Henggeng Han, Song Wang, Chuanjie Zheng, Xue Li, Kai Xiao and Jifeng Liu
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引用次数: 0
摘要
利用来自 ROSAT 观测的同质 X 射线星表,我们对单星和双星的恒星 X 射线活动-旋转关系进行了全面研究。一般来说,单星的关系由两个不同的区域组成:一个是弱衰减区,表明磁动力持续依赖于恒星旋转,而不是恒定活动的饱和状态;另一个是快速衰减区,X射线活动与罗斯比数密切相关。详细分析揭示了这一关系中的更多细微结构:在极速旋转区,观测到 X 射线活动随着旋转速率的增加而减少,这被称为过饱和;而在极慢速旋转区,这一关系趋于平缓,这主要是由于 F 星的散射造成的。这种散射可能是由于恒星活动在一个恒星周期内的内在可变性或存在不同的动力机制造成的。双星表现出与单星类似的关系,但由于样本量有限,无法识别双星关系中的精细结构。我们计算了宿主星的 X 射线辐射引发的行星大气质量损失率。我们的研究结果表明,对于恒星宜居带内的类地行星来说,它很容易就会失去整个原始H/He包层(约等于行星质量的1%)。
Stellar X-Ray Activity and Habitability Revealed by the ROSAT Sky Survey
Using the homogeneous X-ray catalog from ROSAT observations, we conducted a comprehensive investigation into stellar X-ray activity–rotation relations for both single and binary stars. Generally, the relation for single stars consists of two distinct regions: a weak decay region, indicating a continued dependence of the magnetic dynamo on stellar rotation rather than a saturation regime with constant activity, and a rapid decay region, where X-ray activity is strongly correlated with the Rossby number. Detailed analysis reveals more fine structures within the relation: in the extremely fast-rotating regime, a decrease in X-ray activity was observed with increasing rotation rate, referred to as supersaturation, while in the extremely slow-rotating region, the relation flattens, mainly due to the scattering of F stars. This scattering may result from intrinsic variability in stellar activities over one stellar cycle or the presence of different dynamo mechanisms. Binaries exhibit a similar relation to that of single stars while the limited sample size prevented the identification of fine structures in the relation for binaries. We calculated the mass-loss rates of planetary atmospheres triggered by X-ray emissions from host stars. Our findings indicate that for an Earthlike planet within the stellar habitable zone, it would easily lose its entire primordial H/He envelope (equating to about 1% of the planetary mass).