Spectral Indications of Density Variability in the Corona of AD Leonis
  Direct comparison of high-resolution X-ray spectra of the active dMe star AD Leo, observed three times with Chandra, shows variability of key density-sensitive lines, possibly due to flaring activity. In particular, a significant long-duration enhancement of the coronal density is indicated by the Ne IX and Si XIII He-like triplets, and possibly also by density-sensitive Fe XXI line ratios. 
A. Maggio (1), J.-U. Ness (2)((1) INAF -- Osservatorio Astronomico di   Palermo, Italy, (2) Department of Physics, Rudolf Pe...