Astronomy and Astrophysics – Astronomy
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009spd....40.3602m&link_type=abstract
American Astronomical Society, SPD meeting #40, #36.02; Bulletin of the American Astronomical Society, Vol. 41, p.868
Astronomy and Astrophysics
Astronomy
Scientific paper
It is widely assumed that the process of chromospheric evaporation is responsible for much of the EUV and thermal X-ray emission observed during solar flares. Previous studies have relied primarily on the detection of blueshifts of a single, high-temperature emission line (e.g. Ca XIX on SMM/BCS, Fe XIX on SOHO/CDS). With the launch of Hinode, the EUV Imaging Spectrometer (EIS) now offers us the opportunity to diagnose this fundamental process across a broad range of temperatures, at high spatial, spectral and temporal resolution. In this study, the advanced capabilities of EIS were used to measure Doppler shifts in 15 emission lines covering the temperature range T = 0.05 - 16 MK during the impulsive phase of a C-class flare on 2007 December 14. Blueshifts indicative of the evaporated material were observed in six emission lines from Fe XIV-XXIV (2-16 MK). Upflow velocity was found to scale with temperature as vup (km/s) = 5 - 17 T (MK). Although the hottest emission lines, Fe XXIII and Fe XXIV, exhibited upflows of >250 km/s, their line profiles were found to be dominated by a stationary component in contrast to the predictions of the standard flare model. Emission from O VI-Fe XIII lines (0.5-1.5 MK) was found to be redshifted by vdown (km/s) = 60 - 17 T (MK) and was interpreted as the downward-moving `plug’ characteristic of explosive evaporation. These downflows occur at temperatures significantly higher than previously expected; up to 1.5 MK. Both upflows and downflows were spatially and temporally correlated with HXR emission observed by RHESSI that provided the properties of the electron beam deemed to be the driver of the evaporation. The energy contained in the electron beam was found to be >1011 ergs/cm2/s which is consistent with the value required to drive explosive chromospheric evaporation from hydrodynamic simulations.
Dennis Brian
Milligan Ryan
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