Preliminary Results with a Vacuum Solar Spectrograph.

Abstract

New observations of the solar spectrum with a high-resolution vacuum spectrograph reveal a wealth of detail in the cores of all Fraunhofer lines observed both in the normal disk and in areas exhibiting various kinds of solar activity. The lines show fluctuations in width, intensity, and position over intervals as small as 2 seconds of arc. A representative collection of photographs is presented, together with tentative conclusions derived from inspection and preliminary measurement. Measurements of Doppler shifts have been carried out in considerable detail for the two lines Cr X 4626 and Ba+ X 5853. The random turbulent velocity at the center of the disk is 0 70 km/sec for the chromium line and O. km/sec for the ionized barium line. For both lines the random turbulent velocity appears to increase toward the limb. The velocity shifts observed for the Ha and sodium D lines are of the same order of magnitude as those of the weaker metallic lines. The disk observations of the Fraunhofer lines of hydrogen and ionized calcium seem to he consistent with a qualitative model of the low chromosphere, consisting of relatively hot clouds of gas and with cooler regions both above and between the hot regions. Both the K2 emission in ionized calcium and the wide absorption features in Ha seem to originate in the hot regions; from the appearance of these line features near the limb it seems that the hot regions contribute a substantial fraction of the hydrogen and ionized calcium emission in the very low chromosphere. The profiles of Ha at the extreme limb and of the K line and other strong metallic lines on the disk favor the conclusion of Adams and Burwell that central self-reversal is a general characteristic of most strong chromospheric profiles. The similarity between the intensity and velocity fluctuations in the core of the strong magnesium line X 5167 and in those of neighboring weaker lines implies either a chromospheric origin for the centers of these weaker lines or the extension of the photospheric granules into the low chromosphere. The preliminary nature of the foregoing results is emphasized.