Ultraviolet Emission-Line Intensities and Coronal Heating by Velocity Filtration: Collisionless Results

We test the velocity filtration coronal heating model by calculating predicted UV emission-line intensities for comparison with observed values. The essence of velocity filtration is that a non-Maxwellian particle distribution in a gravitational well can have a temperature that increases with height, without any local heating source. To test this theory, we consider in turn five different non-Maxwellian particle distributions in the lower corona and use the collisionless Vlasov equation to estimate the distribution function fe(υ, z) at all heights. For each height we calculate the ionization balance, assuming coronal equilibrium, and predict the emission-line intensity for a number of ions for comparison with Skylab data. To facilitate comparisons with observations, we also present apparent emission measures derived from the predicted UV emission lines. Two results stand out: velocity filtration heating (1) can produce an emission measure curve that decreases with temperature, as observed for lines formed below 105 K, but (2) cannot simultaneously reproduce the increasing emission measure observed for higher temperature lines. This is precisely the opposite problem faced by most heating models. We conclude that the present version of velocity filtration does not match UV observations, but note that it neglects Coulomb collisions, realistic geometry, and ambipolar diffusion. Our methods will provide a useful test for more complete versions of velocity filtration as they emerge.