A型恒星HR 8799的X射线辐射
X-ray emission from the remarkable A-type star HR 8799
摘要：
我们提出了一个特殊的行星轴承A5 V星HR 8799，更准确地分类为kA 5 hF 0 mA5星和搜索的内在X射线发射钱德拉观测。我们清楚地检测HR 8799在软X射线能量与ACIS-S探测器在10 KS曝光;轻微的X射线亮度变化是目前在观察。日冕等离子体可以用一个模型很好地描述，该模型的温度约为3 MK，X射线在0.2-2.0 keV波段的光度约为Lx = 1.3 x 10^28 erg/s，对应的活度水平为log Lx/Lbol ~-6.2。总之，这些发现指向一个相当弱的活动，并给予RASS检测，长期稳定的X射线发射星。HR 8799的X射线发射类似于A型晚期/F型早期的恒星，与氢线和有效温度测定的分类一致，从而解决了与预测中期A型恒星实际上是X射线暗的磁活动标准图像的明显差异。
英文摘要：
We present a Chandra observation of the exceptional planet bearing A5V star HR 8799, more precisely classified as a kA5hF0mA5 star and search for intrinsic X-ray emission. We clearly detect HR 8799 at soft X-ray energies with the ACIS-S detector in a 10 ks exposure; minor X-ray brightness variability is present during the observation. The coronal plasma is described well by a model with a temperature of around 3 MK and an X-ray luminosity of about Lx = 1.3 x 10^28 erg/s in the 0.2-2.0 keV band, corresponding to an activity level of log Lx/Lbol ~ -6.2. Altogether, these findings point to a rather weakly active and given a RASS detection, long-term stable X-ray emitting star. The X-ray emission from HR 8799 resembles those of a late A/early F-type stars, in agreement with its classification from hydrogen lines and effective temperature determination and thus resolving the apparent discrepancy with the standard picture of magnetic activity that predicts mid A-type stars to be virtually X-ray dark.
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