Contour plots of Re(P) = 0 for Alfvén waves as a function of the wavenumber with (A)β_e = 0.01 and (B)β_e = 0.10; and as a function of the plasma beta parameter with (C)ck/ω_pp = 0.5 and (D)ck/ω_pp = 1.0. The solutions for the different oxygen ion concentrations considered are displayed in different colors. Above each curve, the solution is right-hand polarized (KAW) for a specific oxygen ion concentration, while below it is left-hand polarized (EMIC).