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Multi-thermal observations of newly formed loops in a dynamic flare
Authors:Zdeněk F Švestka  Juan M Fontenla  Marcos E Machado  Sara F Martin  Donald F Neidig  Giannina Poletto
Institution:(1) Laboratory for Space Research Utrecht, SRON, The Netherlands;(2) IAFE, Buenos Aires, Argentina;(3) NAS/NRC Research Associate, Space Science Laboratory, NASA MSFC, USA;(4) Space Science Laboratory, NASA MSFC, 35812 Huntsville, AL, USA;(5) Solar Astronomy, CALTECH, 91125 Passadena, CA, USA;(6) Air Force Geophysics Laboratory, National Solar Observatory, Sacramento Peak, 88349 Sunspot, NM, USA;(7) Osservatorio Astrofisico di Arcetri, Firenze, Italy
Abstract:The dynamic flare of 6 November, 1980 (max ap 15:26 UT) developed a rich system of growing loops which could be followed in Hagr 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 1012 cm -3. From measured widths of higher Balmer lines the density at the tops of the loops was found to be 4 x 1012 cm -3 if no non-thermal motions were present, or 5 × 1011 cm -3 for a turbulent velocity of ~ 12 km s -1.It is now general knowledge that flare loops are initially observed in X-rays and become visible in Hagr only after cooling. For such a high density, a loop would cool through radiation from 107 to 104 K within a few minutes so that the dense Hagr 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 Hagr. Therefore, we suggest 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.NAS/NRC Research Associate, on leave from CNIE, Argentina.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. Partial support for the National Solar Observatory is provided by the USAF under a Memorandum of Understanding with the NSF.
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