UV prominences observed with the HRTS: structure and physical properties

Details UV prominences observed with the HRTS: structure and physical properties UV prominences observed with the HRTS: structure and physical properties

Jun 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...273..267w&link_type=abstract

Astronomy and Astrophysics, Vol. 273, p. 267 (1993)

Astronomy and Astrophysics

Astrophysics

27

Sun: Prominences, Sun: Corona, Sun: Uv Prominences

Scientific paper

Ultraviolet spectra of two quiescent prominences (PL1, PL2) observed with the High Resolution Telescope and Spectrograph (HRTS) are described and analyzed. Meudon synoptic maps and spectroheliograms indicate that prominence PL 1 was extremely active during the flight and that material ejections were likely. PL2 appeared to be a more stable prominence. The significant differences between the spectra of the two prominences can perhaps be explained by their levels of activity. The spectrum of the more active prominence PL1 is dominated by transition zone lines formed near 105 K whereas the second prominence PL2 shows considerable emission of cooler chromospheric lines formed near 2 × 1O4 K. PL 1 also exhibits larger bulk flow velocities (up to ˜ 30 km s-1) and non-thermal velocities (˜20km s-1). From line ratios (O IV, N V, N IV, Si IV) a relatively large electron density (˜1011 cm-3) is derived for the PL1 prominence transition region (PTR). In comparison, PL2 is a relatively quiet prominence with bulk flow velocities generally less than ˜3 km s-1.
Different techniques yield greatly different spatial scales for the prominence. The UV spectra show strong variations in intensity and Doppler shift on scales of about 1700km. The combined density and emission measures indicate path lengths of 400 m or less. The optical depth in C IV requires path lengths of 40 km or less. If, as suggested by these analyses, it is assumed that prominence emission is due to a number of micro-structures with a Gaussian velocity distribution, then spatial scales of the micro-structures of a few hundred kilometers are found.

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