标题： 锂丰度的主序星在古老的疏散星团NGC 188中：对超越太阳年龄的恒星演化的探测 显示英文标题

标题： Lithium Abundances of Main-Sequence Stars in the Old Open Cluster NGC 188: Probes of Stellar Evolution Beyond the Solar Age

摘要： 我们展示了使用WIYN/Hydra的高分辨率、高信噪比光谱对63亿年的疏散星团NGC 188中的119颗主序星的锂丰度。我们在多个夜晚观测这些恒星，并为每晚测量径向速度，将这些速度与盖亚的自行结合以识别多重性和星团成员身份。我们识别出95个单星成员，14个双星成员，9个多重性不确定的成员，以及1个可能的单星成员。我们使用经验颜色-温度关系确定有效温度，通过等时线确定表面重力，并通过主序星的经验关系确定微湍流速度。我们的样本包括温度在6000到5300 K之间的G型和K型矮星，这大大扩展了早期的观测。我们发现NGC 188中的锂丰度低于标准恒星演化理论的预测。正如预期的那样，NGC 188中的恒星比年轻的Hyades和Praesepe星团（6.5亿年）中的恒星更缺乏锂。然而，它们的丰度更高，或者至少与稍年轻的M67星团（45亿年）中的恒星相当，这挑战了年龄越大的恒星锂越少的观点。锂的耗损可能取决于年龄和质量以外的因素。 显示英文摘要

摘要： We present lithium abundances for 119 main-sequence stars in the 6.3 Gyr open cluster NGC 188, using high-resolution, high signal-to-noise ratio spectra from WIYN/Hydra. We observe the stars over multiple nights and measure radial velocities for each night, which we combine with Gaia proper motions to identify multiplicity and cluster membership. We identify 95 single members, 14 binary members, 9 members with uncertain multiplicity, and 1 single likely member. We determine effective temperatures using empirical color-temperature relations, surface gravities from isochrones, and microturbulence from empirical relations for main-sequence stars. Our sample includes G and K dwarfs with temperatures between 6000 and 5300 K, which expands significantly on earlier observations. We find that lithium abundances in NGC 188 are lower than predictions from standard stellar evolution theory. As expected, stars in NGC 188 are more lithium-depleted than those in the younger Hyades and Praesepe clusters (650 Myr). However, their abundances are higher, or at least comparable, to those in the slightly younger cluster M67 (4.5 Gyr), challenging the idea that older stars have lower lithium than younger ones. Lithium depletion may depend on factors beyond age and mass.