标题： 天牛星：一颗K巨星的红外光谱的混合性质 显示英文标题

标题： The K giant star Arcturus: the hybrid nature of its infrared spectrum

摘要： 我们研究了毕宿五的红外光谱，以阐明其大气中被称为CO-mosphere的冷组分的本质，使用的IR光谱图集由Hinkle等人（1995年）提供。 CO线的本质在logW/ν = -4.75处显示出突然变化，超过此极限的线不能再用经典的线形成理论分析。 这一事实更为简单的表现形式是，CO线的生长曲线（CG）在logW/ν = -4.75处显示出无法预测的上升趋势。 在其他红色（超）巨星中也证实了类似的异常的CG经验行为，看起来CG似乎是至少两种不同来源成分的混合物。 尽管在毕宿五中观测到的CO基振强线比预测的光球谱有所增强，但较弱的线却略有减弱，我们将这些结果解释为分子云吸收/发射的结果，这些分子云是在扩展的大气中形成的。 恒星大气中真的存在云吗？ 仅靠光谱观测很难回答这个问题，但我们通过对CO线的分析，在毕宿五中找到了几个支持这种可能性的论据。 在更冷的（超）巨星中，其CO线表现出与毕宿五相似的异常行为时，外层大气中分子云的存在已被空间干涉测量的直接观测所证明。 我们认为，分子云的形成是从早期K到晚期M（超）巨星的冷亮星的一般特征。 显示英文摘要

摘要： We study infrared spectrum of Arcturus to clarify the nature of the cool component of its atmosphere, referred to as the CO-mosphere, with the use of the IR spectral atlas by Hinkle et al.(1995). The nature of CO lines shows an abrupt change at logW/nu = -4.75, and the lines stronger than this limit can no longer be analyzed by the classical line-formation theory. A more simple manifestation of this fact is that the curves-of-growth (CG) of CO lines show an unpredictable upturn at logW/nu = -4.75. Similar unusual behaviors of empirical CG are confirmed in other red (super)giant stars, and it looks as if the CG is a hybrid of at least two components of different origins. Although strong lines of the CO fundamentals observed in Arcturus show strengthening compared with the predicted photospheric spectrum, the weaker lines show slight weakening, and we interpret these results as due to absorption/emission by the molecular clouds formed in the extended atmosphere. Now do clouds exist in stellar atmospheres? It is by no means easy to answer this question by spectroscopic observations alone, but we find several arguments in favor of such a possibility in Arcturus by analyzing the CO lines. In cooler (super)giant stars in which CO lines show similar unusual behaviors as in Arcturus, the presence of molecular clouds in the outer atmospheres was demonstrated by direct observations with spatial interferometry. We suggest that the formation of molecular clouds is a general feature in cool luminous stars from early K to late M (super)giant stars.