仙后座γ：一颗有个性的Be型X射线星
gamma Cassiopeiae: an X-ray Be star with personality
摘要：
仙后座γ（gCas）是一颗B0.5 e恒星，具有特殊的X射线发射特性，但它也是一个小类星的原型。在本文中，我们研究的X射线光谱的2004年XMM-牛顿观测和以前发表的2001年钱德拉观测。在这两种情况下，光谱可以用3或4个热分量来建模，这些热分量在温度上是离散的，在空间上是不同的。具有kT ~ 12 keV的主导分量贡献了大部分（~80-90%）通量。次级组件的温度范围为2-3 keV至0.1 keV;这些值可以随时间变化。重要的是，我们发现2001年对软X射线的强吸收在2004年消失了，这意味着源前面的吸收柱已经离开了恒星或已经被移除。其他的差异包括从FeK α复合物的电离线（甚至比2001年的观测更接近太阳），减少了Fe K和可能的Si K荧光特征，以及从NVII和NeX H-α线，N和Ne可能过剩。此外，我们注意到两个光谱中的共同特征，这些特征似乎将gCas与HD 110342分开，HD 110342是该子类的另一个成员。从这个意义上说，这些明星有不同的“个性。“例如，对于gCas，快速的X射线闪烁和光变曲线的缓慢变化很少伴随着硬度的变化，而热的X射线成分保持几乎恒定的温度。此外，光变曲线显示通量中经常性的“平静”，表明弛豫循环是作为（未知的）X射线产生过程的一部分操作的。
英文摘要：
gamma Cassiopeiae (gCas) is a B0.5e star with peculiar X-ray emission properties and yet the prototype of its own small class. In this paper we examine the X-ray spectra for a 2004 XMM-Newton observation and a previously published 2001 Chandra observation. In both cases the spectra can be modeled with 3 or 4 thermal components, which appear be discrete in temperature and spatially distinct. The dominant component, having kT ~ 12 keV contributes most (~80-90%) of the flux. The secondary components have temperatures in the range of 2-3 keV to 0.1 keV; these values can shift in time. Importantly, we find that the strong absorption of soft X-rays in 2001 is absent in 2004, meaning that an absorbing column in front of the source has moved off the star or has been removed. Other differences include a reduced Fe abundance from the ionized lines of the FeKalpha complex (even more subsolar than the 2001 observation), a decrease of the Fe K and possibly of the Si K fluorescence features, and from the NVII and NeX H-alpha lines, a possible overabundance of N and Ne. Also, we note common characteristics in both spectra that seem to set gCas apart from HD110342, another member of this subclass studied in detail. In this sense these stars have different "personalities." For example, for gCas rapid X-ray flaring and slower changes in the light curve are only seldomly accompanied by variations in hardness, and the hot X-ray component remains nearly constant in temperature. Moreover, the light curve shows recurrent "lulls" in flux, suggesting that a relaxation cycle is operates as part of the (unknown) X-ray generation process.
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