Line ratios for helium-like ions: Applications to collision-dominated plasmas

被引:208
作者
Porquet, D [1 ]
Mewe, R
Dubau, J
Raassen, AJJ
Kaastra, JS
机构
[1] CEA Saclay, Serv Astrophys, DAPNIA, DSM, F-91191 Gif Sur Yvette, France
[2] Observ Paris, DAEC, F-92195 Meudon, France
[3] SRON, NL-3584 CA Utrecht, Netherlands
[4] Univ Paris 11, LSAI, CNRS, UMR 8624, F-91405 Orsay, France
[5] Observ Paris, Sect Meudon, DARC, F-92195 Meudon, France
[6] Astron Inst Anton Pannekoek, NL-1098 SJ Amsterdam, Netherlands
来源
ASTRONOMY & ASTROPHYSICS | 2001年 / 376卷 / 03期
关键词
X-rays : stars; atomic processes; stars : coronae; stars : late-type; stars : activity; early-type stars : activity;
D O I
10.1051/0004-6361:20010959
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
The line ratios R and G of the three main lines of He-like ions (triplet: resonance, intercombination, forbidden lines) are calculated for C V, N VI, O VII, Ne IX, Mg XI, and Si XIII. These ratios can be used to derive electron density ne and temperature T-e of hot late-type stellar coronae and O, B stars from high-resolution spectra obtained with Chandra (LETGS, HETGS) and XMM-Newton (RGS). All excitation and radiative processes between the levels and the effect of upper-level cascades from collisional electronic excitation and from dielectronic and radiative recombination have been considered. When possible the best experimental values for radiative transition probabilities are used. For the higher-Z ions (i.e. Ne IX, Mg XI, Si XIII) possible contributions from blended dielectronic satellite lines to each line of the triplets were included in the calculations of the line ratios R and G for four specific spectral resolutions: RGS, LETGS, HETGS-MEG, HETGS-HEG. The influence of an external stellar radiation field on the coupling of the 2(3)S (upper level of the forbidden line) and 2(3)P levels (upper levels of the intercombination lines) is taken into account. This process is mainly important for the lower-Z ions (i.e. C V, N VI, O VII) at moderate radiation temperature (T-rad). These improved calculations were done for plasmas in collisional ionization equilibrium, but will be later extended to photo-ionized plasmas and to transient ionization plasmas. The values for R and G are given in extensive tables, for a large range of parameters, which could be used directly to compare to the observations.
引用
收藏
页码:1113 / 1122
页数:10
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