食近双星系统组成星之间的成分差异显示出化学特性
Compositional differences between the component stars of eclipsing close binary systems showing chemical peculiarities
摘要：
对A型附近的5颗食近双星（AR Aur，beta Aur，YZ Cas，WW Aur，RR Lyn）的主星和次星的CNO和几种重元素的表面化学丰度进行了光谱研究，以探讨这两种成分之间化学差异的本质（由于潮汐同步，它们都是相对慢的自转星）。关于由类似成分组成的系统，β Aur和WW Aur被证实在初级和次级之间没有成分差异，两者都显示出几乎相同的Am异常，尽管在AR Aur的成分星中看到的化学特性显示出明显的差异（HgMn星和Am星）。与此相反，系统（YZ Cas和RR Lyn）组成的相当不同的（A和早期F）的组件，表面丰度显着不同的初级（Am）和次级（正常）。这些观测结果表明，主序上部非磁性星的化学异常具有与Teff相关的特征：（1）在10000 K> Teff > 7000 K的有效温度范围内，自转速度是决定Am异常程度的最重要因素。(2)然而，Am现象的出现似乎在~ 7000 K有一个较低的Teff极限，在该极限以下，无论恒星旋转如何，都没有观测到丰度异常。(3)当Teff从~ 10000 K增加到~ 11000 K时，可能发生从Am异常（CNO的轻度亏损）到HgMn异常（异常大的N亏损）的转变。
英文摘要：
A spectroscopic study was carried out on the surface chemical abundances of CNO and several heavier elements in the primary and secondary components of 5 eclipsing close binaries around A-type (AR Aur, beta Aur, YZ Cas, WW Aur, and RR Lyn), in order to investigate the nature of chemical differences between both components (being comparatively slow rotators alike due to tidal synchronization). Regarding the systems comprising similar components, beta Aur and WW Aur were confirmed to exhibit no compositional difference between the primary and secondary both showing almost the same Am anomaly, though the chemical peculiarities seen in the component stars of AR Aur show distinct differences (HgMn star and Am star). In contrast, as to the systems (YZ Cas and RR Lyn) consisting of considerably different (A and early-F) components, the surface abundances are markedly different between the primary (Am) and secondary (normal). These observational results may indicate Teff-dependent characteristics regarding the chemical anomalies of non-magnetic stars on the upper main sequence: (1) In the effective temperature range of 10000K > Teff > 7000K, rotational velocity is the most important factor for determining the extent of Am peculiarity. (2) However, the emergence of Am phenomenon seems to have a lower Teff limit at ~7000K, below which no abundance anomaly is observed regardless of stellar rotation. (3) The transition from Am anomaly (mild deficiency in CNO) to HgMn anomaly (unusually large N depletion) is likely to take place as Teff increases from ~10000K to ~11000K.
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