1. Supernovae, Nucleosynthesis, and Constraints on Chemical Evolution Jim Truran Astronomy and Astrophysics Enrico Fermi Institute University of Chicago and Argonne National Laboratory Ringberg Workshop on Nuclear Astrophysics March 12, 2008

2. Tracers of Star Formation Histories The heavy element content of the Universe at any point in its history reflects the integrated nucleosynthesis contributions from earlier stellar generations. We can use this knowledge effectively as a tool both to probe its dynamical and star formation histories and to constrain models of stellar and supernova nucleosynthesis. How might we unravel this history? Since distinctive abundance patterns are identified with the nucleosynthesis products of stars of different masses (and lifetimes), constraints on the early nucleosynthesis and star formation histories of the Cosmos will be contained in the spectra of halo stars and QSO absorption line systems, as a function of [Fe/H] or redshift.

3. “Cosmic” Abundances of the Elements Massive Stars & SNe r-process s-process

4. Nucleosynthesis Sites and Production Timescales  Massive stars (M > 10 M  ) and SNe II: synthesis of most of the nuclear species from oxygen through zinc, and of the r-process heavy elements (  < 10 8 years)  Red Giant Stars (1 10 9 years)  SNe Ia: synthesis of the 1/2-2/3 of the iron peak nuclei not produced by SNe II (  > 1.5-2 x10 9 years)

5. Type Ia Supernovae: Theory  “ Standard model” (Hoyle & Fowler 1960):  SNe Ia are thermonuclear explosions of C+O white dwarf stars.  Evolution to criticality:  Accretion from a binary companion (Whelan and Iben 1973) leads to growth of the WD to the critical (Chandrasekhar) mass ( 1.4 solar masses).  After ~1000 years of thermonuclear “cooking”, a violent explosion is triggered at or near the center.  Complete incineration occurs within two seconds, leaving no compact remnant.  Light curve powered by radioactive decay of 56 Ni. (Nickel mass ≈ 0.6 M .) Peak luminosity  M( 56 Ni).

6. Type II Supernovae: Theory  “ Standard model” (Hoyle & Fowler 1960):  SNe II are the product of the evolution of massive stars 10 < M < 100 M .  Evolution to criticality:  A succession of nuclear burning stages yield a layered compositional structure and a core dominated by 56 Fe.  Collapse of the 56 Fe core yields a neutron star.  The gravitational energy is released in the form of neutrinos, which interact with the overlying matter and drive explosion.  Remnants: Neutron star and black hole remnants are both possible SNe II remnants.  Nucleosynthesis contributions: elements from oxygen to iron (formed as 56 Ni) and neutron capture products from krypton through uranium and thorium. (  nucleosynthesis < 10 8 yrs) Production of ≈ 0.1 M  of 56 Fe as 56 Ni. Courtesy Mike Guidry: guidry@utk.edu SNe1054: Crab Nebula SNe1987A Hubble Image

7. Supernova Nucleosynthesis Contributions  Type Ia Supernovae : Thermonuclear explosions of CO white dwarfs.  Type II Supernovae: Core collapse driven events in massive stars.  In both instances,the formation of iron peak elements in explosive nucleosynthesis occurs under neutron-poor conditions. This is reflected in the 56 Ni  56 Co  56 Fe signatures in both Type Ia and Type II supernova light curves and in the isotopic compositions of iron-peak elements in solar matter.  Note the alpha-nuclei (Mg, Si, S, Ar, Ca) to iron-peak abundance ratios in SNe II ejecta. (Iwamoto et al. 1999) (Thielemann et al. 1992) Type Ia Nucleosynthesis Type II Nucleosynthesis

8. Explosive Nucleosynthesis  This behavior can extend well beyond mass A=56, perhaps even through mass A=72, viz: 52 Fe, 56 Ni, 60 Zn, 64 Ge, 68 Se, and 72 Kr.  The “freezing” of these patterns associated with the expansion and cooling of Types Ia and II supernova ejecta underscores the importance of experimental determinations of reaction rates as well as of masses and lifetimes for proton-rich isotopes near the a-line. Trends in Low Metallicity Stars (Cayrel et al. 2005) [Zn/Fe] [Cr/Fe]

9. Synthesis of Nuclei Beyond Iron  Nuclei heavier than iron (A  60) are understood to be formed in neutron capture processes.  The helium shells of red giant stars (  1-10 ) provide the s-process environment, with the 13 C( ,n) 16 O reaction providing neutrons. (  > 10 9 years)  Supernovae II provide the astronomical setting for the r-process. (  < 10 8 years)

10. Heavy Element Synthesis Processes Z N 184 Os 186 Os 187 Os 188 Os 185 Re 186 Re 187 Re 180 W 182 W 183 W 184 W 185 W 186 W 180 Ta 181 Ta 182 Ta 176 Hf 177 Hf 178 Hf 179 Hf 180 Hf 181 Hf 175 Lu 176 Lu 177 Lu 174 Yb 175 Yb 176 Yb 189 Os stable  > 10 10 yrs unstable 4j 7j 42j 115j 75j 91h rs,r s ss s r r p p p p s r r-process s-process p-process r-process

11. r-Process and s-Process Synthesis s-process in red giants r-process in supernovae

13. Calcium Titanium Halo Abundance Trends for -3  [Fe/H]  -1 Oxygen and  -Elements R-Process Elements (Truran et al. 2002)  These behaviors are compatible with nucleosynthesis predictions for SNe II.

