用类氦三重态进行日冕密度诊断：CHANDRA --大陵五、五车二、南河三、Eps Eri、α Cen A&B、UX Ari、AD Leo、YY Gem和HR1099的LETGS观测
Coronal density diagnostics with Helium-like triplets: CHANDRA--LETGS observations of Algol, Capella, Procyon, Eps Eri, Alpha Cen A&B, UX Ari, AD Leo, YY Gem, and HR1099
摘要：
本文分析了钱德拉X射线天文台低能透射光栅光谱仪（LETGS）观测到的10颗冷星（大陵五、五车二、南河三、Eps Eri、Alpha Cen A&B、UX Ari、AD Leo、YY Gem和HR 1099）。这个样本包含了我们目前可用的LETGS观测到的所有冷星，其积分时间足够长，足以保证进行有意义的光谱分析。我们的样本包括不活跃，中度活跃和过度活跃的恒星和样本的大部分活动水平遇到的日冕X射线源。我们使用LETGS光谱进行密度和温度诊断，重点是H-类和He-类离子。我们发现的Lyman-Alpha和He类共振线与平均X射线表面通量的线通量比之间的相关性。我们确定密度使用氦样三重态。对于活跃的恒星，我们没有发现显着偏离低密度极限的离子的Ne，Mg和Si，而测得的线比的离子的C，N和O的证据表明偏离低密度极限的活跃的恒星，但不是在不活跃的恒星。最好的测量可以为OVII三重态，我们发现显着偏离低密度极限的恒星大陵五，南河三，YY宝石，Eps Eri和HR 1099。我们讨论了辐射场的影响解释的He-样的三线态线的比率在低Z离子，这是相关的大陵五，和双电子卫星线的影响，这是相关的南河三。对于活动星YY Gem、Eps Eri和HR 1099，低f/i比可以毫无疑问地归因于OVII温度下1--3 × 10^10 cm^-3范围内的高密度。我们发现我们的LETGS光谱是一个非常有用的工具等离子体诊断恒星日冕。
英文摘要：
We present an analysis of ten cool stars (Algol, Capella, Procyon, Eps Eri, Alpha Cen A&B, UX Ari, AD Leo, YY Gem, and HR1099) observed with the Low Energy Transmission Grating Spectrometer (LETGS) on board the Chandra X-ray Observatory. This sample contains all cools stars observed with the LETGS presently available to us with integration times sufficiently long to warrant a meaningful spectral analysis. Our sample comprises inactive, moderately active, and hyperactive stars and samples the bulk part of activity levels encountered in coronal X-ray sources. We use the LETGS spectra to carry out density and temperature diagnostics with an emphasis on the H-like and the He-like ions. We find a correlation between line flux ratios of the Lyman-Alpha and He-like resonance lines with the mean X-ray surface flux. We determine densities using the He-like triplets. For active stars we find no significant deviations from the low-density limit for the ions of Ne, Mg, and Si, while the measured line ratios for the ions of C, N, and O do show evidence for departures from the low-density limit in the active stars, but not in the inactive stars. Best measurements can be made for the OVII triplet where we find significant deviations from the low-density limit for the stars Algol, Procyon, YY Gem, Eps Eri, and HR1099. We discuss the influence of radiation fields on the interpretation of the He-like triplet line ratios in the low-Z ions, which is relevant for Algol, and the influence of dielectronic satellite lines, which is relevant for Procyon. For the active stars YY Gem, Eps Eri, and HR1099 the low f/i ratios can unambiguously be attributed to high densties in the range 1--3 10^10 cm^-3 at OVII temperatures. We find our LETGS spectra to be an extremely useful tool for plasma diagnostics of stellar coronae.
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