Reconstructing Intrinsic Stellar Noise with Stellar Atmospheric Parameters and Chromospheric Activity

Jinghua Zhang, Maosheng Xiang, Jie Yu, Jian Ge, Ji-Wei Xie, Hui Zhang, Yaguang Li, You Wu, Chun-Qian Li, Shaolan Bi, Hong-Liang Yan, Jian-Rong Shi
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Abstract

Accurately characterizing the intrinsic stellar photometric noise induced by stellar astrophysics, such as stellar activity, granulation, and oscillations, is of crucial importance for detecting transiting exoplanets. In this study, we investigate the relation between the intrinsic stellar photometric noise, quantified by the Kepler combined differential photometric precision (CDPP) metric, and the level of stellar chromospheric activity, indicated by the S-index of Ca ii H K lines derived from LAMOST spectra. Our results reveal a clear positive correlation between the S-index and robust rms values of CDPP, with the correlation becoming more significant at higher activity levels and on longer timescales. We have therefore built an empirical relation between the robust rms values of CDPP and the S-index as well as T eff, log g, [Fe/H], and the apparent magnitude, with the XGBoost regression algorithm, using the LAMOST–Kepler common star sample as the training set. This method achieves a precision of ∼20 ppm for inferring the intrinsic noise from the S-index and other stellar labels on a 6 hr integration duration. We have applied this empirical relation to the full LAMOST DR7 spectra database and obtained the intrinsic noise predictions for 1,358,275 stars. The resultant catalog is publicly available and expected to be valuable for optimizing target selection for future exoplanet-hunting space missions, such as the Earth 2.0 mission.
利用恒星大气层参数和色球活动重构本征恒星噪声
准确描述由恒星天体物理(如恒星活动、颗粒化和振荡)引起的内在恒星测光噪声对于探测凌日系外行星至关重要。在这项研究中,我们研究了由开普勒综合差分光度精度(CDPP)指标量化的恒星固有光度噪声与恒星色球活动水平之间的关系,恒星色球活动水平由从LAMOST光谱中获得的Ca ii H K线的S指数来表示。我们的研究结果表明,S 指数与 CDPP 的稳健均方根值之间存在明显的正相关,在活动水平较高和时间尺度较长的情况下,这种相关性变得更加显著。因此,我们使用 XGBoost 回归算法,以 LAMOST-Kepler 共同恒星样本为训练集,建立了 CDPP 的稳健均方根值与 S 指数以及 Teff、logg、[Fe/H] 和视星等之间的经验关系。在 6 小时的积分时间内,这种方法从 S 指数和其他恒星标签推断出的内在噪声的精度达到了 ∼20 ppm。我们将这一经验关系应用于完整的 LAMOST DR7 光谱数据库,得到了 1,358,275 颗恒星的本征噪声预测值。所得到的星表是公开的,预计将对优化未来系外行星搜寻太空任务(如地球 2.0 任务)的目标选择非常有价值。
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