14. [  /Fe] in Halo Stars and Dwarf Galaxies (Tolstoy et al. 2005) Sculptor Globular Cluster Stars Type Ia and Type II histories yield complicated abundance histories of stellar populations.

15. DLAs: Abundance Evolution with Red Shift (Pettini 2003) (Lu et al. 1996) Lower bound on metallicities due to masses of typical clouds in which first stars formed.

16. Silicon Abundance History in the Cosmos Figure Credit: Francesca Primas (2003)

17. s-Process/r-Process Chemical Evolution (Truran et al. 2002)

19. Abundances in Dwarf Spheroidal Galaxies (Shetrone et al. 2003)

20. Abundance Trends & Chemical Evolution: [Fe/H] > -3  Extremely metal-deficient stars of [Fe/H] ~ -2 to –3 are characterized by both high O/Fe and (Ne-Ca)/Fe ratios and an r- process heavy element pattern   SNe II production (   10 8 years)  Signatures of an increasing s-process contamination first appear at [Fe/H]  -2.5 to –2.0   first input from AGB stars (   10 9 years)  Evidence for entry of SNe Ia ejecta first appears at [Fe/H]  -1.5 to –1.0, as evidenced in the [O/Fe] and [(Ne-Ca)/Fe] histories   input from SNe Ia on timescales > 1.5-2 x 10 9 years

21. Supernova Ia: Progenitors and Sites (Oemler and Tinsley 1979) (Sullivan et al. 2006)

22. Evidence for SNe Ia in the Early Galaxy Thin Disk Thick Disk Observations by Bernkopf and Fuhrmann (2006) reveal distinctive abundance evolution in the thick disk and thin disk components of our Galaxy. Truran and Burkert (2008) argue that this reflects the combined heating and nucleosynthesis contributions from SNe Ia over a period of order 10 9 years at the end of the thick disk star formation epoch.

23. Trends at the Lowest Metallicities Truran et al. (2002) r-Process Scatter Cayrel et al. (2005) [Mn/Fe] [Cr/Fe] [Zn/Fe]

24. Abundance Trends for [Fe/H] < -4 ?? Frebel et al. (2005)  The abundances in the two most “iron-deficient” stars known do not trace the smooth trends found (Cayrel et al. 2004) above [Fe/H] = -4. The details of their evolutions remain uncertain.

25. Abundance Trends/Chemical Evolution: -4 <[Fe/H}< -2.5  Evidence for increasing scatter exists in the (r-process/Fe) ratio below metallicity [Fe/H] ~ -2.5, suggesting both that only a small fraction of massive stars form r-process nuclei - and that   the ISM was highly inhomogeneous at that epoch.  In contrast, the scatter in abundance ratios of nuclei from Mg to Zn with respect to iron is remarkably small. Given the level of inhomogeneity reflected in the r-process/Fe ratio, this quite strongly implies   the massive stars responsible for these early products were extremely robust in their synthesis of nuclei through iron. (Keep in mind that the heavy elements introduced into stars formed at metallicities [Fe/H] ~ -4 are most likely to have come from a single progenitor.)  The paucity of DLAs with metallicities below [Fe/H] ≈ -3 is compatible with their having been enriched by only a very few stars - but in star forming regions typically ~ 10 6 M .   (Note that the introduction of 10 M  of metals from a ~ 20-30 M  star is sufficient to enrich a ~ 10 6 M  cloud to a metallicity ≈ 10 -3 Z .)

26. Look-back Times versus Redshift Red Shift Age of the Universe Look-back Time  0 Gyr 14.5 Gyr 10 (First Stars - 0.5 14.0 6 - SNe II) 1.0 13.5 5 1.2 13.3 4 (AGB Stars)  1.6 12.9 3 (SNe Ia)  2.3 12.2 2 3.5 11.0 1 6.2 8.3 0.5 9.1 5.4  0.4 Birth of Sun 9.9 4.6 0 14.5 0 (H o = 65 km s -1 Mpc -1 ;  baryons = 0.022 h -2 ;  M = 0.3;   =0.7;  cosmos = 14.5 Gyr )

27. Concluding Remarks  Based upon existing observations of abundances in our Galaxy, other galaxies, and QSO absorption line systems, we might conclude: Only normal stars in a Salpeter-like initial mass function are required to produce the elements seen in the oldest stars.  While contributions from massive stars clearly dominate at early epochs, this is more likely a consequence of their shorter production timescales rather than of an altered IMF.  Our present knowledge of the abundance history of the Universe provides no clear evidence for an earlier Population (III?).  The collective trends in halo stars, disk stars, globular clusters, dwarf spheroidal galaxies, and DLAs are generally compatible with our understanding of stellar evolution and supernova nucleosynthesis.