Supernovae, Nucleosynthesis, and

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
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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.
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Cosmic Abundances of the Elements

r-process
s-process
Massive Stars SNe

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Nucleosynthesis Sites and Production Timescales

• Massive stars (M gt 10 M?) and SNe II
  synthesis of most of the nuclear species from
  oxygen through zinc, and of the r-process heavy
  elements (? lt 108 years)
• Red Giant Stars (1 lt M lt 10 M?) synthesis of
  carbon and of the heavy s-process elements (? gt
  109 years)
• SNe Ia synthesis of the 1/2-2/3 of the iron
  peak nuclei not produced by SNe II (? gt 1.5-2
  x109 years)

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Type Ia Supernovae Theory

• Standard model (Hoyle Fowler 1960)
• SNe Ia are thermonuclear explosions of CO
  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
  56Ni. (Nickel mass 0.6 M?.) Peak luminosity ?
  M(56Ni).

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Type II Supernovae Theory

• Standard model (Hoyle Fowler 1960)
• SNe II are the product of the evolution of
  massive stars 10 lt M lt 100 M?.
• Evolution to criticality
• A succession of nuclear burning stages yield a
  layered compositional structure and a core
  dominated by 56Fe.
• Collapse of the 56Fe 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 56Ni) and neutron
  capture products from krypton through uranium and
  thorium. (?nucleosynthesis lt 108 yrs) Production
  of 0.1 M? of 56Fe as 56Ni.

Courtesy Mike Guidry guidry_at_utk.edu
SNe1054 Crab Nebula
SNe1987A Hubble Image
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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 56Ni?56Co?56Fe 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.

Type Ia Nucleosynthesis
Type II Nucleosynthesis
(Iwamoto et al. 1999)
(Thielemann et al. 1992)
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Explosive Nucleosynthesis

• This behavior can extend well beyond mass A56,
  perhaps even through mass A72, viz 52Fe, 56Ni,
  60Zn, 64Ge, 68Se, and 72Kr.
• 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)
Cr/Fe
Zn/Fe
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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
  13C(?,n)16O reaction providing neutrons. (? gt 109
  years)
• ? Supernovae II provide the astronomical setting
  for the r-process. (? lt 108 years)

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Heavy Element Synthesis Processes
184Os
186Os
187Os
188Os
189Os
Z
s-process
s
s
s
s,r
s,r
p
r-process
r
185Re
186Re
187Re
p-process
p
91h
s,r
r
180W
182W
183W
184W
185W
186W
75j
s,r
s,r
s,r
r
p
180Ta
181Ta
182Ta
115j
s,r
p
177Hf
178Hf
179Hf
180Hf
181Hf
176Hf
r-process
42j
s
s,r
s,r
s,r
s,r
175Lu
176Lu
177Lu
stable
7j
s,r
s
? gt 1010 yrs
174Yb
175Yb
176Yb
unstable
r-process
4j
r
s,r
N
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r-Process and s-Process Synthesis
s-process in red giants
r-process in supernovae
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Halo Abundance Trends for -3 ? Fe/H ? -1
Oxygen and ?-Elements
R-Process Elements
Calcium
Titanium
(Truran et al. 2002)

• These behaviors are compatible with
  nucleosynthesis predictions for SNe II.

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?/Fe in Halo Stars and Dwarf Galaxies
Globular Cluster Stars
Type Ia and Type II histories yield complicated
abundance histories of stellar populations.
Sculptor
(Tolstoy et al. 2005)
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DLAs Abundance Evolution with Red Shift
(Pettini 2003)
Lower bound on metallicities due to masses of
typical clouds in which first stars formed.
(Lu et al. 1996)
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Silicon Abundance History in the Cosmos
Figure Credit Francesca Primas (2003)
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s-Process/r-Process Chemical Evolution
(Truran et al. 2002)
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Abundances in Dwarf Spheroidal Galaxies
(Shetrone et al. 2003)
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Abundance Trends Chemical Evolution Fe/H gt
-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 (? ? 108 years)
• Signatures of an increasing s-process
  contamination first appear at Fe/H ? -2.5 to
  2.0
• ? ? first input from AGB stars (? ? 109 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 gt 1.5-2 x
  109 years

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Supernova Ia Progenitors and Sites
(Oemler and Tinsley 1979)
(Sullivan et al. 2006)
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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
109 years at the end of the thick disk star
formation epoch.

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Trends at the Lowest Metallicities

Cr/Fe
r-Process Scatter
Mn/Fe
Zn/Fe
Truran et al. (2002)
Cayrel et al. (2005)
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Abundance Trends for Fe/H lt -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.

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Abundance Trends/Chemical Evolution -4 ltFe/Hlt
-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 106 M?.
• ? ? (Note that the introduction of 10 M? of
  metals from a 20-30 M? star is sufficient to
  enrich a 106 M? cloud to a metallicity 10-3
  Z?.)

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Look-back Times versus Redshift
(Ho 65 km s-1 Mpc-1 ?baryons 0.022 h-2 ?M
0.3 ??0.7 ?cosmos 14.5 Gyr )
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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.