Study of exoplanetary systems via transit timing variations -- Multisite photometric follow-up of Kepler targets using middle-class telescopes around the world

在四年的连续观测中，开普勒太空望远镜探测到了数千颗系外行星。要排除候选者实际上是恒星性质的可能性，就需要对其质量设定上限。在这方面，凌日计时变化(TTV)方法是一种成功的工具，可以在不需要地面径向速度测量的情况下限制大量系外行星候选者。然而，现在开普勒任务已经提前结束，仍然有多个候选者在如此长的时间尺度上显示电视，以至于无法获得足够的拟合来约束行星质量或动态描述系统。为了克服这一困境，我们组织了KOINet，这是一个独特的近乎全球的光度跟踪网络，由总部设在戈廷根天体物理学研究所的20个中型望远镜组成。一方面，大口径的采集区将使我们能够获得精确的光度测量。反过来，这将允许探测浅层初级凌日事件，击败最强烈的观测偏差之一：我们的地球大气及其对光度数据的影响。另一方面，该网络的望远镜在战略上分布在美国和中国之间，将允许近24小时的连续监测。因此，我们将利用KOINet的综合力量来跟踪任何事件，无论其持续时间或频率如何。总之，KOINet将以与开普勒相当的时间精度收集过境光曲线，并将有可能完成开普勒任务由于提前终止而无法完成的一些科学任务。因此，总体项目的目标是描述总共58个系统的TTV的特征，以便1)确认或拒绝开普勒探测到的凌日天体可能的行星性质，2)显著改善现有的对候选行星质量的限制，以及3)通过分析它们对TTV的影响来约束系统中的非凌日植物。该项目将提供大量确定的行星参数(质量、半径、平均密度)和行星系统结构，从此以后增加我们对系外行星种群的了解。只有通过其独特的特征，我们才能揭示行星如何形成和演化等基本未知，或许还能揭示人类一个由来已久的想法的真实性：太阳系的独特性。

During its four years of continuous observations the Kepler space telescope has detected thousands of exoplanet candidates. To exclude the possibility that a candidate is actually of stellar nature, an upper limit on its mass is required. In this context the transit timing variation (TTV) method has been a successful tool to constrain the masses of exoplanet candidates without the need for ground-based radial velocity measurements. However, now that Kepler mission has come to a premature end there are still multiple candidates which display TTVs on such long time scales that a sufficient fit to constrain the planetary masses or to dynamically characterize the system cannot be attained. To overcome this predicament we have organized KOINet, a unique near-global photometric follow-up network consisting of twenty middle-sized telescopes headquartered at the Institut fuer Astrophysik Goettingen. On one hand, large-aperture collecting areas will allow us to obtain precise photometry. This, in turn, will permit the detection of shallow primary transit events, beating one of the strongest observational biases: our Earth's atmosphere and its implications over photometric data. On the other hand the network's telescopes, strategically distributed between the United States and China, will allow almost 24 hours of continuous monitoring. Thus, we will exploit the combined power of KOINet to follow-up any event, regardless its duration or frequency. All together, KOINet will collect transit light curves with timing precisions competitive with Kepler's, and will have the potential to complete some of the science the Kepler mission could not accomplish due to its early termination. Therefore, the goal of the overarching project is to characterize the TTVs of 58 systems in total, in order to 1) confirm or reject the possible planetary nature of the Kepler-detected transiting objects, 2) to significantly improve the existing constraints on the masses of the planetary candidates, and 3) to constrain non-transiting plants in the system by analyzing their effect on the TTVs. The project will provide a significant number of well determined planet parameters (mass, radius, mean density) and planetary system architectures, henceforth increasing our knowledge about the exoplanet population. It is only by its distinctive features that we will be able to shed some light into unknowns so fundamental as how do planets form and evolve, and maybe the truthfulness about a long-established human thought: the uniqueness of our Solar System.