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，开普勒太空望远镜已经探测到数千颗系外行星候选者。为了排除候选恒星实际上具有恒星性质的可能性，需要对其质量设定上限。在这种情况下，过境时间变化（TTV）方法已经成为一种成功的工具，可以在不需要地面径向速度测量的情况下约束系外行星候选者的质量。然而，现在开普勒任务已经过早地结束了，仍然有许多候选者在如此长的时间尺度上显示ttv，以至于无法获得足够的合适来约束行星质量或动态表征系统。为了克服这一困境，我们组织了KOINet，这是一个独特的近全球光度跟踪网络，由总部设在哥廷根天体物理学研究所的20个中型望远镜组成。一方面，大孔径采集区将使我们能够获得精确的光度测定。反过来，这将使探测浅层初级凌日事件成为可能，从而打破最强烈的观测偏差之一：我们的地球大气层及其对光度数据的影响。另一方面，该网络的望远镜，战略性地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的联合力量来跟踪任何事件，无论其持续时间或频率。总而言之，KOINet将收集凌日光曲线，其计时精度可与开普勒相媲美，并且有可能完成开普勒任务由于过早终止而无法完成的一些科学任务。因此，总体项目的目标是对58个系统的ttv进行表征，以便1)确认或拒绝开普勒探测到的过境物体可能的行星性质，2)显着改善现有的行星候选质量约束，以及3)通过分析它们对ttv的影响来约束系统中的非过境植物。该项目将提供大量确定的行星参数（质量、半径、平均密度）和行星系统架构，从此增加我们对系外行星数量的了解。只有通过其独特的特征，我们才能对一些基本的未知事物有所了解，比如行星是如何形成和演化的，也许还能对人类长期以来的一个想法的真实性有所了解：我们太阳系的独特性。

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.