An analysis of Lyman series lines arising from hydrogen-like oxygen and neon ions in the coronae of the active RS CVn-type binaries II Peg and IM Peg, observed using the Chandra High Resolution Transmission Grating Spectrograph, shows significant decrements in the Lyα/Lyβ ratios as compared with theoretical predictions and with the same ratios observed in similar active binaries. We interpret these decrements in terms of resonance scattering of line photons out of the line of sight; these observations present the first strong evidence of this effect in active stellar coronae. The net line photon loss implies a nonuniform and asymmetric surface distribution of emitting structures on these stars. Escape probability arguments, together with the observed line ratios and estimates of the emitting plasma density, imply typical line-of-sight sizes of the coronal structures that dominate the X-ray emission of 1010 cm at temperatures of 3×106 K and of 108 cm at 107 K. These sizes are an order of magnitude larger than predicted by simple quasi-static coronal loops models but are still very small compared to the several 1011 cm radii of the underlying stars.
展开▼
机译:使用Chandra高分辨率透射光栅光谱仪观察到的活性RS CVn型二元II Peg和IM Peg日冕中类似氢的氧和氖离子产生的Lyman系列谱线的分析显示,Lyα/Lyβ显着下降。与理论预测值相比,并且在相似的活动二进制文件中观察到的比率相同。我们用视线外的线光子的共振散射来解释这些减少。这些观察结果首次证明了这种作用在活跃的恒星日冕中的作用。净线光子损失意味着这些恒星上发射结构的表面不均匀且不对称。逸出概率论点,连同观察到的线比和发射等离子体密度的估计值,暗示了在3×106 K和108的温度下,占主导地位的1010 cm X射线的冠状结构的典型视线尺寸在107 K时,厘米。这些大小比简单的准静态日冕环模型所预测的大小大一个数量级,但与下层恒星的几个1011厘米半径相比仍然很小。
展开▼