Stellar Activity on the Young Suns of Orion: COUP Observations of K5-7 Pre-Main-Sequence Stars
Stellar Activity on the Young Suns of Orion: COUP Observations of K5-7 Pre-Main-Sequence Stars
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猎户座年轻太阳上的恒星活动：K5-7 前主序恒星的 COUP 观测
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
E. Feigelson
中科院分区：
文献类型：
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作者：
S. Wolk;E. Flaccomio;G. Micela;F. Favata;A. Glassgold;H. Shang;E. Feigelson
2003年1月，钱德拉猎户座超深项目(COUP)对猎户座星云星团(ONC)进行了13.2天的观测，发现了约1400颗年轻恒星。本文基于COUP数据，研究了28颗质量相当于太阳质量的ONC恒星的X射线性质。我们的目标是描述年轻太阳的类似物的磁场活动，从而更好地理解太阳X射线对行星形成时期太阳星云的影响。考虑到观测时间的长短，我们能够清楚地区分所有恒星的特征周期和耀斑周期。我们发现，活跃的年轻太阳有70%的时间处于磁通量相对恒定的特征状态，等离子体的温度为kt2，≃，2.1xkt1。在特征周期内，0.5-8keV X射线光度约为测辐射光度的0.03%。在这一特征辐射上，通常每周叠加一到两个峰值亮度为lx~30-32ergs S-1的强耀斑，同时伴随着耀斑峰处从≃2.4keV到≃7keV的热等离子体分量的加热。叠加在特征发射能级上的耀斑能量分布符合dN/de∝E-1.7关系。耀斑速率与产生足够高能量的质子是一致的，这些质子产生了在古代陨石中发现的一些重要的短期放射性核素的同源来源。在距离中心恒星1AU的地方，X射线可以以每秒6×10-9电离的速度电离恒星周围的气体，比宇宙射线的电离速率高出一个数量级。估计的高能粒子通量足以解释在陨石包裹体中观察到的许多同位素异常。
In 2003 January, the Chandra Orion Ultradeep Project (COUP) detected about 1400 young stars during a 13.2 day observation of the Orion Nebula Cluster (ONC). This paper is a study of the X-ray properties of a well-defined sample of 28 solar-mass ONC stars based on COUP data. Our goals are to characterize the magnetic activity of analogs of the young Sun and thereby to improve understanding of the effects of solar X-rays on the solar nebula during the era of planet formation. Given the length of the COUP observation we are able to clearly distinguish characteristic and flare periods for all stars. We find that active young suns spend 70% of their time in a characteristic state with relatively constant flux and magnetically confined plasma with temperatures kT2 ≃ 2.1 × kT1. During characteristic periods, the 0.5-8 keV X-ray luminosity is about 0.03% of the bolometric luminosity. One or two powerful flares per week with peak luminosities log LX ~ 30-32 ergs s-1 are typically superposed on this characteristic emission accompanied by heating of the hot plasma component from ≃2.4 to ≃7 keV at the flare peak. The energy distribution of flares superposed on the characteristic emission level follows the relationship dN/dE ∝ E-1.7. The flare rates are consistent with the production of sufficiently energetic protons to spawn a spallogenic origin of some important short-lived radionuclides found in ancient meteorites. The X-rays can ionize gas in the circumstellar disk at a rate of 6 × 10-9 ionizations per second at 1 AU from the central star, orders of magnitude above cosmic-ray ionization rates. The estimated energetic particle fluences are sufficient to account for many isotopic anomalies observed in meteoritic inclusions.