Ion Temperatures in the Low Solar Corona: Polar Coronal Holes at Solar Minimum

摘要

We use a SUMER spectrum of a polar coronal hole to measure the ion temperatures T_i of many ions between 0.03 and 0.17 R_⊙ above the limb. We find that the measured T_i are almost always larger than the electron temperatures (T_e) and exhibit a non-monotonic dependence on the charge-tomass ratio. We use these measurements to provide empirical constraints to a theoretical model of ion heating and acceleration based on gradually replenished ion-cyclotron waves and anisotropic magnetohydrodynamic turbulence. We find that the empirical heating model and the turbulent cascade model agree with one another and with observations for charge-to-mass (Z/A) ratios smaller than about 0.25. Ions with Z/A > 025 disagree with the model.