Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...484l.165s&link_type=abstract
Astrophysical Journal Letters v.484, p.L165
Astronomy and Astrophysics
Astronomy
8
Sun: Abundances, Sun: Flares, Sun: Photosphere, Sun: Solar Wind, Sun: X-Rays, Gamma Rays
Scientific paper
The photospheric 4He/H ratio is not measured directly but is inferred from stellar evolution models, helioseismology, and coronal observations. We suggest a procedure for determining the photospheric ratio on the basis of solar wind isotopic He abundances and gamma -ray line measurements. Recent Ulysses measurements of the 4He/3He isotopic ratio in the solar wind indicate that it is constant over a large range of velocities; long-term averages in the ratio from different experiments are also consistent with one another, with values ranging from 2050 to 2350 and uncertainties ranging from 120 to 200. This constancy supports models indicating that substantial fractionation of these isotopes does not occur as they are transported from the photosphere to the solar wind. Comparison of the time histories of the 2.223 MeV neutron capture line and prompt de-excitation lines from solar flares provides the only direct measurement of the 3He/H ratio in the photosphere. This ratio has been determined for only a few flares. The most reliable ratio determined to date is 2.3 +/- 1.2 x 10-5, where the uncertainty is statistical at the 90% confidence level. By multiplying these solar wind 4He/3He and gamma -ray--derived 3He/H ratios, we obtain estimates of the photospheric 4He/H ratio ranging from ~0.02 to 0.10. Improved observations of the solar wind 4He/3He ratio and modeling of its origin can confirm that it measures the photospheric ratio. Recent improvements in our understanding of flare-accelerated particles, based on gamma -ray line data, can be applied to models of 2.223 MeV line production. Application of these corrected models to high-quality gamma -ray line data obtained from instruments on the Compton Gamma Ray Observatory and the Solar Maximum Mission will result in a more accurate measurement of the photospheric 3He/H ratio and thus the 4He/H ratio.
Murphy Ronald J.
Share Gerald H.
No associations
LandOfFree
A Method for Determining the Photospheric 4He Abundance does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with A Method for Determining the Photospheric 4He Abundance, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A Method for Determining the Photospheric 4He Abundance will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1878133