Extreme ultraviolet spectrum of sunspot plumes. II. Spectral diagnostics and implications for cooling

The extreme ultraviolet emission-line spectrum of very intense sunspot plumes is analyzed. Several of the standard density diagnostics suggest a constant density, rather than constant pressure, emitting region. Temperature diagnostic line ratios of several ions yield temperatures below those expected in ionization equilibrium (and observed in the quiet Sun). This provides strong evidence for the suggestion that the internal energy of cooling, falling gas accounts for the observed radiation. The lack of such departures from equilibrium in the quiet Sun demonstrates that downflows are not the dominant source of energy at transition region temperatures. We assess the accuracy of several atomic rate coefficients