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

Abstract

The dynamic flare of 6 November, 1980 (max about 15:26 UT) developed a rich system of growing loops which could be followed in H..cap 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/sup 12//cc. From measured widths of higher Balmer lines the density at the tops of the loops was found to be 4 x 10/sup 12//cc if no non-thermal motions were present, or 5 x 10/sup 12//cc 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..cap alpha.. only after cooling. For such a high density, a loop would cool through radiation from 10 million to 10 thousand within a few minutes so that the dense H..cap 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 thanmore » the loops in H..cap alpha... 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.« less