标题： 两个好同伴，三个成对手：SALT 揭示极端丰度差异因子行星状星云 Sp 3 核心可能为三合一体系 显示英文标题

标题： Two's company, three's a crowd: SALT reveals the likely triple nature of the nucleus of the extreme abundance discrepancy factor planetary nebula Sp 3

摘要： 已知的大量行星状星云（PNe）的双星核（CSPNe）($\sim$50)揭示了二元性与一些形态特征（包括喷流和低电离结构）之间存在强烈关联。然而，某些特征和不对称性可能过于复杂或微妙，无法单纯归因于双星相互作用。一个第三伴星，即三重核心，可能是产生这些特征所需的缺失成分。目前唯一被证实的三重系统是NGC 246，但其不足以研究三重核心的成形作用；不过，识别更多三重系统的直接方法之一是搜索具有已知视觉伴星的核心中的双星系统。在此，我们报告了SALT HRS在Sp 3的CSPN中发现的一个4.81天轨道周期，该星有一个距离为0.31"的视觉伴星。视觉伴星的光谱距离与星云的距离估计、中央星的GAIA DR2视差以及中央星的重力距离一致，这支持了视觉伴星与4.81天双星之间的物理关联，使Sp 3的核心很可能是一个三重系统。我们通过非局部热平衡（NLTE）模型大气分析确定主星的温度为$T_\mathrm{eff}=68^{+12}_{-6}$kK，半径为$\log g=4.6\pm0.2$cm s$^{-2}$，速度为$v_\mathrm{rot}=80\pm20$km s$^{-1}$。这个特殊的星云呈现出明显的双极形态、喷流以及意外的“极端”氧丰度偏差因子（adf）24.6$^{+4.1}_{-3.4}$。该adf与长周期后共同演化（post-CE）PNe中通常出现正常adf的趋势不符，进一步突显了后共同演化PNe中的选择效应。Sp 3的I型星云丰度通常与更高质量的前身物有关，但Sp 3的银河厚盘成员身份可能表明旋转和双星特性可能在行星状星云（PNe）的AGB核合成过程中起重要作用。（摘要） 显示英文摘要

摘要： The substantial number of binary central stars of planetary nebulae (CSPNe) now known ($\sim$50) has revealed a strong connection between binarity and some morphological features including jets and low-ionisation structures. However, some features and asymmetries might be too complex or subtle to ascribe to binary interactions alone. A tertiary component, i.e. a triple nucleus, could be the missing ingredient required to produce these features. The only proven triple, NGC 246, is insufficient to investigate the shaping role of triple nuclei, but one straight-forward way to identify more triples is to search for binaries in nuclei with known visual companions. Here we report on the SALT HRS discovery of a 4.81 d orbital period in the CSPN of Sp 3 which has a visual companion 0.31" away. The spectroscopic distance of the visual companion agrees with distance estimates to the nebula, the GAIA DR2 parallax of the central star, and the gravity distance of the central star. This supports a physical association between the visual companion and the 4.81 d binary, making the nucleus of Sp 3 a likely triple. We determine $T_\mathrm{eff}=68^{+12}_{-6}$ kK, $\log g=4.6\pm0.2$ cm s$^{-2}$ and $v_\mathrm{rot}=80\pm20$ km s$^{-1}$ for the primary from NLTE model atmosphere analysis. The peculiar nebula presents an apparent bipolar morphology, jets and an unexpected `extreme' oxygen abundance discrepancy factor (adf) of 24.6$^{+4.1}_{-3.4}$. The adf is inconsistent with the purported trend for longer orbital period post-CE PNe to exhibit normal adfs, further highlighting selection effects in post-CE PNe. The Type-I nebular abundances of Sp 3, whose origin is often tied to more massive progenitors, are incongruous with the likely Galactic Thick Disk membership of Sp 3, possibly suggesting that rotation and binarity may play an important role in the AGB nucleosynthesis of PNe. (abridged)