近距离观察英仙座阿尔法日冕之谜
A Closer Look at the Alpha Persei Coronal Conundrum
摘要：
1993年ROSAT对阿尔法Per疏散星团的巡天探测到了它最亮的恒星，中F超巨星阿尔法Persei：X射线光度和光谱硬度与日冕活动的晚型矮星成员相似。后来，在2010年，哈勃宇宙起源光谱仪快照发现英仙座阿尔法星的远紫外日冕代理SiIV出乎意料地弱。这一点，以及ROSAT源的可疑偏移，表明一个晚型伴星可能是造成X射线的原因。最近，一个多方面的计划测试了这一前提。地面光学日冕照相术和HST宽视场照相机3的近紫外成像搜索了任何近距离的微弱候选日冕物体，但没有成功。然后，钱德拉指向发现X射线源单一，并与明亮的恒星重合。值得注意的是，英仙座α的SiIV发射，在HST COS收集的更深的FUV光谱中，作为联合计划的一部分，与色球原子氧（这必须是发光恒星固有的）对齐，在较冷的晚F和早G超巨星的背景下，包括造父变星。这表明X射线是根本的异常。过于明亮的X射线仍然支持一个过度活跃的矮次级星系的情况，尽管现在空间上还没有解决。然而，另一种选择是英仙座阿尔法星代表了一类新的日冕源。现在解决第一种可能性变得更加困难，因为简单的解决方案--一个分离良好的伴侣--已经被排除了。测试另一种可能性需要对早期F超巨星进行更广泛的高能普查。
英文摘要：
A ROSAT survey of the Alpha Per open cluster in 1993 detected its brightest star, mid-F supergiant Alpha Persei: the X-ray luminosity and spectral hardness were similar to coronally active late-type dwarf members. Later, in 2010, a Hubble Cosmic Origins Spectrograph SNAPshot of Alpha Persei found far-ultraviolet coronal proxy SiIV unexpectedly weak. This, and a suspicious offset of the ROSAT source, suggested that a late-type companion might be responsible for the X-rays. Recently, a multi-faceted program tested that premise. Groundbased optical coronography, and near-UV imaging with HST Wide Field Camera 3, searched for any close-in faint candidate coronal objects, but without success. Then, a Chandra pointing found the X-ray source single and coincident with the bright star. Significantly, the SiIV emissions of Alpha Persei, in a deeper FUV spectrum collected by HST COS as part of the joint program, aligned well with chromospheric atomic oxygen (which must be intrinsic to the luminous star), within the context of cooler late-F and early-G supergiants, including Cepheid variables. This pointed to the X-rays as the fundamental anomaly. The over-luminous X-rays still support the case for a hyperactive dwarf secondary, albeit now spatially unresolved. However, an alternative is that Alpha Persei represents a novel class of coronal source. Resolving the first possibility now has become more difficult, because the easy solution -- a well separated companion -- has been eliminated. Testing the other possibility will require a broader high-energy census of the early-F supergiants.
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