Abundances in Presolar Grains, Stars and the Galaxy Larry R. Nittler Department of Terrestrial Magnetism Carnegie Institution of Washington

or Larry R. Nittler Department of Terrestrial Magnetism Carnegie Institution of Washington

What can presolar grains tell us about the history of the Galaxy? Larry R. Nittler Department of Terrestrial Magnetism Carnegie Institution of Washington

Galactic Chemical Evolution As succeeding generations of stars are born, die and eject newly-synthesized nuclei into the ISM, chemical composition of the Galaxy evolves. ISM composition at any time or place depends on entire history of stellar birth, death, and nucleosynthesis, as well as galactic dynamics In particular, average metallicity increases with time –Z=mass fraction of elements heavier than He (Z  =1.5-2%) –[Fe/H]= log (Fe/H) – log (Fe/H) 

GCE: Astronomical Clues Many (but not all) studies indicate general decline in metallicity with stellar age. Very large scatter in metallicity for stars of given age and galactocentric radius.

GCE: Astronomical Clues “alpha”-elements overabundant relative to Fe at low metallicity –Type Ia versus Type II supernovae Reddy et al (2003)

Presolar grain compositions reflect interplay of galactic chemical evolution, nucleosynthesis, physicochemical conditions of stellar dust formation Represent sample of stars that was present shortly before formation of solar System but had formed over long history of galactic disk. –Provide complementary data set to astronomical observations on Galactic Chemical Evolution GCE: Presolar Grains

GCE and Presolar Stardust Can we use presolar grain data to constrain nucleosynthesis and GCE models? Can we constrain homogeneity of ISM with presolar grain data? Are there metallicity effects on the abundances and types of dust formed by stars?

GCE of Isotopic Ratios “Primary” isotopes can be made in star of H, He; “Secondary” require pre-existing CNO. –e.g., 28 Si, 16 O, 48 Ti primary, rare isotopes secondary D. D. Clayton (1988): –(S/P)/(S/P)   Zp/Zp  –e.g.: ( 29 Si/ 28 Si)/ ( 29 Si/ 28 Si)   Z/Z  Actual evolution depends on balance of yields from different types of stars and many details of Galactic evolution

Presolar Silicon Carbide (SiC) Best-studied presolar phase 0.1 – 20  m, ~20ppm Anomalous in C, Si, N, Ca, Mg, Ti, Ne, Xe, Kr, Ba, Nd, Sr, Sm, Dy, Mo, Zr At least six isotopically distinct groups Mainstream (90%), Y (2%) and Z (2%) grains from AGB stars –C, N, Mo, Zr … reflect nucleosynthesis in parent stars (see talk by M. Lugaro) 1m1m Minimum of sources (Alexander 1993)

GCE and presolar SiC Si and Ti reflect GCE

GCE and rare presolar SiC types Nittler and Alexander (2003)

GCE and rare presolar SiC types 30 Si, C isotopes in Z grains point to low- mass, low-metallicity AGB origin –Supported also by Ti data for a few Z grains –Lie on extension of mainstream correlations; depleted in secondary isotopes as expected for GCE Zinner et al, 2005

GCE and rare presolar SiC types Use large grid of AGB nucleosynthesis models (R. Gallino) to estimate initial metallicity of Z grains Early rise of 29 Si –Role of SN Ia? Nittler et al. (2004) Nuclei in the Cosmos; Zinner et al (2006), ApJ, in press

GCE of N isotopes N nucleosynthesis poorly understood: – 14 N mostly secondary (CNO-cycle in massive stars), partly primary from low-Z SNe, red giants – 15 N?? ~Secondary in novae; primary in SNe, but both sources fail to make enough Does 14 N/ 15 N increase or decrease with Z?

N isotopic evolution Dahmen et al. (1995) found N isotopic gradient: – 14 N/ 15 N decreases with Z (secondary 15 N) Chin et al. (1999) found 14 N/ 15 N ~ 100 in starburst galaxies and LMC SFR: – 14 N/ 15 N increases with Z (primary 15 N)

N isotopic evolution Owen et al (2001): – 14 N/ 15 N of Jupiter (Solar?) ~ 430 Presolar grains: –SNe-derived SiC imply 15 N production higher than predicted (e.g., Nittler et al. 1995, Amari talk) –Consistent with Chin results –Mainstream SiC 15 N/ 14 N ranges from ~200 to 20,000, implies that presolar parent stars started with lower ratios than solar –Data point towards primary 15 N production, but inconsistent with galactic gradient.

