标题： 恒星黑子对通过锂丰度边界确定的低质量恒星年龄的影响 显示英文标题

标题： The effect of starspots on the ages of low-mass stars determined from the lithium depletion boundary

摘要： 在一个年龄相同的低质量恒星群中，那些保留初始锂含量的恒星与稍高一些质量的恒星之间（后者的锂由于核反应而耗尽）的亮度尖锐过渡被称为锂丰度降界（LDB），它被提出作为一种几乎不依赖模型的方法来建立年轻恒星的年龄标尺。 在这里，我们构建了收缩中的前主序星（PMS）多项式模型，这些模型具有冷却的、带有磁场的恒星黑子，这些黑子遮挡了光球总通量的一部分 $\beta$。 恒星黑子减缓了沿Hayashi轨迹的下降过程，导致在给定质量和年龄下核心温度更低，锂的破坏程度也更小。 年龄， $\tau_{\rm LDB}$，由亮星系团 (LDB) 的光度确定，即 $L_{\rm LDB}$，比从无斑模型推断的年龄增加了因子 $(1-\beta)^{-E}$，其中 $E \simeq 1 + d\log \tau_{\rm LDB}/d \log L_{\rm LDB}$并且在年龄为 $< 80$百万年时值为 $\sim 0.5$，对于更老的恒星则下降到 $\sim 0.3$。 有斑点的恒星与无斑点的恒星在 K 波段光度修正与颜色之间的关系几乎相同，因此该关系同样适用于从亮星系团 (LDB) 的绝对 K 光度推断的年龄。 低质量的金牛座T型星确实存在恒星黑子，但参数 $\beta$ 的合适值极不确定，可能的范围为 $0.1 < \beta < 0.4$。 对于较小的 $\beta$ 值，我们的结果表明LDB年龄有适度的系统性增加，这一增加幅度与之前对该方法所声称的最大理论不确定性相当。 然而，对于最大的 $\beta$ 值，LDB年龄会增加20%-30%，需要重新评估其他以LDB年龄为校准依据的年龄估算技术。 显示英文摘要

摘要： In a coeval group of low-mass stars, the luminosity of the sharp transition between stars that retain their initial lithium and those at slightly higher masses in which Li has been depleted by nuclear reactions, the lithium depletion boundary (LDB), has been advanced as an almost model-independent means of establishing an age scale for young stars. Here we construct polytropic models of contracting pre-main sequence stars (PMS) that have cool, magnetic starspots blocking a fraction $\beta$ of their photospheric flux. Starspots slow the descent along Hayashi tracks, leading to lower core temperatures and less Li destruction at a given mass and age. The age, $\tau_{\rm LDB}$, determined from the luminosity of the LDB, $L_{\rm LDB}$, is increased by a factor $(1-\beta)^{-E}$ compared to that inferred from unspotted models, where $E \simeq 1 + d\log \tau_{\rm LDB}/d \log L_{\rm LDB}$ and has a value $\sim 0.5$ at ages $< 80$ Myr, decreasing to $\sim 0.3$ for older stars. Spotted stars have virtually the same relationship between K-band bolometric correction and colour as unspotted stars, so this relationship applies equally to ages inferred from the absolute K magnitude of the LDB. Low-mass PMS stars do have starspots, but the appropriate value of $\beta$ is highly uncertain with a probable range of $0.1 < \beta < 0.4$. For the smaller $\beta$ values our result suggests a modest systematic increase in LDB ages that is comparable with the maximum levels of theoretical uncertainty previously claimed for the technique. The largest $\beta$ values would however increase LDB ages by 20-30 per cent and demand a re-evaluation of other age estimation techniques calibrated using LDB ages.