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

Title: 主序星在古老疏散星团NGC 188中的锂丰度：对太阳年龄以外恒星演化的探测

Abstract: We present lithium abundances for 119 main-sequence stars in the old open cluster NGC 188 (age = 6.3 Gyr), 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, such as metallicity. Show Chinese abstract

Abstract: 我们使用WIYN/Hydra的高分辨率、高信噪比光谱，给出了119颗主序星在古老疏散星团NGC 188（年龄=6.3 Gyr）中的锂丰度。 我们在多个夜晚观测这些恒星，并测量每晚的视向速度，将这些速度与盖亚（Gaia）自行结合，以确定多星系统和星团成员身份。 我们识别出95颗单星成员，14颗双星成员，9颗多星性质不确定的成员，以及1颗可能的单星成员。 我们利用经验色-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，这显著扩展了早期的观测结果。 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中的恒星比年轻星团Hyades和Praesepe（650 Myr）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（4.5 Gyr）中的恒星相当，这挑战了年老恒星比年轻恒星锂含量更低的观点。 锂的耗损可能还取决于其他因素，如金属量。