Multi-thermal observations of newly formed loops in a dynamic flare

Details Multi-thermal observations of newly formed loops in a dynamic flare Multi-thermal observations of newly formed loops in a dynamic flare

Sep 1987

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987soph..108..237s&link_type=abstract

Solar Physics (ISSN 0038-0938), vol. 108, no. 2, 1987, p. 237-250. Research supported by the Space Research Organization of the

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107

Electron Density (Concentration), Emission Spectra, Solar Flares, Computational Astrophysics, H Alpha Line, Hydrogen Atoms, Solar Limb, X Ray Spectra

Scientific paper

The dynamic flare of November 6, 1980 (max at about 15:26 UT) developed a rich system of growing loops which could be followed in H-alpha for 1.5 hr. Throughout the flare, these loops, near the limb, were seen in emission against the disk. Theoretical computations of deviations from LTE populations for a hydrogen atom reveal that this requires electron densities in the loops close to, or in excess of 10 to the 12th/cu cm. From measured widths of higher Balmer lines the density at the tops of the loops was found to be 4 x 10 to the 12th/cu cm if no nonthermal motions were present, or 5 x 10 to the 11th/cu cm for a turbulent velocity of about 12 km/s. It is now general knowledge that flare loops are initially observed in X-rays and become visible in H-alpha only after cooling. For such a high density, a loop would cool through radiation from 10 to the 7th to 10 to the 4th K within a few minutes so that the dense H-alpha loops should have heights very close to the heights of the X-ray loops. This, however, contradicts the observations obtained by the HXIS and FCS instruments on board SMM which show the X-ray loops at much higher altitudes than the loops in H-alpha. Therefore, it is suggested that the density must have been significantly lower when the loops were formed, and that the flare loops were apparently both shrinking and increasing in density while cooling.

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