1. Department of Terrestrial Magnetism Carnegie Institution of Washington
Presolar Stardust in the Solar System: Implications for Nucleosynthesis and Galactic Chemical Evolution
Larry R. Nittler
Department of Terrestrial Magnetism
Carnegie Institution of Washington

2. Presolar Stardust in The Solar System
Bona-fide stardust from ancient red giants and supernovae
Survived interstellar processes and solar system formation
Found today surviving in meteorites and interplanetary dust particles.
Astronomy in the Laboratory!

3. How do we know?
Solar System materials have highly uniform isotopic compositions, reflecting homogenization processes
Presolar grains can show huge variations (orders-of-magnitude vs %)
17O/16O
18O/16O
Presolar Silicate Grains
NanoSIMS measurement of ALH77307 (Nguyen & Nittler, unpub.)

4. How do we know?
Isotopic variations too large for chemical processes, require nuclear origin
Origin in natural nuclear reactors: STARS
17O/16O
17O/16O= 2 × , 18O/16O=0.8 × 
CNO-cycle H-burning
AGB star
18O/16O
17O/16O = 1.1×, 18O/16O=1.3×
He burning (14N +a)
Supernova?

5. Pristine nature of presolar grains makes them useful probes of:
Cosmology
Stellar nucleosynthesis
Stellar evolution and mixing
Galactic chemical evolution
Dust formation in stellar environments
Dust processing in the interstellar medium
Sources of material for Solar System
Early Solar System processes

6. Stellar nucleosynthesis Stellar evolution and mixing
Pristine nature of presolar grains makes them useful probes of:
Cosmology
Stellar nucleosynthesis
Stellar evolution and mixing
Galactic chemical evolution
Dust formation in stellar environments
Dust processing in the interstellar medium
Sources of material for Solar System
Early Solar System processes

7. Types of Presolar Grains
Nanodiamonds: 2nm; ~1400 ppm
Graphite:
1-20 mm; ~5 ppm
Oxides and silicates (Al2O3, MgAl2O4, Mg2SiO4, …): mm; ~100 ppb - ~100ppm
SiC mm; ~20 ppm

8. Types of Presolar Grains
Nanodiamonds: 2nm; ~1400 ppm
Graphite:
1-20 mm; ~5 ppm
Talk by S. Amari
Oxides and silicates (Al2O3, MgAl2O4, Mg2SiO4, …): mm; ~100 ppb - ~100ppm
SiC mm; ~20 ppm

9. Stardust “telescopes”
Electron Microscopy
Morphology/ mineralogy/ microstructure (>1nm)
Transmission Electron Microscope
Secondary Ion Mass Spectrometry (SIMS)
Major/minor element isotope ratios (>100nm)
Washington Univ. NanoSIMS
Resonance Ionization Mass Spectrometry (RIMS)
Trace-element isotopes (>1mm)
Argonne “CHARISMA”

10. Problem: Do not a priori know origin of given grain
Each presolar grain is a solid piece of a single star at a given time in its evolution
High-precision isotopic measurements of multiple elements possible in single grains
Provides tight constraints on stellar nucleosynthesis models, complementary to astronomical observations
Problem: Do not a priori know origin of given grain
Use iterative approach

11. Presolar SiC Grains

12. Presolar SiC Grains

13. Mainstream SiC (>90%)
Carbon isotopes match AGB stars, 13C rich and 15N-poor from dredge-up of CNO cycle
Also show s-process signatures!
Formed in AGB stars

14. AGB Star Schematic

15. Heavy elements in AGB SiC
RIMS used to analyze Mo, Zr, Sr, Ru, Ba isotopes in single SiC grains
Data from Argonne/Chicago group

16. Heavy elements in AGB SiC
Data agree well with s-process models of AGB stars
Requires low-mass (<3 M) parent stars(13C neutron source)
Can constrain amount of 13C (sets neutron exposure, adj. parameter in s-process models)
Barzyk et al (2007): close to “Standard” 13C amount
Confirms s-process as a specific
nucleosynthetic process
Data from Argonne/Chicago group
Models from Lugaro et al 2003

17. 26Al
26Al (t½=7.3×105 yr) produced by p capture on 25Mg in AGB stars, supernova, novae, Wolf-Rayet stars
Observed in Galaxy by g-ray emission
Observed as nuclear “fossil” in meteorites and presolar grains (26Mg excess)

18. AGB Models (R. Gallino) in good agreement with data
26Al in AGB SiC
Supernova grains
AGB Models (R. Gallino) in good agreement with data
26Al/27Al~10-4 to 5×10-3
AGB grains and models
Zinner et al., Geochim Cosmichim. Acta, 2007

19. Presolar O-rich Grains

20. Presolar O-rich Grains

21. Presolar O-rich Grains

22. Majority of data well-explained by origin in low-mass (1. 3-2
Majority of data well-explained by origin in low-mass ( M) red giants and AGB stars
Requires range of metallicities (Galactic Chemical Evolution)

