论文标题
在三个金属贫困星的紫外光谱中检测PB II
Detection of Pb II in the Ultraviolet Spectra of Three Metal-Poor Stars
论文作者
论文摘要
我们使用在哈勃太空望远镜上使用空间望远镜成像光谱仪获得的紫外光谱，报告了三个金属贫困星的PB II线在2203.534埃的第一次检测。假设局部热力学平衡（LTE）得出铅（Pb，Z = 82）丰度，我们进行了标准丰度分析。 PB II线的丰度比PB I线的丰度更高，+0.36 +/- 0.34 DEX和+0.49 +/- 0.28 DEX在恒星HD 94028和HD 196944中，以前曾检测到PB I线。 PB II线可能是在LTE中形成的，这些偏移确认了先前的计算表明，PB I线通常用作丰度指标，低估了LTE中的Pb丰度。 S-process增强星HD 94028（[PB/FE] = +0.95 +/- 0.14）和HD 196944（[[PB/Fe] = +2.28 +/- 0.23）中PB增强了PB，我们显示PB-2018是这两颗星星中的主要PB同位素。 R-Process-增强星HD 222925中的log Epsilon（PB/EU）比为0.76 +/- 0.14，它与太阳系R-Process比率匹配，并表明PB的太阳系R-Process残差是正聚体的。 HD 222925中的TH/PB计时仪的年龄为8.2 +/- 5.8 GYR，我们强调了TH/PB计时量表作为R-Process-Enhanchench恒星中相对不敏感的年龄指标的潜力。
We report the first detection of the Pb II line at 2203.534 Angstroms in three metal-poor stars, using ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. We perform a standard abundance analysis assuming local thermodynamic equilibrium (LTE) to derive lead (Pb, Z=82) abundances. The Pb II line yields a higher abundance than Pb I lines by +0.36 +/- 0.34 dex and +0.49 +/- 0.28 dex in the stars HD 94028 and HD 196944, where Pb I lines had been detected previously. The Pb II line is likely formed in LTE, and these offsets affirm previous calculations showing that Pb I lines commonly used as abundance indicators underestimate the Pb abundance in LTE. Pb is enhanced in the s-process-enriched stars HD 94028 ([Pb/Fe] = +0.95 +/- 0.14) and HD 196944 ([Pb/Fe] = +2.28 +/- 0.23), and we show that Pb-208 is the dominant Pb isotope in these two stars. The log epsilon(Pb/Eu) ratio in the r-process-enhanced star HD 222925 is 0.76 +/- 0.14, which matches the Solar System r-process ratio and indicates that the Solar System r-process residuals for Pb are, in aggregate, correct. The Th/Pb chronometer in HD 222925 yields an age of 8.2 +/- 5.8 Gyr, and we highlight the potential of the Th/Pb chronometer as a relatively model-insensitive age indicator in r-process-enhanced stars.
