Line intensity enhancements in stellar coronal X-ray spectra due to opacity effects
Abstract
Context. The I(15.01 A)/I(16.78 A) emission line intensity ratio in Fe XVII has been reported to deviate from its theoretical value in solar and stellar X-ray spectra. This is attributed to opacity in the 15.01 A line, leading to a reduction in its intensity, and was interpreted in terms of a geometry in which the emitters and absorbers are spatially distinct. Aims. We study the I(15.01 A)/I(16.78 A) intensity ratio for the active cool dwarf EV Lac, in both flare and quiescent spectra. Methods. The observations were obtained with the Reflection Grating Spectrometer on the XMM-Newton satellite. The emission measure distribution versus temperature reconstruction technique is used for our analysis. Results. We find that the 15.01 A line exhibits a significant enhancement in intensity over the optically thin value. To our knowledge, this is the first time that such an enhancement has been detected on such a sound statistical basis. We interpret this enhancement in terms of a geometry in which the emitters and absorbers are not spatially distinct, and where the geometry is such that resonant pumping of the upper level has a greater effect on the observed line intensity than resonant absorption in the line-of-sight.
Cite
@article{arxiv.0803.3184,
title = {Line intensity enhancements in stellar coronal X-ray spectra due to opacity effects},
author = {S. J. Rose and M. Matranga and M. Mathioudakis and F. P. Keenan and J. S. Wark},
journal= {arXiv preprint arXiv:0803.3184},
year = {2009}
}
Comments
accepted for publication in A&A