23. 26Al in presolar grains
Many O-rich grains with 26Al/27Al higher than models/SiC
Zinner et al., Geochim Cosmichim. Acta, 2007

24. 26Al and 41Ca
Presolar Hibonite (CaAl12O19) shows 41K excess from decay of 41Ca (t½= 105 yr )
Produced in He-shell by n-capture
Inferred 41Ca/40Ca ratios agree with models
Again, 26Al/27Al ratios higher than standard models.
Nittler et al, ApJ, submitted
Points to “extra mixing”

25. Extra Mixing (Cool-bottom Processing)
“Extra mixing” process believed to be responsible for low 12C/13C ratios observed in low-mass red giants
Envelope material mixed to hotter inner regions of star, where burning can occur
Likely related to rotation (Eggleton et al 2006)
In AGB stars, can also affect O isotopes and produce 26Al (Wasserburg et al., 1995, Nollett et al., 2003)
Reflected in presolar oxides/silicates

26. Extra Mixing (Cool-bottom Processing)
Parameterized models can explain large 18O depletions in fraction of grains

27. Extra Mixing (Cool-bottom Processing)
Parameterized models can also explain high 26Al/27Al ratios.
O and Al decoupled and can constrain model parameters (temperature, mixing rate)
Nollett et al, 2003

28. Supernova Grains (SiC, Graphite, Si3N4, oxides/silicates)
“Smoking gun” is inferred presence of 44Ti
Inferred from 44Ca excesses
Half-life=50yr
Produced only in SNe
Many other isotope signatures point to SN sources as well.
Only Type II consistent with most isotopes (esp. “Neutron-burst” signature of Zr, Mo)
Nittler et al. 1996, Amari & Zinner 1997
TiC

29. Presolar Supernova Grains
Isotope compositions require contributions from different SN shells
Requires extensive and heterogeneous mixing
Attempts to quantitatively match data with SN models have had mixed success (e.g. Travaglio et al 1999, Hoppe et al 2000, Yoshida &Hashimoto 2004, Nittler et al, submitted)
SN models underproduce 15N

30. Presolar O-rich Grains
Origin of 18O-rich grains?

31. Hibonite Grain KH2 (Nittler et al, ApJ submitted)
17,18O-rich grain
30% 25Mg depletion
5% 42,43Ca depletions
3% 44Ca excess
Very high 41Ca/40Ca, 26Al/27Al ratios

32. 15M SN mixing model matches comp.
Mix dominated by envelope, with small amount from He/C and inner zones
Hibonite KH2 formed in a supernova
True for all or most 18O-rich presolar grains?
16O-rich grains from inner zones destroyed by reverse shock?

33. Heavy Elements
SiC SN grains show unusual heavy element isotope patterns
95,97Mo, 96Zr, 88Sr, 138Ba excesses
Not r-process patterns
Point to “neutron burst” nucleosynthesis process (Meyer et al. 2001)
Subsequently seen in He shell of SN models (Rauscher et al 2002)
Pellin et al, 1999

34. Nova Grains?
Tiny fraction of presolar SiC/graphite has very low 12C/13C and 14N/15N ratios (also unusual Si and 26Al)
Amari et al. (2001) argued for nova origin, requires extreme mixing of nova ejecta with normal material
Nittler & Hoppe (2005) found similar grain that formed in SN (based on 44Ti, 26Al, Ti isotopes),
Indicates SNe can make unusual C-N signature
Amari et al., 2001

35. Nova Grains?
More recently found unusual (Al2(SiC)3) grain with 12C/13C=1, best candidate yet for nova origin; doesn’t require extreme mixing. (Nittler et al., 2006)

36. Models from José et al, ApJ 2004
26Al/27Al lower than predicted by most nova models, esp. those that match C,N isotopes
Nova models overproduce 26Al?
Nova grains difficult to identify, but can potentially provide unique constraints on models

37. Recently, extremely unusual Ca-Ti isotopic compositions found in presolar graphites (Jadhav et al 2007)
Hard to reconcile with models

38. Conclusions THANKS TO ORGANIZERS FOR INVITATION AND TRAVEL SUPPORT!
Meteorites contain grains of presolar stardust
Bona fide pieces of stars that can be studied in the laboratory
Most presolar SiC, graphite, oxides, silicates formed in red giants and AGB stars
Provide constraints on stellar evolution, nucleosynthesis and Galactic evolution
Confirm (and constrain) s-process as distinct nucleosynthetic process
Some grains from supernovae
Provide evidence for extensive, heterogeneous mixing in SN ejecta
Indicate new “neutron burst” process of supernova nucleosynthesis
Indicate SN models underproduce 15N
THANKS TO ORGANIZERS FOR INVITATION AND TRAVEL SUPPORT!