RV exoplanets and stellar activity

虽然径向速度（RV）方法在系外行星发现领域占主导地位已有十多年，但近年来，开普勒使命等天基凌日观测的大量结果使其黯然失色。然而，RV仍然是在附近恒星周围的温和轨道上寻找低质量行星的强大工具，这是描述任何过境行星的关键组成部分，也是对探测行星系统外部的直接成像方法的直接（和更便宜）补充。如今，RV光谱仪通常达到亚m/s的精度，而天体物理噪声源，特别是恒星活动，限制了它们对温和轨道上低质量行星的灵敏度。为了克服这一点，我们正在开发创新的方法来提取和建模RV，并使用最先进的贝叶斯机器学习技术区分恒星和行星信号。具体而言，恒星光谱直接建模为在略有不同的休息波长采样的高斯过程（GP）的多个观测，并与GP的参数一起优化历元之间的波长偏移。由此产生的相对RV与各种恒星活动指标同时进行分析，以解开活动和行星信号的纠缠。这些工具仍需进一步开发，但已经给出了非常有希望的结果。该博士项目将进一步开发和测试这些方法，并将其应用于RV调查的新数据，以及K2和TESS卫星发现的新凌日行星的RV后续行动。它可以为CHEOPS使命提供支持，并最终帮助优化PLATO使命的后续工作，以及对来自未来RV光谱仪（如INT/HARPS 3，VLT/ESTERO和E-ELT/HIRES）的数据进行分析。该项目福尔斯STFC关键科学问题：B：恒星和行星系统是如何发展的？它将涉及与一些领导RV搜索系外行星的团体的合作，包括D。剑桥大学的Queloz小组，以及将GPS应用于系外行星数据集的专家，包括D。Foreman-Mackey（熨斗研究所计算天体物理中心）。

While the radial velocity (RV) method dominated the field of exoplanet discovery for over a decade, in recent years it has been somewhat overshadowed by the wealth of results from space-based transit surveys such as the Kepler mission. However, RVs remain a powerful tool to search for low-mass planets in temperate orbits around nearby stars, a crucial component of the characterisation of any transiting planet, and a direct (and much cheaper) complement to direct imaging methods which probe the outer parts of planetary systems. Nowadays, RV spectrographs routinely reach sub-m/s precision, and it is astrophysical noise sources, particularly stellar activity, that limit their sensitivity to low-mass planets on temperate orbits. To overcome this, we are developing innovative methods to extract and model RVs and distinguish between stellar and planetary signals, using state-of-the art Bayesian machine learning techniques. Specifically, the stellar spectra are modelled directly as multiple observations of a Gaussian process (GP) sampled at slightly different rest wavelengths, and the wavelength shifts between epoch are optimized together with the parameters of the GP. The resulting relative RVs are then analysed simultaneously with various stellar activity indicators to disentangle activity and planetary signals.These tools still need further development, but are already giving very promising results. This PhD project will consist in developing and testing these methods further, and applying them to new data from RV surveys, as well as RV follow-up of new transiting planets discovered by the K2 and TESS satellites. It may provide support to the CHEOPS mission and will ultimately help optimized the follow-up of the PLATO mission, as well as the analysis of data from future RV spectrographs such as INT/HARPS3, VLT/ESPRESSO and E-ELT/HIRES.This project falls within the STFC key science question: B: How do stars and planetary systems develop and is life unique to our planet? It will involve collaborations with a number of groups leading RV searches for exoplanets, including Prof D. Queloz's group at the University of Cambridge, as well as with experts in the application of GPs to exoplanet datasets, including Dr D. Foreman-Mackey (Center for Computational Astrophysics, Flatiron Institute).