26 June 2008SHINE, Zermatt, UT1 High-energy Elemental, Isotopic, and Charge-State Composition in 3...
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Transcript of 26 June 2008SHINE, Zermatt, UT1 High-energy Elemental, Isotopic, and Charge-State Composition in 3...
![Page 1: 26 June 2008SHINE, Zermatt, UT1 High-energy Elemental, Isotopic, and Charge-State Composition in 3 He-rich Solar Energetic Particle Events M.E. Wiedenbeck.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649ea75503460f94ba946b/html5/thumbnails/1.jpg)
26 June 2008 SHINE, Zermatt, UT 1
High-energy Elemental, Isotopic, and Charge-State Composition in 3He-rich Solar Energetic Particle
EventsM.E. Wiedenbeck (JPL/Caltech)
R.A. Leske, C.M.S. Cohen, A.C. Cummings, R.A. Mewaldt, E.C. Stone (Caltech)
T.T. von Rosenvinge (NASA/GSFC)
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26 June 2008 SHINE, Zermatt, UT 2
Breneman & Stone 1985
Leske et al. 2007
Fractionation in Gradual SEP Events
• abundance enhancements organized as power law in (Q/M)a, where the exponent a varies from event to event
• assuming that the isotopes of an element have the same distribution of charge states, correlation between different isotope ratios can be calculated with no free parameters
![Page 3: 26 June 2008SHINE, Zermatt, UT1 High-energy Elemental, Isotopic, and Charge-State Composition in 3 He-rich Solar Energetic Particle Events M.E. Wiedenbeck.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649ea75503460f94ba946b/html5/thumbnails/3.jpg)
26 June 2008 SHINE, Zermatt, UT 3
Correlation between isotope ratios: 26Mg/24Mg versus 22Ne/20Ne
• - gradual events analyzed by Leske et al. 2007• - 3He-rich events (larger symbols for events with better statistical accuracy)• diagonal lines - expected correlation if fractionation is a power law function of Q/M• the larger, more precisely measured 3He-rich events tend to fall near the predicted correlation line
20 Aug 2002event
![Page 4: 26 June 2008SHINE, Zermatt, UT1 High-energy Elemental, Isotopic, and Charge-State Composition in 3 He-rich Solar Energetic Particle Events M.E. Wiedenbeck.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649ea75503460f94ba946b/html5/thumbnails/4.jpg)
26 June 2008 SHINE, Zermatt, UT 4
Hypothesis: Fractionation in 3He-rich Events is also Organized as a Power Law in Q/M
Use technique introduced and applied to 6 Nov 1997 SEP Event by
Cohen et al., GRL 26, 149 (1999)
![Page 5: 26 June 2008SHINE, Zermatt, UT1 High-energy Elemental, Isotopic, and Charge-State Composition in 3 He-rich Solar Energetic Particle Events M.E. Wiedenbeck.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649ea75503460f94ba946b/html5/thumbnails/5.jpg)
26 June 2008 SHINE, Zermatt, UT 5
Isotopic Fractionation in the 3He-rich Event of 20 Aug 2002
• fit with power law in the mass ratio
• fit dominated by Ne and Mg isotope ratios
![Page 6: 26 June 2008SHINE, Zermatt, UT1 High-energy Elemental, Isotopic, and Charge-State Composition in 3 He-rich Solar Energetic Particle Events M.E. Wiedenbeck.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649ea75503460f94ba946b/html5/thumbnails/6.jpg)
26 June 2008 SHINE, Zermatt, UT 6
Combining Elemental and Isotopic Composition to Estimate Charge States
• fractionation power-law exponent, a, calculated from the enhancement of 22Ne/20Ne
• combining this value of a with the Fe/O ratio yields the the corresponding ionic charge state ratio, QFe/QO (given the known ratio of masses)
• same approach applied to other elemental abundance ratios yields charge states of additional elements
• fractionation exponents tend to have large negative values, -10 to -25 in many casesfractionation
exponent
Q(Fe)
20 Aug 2002
1 May 20009 Sep 1998
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26 June 2008 SHINE, Zermatt, UT 7
Comparison with Direct Measurements of <QFe>
• for two of the SIS events the are direct measurements from SEPICA below ~0.6 MeV/nuc
• for the 20 Aug 2002 event Joe Mazur has obtained charge states using the geomagnetic cutoff method with LICA on SAMPEX -- may have some contamination from particles from large 3He-rich event on the preceding day
• comparison suggests that increase of QFe with E/M continues to rise above 1 MeV/nuc
• low energy values of QFe represent charge states at 1 AU, values inferred from SIS are at the site where the fractionation occured
ACE/ SEPICA
ACE/SIS
SAMPEX/LICA
9 September 1998
1 May 2000
20 August 2002
![Page 8: 26 June 2008SHINE, Zermatt, UT1 High-energy Elemental, Isotopic, and Charge-State Composition in 3 He-rich Solar Energetic Particle Events M.E. Wiedenbeck.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649ea75503460f94ba946b/html5/thumbnails/8.jpg)
26 June 2008 SHINE, Zermatt, UT 8
Is fractionation a function of Q/M?
