Impulsive Brightenings in Quiescent Solar Prominences

At large spatial scales, quiescent solar prominences appear static in nature, but they are dynamic at smaller scales. This thesis reports on high resolution observations of quiescent prominences using the tunable, Universal Birefringent Filter and the echelle spectrograph on the Vacuum Tower Telescope at Sacramento Peak Observatory. More than 40 hours of wavelength scans of H alpha and He D(,3) disclose a class of activity near the edges of quiescent prominences, characterized by enhancement of H alpha radiative power by as much as 4 x 10('24) erg s('-1) and enhanced line widths of up to 0.92 A, over areas 5 to 25 arcseconds across, for lifetimes of tens of minutes; we call this activity "impulsive brightenings". The H alpha profile is centrally reversed by as much as 25% in some, while others contain significant line-of-sight velocities. Brightenings with H alpha reversal show correlations between depth of reversal and both line width and peak intensity. The correlation between line width and reversal depth is closest; as functions of time and position these quantities display similar behavior. Comparison of the reversed profiles with those from a surge, suggest an opacity -related cause of the central reversals. The other activity displays doppler shifts corresponding to 2 to 50 km s(' -1) and the H alpha profiles indicate high opacities, but are not necessarily reversed. We consider three models for impulsive brightenings: a layer of cool material between the observer and the prominence, magnetic reconnection as an energy source for the activity, and condensation of coronal material into the prominence. We conclude that condensation is the most likely. Detailed numerical models have predicted periods during condensation when densities are 2 or 3 times normal prominence values. Our observations are consistent with such densities. Estimates of the radiative cooling rate and energy capacity of the near-prominence corona agree with the observed lifetimes and energies of the activity. Furthermore, an estimate of the mass contributed to a quiescent prominence by each impulsive brightening suggests they are the major source of material to offset the mass lost by downdraining of material.