Trace Element Abundances in Single Presolar SiC Stardust Grains by Synchrotron X-Ray Fluorescence (SXRF) Zhonghu Cai (XOR) Barry Lai (XOR) Steve Sutton (CARS) Bob Clayton Andy Davis Roy Lewis Yoav Kashiv
The never ending story… Zhonghu Cai (XOR) Barry Lai (XOR) Steve Sutton (CARS) Bob Clayton Andy Davis Roy Lewis Yoav Kashiv
Types of presolar stardust grains found (an incomplete list) Carbides Diamond (C) SiC Graphite (C) TiC (subgrains) Fe-Zr-Mo-Ru carbides (subgrains) Oxides Corundum (Al 2 O 3 ) Spinel (MgAl 2 O 4 ) Hibonite (CaAl 12 O 19 ) TiO 2 Mg-Fe Silicate [(Mg,Fe)SiO 2, olivine?] Other Si 3 N 4
Summary of properties of some grains (Zinner, 1998; Bernatowicz et al., 1996)
How do we identify and classify stardust grains? By their isotopic composition which is very different from ‘average’ solar system composition. (Plot by A. Davis, compilation of data from several sources)
And classified by their Si isotopic composition as well. (Plot by A. Davis, compilation of data from several sources)
A Fe-rich sub-grain (metallic Fe or Fe-carbide) inside A presolar graphite grain. (Bernatowicz et al., 1996)
What affects the abundance of a trace element in the grains? 1. The composition of the stellar atmosphere gas: The initial composition of the star. Nuclear burning in the star (if applies). Mixing in the star (dredge-up events). 2. The time dependent physical conditions in the stellar atmosphere: p-T curves. 3. The thermochemical behavior of the element under the chemical and physical conditions: refractory, volatile, etc. 4. The trace element incorporation mechanism: condensation as an inclusion, condensation in solid solution, other?
The experiment was conducted at the Advanced Photon Source (APS) at Argonne National Lab (ANL).
The experimental technique that was used is Synchrotron X-Ray Fluorescence (SXRF). Unlike in astronomical spectroscopy here we are looking at electronic transitions between inner shells.
Unlike starlight the x-ray beam energy is tunable. This is done with an insertion device (ID) called an undulator.
A residual grain spectrum (i.e., with background subtracted) taken with a primary x-ray beam energy of 22.5 keV.
Minor and trace elements detected in presolar SiC grains (an incomplete list) In aggregates Ne, Ar, Kr, Xe, Sm, Dy. In single grains 1. Abundance: N, Mg, Al, Ca, Ti, V, Fe, Sr, Y, Zr, Nb, Ba, Ce, Nd. 2. Isotopic composition: B, N, Mg (Al), Ti (V), Fe, Sr, Zr, Mo, Ru (Tc), Ba. This study 1. Detected before: Ca, Ti, V, Fe, Sr, Y, Zr, Nb. 2. New elements: S, Cr, Mn, Co, Ni, Mo, Ru, W, Os, Ir, Pt.
The general grain pattern.
Examples of specific grain patterns.
Comparison of the general grain pattern with calculations of a 1.5 M solar AGB star. (Gallino et al., private communication)
Comparison of the general grain pattern with ISM depletions. (Welty et al., 1999)
Schematic correlations between two trace elements in the grains: nuclear and chemical effects.
Example of two correlated trace elements (1): no nuclear enrichment, but with chemical enrichment (both) - V vs. Ti.
Example of two correlated trace elements (2): no nuclear enrichment and chemical depletion (both) - Ni vs. Fe.
Example of two correlated trace elements (3): nuclear (Zr) and chemical enrichments (both) - Zr vs. Ti.
Example of two correlated trace elements (4): nuclear enrichment (Sr), and chemical depletion (Sr) - Sr vs. Ti.
Example of two correlated trace elements (5): nuclear and chemical enrichments (both) - Mo vs. Zr.
Example of two correlated trace elements (6): nuclear and chemical enrichments (both) – Nb vs. Zr.