view Abstract Citations (3) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The active region on the west solar limb during the eclipse of 25 February 1952. Athay, R. G. ; Evans, J. W. ; Roberts, W. O. Abstract At the Khartoum eclipse there was an active region at io0S latitude on the west limb. This region was first observed as a small sunspot group and plage area near the east limb on 12 February. One flare was reported in this region on 13 February, one on i6 February, two on 24 February and two on 25 February."2 The west limb spectrograms of the chromospheric flash obtained by the High Altitude Observatory showed a small region of enhanced emission and immediately adjacent to it a small region of greatly reduced emission. Moon profile pictures taken at Khartoum showed that the observed effects could not be attributed to irregularities in the moon's profile. A few degrees away from these regions there was a bright prominence that appeared to be of a surge type. The region of reduced emission showed mainly in the chromospheric lines. There was also an apparent decrease in the coronal line intensities in the lowest levels of the corona, but there was no marked decrease in the continuum intensity. The decrease in the line intensities apparently resulted from either a cloud of absorbing matter or an actual decrease in chromospheric emission. The region of enhanced emission showed a maximum in the continuum and all chromospheric and coronal line intensities. The greatest increase in chromospheric lines was in He+, X4686. The yellow coronal line, X5694, showed in this region on our spectrograms. It did not show at any other positions, and to our knowledge has not been observed at previous eclipses. Lyot and Doilfus have also reported this coronal line and four new coronal lines from observations at Khartoum.3 All of these lines were found in this region of enhanced emission. The intensities of all of the chromospheric lines decreased much more slowly with height in this region than in an east limb region previously analyzed,4 which seemed to represent the undisturbed chromosphere. It was suggested that the region of enhanced emission was caused by a limb flare. A preliminary interpretation of the data from this region showed that both the electron density and kinetic temperature were greater than in the east limb region, and that the temperature increased less rapidly with height. A more detailed analysis of this region will be published elsewhere. This work was supported by the Office of Naval Research and carried out in cooperation with the Naval Research Laboratory. Publication: The Astronomical Journal Pub Date: June 1954 DOI: 10.1086/106983 Bibcode: 1954AJ.....59..182A full text sources ADS |