Planets and stellar activity: hide and seek in the CoRoT-7 system?
Planets and stellar activity: hide and seek in the CoRoT-7 system?
复制标题
行星和恒星活动：CoRoT-7 系统中的捉迷藏？
DOI：
10.1093/mnras/stu1320
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发表时间：
2014
影响因子：
4.8
通讯作者：
Haywood R
中科院分区：
文献类型：
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作者：
Haywood R
自从发现凌日的超级地球CoRoT-7 b以来，几项研究对该系统中行星的数量和质量产生了不同的结果，主要是由于星星的高水平活动。我们在2012年1月用HARPS和CoRoT重新观测了CoRoT-7，因此我们现在可以同时获得径向速度和光度数据。这使我们能够使用非凌日变化的星星的光变曲线来估计径向速度的变化引起的抑制对流蓝移和恒星黑子阻止的流量。为了解释没有光度特征的径向速度中与活动相关的效应，我们还在径向速度模型中包含了一个额外的活动项，我们将其视为具有与光变曲线相同协方差特性（因此具有相同的频率结构）的高斯过程。我们的模型被纳入到一个蒙特卡洛马尔可夫链，以使一个精确的确定的轨道的CoRoT-7 b和CoRoT-7 c。我们测得行星B和c的质量分别为4.73 ± 0.95和13.56 ± 1.08 M。CoRoT-7 b的密度为（6.61 ± 1.72）（Rp/1.58 R）−3g cm−3，与岩石组成相容。我们寻找一个额外的行星d的证据，由以前的作者确定的周期接近9 d。我们无法确认存在一颗具有这种轨道周期的行星，它接近于恒星旋转的第二谐波，为2.7.9 d。使用贝叶斯模型选择，我们发现，一个模型与两个行星加上活动引起的变化是最有利的。
Since the discovery of the transiting super-Earth CoRoT-7b, several investigations have yielded different results for the number and masses of planets present in the system, mainly owing to the star's high level of activity. We re-observed CoRoT-7 in 2012 January with both HARPS and CoRoT, so that we now have the benefit of simultaneous radial-velocity and photometric data. This allows us to use the off-transit variations in the star's light curve to estimate the radial-velocity variations induced by the suppression of convective blueshift and the flux blocked by starspots. To account for activity-related effects in the radial velocities which do not have a photometric signature, we also include an additional activity term in the radial-velocity model, which we treat as a Gaussian process with the same covariance properties (and hence the same frequency structure) as the light curve. Our model was incorporated into a Monte Carlo Markov Chain in order to make a precise determination of the orbits of CoRoT-7b and CoRoT-7c. We measure the masses of planets b and c to be 4.73 ± 0.95 and 13.56 ± 1.08 M⊕, respectively. The density of CoRoT-7b is (6.61 ± 1.72)(Rp/1.58 R⊕)−3g cm−3, which is compatible with a rocky composition. We search for evidence of an additional planet d, identified by previous authors with a period close to 9 d. We are not able to confirm the existence of a planet with this orbital period, which is close to the second harmonic of the stellar rotation at ∼7.9 d. Using Bayesian model selection, we find that a model with two planets plus activity-induced variations is most favoured.