标题： 恒星考古学：来自汉堡/ESO巡天的极贫金属星凯克试点计划。 III. 铅星 HE 0024-2523 显示英文标题

标题： Stellar Archaeology: a Keck Pilot Program on Extremely Metal- Poor Stars From the Hamburg/ESO Survey. III. The Lead (Pb) Star HE 0024-2523

摘要： 我们对一颗非常贫金属（[Fe/H] = -2.7）、特殊的主序星 HE0024-2523 进行了详细的丰度分析，包括光谱合成，该星是在 Keck 先导计划的观测过程中发现的。 这颗恒星的视向速度在 1.1 年的时间跨度内的四次不同观测运行中获得，表明它显然是一个短周期光谱双星。 得到了轨道解，并以高精度确定了轨道参数。 还测量了它的旋转速度（vsin i = 9.7$\pm$1.5 km/s）；旋转似乎与轨道同步。 丰度分析和光谱合成表明，该天体是一颗 CH 星，具有极端的 s 过程富集，这可能是由于从一颗演化的伴星吸积质量所致，现在可能已经变成白矮星。 HE0024-2523 的铅（Pb）丰度非常高，与最近发现的富含铅的贫金属星 CS 29526-110 相同，[Pb/Fe] = +3.3。 由 Pb 和 Ba 表征的重 s 元素与轻 s 元素的丰度比 [Pb/Ba] = +1.9 是任何贫金属星中发现的最高值，比 CS29526-110 高约 0.7 dex。 根据碳的测量同位素比（12C/13C 大约为 6），我们认为供体星的质量至少必须为 3 倍太阳质量。 这颗 CH 星异常短的轨道周期表明它曾经经历过与演化伴星的共同包层阶段。 我们将结果与最新的 AGB 星风产出和 s 过程核合成模型进行了比较。 我们还讨论了 HE0024-2523 与晕族恒星锂丰度下降以及晕族蓝离散星形成之间的可能联系。 显示英文摘要

摘要： We present a detailed abundance analysis, including spectral syntheses, of a very metal-poor ([Fe/H]= -2.7), peculiar main sequence star, HE0024-2523 detected during the course of the Keck Pilot Program. Radial velocities of this star were obtained during four different observing runs over a time span of 1.1 years, and demonstrate that it is clearly a short period spectroscopic binary. An orbital solution was obtained, and orbital parameters were determined with high precision. The rotational velocity was also measured (vsin i=9.7$\pm$1.5 kms); rotation appears likely to be synchronous with the orbit. The abundance analysis and spectral syntheses indicate that the object is a CH star characterized by extreme s-process enrichment, likely due to mass accretion from an evolved companion which has now probably become a white dwarf. The lead (Pb) abundance of HE0024-2523 is very high, the same as that of the recently discovered lead-rich metal-poor star CS 29526-110, [Pb/Fe]=+3.3. The abundance ratio of the heavy-s to light-s elements, as characterized by Pb and Ba, [Pb/Ba]=+1.9, is the highest yet found for any metal-poor star, and is about 0.7 dex higher than that of CS29526-110. On the basis of the measured isotopic ratio of carbon (12C/13C about 6) we argue that the mass donor must have had an original mass of at least 3 Msun. The unusually short period of this CH star suggests that it underwent a past common-envelope phase with its evolved companion. Our results are compared to the latest available models for AGB yields and s-process nucleosynthesis. We also discuss the possible connection between HE0024-2523 the lithium depletion of halo stars, and halo blue straggler formation.