Analytic Estimates of the Achievable Precision on the Physical Properties of Transiting Planets Using Purely Empirical Measurements
Analytic Estimates of the Achievable Precision on the Physical Properties of Transiting Planets Using Purely Empirical Measurements
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DOI：
10.3847/1538-4357/abe941
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发表时间：
2021-01
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影响因子：
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通讯作者：
R. Rodríguez Martínez;D. Stevens;B. Gaudi;J. Schulze;W. R. Panero;Jennifer A. Johnson;Ji Wang
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作者：
R. Rodríguez Martínez;D. Stevens;B. Gaudi;J. Schulze;W. R. Panero;Jennifer A. Johnson;Ji Wang
我们仅使用经验或半经验的测量方法，对凌日行星的质量、半径、表面重力和密度的分数不确定度进行了解析估计。我们首先用凌日光度和径向速度(RV)观测值来表示这些参数，如果需要的话，还可以表示恒星半径R⋆。与前人的结果一致，我们发现，在圆形轨道的假设下，行星的表面重力(Gp)只取决于经验的凌日和RV参数，即行星周期P、凌日深度δ、RV半振幅K⋆、凌日持续时间T和进出持续时间τ。然而，行星的质量和密度取决于所有这些量，加上R⋆。因此，关于行星质量、半径和密度的推断必须依赖于外部约束，如恒星半径。对于明亮的恒星，现在可以通过测量恒星测辐射热通量、有效温度和通过其视差到恒星的距离来近乎经验地测量恒星半径，而消光A-V是唯一的自由参数。对于任何给定的系统，行星参数都有一个可达到的精度等级，因此行星表面的重力比密度更准确地测量，密度又比质量更准确地测量。我们发现，表面引力对类地行星的核心质量分数有很强的制约作用。这是有用的，因为表面重力可能是地球上测量到的最好的属性之一。
We present analytic estimates of the fractional uncertainties on the mass, radius, surface gravity, and density of a transiting planet, using only empirical or semi-empirical measurements. We first express these parameters in terms of transit photometry and radial velocity (RV) observables, as well as the stellar radius R ⋆, if required. In agreement with previous results, we find that, assuming a circular orbit, the surface gravity of the planet (g p ) depends only on empirical transit and RV parameters, namely the planet period P, the transit depth δ, the RV semi-amplitude K ⋆, the transit duration T, and the ingress/egress duration τ. However, the planet mass and density depend on all these quantities, plus R ⋆. Thus, an inference about the planet mass, radius, and density must rely upon an external constraint such as the stellar radius. For bright stars, stellar radii can now be measured nearly empirically by using measurements of the stellar bolometric flux, the effective temperature, and the distance to the star via its parallax, with the extinction A V being the only free parameter. For any given system, there is a hierarchy of achievable precisions on the planetary parameters, such that the planetary surface gravity is more accurately measured than the density, which in turn is more accurately measured than the mass. We find that surface gravity provides a strong constraint on the core mass fraction of terrestrial planets. This is useful, given that the surface gravity may be one of the best measured properties of a terrestrial planet.