A Relationship Between Transition Region Brightenings,Abundances, and Magnetic Topology |
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Authors: | Fletcher Lyndsay López Fuentes Marcelo C Mandrini Cristina H Schmieder Brigitte Démoulin Pascal Mason Helen E Young Peter R Nitta Nariaki |
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Institution: | (1) Org L9-41, B252, Lockheed Martin Solar and Astrophysics Lab., 2351 Hanover Street, Palo Alto, CA, 94306, U.S.A.;(2) IAFE, CC67, Suc 28, Instituto de Astronomí a y Fí sica del Espacio, 1428 Buenos Aires, Argentina;(3) Observatoire de Paris, 92195 Meudon, Cedex Principal, France;(4) Harvard Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA, 02138, U.S.A |
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Abstract: | We present multi-instrument observations of active region (AR) 8048, made between 3 June and 5 June 1997, as part of the SOHO
Joint Observing Program 33. This AR has a sigmoid-like global shape and undergoes transient brightenings in both soft X-rays
and transition region (TR) lines. We compute a magneto-hydrostatic model of the AR magnetic field, using as boundary condition
the photospheric observations of SOHO/MDI. The computed large-scale magnetic field lines show that the large-scale sigmoid
is formed by two sets of coronal loops. Shorter loops, associated with the core of the SXT emission, coincide with the loops
observed in the hotter CDS lines. These loops reveal a gradient of temperature, from 2 MK at the top to 1 MK at the ends.
The field lines most closely matching these hot loops extend along the quasi-separatrix layers (QSLs) of the computed coronal
field. The TR brightenings observed with SOHO/CDS can also be associated with the magnetic field topology, both QSL intersections
with the photosphere, and places where separatrices issuing from bald patches (sites where field lines coming from the corona
are tangent to the photosphere) intersect the photosphere. There are, furthermore, suggestions that the element abundances
measured in the TR may depend on the type of topological structure present. Typically, the TR brightenings associated with
QSLs have coronal abundances, while those associated with BP separatrices have abundances closer to photospheric values. We
suggest that this difference is due to the location and manner in which magnetic reconnection occurs in two different topological
structures.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1013302317042 |
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