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What can we learn about solar coronal mass ejections, coronal dimmings, and Extreme-Ultraviolet jets through spectroscopic observations?
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Hui Tian Submitted: 2012-01-10 16:02
Solar eruptions, particularly coronal mass ejections (CMEs) and
extreme-ultraviolet (EUV) jets, have
rarely been investigated with spectroscopic observations. We analyze
several data sets obtained by the
EUV Imaging Spectrometer onboard Hinode and find various types of
flows during CMEs and jet eruptions.
CME-induced dimming regions are found to be characterized by
significant blueshift and enhanced
line width by using a single Gaussian fit. While a red-blue (RB)
asymmetry analysis and a RB-guided
double Gaussian fit of the coronal line profiles indicate that these
are likely caused by the superposition of
a strong background emission component and a relatively weak (~10%)
high-speed (~100 km s-1) upflow
component. This finding suggests that the outflow velocity in the
dimming region is probably of the
order of 100 km s-1 not ~20 km s-1 as reported previously. Density and
temperature diagnostics of the
dimming region suggest that dimming is primarily an effect of density
decrease rather than temperature
change. The mass losses in dimming regions as estimated from different
methods are roughly consistent
with each other and they are 20%-60% of the masses of the associated
CMEs. With the guide of RB
asymmetry analysis, we also find several temperature-dependent
outflows (speed increases with temperature)
immediately outside the (deepest) dimming region. These outflows may
be evaporation flows which
are caused by the enhanced thermal conduction or nonthermal electron
beams along reconnecting field
lines, or induced by the interaction between the opened field lines in
the dimming region and the closed
loops in the surrounding plage region. In an erupted CME loop and an
EUV jet, profiles of emission
lines formed at coronal and transition region temperatures are found
to exhibit two well-separated components,
an almost stationary component accounting for the background emission
and a highly blueshifted
(~200 km s-1 component representing emission from the erupting material.
The two components can
easily be decomposed through a double Gaussian fit and we can diagnose
the electron density, temperature
and mass of the ejecta. Combining the speed of the blueshifted
component and the projected speed
of the erupting material derived from simultaneous imaging
observations, we can calculate the real speed
of the ejecta.
Authors: Hui Tian, Scott W. McIntosh, Lidong Xia, Jiansen He, Xin Wang
Projects: None
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Publication Status: ApJ, in press
Last Modified: 2012-01-11 09:11
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