论文标题
关于威尔逊 - 巴布效应的物理性质：修改重力和温度依赖性
On the physical nature of the Wilson-Bappu effect: revising the gravity and temperature dependence
论文作者
论文摘要
我们提出了32颗恒星的频谱类型G和K的样本，以及I到V的光度I类，具有中等的活性水平，涵盖了四个数量级的表面重力和有效温度的代表性范围。对于每个恒星，我们获得了高S/N Tigre-Heros Spectra，具有$ r \ \ r \ 20,000 $的光谱解析能力，并测量了CA II K II K线的利息宽度，$ W_0 $和$ W_1 $。主要的物理参数是通过ISPEC合成和GAIA EDR3可视性确定的。质量估计基于与演化模型的匹配。在光谱质量和评估方面，使用此恒星样本，我们得出了排放线宽度和重力$ g $之间最合适的关系，包括对有效温度$ t _ {\ rm eff} $的显着依赖，形式为$ w_1 \ propto g^{ - 0.229} t _ $ w_1 \ propto g^{ - 0.229} t _ $ fef。该结果证实了Wilson-Bappu效应的物理解释是在染色体底部的静液压平衡的假设下，在色层CA II柱密度中的线饱和度和光子重新分布效应。尽管色谱柱密度（以及$ w_1 $）在较低的重力方面增加，但随后观察到的温度依赖性被理解为一种简单的电离效应 - 在较冷的恒星中，Ca II密度降低了CAI。
We present a sample of 32 stars of spectral types G and K, and luminosity classes I to V, with moderate activity levels, covering four orders of magnitude of surface gravity and a representative range of effective temperature. For each star we obtained high S/N TIGRE-HEROS spectra with a spectral resolving power of $R\approx20,000$ and have measured the Ca II K line-widths of interest, $W_0$ and $W_1$. The main physical parameters are determined by means of iSpec synthesis and Gaia EDR3 parallaxes. Mass estimates are based on matching to evolution models. Using this stellar sample, that is highly uniform in terms of spectral quality and assessment, we derive the best-fit relation between emission line width and gravity $g$, including a notable dependence on effective temperature $T_{\rm eff}$, of the form $W_1 \propto g^{-0.229} T_{\rm eff}^{+2.41}$. This result confirms the physical interpretation of the Wilson-Bappu effect as a line saturation and photon redistribution effect in the chromospheric Ca II column density, under the assumption of hydrostatic equilibrium at the bottom of the chromosphere. While the column density (and so $W_1$) increases towards lower gravities, the observed temperature dependence is then understood as a simple ionization effect -- in cooler stars, Ca II densities decrease in favor of Ca I.
