On the Rate of Abundance Modifications versus Time in Active Region Plasmas
Abstract
Four emerging and developing active regions observed on Skylab spectroheliograms (300-600 Å) have been studied over intervals of 3 to 7 days to determine the change in their Mg/Ne abundance ratio. The Mg/Ne abundance ratio is used as a measure of the FIP effect on element abundances in the solar upper atmosphere. Mg/Ne abundance ratios were derived from diagnostic intensity ratios of Mg VI lines at 400 Å relative to adjacent Ne VI lines. Intensity ratios were estimated from the active region images in the Skylab Atlas of Extreme-Ultraviolet Spectroheliograms. The resulting abundance ratios expressed in terms of the FIP bias β (see text) are plotted as a function of elapsed time since emergence. After emergence the newborn region shows photospheric composition: i.e., the abundance ratio of Mg/Ne=0.296, β=1. Thereafter, the developing regions show a progressive increase in the Mg/Ne abundance ratio with the value of β reaching after 2 days coronal-type abundances: Mg/Ne=1.43, β~4.8. In the later stages, the bias increases to values between 7 and 9 after 3 to 7 days. Some implications of the abundance modifications are briefly discussed.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2001
- DOI:
- 10.1086/321482
- Bibcode:
- 2001ApJ...555..426W
- Keywords:
-
- Sun: Abundances;
- Sun: Activity;
- Sun: Corona