低质量恒星中非太阳混合长度的经典案例
Classical Cases of Non-solar Mixing Length in Low Mass Stars
- Dartmouth College（达特茅斯学院）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本研究利用经典几何半径和可变混合长度参数的MIST等时线，在分离食双星和干涉测量恒星中测量混合长度，发现非太阳混合长度证据，并质疑低质量恒星中普遍校准的存在性。
AI中文摘要：
对流处理是低质量恒星模型中最大的剩余不确定性之一。用于超绝热对流的混合长度理论（MLT）尤其受到关注。越来越多的证据表明，混合长度参数（$\alpha_\mathrm{MLT}$）的单一值不应普遍应用于恒星模型网格，尽管模拟和星震学校准对其如何随恒星参数变化存在分歧。可变的$\alpha_\mathrm{MLT}$会导致低质量恒星年龄（星系和系外行星研究的关键年龄示踪物）发生关键的系统性变化。在本工作中，我们使用经典（非地震）几何半径和具有可变$\alpha_\mathrm{MLT}$的专用MIST等时线，在分离食双星（DEBs）和干涉测量解析的恒星中测量混合长度，发现了大量非太阳$\alpha_\mathrm{MLT}$的证据。特别是，我们发现标准演化模型高估了贫金属干涉测量恒星的半径，而亚太阳$\alpha_\mathrm{MLT}$/$\alpha_{\mathrm{MLT},\odot}\sim0.50-0.75$可以很好地解释这一差异，这与其他经验校准一致，但与模拟形成鲜明对比。我们推断出冷的、快速旋转的低主序恒星具有低对流效率，这与已知的磁致半径膨胀现象一致。我们还识别出几个缓慢旋转的DEBs，其测量结果无法用标准等时线重现，我们提出这些系统作为太阳以外恒星中非太阳混合长度的有用案例研究。然而，我们在DEBs中未发现$\alpha_\mathrm{MLT}$与恒星参数之间存在确定性的群体水平相关性，这对低质量恒星中普遍存在的混合长度校准的存在性提出了质疑。
英文摘要：
The treatment of convection is one of the largest remaining uncertainties in models of low mass stars. The Mixing Length Theory (MLT) for super-adiabatic convection has come under particular scrutiny. Evidence is mounting that a single value of the mixing length parameter ($α_\mathrm{MLT}$) should not be applied universally across stellar model grids, although simulations and asteroseismic calibrations disagree on how it should vary with stellar parameters. A variable $α_\mathrm{MLT}$ causes critical systematic changes to the ages of low mass stars, the key age tracers for galactic and exoplanetary studies. In this work we use classical (non-seismic) geometric radii and specialized MIST isochrones with a variable $α_\mathrm{MLT}$ to measure mixing length in detached eclipsing binaries (DEBs) and interferometrically resolved stars, finding plenty of evidence for non-solar $α_\mathrm{MLT}$. In particular we find that standard evolutionary models overpredict the radii of metal-poor interferometric stars and that a sub-solar $α_\mathrm{MLT}$/$α_{\mathrm{MLT},\odot}\sim0.50-0.75$ can neatly explain this discrepancy, consistent with other empirical calibrations and in stark contrast to simulations. We infer low convective efficiency in cool, rapidly rotating lower main-sequence stars, consistent with the known phenomenon of magnetically-induced radius inflation. We also identify several slowly rotating DEBs whose measurements cannot be reproduced by standard isochrones, and we propose these systems as useful case studies of non-solar mixing length in stars outside of the Sun. However, we find no definitive population level correlations between $α_\mathrm{MLT}$ and stellar parameters among the DEBs, calling into question the existence of a ubiquitous mixing length calibration in low mass stars.
