IP Eri：一个令人惊讶的长周期双星系统，拥有He白矮星
IP Eri: A surprising long-period binary system hosting a He white dwarf
摘要：
我们确定的K 0 IV +白矮星（WD）系统IP Eri，这似乎有一个令人惊讶的1071 d的长周期和0.25的显着偏心率的轨道要素。先前对WD的光谱分析，基于依巴谷视差推断的101 pc的距离，得出的质量只有0.43 M $_\odot$，这意味着它是一个氦核WD。IP Eri的轨道性质与新发现的长周期亚矮星B（sdB）双星相似，后者的恒星具有燃烧He的核心，周围环绕着极薄的H包层，因此与He WD是近亲。我们对来自HERMES/Mercator摄谱仪的高分辨率光谱进行了光谱分析，并得出结论，K 0分量的大气参数为$T_{\rm eff} = 4960$ K、$\log{g} = 3.3$、[Fe/H] = 0.09和$ξ= 1.5$ km/s。详细的丰度分析侧重于C、N、O丰度、碳同位素比值、轻元素（Na、Mg、Al、Si、Ca、Ti）和s-过程元素（Sr、Y、Zr、Ba、La、Ce、Nd）。我们的结论是IP Eri丰度同意正常场的恒星相同的金属丰度。长周期和非零偏心率表明，这个系统不可能是一个共同包络相位的最终产物;它需要另一个灾难性较小的双星演化通道（Siess等人，2014）。
英文摘要：
We determine the orbital elements for the K0 IV + white dwarf (WD) system IP Eri, which appears to have a surprisingly long period of 1071 d and a significant eccentricity of 0.25. Previous spectroscopic analyses of the WD, based on a distance of 101 pc inferred from its Hipparcos parallax, yielded a mass of only 0.43 M$_\odot$, implying it to be a helium-core WD. The orbital properties of IP Eri are similar to those of the newly discovered long-period subdwarf B star (sdB) binaries, which involve stars with He-burning cores surrounded by extremely thin H envelopes, and are therefore close relatives to He WDs. We performed a spectroscopic analysis of high-resolution spectra from the HERMES/Mercator spectrograph and concluded that the atmospheric parameters of the K0 component are $T_{\rm eff} = 4960$ K, $\log{g} = 3.3$, [Fe/H] = 0.09 and $ξ= 1.5$ km/s. The detailed abundance analysis focuses on C, N, O abundances, carbon isotopic ratio, light (Na, Mg, Al, Si, Ca, Ti) and s-process (Sr, Y, Zr, Ba, La, Ce, Nd) elements. We conclude that IP Eri abundances agree with those of normal field stars of the same metallicity. The long period and non-null eccentricity indicate that this system cannot be the end product of a common-envelope phase; it calls instead for another less catastrophic binary-evolution channel presented in detail in a companion paper (Siess et al. 2014).
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