We present results from an empirical study of the Mg II h & k emission lines of selected Mira variable stars , using spectra from the International Ultraviolet Explorer ( IUE ) .
The stars all exhibit similar Mg II behavior during the course of their pulsation cycles .
The Mg II flux always peaks after optical maximum near pulsation phase \phi = 0.2 - 0.5 , although the Mg II flux can vary greatly from one cycle to the next .
The lines are highly blueshifted , with the magnitude of the blueshift decreasing with phase .
The widths of the Mg II lines are also phase-dependent , decreasing from about 70 km s ^ { -1 } to 40 km s ^ { -1 } between \phi = 0.2 and \phi = 0.6 .
We also study other UV emission lines apparent in the IUE spectra , most of them Fe II lines .
These lines are much narrower and not nearly as blueshifted as the Mg II lines .
They exhibit the same phase-dependent flux behavior as Mg II , but they do not show similar velocity or width variations .