No abstract

Coronal holes are extensive regions of extremely low density in the solar corona within 60 ~ of latitude from the equator. (They are not to be confused with the well-known coronal cavities which surround quiescent prominences beneath helmet streamers.) We have superposed maps of the calculated current-free (potential) coronal magnetic field with maps of the coronal electron density for the period of November 1966, and find that coronal holes are generally characterized by weak and diverging magnetic field lines. The chromosphere underlying the holes is extremely quiet, being free of weak plages and filaments. The existence of coronal holes clearly has important implications for the energy balance in the transition region and the solar wind.

A series of spectrograms of the inner solar corona were obtained at the total solar eclipse of 30 May 1965 using a fast spectrograph with a circular slit that recorded the spectrum from 23000 to 29000 at all position angles around the limb simultaneously. In this paper absolute intensity is given as a function of position angle for the stronger lines and the continuum. In the coronal enhancement or condensation centered at heliocentric position angle 293 ~ absolute intensity is given for 34 forbidden emission lines and the continuum.

The intensities of 52 EUV emission lines from each of 9 hedgerow prominences observed at the limb with the Harvard experiment on ATM-Skylab have been compared with intensities from the interior of network cells at the center of the disk, in order to compare the prominence-corona (P-C) interface with the chromosphere-c0rona (C-C) transition region. The intensity ratio lcell/Ipremi ..... for each line varies systematically (in all of the prominences observed), with the temperature of formation of the line as T -~ The density sensitive C Jli (formed at T~9 x 104 K) line ratio I~117s/I~977 implies an average density 1.3 x 109 electrons cm-3 in the P-C interface and ~ 4 times this value in the C-C transition of the cells. The total optical thickness at the head of the Lyman continuum is < 10 in most of the prominences studied; in two of the prominences, however, we cannot reject the possibility that % is large. Methods of analysis of these EUV data are developed assuming both a resolved and an unresolved internal prominence structure. Although the systematic differences between the P-C interface and the C-C transition are stressed, the similarities are probably more remarkable and may be a result of fine structure in the C-C transition.