AK Sco，在前主序星密近双星中首次探测到高度扰动大气
AK Sco, first detection of a highly disturbed atmosphere in a pre-main sequence close binary
摘要：
AK Sco是一个独特的来源：一个约1000万年前的主序光谱双星，由两颗几乎相等的F5恒星组成，在近星点仅相隔11个恒星半径，因此，恒星磁层充满了近星点的洛希瓣。轨道尚未圆化（e=0.47），预计会有非常强的潮汐。这使得AK Sco成为研究前主序星（PMS）演化过程中恒星磁场形成中引力潮汐效应的理想实验室。在这封信中，高度扰动（sigma ~ 100 km/s）和非常稠密的大气（ne = 1.6e ~（10）cm ~（-3））的检测报告。显著的谱线增宽模糊了大气等离子体光谱中离子带或弓形激波的任何迹象。辐射损失不能仅仅由恒星大气中传播的潮汐波的能量耗散来解释，也不能由吸积物质来解释。恒星释放的内能似乎是等离子体加热的最可能来源。这是第一次明确表明主序前近距离双星周围存在高度扰动的大气。
英文摘要：
AK Sco is a unique source: a ~10 Myrs old pre-main sequence spectroscopic binary composed of two nearly equal F5 stars that at periastron are separated by barely eleven stellar radii so, the stellar magnetospheres fill the Roche lobe at periastron. The orbit is not yet circularized (e=0.47) and very strong tides are expected. This makes of AK Sco, the ideal laboratory to study the effect of gravitational tides in the stellar magnetic field building up during pre-main sequence (PMS) evolution. In this letter, the detection of a highly disturbed (sigma ~ 100 km/s) and very dense atmosphere (ne = 1.6e10cm-3) is reported. Significant line broadening blurs any signs of ion belts or bow shocks in the spectrum of the atmospheric plasma. The radiative loses cannot be accounted solely by the dissipation of energy from the tidal wave propagating in the stellar atmosphere; neither by the accreting material. The release of internal energy from the star seems to be the most likely source of the plasma heating. This is the first clear indication of a highly disturbed atmosphere surrounding a pre-main sequence close binary.
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