Presolar grains: Interstellar Messengers to Study Hands-On Astrophysics

• 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 ‰
• Presolar grains have extreme isotope compositions
• Classified by analyzing Si, C, & N isotopes
• Fingerprint of the parent star's composition
• Hands-on astrophysical samples
  • Galactic chemical evolution
  • Stellar nucleosynthesis

• δ-units: Deviation from solar in ‰
• Presolar grains have extreme isotope compositions
• Classified by analyzing Si, C, & N isotopes
• Fingerprint of the parent star's composition
• Hands-on astrophysical samples
  • Galactic chemical evolution
  • Stellar nucleosynthesis

• Cosmic-rays induce production of nuclides
• Ideal proxy for exposure age:
  ²¹Ne concentration
  • Does not condense into grain
  • Produced from Si
• Most grains formed <1 Ga prior to solar system
• Some grains are several billion years old!

• Expand rapidly and cool
• Cycles between H and He burning
• Copious dust producers
• Host of the s-process
• Two important neutron sources
  • ¹³C(α,n)¹⁶O
  • ²²Ne(α,n)²⁵Mg

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 condense 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 condense 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 condense 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 condense 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 condense 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 condense 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)

• Dust condensation timeframe:
  ~20 years (Ott et al., 2009)

• State-of-the art: 1D mixing models

• Future: 3D condensation models

  • Directly compare to presolar grains
  • Understand the dust formation process

• We need more measurements and detailed models!

Brooker et al (2022)

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

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

Fok et al. (in prep.)

• Presolar grains are isotopic messenger
• Fine probes for many processes
  • GCE
  • Rare nucleosynthesis processes
  • Ejecta mixing & condensation
• Recent advances in measurement techniques

Stay tuned!

SiC grain imaged in the secondary electron microscope

• Presolar grains are isotopic messenger
• Fine probes for many processes
  • GCE
  • Rare nucleosynthesis processes
  • Ejecta mixing & condensation
• Recent advances in measurement techniques

Stay tuned!

NASA, ESA, NRAO/AUI/NSF and G. Dubner (Univ. of Buenos Aires)