Presolar O-rich Grains More difficult to locate in meteorites than C-rich grains Several hundred oxide and silicate grains identified Data from Nittler et al ; Choi et al 1997, 1998; Zinner et al. 2003; Messenger et al 2003, Nguyen and Zinner 2004; Messenger et al 2005

Most grains formed in red giants/AGB stars

Group 1 and 3 grains well- explained by 1 st dredge-up models; require range of masses and metallicities

Simulate oxide distribution –Assume parent stars Solar Masses –No age-metallicity relationship (Nordstrom et al 2004)

Simulate oxide distribution –Assume parent stars Solar Masses –No age-metallicity relationship (Nordstrom et al 2004) –Poor Match to Data

Simulate oxide distribution –Assume parent stars Solar Masses –Assume age-metallicity relationship of Reddy et al (2003) –Much better match! Data point to AMR with scatter

GCE of Mg Isotopes Stellar obs. and high-precision Mg measurements of presolar spinel support shallow GCE model of Fenner et al (role of low-Z AGB stars) Scatter large in stars –Mass transfer from companion AGB stars in low-Z binary systems??

SiC-Oxide Consistency? Use Si-Ti correlation in SiC and Ti-Z (determined from 18 O/ 16 O) correlation in oxides to predict Si-Z relationship for Galaxy

SiC-Oxide Consistency? Predicted trend is somewhat consistent with limited silicate dataset (Nguyen et al 2006; Mostefaoui & Hoppe 2004) – Instrumental effects can strongly affect plot –Need better data Predicted trend

Homogeneity of GCE Scatter in age-metallicity relation suggests ISM is heterogeneous (1)Inhomogeneous mixing of stellar ejecta? (2) Orbital diffusion of stars? (3) Inhomogeneous infall of low-Z matter from halo? Low scatter in element/Fe ratios in nearby stars argues against (1), but uncertainty ~10-20% (Edvardsson et al. 1993, Reddy et al. 2003) –Can high-precision presolar grain data help?

Heterogeneous GCE and SIC Lugaro et al. (1999) used Monte Carlo methods to model heterogeneous mixing of SN ejecta into ISM Can explain range and scatter of SiC Si isotopes very well

Heterogeneous GCE and SIC As found by Lugaro et al. (1999), Si isotopes can be well explained Correlation between Si and Ti not reproduced, though. –Grain correlation indicates Si and Ti isotopes locally well-mixed in the ISM! Nittler, ApJ, 2005

Maximum heterogeneity allowed by Si-Ti correlation provides constraints on elemental variations in ISM –Few % for el/Fe Nittler, ApJ, 2005

Mineralogy vs metallicity? “High-density” presolar graphite probably from AGB stars (e.g. s-process enrichments, Croat et al. 2005) Higher 12 C/ 13 C ratios than SiC point to either higher-mass or lower-metallicity parents

Mineralogy vs metallicity? Recent Spitzer observations indicate that low-metallicity (SMC) C stars produce similar amounts of dust as Galactic ones, but much less SiC (Sloan et al, ApJ, 2006) –Low-Z AGB stars have much higher C/Si ratios, preferentially produce graphite? –Presolar grains might provide information on how galactic inventory of dust changes with Z

Conclusions Presolar grains can be used as sensitive probes of Galactic Chemical Evolution –Indicate enhanced low- metallicity production of 29,30 Si and 25 Mg (role of SN-Ia and AGB stars, respectively) –Grain data indicate 15 N is primary isotope and 15 N/ 14 N ratio increases with metallicity –Oxide/Silicate data indicate that age-metallicity relation (AMR) with large scatter does exist –Isotopic correlations indicate ISM is well-mixed; heterogeneous mixing of SN ejecta does not explain scatter in AMR –C isotopes in SiC and graphite indicate former from high metallicity, latter from low metallicity stars, consistent with recent Spitzer observations

Presolar Galactic Merger? (D. D. Clayton 2003) Explains correlation lines (Si, Ti) Might explain 18 O/ 17 O of Sun Requires supporting evidence

Presolar galactic merger? Max 12 C/ 13 C decreases with increasing 29 Si/ 28 Si Larger 12 C/ 13 C requires higher mass AGB stars (>3 M  for Y grains) –Shorter lived Implies temporal evolution down mainstream line? –Increasing mixing fraction from merging galaxy? More than 3700 grains plotted; Nittler & Alexander 2003

GCE of Si isotopes 29 Si/ 28 Si, 30 Si/ 28 Si increase with Z ([Fe/H]) 30 Si/ 29 Si misses Solar! –(“renormalize” calc.) (Timmes & Clayton 1996)

GCE and presolar SiC Slope of Si trend (1.3) steeper than GCE model predictions (1.0) –Indicates low metallicity source of 30 Si not included in GCE models –Novae? –AGB stars? Most grains isotopically heavy, from stars with [Fe/H]>0, despite being older than Sun –Sun isotopically anomalous? –Large observed scatter in metallicity of stars in galaxy