ULTRAVIOLET OBSERVATIONS OF THE STRUCTURE AND DYNAMICS OF AN ACTIVE-REGION AT THE LIMB

The structure and dynamics of active region NOAA 7260 at the limb has been studied using ultraviolet spectra and spectroheliograms obtained during the eighth rocket flight of the Naval Research Laboratory's Hig h Resolution Telescope and Spectrograph (HRTS). The instrument configu ration included a narrow-bandpass spectroheliograph to observe the Sun in the lines of C IV lambda 1550 and a tandem-Wadsworth mount spectro graph to record the profiles of chromospheric, transition region and c oronal lines in the 1850-2670 Angstrom region. The combination of high spatial resolution and high spectral purity C IV slit jaw images with ultraviolet emission-line spectra corresponding allows examination of a variety of active region phenomena. A time series of spectroheliogr ams show large-scale loop systems composed of fine-scale threads with some extending up to 100 Mm above the limb. The proper motion of sever al supersonic features, including a surge were measured. The accelerat ed plasmas appear in several different geometries and environments. Sp ectrogaph exposures were taken with the slit positioned at a range of altitudes above the limb and provide a direct comparison between coron al, transition region and chromospheric emission line profiles. The sp ectral profiles of chromospheric and transition region emission lines show line-of-sight velocities up to 70 km s(-1). These lower temperatu re, emission-line spectra show small-scale spatial and velocity variat ions which are correlated with the threadlike structures seen in C IV. Coronal lines of Fe XII show much lower velocities and no fine struct ure.