Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 1988
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988jphys..49..325g&link_type=abstract
(IAU, ESA, CNRS, et al., Colloquium on UV and X-ray Spectroscopy of Astrophysical and Laboratory Plasmas, 102nd, Beaulieu-sur-Me
Astronomy and Astrophysics
Astrophysics
Chromosphere, Solar Flares, X Ray Spectra, Error Analysis, Resonance Lines, Solar Limb, Solar Maximum Mission, Spectrum Analysis
Scientific paper
Analysis of solar flares using the data from the Bent Crystal Spectrometer on the SMM solar flare satellite, shows a thermal plasma which expands vertically at a velocity of up to 350 km/s. This plasma, at a temperature of the order 25 x 10 to the 6th K is observed in the line radiation of He-like Ca XIX. Its velocity is determined by measuring the blue shift of the resonance line 'w', whereas its intensity is expressed relatively to that of the stationary component. The variations of velocity and relative intensity of the evaporating plasma are studied as a function of its location on the solar disk for 33 flares during the year 1980. The results are compared with the values expected from two alternative models A and B. On the basis that when observed at the limb, such flares do not usually show a blue shift, model A interprets this as due to the fact that the motion of the explosive plasma is perpendicular to the line-of-sight. Model B assumes that the process of chromospheric evaporation produces a 'well' in the chromosphere, and thereby occults some of the emission of the ejected material. It is clear that the two models predict different velocity and relative intensity variations as a function of the distance of the flare from disk center. The lack of blue shift for 10 disk flares supports strongly the model B, i.e. the existence of a 'well' whose depth/diameter is between 0.1 and 5 as shown by the observations.
Gabriel Alan H.
Lizambert N.
Millier Frederic
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