086507

Red giants like Arcturus occupy a region in the X-ray Hertzsprung-Russell Diagram openParHRDclosePar known as the coronal graveyard. The physical cause for the sharp decline of X-ray emission beyond a so-called dividing line that separates X-ray emitting yellow giants from X-ray dark red giants is comma despite decades of research comma not finally answered. The recent X-ray detection of Arcturus with Chandra HRC-I motivates our request to obtain spectral information with XMM-Newton EPIC spectroscopy. An 80 ks exposure is sufficient to detect large absorbing column densities that may be expected if severe obscuration by layers above the giant.s corona cause the decrease in their observed X-ray luminosity.诸如大角星（Arcturus）这类红巨星，在X射线赫罗图（X-ray Hertzsprung-Russell Diagram，HRD）中处于被称为‘日冕消亡区’的区域。在用以区分发射X射线的黄巨星与X射线暗弱红巨星的所谓分界线之外，X射线辐射会出现急剧下降，这一现象的物理成因尽管历经数十年研究，至今仍未得到最终解答。近期借助钱德拉（Chandra）HRC-I探测器对大角星开展的X射线探测结果，促使我们提出使用XMM-牛顿（XMM-Newton）卫星的EPIC光谱仪获取其光谱信息的申请。若红巨星光冕上方的物质层造成严重遮蔽，进而导致其观测到的X射线光度下降，那么80千秒的曝光时长足以探测到这类情形下可能存在的大吸收柱密度。