Studying the Pulsation of Mira Variables in the Ultraviolet

We present results from an empirical study of the Mg II h & k emission linesof selected Mira variable stars, using spectra from the InternationalUltraviolet Explorer (IUE). The stars all exhibit similar Mg II behavior duringthe course of their pulsation cycles. The Mg II flux always peaks after opticalmaximum near pulsation phase 0.2-0.5, although the Mg II flux can vary greatlyfrom one cycle to the next. The lines are highly blueshifted, with themagnitude of the blueshift decreasing with phase. The widths of the Mg II linesare also phase-dependent, decreasing from about 70 km/s to 40 km/s betweenphase 0.2 and 0.6. We also study other UV emission lines apparent in the IUEspectra, most of them Fe II lines. These lines are much narrower and not nearlyas blueshifted as the Mg II lines. They exhibit the same phase-dependent fluxbehavior as Mg II, but they do not show similar velocity or width variations.Comment: 26 pages, 12 figures; AASTEX v5.0 plus EPSF extensions in mkfig.sty; to appear in Ap