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

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!

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.)

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?

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

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

Types of Presolar Grains Nanodiamonds: 2nm; ~1400 ppm Graphite: 1-20 mm; ~5 ppm Oxides and silicates (Al2O3, MgAl2O4, Mg2SiO4, …): 0.5-5 mm; ~100 ppb - ~100ppm SiC 0.3-20 mm; ~20 ppm

Types of Presolar Grains Nanodiamonds: 2nm; ~1400 ppm Graphite: 1-20 mm; ~5 ppm Talk by S. Amari Oxides and silicates (Al2O3, MgAl2O4, Mg2SiO4, …): 0.5-5 mm; ~100 ppb - ~100ppm SiC 0.3-20 mm; ~20 ppm

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”

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

Presolar SiC Grains

Presolar SiC Grains

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

AGB Star Schematic

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

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

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)

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

Presolar O-rich Grains

Presolar O-rich Grains

Presolar O-rich Grains

Majority of data well-explained by origin in low-mass (1. 3-2 Majority of data well-explained by origin in low-mass (1.3-2.5M) red giants and AGB stars Requires range of metallicities (Galactic Chemical Evolution)

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

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”

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

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

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

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

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

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

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

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?

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

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

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)

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

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

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!