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Space Science MO&DA Programs - January 2001 - Page 1

•We report a preliminary search for trans-iron particles from flares using the ACE/ULEIS instrument which is sensitive at energies (>30 keV/nuc) where solar-particle fluxes are highest.

•The figure shows abundances from a sum of at least 8 flares (black trace). The ULEIS mass scale beyond 70 is preliminary and will be verified by accelerator calibration of a backup unit.

•Compared to meteorites and the photosphere (blue trace) we find > 100-fold enrichments of elements beyond iron in particles from flares. Reames has also recently reported large enhancements of trans-iron elements in impulsive flares above ~3 MeV/nucleon.

10-7

10-5

10-3

10-1

101

10 100

abu

ndan

ce (

ox

yg

en=

1)

mass (amu)

C NO

NeMgSi

SCa

Fe

preliminary ACE/ULEIS trans-Fe abundances &

mass ranges

solar photosphere and meteorites(Grevesse & Sauval 1998)

ACE/ULEIS impulsive flares

As-Mo

Sb-Ce Tb-Bi

•Trans-iron elements are extremely rare in the solar system composition: in the mass range from germanium to bismuth (32≤Z≤83), their total meteoritic abundance is only ~10-4 that of iron.

Enhancement of Trans-Iron Elements in Impulsive Solar Flares

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Space Science MO&DA Programs - January 2001 - Page 2

•The impulsive flare particles are easily seen at the beginning of 7/1/99 where the high iron/oxygen  ratio is typical for flares. The count rate of ultra-heavy ions peaked at the same time as the iron.

•The composition was more coronal-like on 7/2/99, but there were far fewer ultra-heavies.

•Most of the ions with mass > 70 amu arrived at ACE during impulsive solar flares. Shown above are oxygen and iron fluxes at ~0.2 MeV/nucleon energy for 4 days in 1999.

10-2

10-1

100

101

0

4

8

6/30/1999 7/2/1999 7/4/1999

part

icle

flu

x

counts per hour

oxygeniron

ions withmass >70 amu

•These preliminary results show that either before or during acceleration, an enrichment mechanism favoring higher mass species brings the rare trans-iron abundances within reach of present instrumentation.

Enhancement of Trans-Iron Elements in Impulsive Solar Flares (2)

Contributed by Joe Mazur, Glenn Mason, Joe Dwyer, Rob Gold and Tom Krimigis