系外行星系统掩星周期变化研究进展

Research Progress on the Transit Timing Variations in Extrasolar Planets

在掩星法发现的系外行星系统中,如果存在其他未知的伴星绕同一颗恒星运动,掩星行星由于受到伴星引力的影响,运动轨道将发生变化,轨道周期不再是常数,而是变化的。利用这种变化探测掩星系统中的其他行星,已成为一种新的方法。主要介绍了未知行星与掩星行星之间的引力作用引起的掩星周期变化效应,以及掩星周期变化法探测系外行星的理论和研究进展状况,最后简要讨论了几种影响掩星周期变化的其他因素:共轨行星、卫星、潮汐效应、相对论效应及恒星的引力四极矩等。

To date, more than 120 transit planets have been discovered, but only two multiple systems in which all the planets found by transit timing, Kepler-9 and Kepler-ll. Transit of a single planet on a Keplerian orbit around its star must be strictly periodic. In contrast, the gravitational interactions among planets in a multiple planet system cause planets to speed up and slow down by small amounts, leading to deviations from exact periodicity of transits called transit timing variation （TTV）, which has become one important method to detect additional planets recently. TTV is largest when planetary orbital periods are commensurate or nearly so, which is widely used to detect terrestrial planets on resonant orbit. More than 13 transit systems have been analyzed using TTV, however, they don＇t show clear TTV of additional planets, only give the upper-limited mass of the hidden companion on some common resonant orbits. TTV caused by companions in the system of Kepler- 9/Kepler-11 is obviously found, and then confirms the multiple systems further. Theoretical investigations of TTV combining observations with numerical simulations give what TTV depends on. Not only companions but also co-orbital planets and extramoons cause TTV. Stellar oblateness, general relativity and tidal effects cause periastron precession, then change the transit timing of the transit planet. TTV is dependent on observations, so the research of TTV will be helpful to observers to detect the expected companions. With the development of space missions such as Kepler and CoRoT, more multiple-planet systems will be discovered. Research on these multiple systems will be valuable to understand the formation and evolution of planet systems.