Phase velocity λ in dependence on several plasma parameters, where (a) Phase velocity λ in dependence on the relative density α(= n_O0/n_H0), where σ_sp(= T_sp/T_e) = 1.5 and u_sp0 = 3.2. (b) Phase velocity in dependence on the relative temperature σ_sp, where α = 3.65 and u_sp0 = 3.2. (c) Phase velocity in dependence on the normalized proton streaming velocity u_sp0. The other plasma parameters are Q₀(= m_H/m_O) = 1/16, Q_sp(= m_H/m_sp) = 1, σ_O(= T_O/T_e) =σ_H(= T_H/T_e) = 0.2, σ_se(= T_se/T_e) = 2, β(= n_sp0/n_H0) = χ(= n_se0/n_H0) = 1.4.