Evolution of active region outflows throughout an active region lifetime
Journal
Date Issued
2016
Author(s)
Abstract
We have shown previously that SOHO/UVCS data allow us to detect active region
(AR) outflows at coronal altitudes higher than those reached by other
instrumentation. These outflows are thought to be a component of the slow solar
wind. Our purpose is to study the evolution of the outflows in the intermediate
corona from AR 8100, from the time the AR first forms until it dissolves, after
several transits at the solar limb. Data acquired by SOHO/UVCS at the time of
the AR limb transits, at medium latitudes and at altitudes ranging from 1.5 to
2.3 R_sun, were used to infer the physical properties of the outflows through
the AR evolution. To this end, we applied the Doppler dimming technique to UVCS
spectra. These spectra include the H I Lyman alpha line and the O VI doublet
lines at 1031.9 and 1037.6 A. Plasma speeds and electron densities of the
outflows were inferred over several rotations of the Sun. AR outflows are
present in the newly born AR and persist throughout the entire AR life.
Moreover, we found two types of outflows at different latitudes, both possibly
originating in the same negative polarity area of the AR. We also analyzed the
behavior of the Si XII 520 A line along the UVCS slit in an attempt to reveal
changes in the Si abundance when different regions are traversed. Although we
found some evidence for a Si enrichment in the AR outflows, alternative
interpretations are also plausible. Our results demonstrate that outflows from
ARs are detectable in the intermediate corona throughout the whole AR lifetime.
This confirms that outflows contribute to the slow wind.
Volume
594
Start page
A40
Issn Identifier
0004-6361
Ads BibCode
2016A&A...594A..40Z
Rights
open.access
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