SOAP-GPU：利用图形处理单元进行恒星活动的有效光谱模拟
SOAP-GPU: Efficient Spectral Modelling of Stellar Activity Using Graphical Processing Units
摘要：
恒星活动减缓是径向速度（RV）测量中检测类地系外行星的主要挑战之一。现在有几种很有前途的技术正在研究光谱时间序列的使用，以区分恒星和行星扰动。在本文中，我们提出了一个新版本的现货振荡和行星（SOAP）2.0代码，可以使用图形处理单元（GPU）在光谱水平上模拟恒星活动。我们利用GPU的计算能力来优化原始SOAP 2.0代码背后的计算昂贵的算法。我们开发的GPU内核允许在任何给定的波长范围内模拟恒星活动。SOAP-GPU除了在光谱水平上处理恒星活动外，还包括从中心到边缘的谱线平分线的变化，并且可以将PHOENIX光谱作为输入来模拟安静的光球，斑点和光斑，这允许在恒星属性中模拟宽空间的恒星活动。基准计算表明，对于相同的精度，这个新的代码提高了60倍的计算速度相比，SOAP 2.0的修改版本，产生光谱，当建模恒星活动的全可见光谱范围内的分辨率为R=115'000。尽管代码现在包括谱线平分线随中心到边缘角的变化，但对导出的RV的影响很小。公开的SOAP-GPU代码允许在光谱水平上有效地模拟恒星活动，这对于测试在不受其他噪声源影响的光谱时间序列水平上工作的进一步恒星活动缓解技术至关重要。除了性能上的巨大提升外，SOAP-GPU还包括更多的物理特性，并且由于使用了PHOENIX光谱库，它能够对太阳以外的不同恒星进行建模，从F到K矮星。
英文摘要：
Stellar activity mitigation is one of the major challenges for the detection of earth-like exoplanets in radial velocity (RV) measurements. Several promising techniques are now investigating the use of spectral time-series, to differentiate between stellar and planetary perturbations. In this paper, we present a new version of the Spot Oscillation And Planet (SOAP) 2.0 code that can model stellar activity at the spectral level using graphical processing units (GPUs). We take advantage of the computational power of GPUs to optimise the computationally expensive algorithms behind the original SOAP 2.0 code. We develope GPU kernels that allow to model stellar activity on any given wavelength range. In addition to the treatment of stellar activity at the spectral level, SOAP-GPU also includes the change of spectral line bisectors from center to limb, and can take as input PHOENIX spectra to model the quiet photosphere, spots and faculae, which allow to simulate stellar activity for a wide space in stellar properties. Benchmark calculations show that for the same accuracy, this new code improves the computational speed by a factor of 60 compared with a modified version of SOAP 2.0 that generates spectra, when modeling stellar activity on the full visible spectral range with a resolution of R=115'000. Although the code now includes the variation of spectral line bisector with center to limb angle, the effect on the derived RVs is small. The publicly available SOAP-GPU code allows to efficiently model stellar activity at the spectral level, which is essential to test further stellar activity mitigation techniques working at the level of spectral timeseries not affected by other sources of noise. Besides a huge gain in performance, SOAP-GPU also includes more physics and is able to model different stars than the Sun, from F to K dwarfs, thanks to the use of the PHOENIX spectral library.
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