Observation of Fe II in cool variables

Many cool stars show different forms of variability associated with the presence of emission lines. The following categories of stars are mentioned: cool main sequence - dMe, flare, BY Dra stars, pre main sequence - T Tau stars, Herbig-Haro objects, R CrB stars, Mira variables, binaries with a hot component - ζ Aur/VV Cep systems, symbiotic stars, cataclysmic binaries. In the cool variables here discussed Fe II emission lines probably arise in regions hotter than the cool star's photosphere. The observation of these lines in the optical and UV during different phases of their time variability should be of very much help to diagnose physical conditions in the outer atmospheres and circumstellar envelopes of these stars.