Signatures of stellar nucleosynthesis in meteorites

• Falls and finds
• Generally found in hot and cold deserts

Differentiated

• Got hot and (partially) melted
• Highly altered due to the heat

Undifferentiated

• Silicates and metals still mixed
• Most primitive meteorites

• Early infall of material: forms the first material (CAIs)
• Late infall: separation of NC & CC
• Jupiter core formation: Separates the two reservoirs
• After asteroids formed:
  • Migration of Jupiter and Saturn
  • Mixes material in solar system (grand tack model)

after Kleine et al. (2020)

• Early infall of material: forms the first material (CAIs)
• Late infall: separation of NC & CC
• Jupiter core formation: Separates the two reservoirs
• After asteroids formed:
  • Migration of Jupiter and Saturn
  • Mixes material in solar system (grand tack model)

after Kleine et al. (2020)

• Nanodiamonds: ~10⁶ atoms
• Silicon carbide: The hardy ones
• Graphites: Large but fragile
• Silicates: Small and fragile
• ...

Silicon Carbide (SiC) are the best studied phase due to their size and hardiness

• δ-units: Deviation from solar in ‰
• Extreme isotope compositions
• Determine provenance by analyzing Si, C, & N isotopes
• Hands-on astrophysical samples
  • Stellar nucleosynthesis
  • Galactic chemical evolution

Each grain contains its parent star's nucleosynthetic signature

• δ-units: Deviation from solar in ‰
• Extreme isotope compositions
• Determine provenance by analyzing Si, C, & N isotopes
• Hands-on astrophysical samples
  • Stellar nucleosynthesis
  • Galactic chemical evolution

Each grain contains its parent star's nucleosynthetic signature

• Copious dust producers
• Host of the s-process
• Two important neutron sources
  • ¹³C(α,n)¹⁶O
  • ²²Ne(α,n)²⁵Mg
• Envelope well mixed
• Form SiC grains

Presolar SiC grains: directly probe the stellar envelope!

V838 Monocerotis (Credit: ESA/Hubble)

¹³C(α,n)¹⁶O

• Main s-process neutron source
• Neutron density: < 10⁷ cm^-3
• Thousands of years

²²Ne(α,n)²⁵Mg

• Bottom of He intershell
• Max. neutron density ~10⁹ cm^-3
• A few years

• SiC condenses only if C/O > 1
• Heavier stars get hotter
  • Stronger ²²Ne(α,n)²⁵Mg
  • Produce more ⁹⁶Zr
• Nuclear physics complicates picture further
• Presolar grains allow deciphering stellar conditions

see, e.g., Liu et al. (20xx), Stephan et al. (2019)

AGB models: Lugaro et al. (2018)

• SiC condenses only if C/O > 1
• Heavier stars get hotter
  • Stronger ²²Ne(α,n)²⁵Mg
  • Produce more ⁹⁶Zr
• Nuclear physics complicates picture further
• Presolar grains allow deciphering stellar conditions

see, e.g., Liu et al. (20xx), Stephan et al. (2019)

AGB models: Lugaro et al. (2018)

• SiC condenses only if C/O > 1
• Heavier stars get hotter
  • Stronger ²²Ne(α,n)²⁵Mg
  • Produce more ⁹⁶Zr
• Nuclear physics complicates picture further
• Presolar grains allow deciphering stellar conditions

see, e.g., Liu et al. (20xx), Stephan et al. (2019)

AGB models: Lugaro et al. (2018)

• SiC condenses only if C/O > 1
• Heavier stars get hotter
  • Stronger ²²Ne(α,n)²⁵Mg
  • Produce more ⁹⁶Zr
• Nuclear physics complicates picture further
• Presolar grains allow deciphering stellar conditions

see, e.g., Liu et al. (20xx), Stephan et al. (2019)

AGB models: Lugaro et al. (2018)

• SiC condenses only if C/O > 1
• Heavier stars get hotter
  • Stronger ²²Ne(α,n)²⁵Mg
  • Produce more ⁹⁶Zr
• Nuclear physics complicates picture further
• Presolar grains allow deciphering stellar conditions

see, e.g., Liu et al. (20xx), Stephan et al. (2019)

AGB models: Lugaro et al. (2018)

• SiC condenses only if C/O > 1
• Heavier stars get hotter
  • Stronger ²²Ne(α,n)²⁵Mg
  • Produce more ⁹⁶Zr
• Nuclear physics complicates picture further
• Presolar grains allow deciphering stellar conditions

see, e.g., Liu et al. (20xx), Stephan et al. (2019)

AGB models: Lugaro et al. (2018)

• Presolar grains are older than the solar system
• Many of them are enriched in ²⁹Si and ³⁰Si compared to the sun
• Heterogeneous GCE
• GCE models predict a slope ~1 line for correlation
• Actual measurements show slope 1.34 (Stephan et al., 2024)

What is going on?

Nuclear reaction rate uncertainties have a large influence, especially on ²⁹Si

Fok et al. (in review)

• Isotopic messenger
• Fine probes for many processes
  • s-process nucleosynthesis
  • Rare nucleosynthesis processes
  • GCE
  • ...
• Recent advances in measurement techniques

Stay tuned!

SiC grain imaged in the secondary electron microscope