• Q/M is relevant for rigidity-dependent processes
• Coulomb losses depend on Q2/M
• isotope fractionation as a power law in the mass ratio would be unchanged if Q were replaced by any function of Q -- it cancels when comparing isotopes of the same element
• assume fractionation is a power law in Qk/M and use constraints that QFe26 and QFelargest value of QFe measured at lower energies -- highlighted portions of curves satisfy these conditions for the three events where lower energy data are available
• only values of k within ~20% of 1.0 are acceptable using this criterion
9 September 1998
1 May 2000
20 August 2002
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26 June 2008 SHINE, Zermatt, UT 9
Inferred Charge States
• using the fractionation exponent derived from the isotopic ratios, one can derive ratios of <Q> values for any pair of elements
• assume <QC>=6.0 to obtain Q values for other elements
• plot shows Q expresses as Z-QZ (i.e., number of electrons attached)
• find sequences of elements with a given Z-QZ values -- note particularly that Ne through S have He-like structure (2 electrons attached) -- previously noted by Reames, Meyer, & von Rosenvinge (1994)
He-like ions
![Page 10: 26 June 2008SHINE, Zermatt, UT1 High-energy Elemental, Isotopic, and Charge-State Composition in 3 He-rich Solar Energetic Particle Events M.E. Wiedenbeck.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649ea75503460f94ba946b/html5/thumbnails/10.jpg)
26 June 2008 SHINE, Zermatt, UT 10
Source Temperature?
Ca, Fe, Ni
N, O
C
4He+2
3He+2
3He+1
What about 3He/4He?
Origin of non-monotonic dependence of element enhancement on Z?
7 large 3He-rich events above 10 MeV/nuc
How well does the assumption of fractionation as a power law in Q/M organize the
composition observations?
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26 June 2008 SHINE, Zermatt, UT 11
Summary
• isotope fractionation in 3He-rich SEP events appears to be organized as a power-law in the ratio of the isotope masses, at least at energies >10 MeV/nuc
• assuming that the isotopic fractionation result is due to a general fractionation that has the form of a power-law in Q/M, combining the isotope results with elemental composition measurements makes it possible to infer Q-states
• comparison with direct measurements of Q-states in a few events suggests that increase of <QFe> with increasing E/M below 1 MeV/nuc continues to higher energies
• if one assumes that the fractionation depends on Qk/M (allowing the possibility k1), find that k should be in the range ~0.8-1.2 to assure QFe26 and value measured by ACE/SEPICA below 1 MeV/nuc
• derived Q-states are not consistent with a single source temperature for all the elements in the range 6Z28 -- not surprising given that Q-states measured at lower energies have an energy dependence attributed to stripping during acceleration
• fractionation as a power-law in Q/M in 3He-rich events is similar to fractionation in gradual (shock acceleration) events -- may indicate that coronal shocks play a role in accelerating the highest energy particles in 3He-rich events
• Q-values greater than those measured below 1 MeV/nuc suggests that the seed material being fractionated had already reached a significant fraction of 1 MeV/nuc
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26 June 2008 SHINE, Zermatt, UT 12
Key Questions
• Is the technique yielding correct Q-state values?
- need to compare with direct measurements in additional events -- this is possible for a number of gradual events; data are not available for many 3He-rich events unless the same fractionation pattern can be found at lower energies
• What mechanism is producing these Q-states?
- source population is not thermal
- Fe undergoes a great deal of stripping before the fractionation occurs
• What is the physical origin of the fractionation as a power-law in Q/M?
- large exponents required suggest that this may just be an approximation
- is Q/M really the important parameter in the fractionation?
• Why is the fractionation so much stronger in 3He-rich events than in gradual events?
• What exactly is the connection between the composition (Z,M,Q) below 1 MeV/nuc and that above 10 MeV/nuc?
• Can the huge enhancement of 3He be fit into this picture?