Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...447..915n&link_type=abstract
Astrophysical Journal v.447, p.915
Astronomy and Astrophysics
Astronomy
15
Sun: Corona, Sun: Flares, Sun: Particle Emission, Sun: X-Rays, Gamma Rays
Scientific paper
Mass motions are a ubiquitous product of solar flare energy release. A better understanding of the flare plasma's distribution how much is moving and how fast permits insight into the mechanisms of energy transport (and release) which lead to those motions. Observationally, mass motions during flares are often manifested in the shape and location of soft X-ray emission lines. Observed line profiles generally exhibit a width greater than the thermal Doppler width and a blue-wing asymmetry which has been cited as evidence for plasma motions along the line of sight. Past efforts to characterize this excess width and asymmetry have primarily involved the parametric fitting of a double-Gaussian form. In this paper we show, however, that simple two-component models are inconsistent with the observed evolution of spectral lines and hence serve as a poor diagnostic of plasma motions. We therefore generalize the synthesis of line profiles to the case of a continuum of Gaussian components, by introducing a quantity which we term the velocity differential emission measure (VDEM). The VDEM measures the distribution of emission from a volume of plasma as a function of its line-of-sight velocity. It can either be computed from theoretical model atmospheres, or recovered from observed line profiles using an inversion technique. We present the VDEMs of two model flare atmospheres and discuss the differences between them. We also deconvolve a VDEM from a representative Ca XIX flare spectrum observed by the Bragg Crystal Spectrometer instrument aboard Yohkoh
Emslie Gordon A.
Mariska John T.
Newton Elizabeth K.
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