共生系统巨星的化学丰度分析。14个北天S型系统的金属丰度与CNO丰度模式
Chemical abundance analysis of symbiotic giants. Metallicity and CNO abundance patterns in 14 northern S-type systems
AI总结：
本文分析了14个北天S型共生系统红巨星的化学丰度，发现其略低于太阳的金属丰度及CNO模式揭示了首次上翻与额外混合过程，并在AG Peg中发现了可能与吸积有关的蓝移分量。
摘要：
在先前的研究中，我们计算了近四打S型共生系统（SySt）中红巨星的丰度。这些丰度提供了关于金属丰度、演化状态以及银河系恒星族群成员可能性的信息。在此，我们利用北半球的SySt样本扩展了我们的研究。该北天样本以银河系盘/晕族天体为主，而我们先前的南天样本则严重偏向于核球族群。我们利用高分辨率（R$\sim$50000）的近红外光谱，采用标准LTE分析和大气模型，测量了红巨星组分大气中CNO及铁峰附近元素（Fe, Ti, Ni, Sc）的丰度。正如对较老盘族所预期的那样，该SySt样本普遍表现出略低于太阳的金属丰度，中位数为[Fe/H]$\sim -0.2$ dex。增强的$^{14}$N、贫化的$^{12}$C以及降低的$^{12}$C/$^{13}$C表明，所有这些巨星都经历了首次上翻。与理论预测的比较表明，必须发生额外的混合过程才能解释观测到的C和N丰度。相对O和Fe丰度与APOGEE数据中代表的银河系盘和核球巨星族群的丰度一致，有少数情况可归因于属于延伸的厚盘/晕。作为本研究的一个有趣副产品，我们在AG Peg光谱的吸收线翼上观测到了一个蓝移的附加分量，这可能与向热组分的吸积有关。
英文摘要：
In previous works, we computed abundances for the red giant in nearly four dozen S-type symbiotic systems (SySt). The abundances provide information about metallicity, evolutionary status, and possible memberships in Galactic stellar populations. Here, we extend our studies with a northern hemisphere sample of SySt. This northern sample is dominated by Galactic disk/halo objects, whereas our previous southern sample is heavily biased toward the bulge population. Spectrum synthesis of high-resolution (R$\sim$50000), near-$IR$ spectra using standard LTE analysis and atmospheric models have been used to measure abundances of CNO and elements around the iron peak (Fe, Ti, Ni, Sc) in the atmospheres of the red giant component. The SySt sample shows generally slightly sub-solar metallicity, as expected for an older disk population, with a median at [Fe/H]\,$\sim -0.2$ dex. Enhanced $^{14}$N, depleted $^{12}$C, and decreased $^{12}$C/$^{13}$C indicate that all these giants have experienced the first dredge-up. Comparison with theoretical predictions indicates that additional mixing processes had to occur to explain the observed C and N abundances. Relative O and Fe abundances agree with those represented by Galactic disc and bulge giant populations in the {\sl APOGEE} data, with a few cases that can be attributed to membership in the extended thick-disc/halo. As an interesting byproduct of this study, we observed a blue-shifted additional component on the wings of absorption lines in the spectra of AG Peg which could be connected with accretion onto the hot component.
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