Spectroscopy and Differential Emission Measure Diagnostics of a Coronal Dimming Associated with a Fast Halo CME

Abstract

We study the coronal dimming caused by the fast halo CME (deprojected speed v  = 1250 km s −1 ) associated with the C3.7 two-ribbon flare on 2012 September 27, using Hinode /EIS spectroscopy and Solar Dynamics Observatory ( SDO )/AIA Differential Emission Measure (DEM) analysis. The event reveals bipolar core dimmings encompassed by hook-shaped flare ribbons located at the ends of the flare-related polarity inversion line, and marking the footpoints of the erupting filament. In coronal emission lines of log T [K] = 5.8–6.3, distinct double-component spectra indicative of the superposition of a stationary and a fast upflowing plasma component with velocities up to 130 km s −1 are observed at these regions, which were mapped by the scanning EIS slit close in time to their impulsive dimming onset. The outflowing plasma component is found to be of the same order as and even dominant over the stationary one, with electron densities in the upflowing component of 2 × 10 9 cm −3 at log T [K] = 6.2. The density evolution in core-dimming regions derived from SDO /AIA DEM analysis reveals impulsive reductions by 40%–50% within ≲10 minutes and remains at these reduced levels for hours. The mass-loss rate derived from the EIS spectroscopy in the dimming regions is of the same order as the mass increase rate observed in the associated white-light CME (1 × 10 12 g s −1 ), indicating that the CME mass increase in the coronagraphic field of view results from plasma flows from below and not from material piled up ahead of the outward-moving and expanding CME front.