestovic;P. Robutel;A. Correia;N. Hara;D. Angerhausen;S. Grimm;J. Schneider
尽管太阳系中存在共轨天体，并且通过行星系统形成模型预测了共轨行星的形成，但迄今为止还没有发现共轨系外行星（也称为特洛伊行星）。在这里，我们研究了在凌日巡天中，当系统中的两个候选行星以相似的周期围绕恒星运行时，共轨道系外行星的特征。这样一对候选结果可以作为假阳性而被丢弃，因为它们不是希尔稳定的。然而，马蹄形或长振动周期蝌蚪共轨道结构可以解释这种周期相似性。这种简并可以通过考虑每个行星的凌日时间变化（TTVs）来解决。我们随后将重点放在三行星候选系统TOI-178上：该系统的两个外部候选系统具有相似的轨道周期，并且在对扇区2的TESS观测中发现其角距接近π∕3。根据已公布的轨道，该系统的长期稳定性要求两颗近周期行星共轨运行。我们的独立趋势和凌日搜索恢复并略微偏向于TESS管道发现的接近3:2:2共振链的三个轨道，尽管我们不能排除将系统接近4:3:2配置的别名。然后，我们更详细地分析了共轨情况，并表明，尽管在2:3 MMR之外有一颗内行星的影响，但对于各种行星质量，无论是特洛伊轨道还是马蹄形轨道，这个潜在的共轨系统在十亿年的时间尺度上都是稳定的。我们预测，在这样的配置下，大型电视将以几百天的周期出现。然后，我们展示了如何从这些电视中获取每个行星的质量。
Despite the existence of co-orbital bodies in the solar system, and the prediction of the formation of co-orbital planets by planetary system formation models, no co-orbital exoplanets (also called trojans) have been detected thus far. Here we study the signature of co-orbital exoplanets in transit surveys when two planet candidates in the system orbit the star with similar periods. Such a pair of candidates could be discarded as false positives because they are not Hill-stable. However, horseshoe or long-libration-period tadpole co-orbital configurations can explain such period similarity. This degeneracy can be solved by considering the transit timing variations (TTVs) of each planet. We subsequently focus on the three-planet-candidate system TOI-178: the two outer candidates of that system have similar orbital periods and were found to have an angular separation close to π∕3 during the TESS observation of sector 2. Based on the announced orbits, the long-term stability of the system requires the two close-period planets to be co-orbital. Our independent detrending and transit search recover and slightly favour the three orbits close to a 3:2:2 resonant chain found by the TESS pipeline, although we cannot exclude an alias that would put the system close to a 4:3:2 configuration. We then analyse the co-orbital scenario in more detail, and show that despite the influence of an inner planet just outside the 2:3 MMR, this potential co-orbital system could be stable on a gigayear time-scale for a variety of planetary masses, either on a trojan or a horseshoe orbit. We predict that large TTVs should arise in such a configuration with a period of several hundred days. We then show how the mass of each planet can be retrieved from these TTVs.