CHARGE-TRANSFER IN HELIUM-RICH SUPERNOVA PLASMA

Charge transfer rate coefficients are estimated using Landau-Zener and modified Demkov approximations. The coefficients, augmented by those available from the literature, are used in statistical equilibrium equ ations describing the state of helium-rich supernova plasma. Such a pl asma may describe both Type Ib and Type Ic supernova ejecta. The hypot hesis that extensive mixing of metals with helium in Type Ic supernova e may provide a catalyst for rapid charge transfer that weakens the he lium line emission by altering the excitation balance is tested. It is shown that charge transfer as a mechanism for suppressing helium line emission is ineffective unless the metal abundance is comparable to o r larger than the helium abundance. This result supports an earlier co nclusion that Type Ic supernovae must be helium poor relative to Type Ib events.