一颗极其奇特的热亚矮星，锆、钇和锶含量超过一万倍
An extremely peculiar hot subdwarf with a ten-thousand-fold excess of zirconium, yttrium, and strontium
摘要：
富氦亚矮星B（He-sdB）是一小部分低质量的热星，其光度大于常规亚矮星B，有效温度低于亚矮星O。通过测量它们的表面化学，我们的目标是探索He-sdB星，富He sdO星和正常sdB星之间的联系。LS IV-14 116是一颗相对中等的He-sdB恒星，也是一颗光度变星。高分辨率的蓝色光谱是由英澳望远镜获得的。光谱分析表明LS IV-14 116的有效温度Teff = 34 000 +/- 500 K，表面重力log g = 5.6 +/- 0.2，表面氦丰度nHe = 0.16 +/- 0.03。这会将星形放置在标准延伸水平分支的上方，如正常sdB星形所示。镁和硅的丰度表明这颗恒星相对于太阳来说是贫金属的。一些重要的，但不熟悉的吸收线被确定为是由于锗，锶，钇和锆。在计算振子强度（Ge，Y和Zr）后，这些元素的光球丰度范围从3 dex（Ge）到4 dex（Sr，Y和Zr）。最可能的解释是，这些过剩是由辐射驱动的扩散造成的，在光球层中形成了化学云层。据证实，这种云的形成可以通过一个强磁场介导。
英文摘要：
Helium-rich subdwarf B (He-sdB) stars represent a small group of low-mass hot stars with luminosities greater than those of conventional subdwarf B stars, and effective temperatures lower than those of subdwarf O stars. By measuring their surface chemistry, we aim to explore the connection between He-sdB stars, He-rich sdO stars and normal sdB stars. LS IV-14 116 is a relatively intermediate He-sdB star, also known to be a photometric variable. High-resolution blue-optical spectroscopy was obtained with the Anglo-Australian Telescope. Analysis of the spectrum shows LS IV-14 116 to have effective temperature Teff = 34 000 +/- 500 K, surface gravity log g = 5.6 +/- 0.2, and surface helium abundance nHe = 0.16 +/- 0.03 by number. This places the star slightly above the standard extended horizontal branch, as represented by normal sdB stars. The magnesium and silicon abundances indicate the star to be metal poor relative to the Sun. A number of significant but unfamiliar absorption lines were identified as being due to germanium, strontium, yttrium and zirconium. After calculating oscillator strengths (for Ge, Y and Zr), the photospheric abundances of these elements were established to range from 3 dex (Ge) to 4 dex (Sr, Y and Zr) above solar. The most likely explanation is that these overabundances are caused by radiatively-driven diffusion forming a chemical cloud layer in the photosphere. It is conjectured that this cloud formation could be mediated by a strong magnetic field.
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