Elemental Abundances and Post-Coronal Mass Ejection Current Sheet in a Very Hot Active Region

Details Elemental Abundances and Post-Coronal Mass Ejection Current Sheet in a Very Hot Active Region Elemental Abundances and Post-Coronal Mass Ejection Current Sheet in a Very Hot Active Region

Aug 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002apj...575.1116c&link_type=abstract

The Astrophysical Journal, Volume 575, Issue 2, pp. 1116-1130.

Astronomy and Astrophysics

Astronomy

67

Sun: Abundances, Sun: Activity, Sun: Corona, Sun: Coronal Mass Ejections (Cmes), Sun: Uv Radiation

Scientific paper

A peculiar young active region was observed in 1998 March with the Ultraviolet Coronagraph Spectrometer (UVCS) over the southwest limb. The spectra showed strong emission in the λ974 line of fluorine-like iron, [Fe XVIII], which is brightest at an electron temperature of 106.8 K, and lines of Ne IX, [Ca XIV], [Ca XV], Fe XVII, [Ni XIV], and [Ni XV]. It is the only active region so far observed to show such high temperatures 0.5 Rsolar above the solar limb. We derive the emission measure and estimate elemental abundances. The active region produced a number of coronal mass ejections (CMEs). After one CME on March 23, a bright post-CME arcade was seen in EIT and Yohkoh/SXT images. Between the arcade and the CME core, UVCS detected a very narrow, very hot feature, most prominently in the [Fe XVIII] line. This feature seems to be the reconnection current sheet predicted by flux rope models of CMEs. Its thickness, luminosity, and duration seem to be consistent with the expectations of the flux rope models for CME. The elemental abundances in the bright feature are enhanced by a factor of 2 compared to those in the surrounding active region, i.e., a first ionization potential enhancement of 7-8 compared to the usual factor of 3-4.

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