Stellar Archaeology: A Keck Pilot Program on Extremely Metal-Poor Stars From the Hamburg/ESO Survey. III. The Lead (Pb) Star HE 0024−2523
Stellar Archaeology: A Keck Pilot Program on Extremely Metal-Poor Stars From the Hamburg/ESO Survey. III. The Lead (Pb) Star HE 0024−2523
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DOI：
10.1086/345886
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发表时间：
2002-11
期刊：
影响因子：
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通讯作者：
S. Lucatello;R. Gratton;J. Cohen;T. Beers;N. Christlieb;E. Carretta;S. Ramírez
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文献类型：
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作者：
S. Lucatello;R. Gratton;J. Cohen;T. Beers;N. Christlieb;E. Carretta;S. Ramírez
我们提出了一个详细的丰度分析，包括光谱合成，一个非常贫金属（[Fe/H]<$-2.7）奇特的星星（HE 0024-2523）的过程中发现的凯克试点计划。这颗星星的径向速度是在1.1年的时间跨度内的四次不同的观测运行中获得的，表明它显然是一个短周期的光谱双星。获得了轨道解，并高精度地确定了轨道参数。还测量了旋转速度（vrot sin i = 9.7 ± 1.5 km s-1）;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星星，其特征是极端的s-过程富集，可能是由于一个进化的伴星的质量吸积，现在可能已经成为一颗白色矮星。（HE 0024-2523）的铅（Pb）丰度很高，与最近发现的富铅贫金属星星CS 29526-110相同，[Pb/Fe] =+3.3。重轻s元素的丰度比，以Pb和Ba为特征，[Pb/Ba] =+1.9，是迄今发现的贫金属星星中最高的，比CS 29526-110高出约0.7 dex。根据测得的碳同位素比值（C12/C13 = 6），我们认为质量供体的原始质量必须至少为1.33 M。这颗CH星星异常短的周期表明，它与其演化的伴星经历了一个共同的包络阶段。我们的结果进行了比较，与最新的可用模型的渐近巨分支产额和s-过程核合成。我们还讨论了HE 0024-2523，晕星的锂耗尽和晕蓝离散星形成之间的可能联系。
We present a detailed abundance analysis, including spectral syntheses, of a very metal-poor ([Fe/H] ≃ -2.7) peculiar main-sequence star (HE 0024-2523) 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 yr 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 (vrot sin i = 9.7 ± 1.5 km s-1); 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 that has now probably become a white dwarf. The lead (Pb) abundance of (HE 0024-2523) 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 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 CS 29526-110. On the basis of the measured isotopic ratio of carbon (C12/C13 ∼ 6) we argue that the mass donor must have had an original mass of at least ∼3 M⊙. 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 with the latest available models for asymptotic giant branch yields and s-process nucleosynthesis. We also discuss the possible connection between HE 0024-2523, the lithium depletion of halo stars, and halo blue straggler formation.