26 June 2008SHINE, Zermatt, UT1 High-energy Elemental, Isotopic, and Charge-State Composition in 3 He-rich Solar Energetic Particle Events M.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)

26 June 2008SHINE, Zermatt, UT2 Breneman & Stone 1985 Leske et al 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

26 June 2008SHINE, Zermatt, UT3 Correlation between isotope ratios: 26 Mg/ 24 Mg versus 22 Ne/ 20 Ne  - gradual events analyzed by Leske et al He-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 3 He-rich events tend to fall near the predicted correlation line 20 Aug 2002 event

26 June 2008SHINE, Zermatt, UT4 Hypothesis: Fractionation in 3 He-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)

26 June 2008SHINE, Zermatt, UT5 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

26 June 2008SHINE, Zermatt, UT6 Combining Elemental and Isotopic Composition to Estimate Charge States fractionation power-law exponent, a, calculated from the enhancement of 22 Ne/ 20 Ne combining this value of a with the Fe/O ratio yields the the corresponding ionic charge state ratio, Q Fe /Q O (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 cases fractionation exponent Q(Fe) 20 Aug May Sep 1998

26 June 2008SHINE, Zermatt, UT7 Comparison with Direct Measurements of 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 3 He-rich event on the preceding day comparison suggests that increase of Q Fe with E/M continues to rise above 1 MeV/nuc low energy values of Q Fe 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 May August 2002

26 June 2008SHINE, Zermatt, UT8 Is fractionation a function of Q/M? Q/M is relevant for rigidity-dependent processes Coulomb losses depend on Q 2 /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 Q k /M and use constraints that Q Fe  26 and Q Fe  largest value of Q Fe 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 May August 2002

26 June 2008SHINE, Zermatt, UT9 Inferred Charge States using the fractionation exponent derived from the isotopic ratios, one can derive ratios of values for any pair of elements assume =6.0 to obtain Q values for other elements plot shows Q expresses as Z-Q Z (i.e., number of electrons attached) find sequences of elements with a given Z-Q Z 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

26 June 2008SHINE, Zermatt, UT10 Source Temperature? Ca, Fe, Ni N, O C 4 He +2 3 He +2 3 He +1 What about 3 He/ 4 He? Origin of non-monotonic dependence of element enhancement on Z? 7 large 3 He-rich events above 10 MeV/nuc How well does the assumption of fractionation as a power law in Q/M organize the composition observations?

26 June 2008SHINE, Zermatt, UT11 Summary isotope fractionation in 3 He-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 with increasing E/M below 1 MeV/nuc continues to higher energies if one assumes that the fractionation depends on Q k /M (allowing the possibility k  1), find that k should be in the range ~ to assure Q Fe  26 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 6  Z  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 3 He-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 3 He-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

26 June 2008SHINE, Zermatt, UT12 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 3 He-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 3 He-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 3 He be fit into this picture?