Search for exoplanets with the radial-velocity technique : quantitative diagnostics of stellar activity
Search for exoplanets with the radial-velocity technique : quantitative diagnostics of stellar activity
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DOI：
10.1051/0004-6361:20078144
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发表时间：
2007-08
影响因子：
6.5
通讯作者：
M. Desort;A. Lagrange;F. Galland;S. Udry;M. Mayor
中科院分区：
文献类型：
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作者：
M. Desort;A. Lagrange;F. Galland;S. Udry;M. Mayor
目标。众所周知，在寻找系外行星特征时，恒星活动可能会使高精度径向速度光谱数据的分析复杂化。我们的目标是量化恒星黑子对具有不同光谱类型和自转速度的恒星的影响，并将模拟结果与HARPS光谱仪获得的数据进行比较。方法：研究方法。我们开发了详细的恒星黑子模拟，并估计了它们对寻找太阳系外行星时径向速度数据分析中常用的一些可观测参数的影响，例如径向速度曲线、互相关函数、平分线速度跨度和光度曲线。考虑了恒星和黑子的特性，以及所使用的光谱仪的特性(通常为HARPS)。然后，以搜索系外行星时相同的方式分析计算出的恒星光谱。结果。1)建立了具有不同恒星和黑子性质的F-K型恒星的第一个模拟结果网格(径向速度幅值、平分线速度跨度幅值和形状以及光度学)。2)定量地表明，典型大小为1%的恒星黑子既可以模拟短周期巨行星的径向速度曲线，也可以模拟短周期巨行星围绕G-K型恒星的平分线行为，其vSINI低于光谱仪分辨率。对于中等vSini的恒星，较小的斑点可能会产生类似的特征。这样的黑子可能会使寻找短周期轨道上的低质量行星变得复杂。在这些情况下，必须使用额外的观测数据(例如光度、光谱诊断)来确认短周期行星的存在。我们讨论了这些可能性，并表明，在某些情况下，光度变化可能不足以清楚地排除斑点作为对观测到的径向速度变化的解释。在寻找超级地球行星时，这一点尤为重要。3)还强调指出，获得的径向速度和平分线速度-跨度振幅的量化值很大程度上取决于恒星的详细性质、所用的光谱仪、所用的一条或多条线以及它们的测量方法。高分辨率光谱仪将有助于区分黑子和行星。
Aims. It is known that stellar activity may complicate the analysis of high-precision radial-velocity spectroscopic data when looking for exoplanets signatures. We aim at quantifying the impact of stellar spots on stars with various spectral types and rotational velocities and comparing the simulations with data obtained with the HARPS spectrograph. Methods. We have developed detailed simulations of stellar spots and estimated their effects on a number of observables commonly used in the analysis of radial-velocity data when looking for extrasolar planets, such as radial-velocity curves, cross-correlation functions, bisector velocity spans, and photometric curves. Stellar and spot properties are taken into account, as well as the characteristics of the spectrograph used (generally HARPS). The computed stellar spectra are then analyzed in the same way as when searching for exoplanets. Results. 1) A first grid of simulation results (radial-velocity amplitudes, bisector velocity-span amplitudes and shapes, and photometry) is built for F-K type stars, with different stellar and spot properties. 2) It is shown quantitatively that star spots with typical sizes of 1% can mimic both radial-velocity curves and the bisector behavior of short-period giant planets around G-K type stars with a v sini lower than the spectrograph resolution. For stars with intermediate v sini, smaller spots may produce similar features. Such spots may complicate the search for low-mass planets on short-period orbits. In these cases, additional observables (e.g., photometry, spectroscopic diagnostics) are mandatory to confirm the presence of short-period planets. We discuss these possibilities and show that, in some cases, photometric variations may not be enough to clearly rule out spots as explanations of the observed radial-velocity variations. This is particularly important when searching for super-Earth planets. 3) It is also stressed that quantitative values obtained for radial-velocity and bisector velocity-span amplitudes depend strongly on the detailed star properties, on the spectrograph used, on the line or set of lines used, and on the way they are measured. High-resolution spectrographs will help in distinguishing between spots and planets.