类地行星形成时期的X射线环境：英仙座h星的Chandra观测
The X-Ray Environment During the Epoch of Terrestrial Planet Formation: Chandra Observations of h Persei
摘要：
我们描述了Chandra/ACIS-I对英仙座中著名的双星团（英仙座h和英仙座chi）的一部分英仙座h星团的观测。结合钱德拉探测到的源列表和新的光学/红外测光和光谱学，发现了大约165颗V < 23的X射线亮星。大约有142个星系具有与星系团成员一致的光学星等和颜色。观测到的Lx分布在Lx ~ 10 ^30.3尔格/秒处达到峰值，可能是一个更大的~ 0.4--2 Msun X射线活跃恒星群的亮边。从一个简短的列表中的X射线活跃的恒星与IRAC 8微米多余的温暖，地球区的尘埃，我们得到一个最大的X射线通量事件形成类地行星。虽然X射线活度和IRAC过量之间没有相关性，但分数X射线光度与光学颜色和光谱类型相关。通过比较Lx/L* 与光谱类型和V-I在h Per中的分布与其他1- 1亿年年龄的星团的结果，我们表明，质量稍大于太阳（> 1.5 Msun）的恒星在1 - 15亿年的时间内脱离X射线饱和。对于大于1.5 Msun的恒星，恒星结构的变化可能在X射线发射的下降中起着重要的作用。
英文摘要：
We describe Chandra/ACIS-I observations of the massive ~ 13--14 Myr-old cluster, h Persei, part of the famous Double Cluster (h and chi Persei) in Perseus. Combining the list of Chandra-detected sources with new optical/IR photometry and optical spectroscopy reveals ~ 165 X-ray bright stars with V < 23. Roughly 142 have optical magnitudes and colors consistent with cluster membership. The observed distribution of Lx peaks at Lx ~ 10^30.3 ergs/s and likely traces the bright edge of a far larger population of ~ 0.4--2 Msun X-ray active stars. From a short list of X-ray active stars with IRAC 8 micron excess from warm, terrestrial-zone dust, we derive a maximum X-ray flux incident on forming terrestrial planets. Although there is no correlation between X-ray activity and IRAC excess, the fractional X-ray luminosity correlates with optical colors and spectral type. By comparing the distribution of Lx/L* vs. spectral type and V-I in h Per with results for other 1--100 Myr-old clusters, we show that stars slightly more massive than the Sun (> 1.5 Msun) fall out of X-ray saturation by ~ 10--15 Myr. Changes in stellar structure for > 1.5 Msun stars likely play an important role in this decline of X-ray emission.
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