The evolution of substellar companions of intermediate mass stars

与类太阳恒星的行星相比，人们对中等质量恒星的行星知之甚少。到目前为止，我们的知识几乎完全是基于理论研究和对巨星的观测。两者都暗示，这些恒星的行星和褐矮星伴星的出现频率远远高于低质量恒星。然而，没有探测到围绕一颗距离小于0.5AU的巨星运行的恒星下伴星，这一事实引发了这样一个问题：这些天体是从未形成过，还是在恒星变成巨星时被吞没并摧毁了。因此，恒星下伴星的命运与其主星的演化息息相关，特别是在主星演化的巨大分支阶段。因此，为了了解行星的演化，有必要跟踪它们从主序到巨型分支甚至更远的演化。我们知识中的两大空白是主序上的中等质量恒星的行星和水平分支上的恒星。通过研究两个紧密相连的博士项目中的主序A星和B星以及蓝色水平分支星，从而包围红巨星阶段，我们计划从经验上考察主星演化对星下伴星的影响。通过选择一个用CoRoT卫星观测到的定义良好的恒星样本，使用已经获取的20000个光谱，我们预计可以找到10到20个这些类型的恒星的亚星伴星。这样，我们就能知道当一颗中等质量恒星演化成巨星时，被吞没的行星比例是多少，并通过对BHB恒星的研究，我们将知道在巨型分支阶段之后，亚恒星伴星的命运是什么，以及亚恒星伴星是否能影响它们所在恒星的演化。

In contrast to planets of solar-like stars, very little is known about the planets of intermediate mass stars. Up to now, our knowledge is almost exclusively based on theoretical studies and observations of giants stars. Both imply that the frequency of planets and brown dwarf companions of these stars is much higher than that of low mass stars. However, the fact that no substellar companion orbiting a giant star closer than 0.5 AU has been detected raises the question whether such objects never formed or whether they were engulfed and destroyed when the star became a giant. The fate of substellar companions thus is tied to the evolution of their host stars, in particular in the giant branch phases of the host stars’ evolution. In order to understand the evolution of planets, it is thus essential to follow their evolution from the main sequence to the giant branch and beyond. The two big gaps in our knowledge are planets of intermediate-mass stars on the main-sequence, and stars on the horizontal branch. By studying main sequence A and B stars as well as blue horizontal branch stars in two closely interlinked Ph.D. projects, thereby bracketing the red giant phase, we plan to investigate empirically the impact of host star evolution on the substellar companion. By selecting a well defined sample of stars that has been observed with the CoRoT satellite, using 20000 spectra already taken, we expect to find between 10 and 20 substellar companions of these types of stars. In this way, we will find out what fraction of planets are engulfed when an intermediate-mass star evolves to become a giant, and by studying the BHB stars, we will find out what the fate of substellar companions is after the giant branch phase, and whether substellar companions can effect the evolution of their host stars.