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arXiv 0906.4619astro-ph.EPastro-ph.SR
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低质量系外行星的频率

The Frequency of Low-mass Exoplanets

S. J. O'Toole, H. R. A. Jones, C. G. Tinney, R. P. Butler, G. W. Marcy, B. Carter, J. Bailey, R. A. Wittenmyer

摘要:

我们报告了英澳望远镜洛基行星搜索的第一个结果-一个密集的,高精度的多普勒行星搜索,目标是连续48个夜间观测区块的低质量系外行星。在这次运行中,我们瞄准了从英澳行星搜索的主要样本中选出的24颗明亮,附近和本质稳定的类太阳恒星。这些观测已经发现了一颗其他地方报道的低质量行星(HD 16417 b),在这里我们再次确认了HD 4308 b的发现。此外,我们还使用蒙特卡罗方法对逐星运行的数据进行了模拟,以产生强大的检测约束。这些模拟表明,由于采样、数据质量和恒星内在稳定性的差异,不同恒星的系外行星可探测性函数存在明显差异。它们加强了逐星模拟在解释多普勒行星搜索数据时的重要性。模拟表明,对于我们的一些目标恒星,我们对小到几个地球质量的近轨道行星很敏感。我们的24颗恒星样本中存在的两颗低质量行星表明,在低质量时系外行星最小质量函数很可能是平坦的α ~ -1(对于与M^alpha成比例的dN/dM)和15+/-10%(α =-0.3)和48+/-34%(α =-1.3)的恒星拥有轨道周期小于16天的行星,最小质量大于3地球。

英文摘要:

We report first results from the Anglo-Australian Telescope Rocky Planet Search - an intensive, high-precision Doppler planet search targeting low-mass exoplanets in contiguous 48 night observing blocks. On this run we targeted 24 bright, nearby and intrinsically stable Sun-like stars selected from the Anglo-Australian Planet Search's main sample. These observations have already detected one low-mass planet reported elsewhere (HD16417b), and here we reconfirm the detection of HD4308b. Further, we have Monte-Carlo simulated the data from this run on a star-by-star basis to produce robust detection constraints. These simulations demonstrate clear differences in the exoplanet detectability functions from star to star due to differences in sampling, data quality and intrinsic stellar stability. They reinforce the importance of star-by-star simulation when interpreting the data from Doppler planet searches. The simulations indicate that for some of our target stars we are sensitive to close-orbiting planets as small as a few Earth masses. The two low-mass planets present in our 24 star sample indicate that the exoplanet minimum mass function at low masses is likely to be a flat alpha ~ -1 (for dN/dM proportional to M^alpha) and that between 15+/-10% (at alpha=-0.3) and 48+/-34% (at alpha=-1.3) of stars host planets with orbital periods of less than 16 days and minimum masses greater than 3 Mearth.

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