碎片-盘双星系统Zet2 Ret的温度凝聚趋势
A temperature condensation trend in the debris-disk binary system Zet2 Ret
摘要：
我们探索了独特的双星系统Zet 1 Ret -Zet 2 Ret中的冷凝温度Tc趋势，以确定是否存在耐火材料的耗尽，这可能与行星形成过程有关。恒星Zet 2 Ret拥有一个碎片盘，该碎片盘被红外过量探测到，并通过直接成像和数值模拟证实，而Zet 1 Ret没有红外过量，也没有行星。我们进行了一个高精度的丰度测定的两个组成部分的二元系统通过一行一行，严格微分的方法。利用FUNDPAR程序，通过对Fe I和Fe II谱线的微分电离和激发平衡，测定了恒星参数Teff、log g、[Fe/H]和vturb。恒星Zet 1 Ret的金属含量比Zet 2 Ret略高0.02 dex。在以Zet 2 Ret为参考的Zet 1 Ret微分计算中，难熔元素的丰度高于挥发性元素，且难熔元素与Tc的变化趋势呈正斜率。这些事实共同表明，相对于Zet 1 Ret，Zet 2 Ret（一个碎片磁盘宿主）中缺乏耐火元素。Tc的趋势将与行星形成（Melendez et al. 2009）而不是可能的银河系化学演化或年龄效应（在这里被大大削弱）的建议签名一致。然后，根据Melendez等人（2009）的解释，我们提出了一种假设，即Zet 2 Ret中耗尽的难熔元素可能被锁定在围绕该恒星运行的岩石材料中，并产生了在该物体周围观察到的碎片盘。我们估计耗尽物质的岩石质量的下限为Mrock = 3 Me，这与太阳型恒星周围碎片盘质量的粗略估计3-50 Me是一致的（Krivov等人，2008）。（节略）
英文摘要：
We explore condensation temperature Tc trends in the unique binary system Zet1 Ret - Zet2 Ret, to determine whether there is a depletion of refractories, which could be related to the planet formation process. The star Zet2 Ret hosts a debris disk which was detected by an IR excess and confirmed by direct imaging and numerical simulations, while Zet1 Ret does not present IR excess nor planets. We carried out a high-precision abundance determination in both components of the binary system via a line-by-line, strictly differential approach. The stellar parameters Teff , log g, [Fe/H] and vturb were determined by imposing differential ionization and excitation equilibrium of Fe I and Fe II lines, with an updated version of the program FUNDPAR. The star Zet1 Ret resulted slightly more metal rich than Zet2 Ret by 0.02 dex. In the differential calculation of Zet1 Ret using Zet2 Ret as reference, the abundances of the refractory elements resulted higher than the volatile elements, and the trend of the refractory elements with Tc showed a positive slope. These facts together show a lack of refractory elements in Zet2 Ret (a debris-disk host) relative to Zet1 Ret. The Tc trend would be in agreement with the proposed signature of planet formation (Melendez et al. 2009) rather than possible Galactic Chemical Evolution or age effects, which are largely diminished here. Then, following the interpretation of Melendez et al. (2009), we propose an scenario in which the refractory elements depleted in Zet2 Ret are possibly locked-up in the rocky material that orbits this star and produce the debris disk observed around this object. We estimated a lower limit of Mrock = 3 Me for the rocky mass of depleted material, which is compatible with a rough estimation of 3-50 Me of a debris disk mass around a solar-type star (Krivov et al. 2008). (abridged)
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