ULTRAVIOLET EMISSION-LINE INTENSITIES AND CORONAL HEATING BY VELOCITYFILTRATION - COLLISIONLESS RESULTS

We test the velocity filtration coronal heating model by calculating p redicted UV emission-line intensities for comparison with observed val ues. The essence of velocity filtration is that a non-Maxwellian parti cle distribution in a gravitational well can have a temperature that i ncreases with height, without any local heating source. To test this t heory, we consider in turn five different non-Maxwellian particle dist ributions in the lower corona and use the collisionless Vlasov equatio n to estimate the distribution function f(e)(v, z) at all heights. For each height we calculate the ionization balance, assuming coronal equ ilibrium, and predict the emission-line intensity for a number of ions for comparison with Skylab data. To facilitate comparisons with obser vations, we also present apparent emission measures derived from the p redicted 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 10(5) K, but (2) cann ot simultaneously reproduce the increasing emission measure observed f or higher temperature lines. This is precisely the opposite problem fa ced by most heating models. We conclude that the present version of ve locity filtration does not match UV observations, but note that it neg lects Coulomb collisions, realistic geometry, and ambipolar diffusion. Our methods will provide a useful test for more complete versions of velocity filtration as they emerge.