EXPRES. II. Searching for Planets around Active Stars: A Case Study of HD 101501
EXPRES. II. Searching for Planets around Active Stars: A Case Study of HD 101501
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DOI：
10.3847/1538-3881/abc41e
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发表时间：
2020-10
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通讯作者：
S. Cabot;R. Roettenbacher;G. Henry;Lily L. Zhao;R. Harmon;D. Fischer;J. Brewer;J. Llama;R. R. P
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作者：
S. Cabot;R. Roettenbacher;G. Henry;Lily L. Zhao;R. Harmon;D. Fischer;J. Brewer;J. Llama;R. R. P
通过将仪器误差控制在10 cm s−1以下，EXPRES（EXPREME PRECISE Spectrograph）可以更深入地研究光球速度，从而掩盖微弱的开普勒信号。高斯过程（GP）已成为径向速度数据集相关噪声建模的标准工具。虽然GPS受到星星物理特性的限制和激励，但在某些情况下，它们仍然足够灵活，可以吸收未解决的开普勒信号。我们应用GP回归EXPRESS径向速度测量的3.5 Gyr老色球活跃的类太阳星星，HD 101501。我们得到严格的限制恒星自转周期和斑点分布的演变，使用28个赛季的地基测光，以及最近的凌日系外行星调查卫星数据。对两组测光数据进行光变曲线反演，以揭示星星上的斑点分布和斑点演化时间尺度。我们发现HD 101501中大于5 m s−1的均方根径向速度变化可以用没有行星的GP恒星活动模型很好地模拟，产生45 cm s−1的残余均方根散射。我们进行了模拟，用GP框架注入和恢复信号，以证明需要高节奏的观测才能最有效地使用GP来检测像HD 101501这样的活跃恒星周围的低质量行星。稀疏采样防止GP学习相关的噪声结构，并且可以允许它吸收预期的开普勒信号。我们量化的中到高的节奏监测，提供必要的信息，解开光球功能使用GPS和探测活跃的恒星周围的行星。
By controlling instrumental errors to below 10 cm s−1, the EXtreme PREcision Spectrograph (EXPRES) allows for a more insightful study of photospheric velocities that can mask weak Keplerian signals. Gaussian processes (GP) have become a standard tool for modeling correlated noise in radial velocity data sets. While GPs are constrained and motivated by physical properties of the star, in some cases they are still flexible enough to absorb unresolved Keplerian signals. We apply GP regression to EXPRES radial velocity measurements of the 3.5 Gyr old chromospherically active Sun-like star, HD 101501. We obtain tight constraints on the stellar rotation period and the evolution of spot distributions using 28 seasons of ground-based photometry, as well as recent Transiting Exoplanet Survey Satellite data. Light-curve inversion was carried out on both photometry data sets to reveal the spot distribution and spot evolution timescales on the star. We find that the >5 m s−1 rms radial velocity variations in HD 101501 are well modeled with a GP stellar activity model without planets, yielding a residual rms scatter of 45 cm s−1. We carry out simulations, injecting and recovering signals with the GP framework, to demonstrate that high-cadence observations are required to use GPs most efficiently to detect low-mass planets around active stars like HD 101501. Sparse sampling prevents GPs from learning the correlated noise structure and can allow it to absorb prospective Keplerian signals. We quantify the moderate to high-cadence monitoring that provides the necessary information to disentangle photospheric features using GPs and to detect planets around active stars.