Volume 376, Number 3, September IV 2001
|Page(s)||1113 - 1122|
|Published online||15 September 2001|
Line ratios for helium-like ions: Applications to collision-dominated plasmas*
CEA/DSM/DAPNIA, Service d'Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France
2 DAEC, Observatoire de Paris, Section Meudon, 92195 Meudon Cedex, France
3 Space Research Organization Netherlands (SRON), Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
4 LSAI, U.M.R. 8624, CNRS, Université de Paris Sud, 91405 Orsay Cedex, France
5 DARC, Observatoire de Paris, Section Meudon, 92195 Meudon Cedex, France
6 Astronomical Institute "Anton Pannekoek", Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
Corresponding author: D. Porquet, email@example.com
Accepted: 21 June 2001
The line ratios R and G of the three main lines of He-like ions (triplet: resonance, intercombination, forbidden lines) are calculated for Cv, Nvi, Ovii, Neix, Mgxi, and Sixiii. These ratios can be used to derive electron density ne and temperature Te 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. Neix, Mgxi, Sixiii) 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 23S (upper level of the forbidden line) and 23P levels (upper levels of the intercombination lines) is taken into account. This process is mainly important for the lower-Z ions (i.e. Cv, Nvi, Ovii) at moderate radiation temperature (Trad). 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.
Key words: X-rays: stars / atomic processes / stars: coronae / stars: late-type / stars: activity / stars: early-type / stars: activity
© ESO, 2001
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.