2015/05/31 by Hui Tian, Peter R. Young, Katharine K. Reeves +3 · 1 citation
Physics and Astronomy · #astro-ph.SR
paper · pdf · doi:10.1088/0004-637x/811/2/139
14 figures, ApJ
arxiv created 2015/07/24 · arxiv updated 2015/10/07
With observations from the Interface Region Imaging Spectrograph (IRIS), we track the complete evolution of ∼11 MK evaporation flows in an M1.1 flare on 2014 September 6 and an X1.6 flare on 2014 September 10. These hot flows, as indicated by the blueshifted Fe~\scxxi~1354.08Å~line, evolve smoothly with a velocity decreasing exponentially from ∼200~km~s-1 to almost stationary within a few minutes. We find a good correlation between the flow velocity and energy deposition rate as represented by the hard X-Ray flux observed with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), or time derivative of the soft X-Ray flux observed with the Geostationary Operational Environmental Satellites (GOES) and the HINODE X-ray Telescope (XRT), which is in general agreement with models of nonthermal electron heating. The maximum blue shift of Fe~\scxxi~appears approximately at the same time as or slightly after the impulsive enhancement of the ultraviolet continuum and the Mg~\scii~2798.8Å~line emission, demonstrating that the evaporation flow is closely related to heating of the lower chromosphere. Finally, while the hot Fe~\scxxi~1354.08Å line is entirely blueshifted with no obvious rest component, cool chromospheric and transition region lines like Si~\sciv~1402.77Å are often not entirely redshifted but just reveal an obvious red wing enhancement at the ribbons, suggesting that the speed of chromospheric condensation might be larger than previously thought.