p-process signatures in presolar grains

Reto Trappitsch
October 18, 2024

A window into the past

• Presolar grains are at least 4.567 Ga old
• Interstellar residence time:
  • Determined via cosmic ray exposure ages
  • Heck et al. (2020)

Which type of star made these grains?

• Most SiC grains from AGB stars
  • Condensed from convective envelope
  • Study the s-process
• Some grains from core-collapse supernovae
  • Condensed in heterogeneous ejecta
  • Trace nucleosynthesis and the stellar engine

Probing the p nuclei

• Presolar CCSNe grains
  • Search for signatures of various nucleosynthesis processes
  • νp-process, ...
• Presolar grains from AGB star
  • Majority of p nuclei are destroyed
  • Derive p abundance via precise s isotope measurements

Probing the p nuclei

• Presolar CCSNe grains
  • Search for signatures of various nucleosynthesis processes
  • νp-process, ...
• Presolar grains from AGB star
  • Majority of p nuclei are destroyed
  • Derive p abundance via precise s isotope measurements

Separating isobars by laser ionization

Presolar CCSN grains: Ru, Mo, and Ba isotopes

• Very limited measurements for these grains are availasble
• The p nuclei are often missing due to their low abundance

What can we do with these measurements?

• Strange Mo isotopic pattern with enhancements in ^96,97Mo
  • No p nuclei anomaly
  • Anomaly could be explained by neutrino driven winds (Bliss et al., 2018)
• Ru isotopic pattern
  • Clear, correlated p and r nuclei enhancements
• Contamination with solar material is a huge concern for these measurements

Mo in AGB star grains is especially interesting

Peek inside an AGB star

• s-process in He intershell
  → Destroys p nuclei
• Dredge-up: Mix into convective envelope
• Some p nuclei never see the s-process
  • Proxies for galactic chemical evolution
  • Determine abundance with precision measurements

Measurements indicate constant r/p isotope production

Stephan et al. (2019)

• ⁹²Mo not made in s-process but destroyed
• Extrapolation towards no-⁹²Mo yield pure s-process composition
• This would be possible for other elements, e.g., Ru, Sm, and (maybe) Pt

Varying stellar conditions

• ^97,98Mo constant
• ^{94, 95, 100}Mo vary more than expected
• Variations likely indicate varying temperature/neutron density effects on branch points

Remember the chart of the isotopes!

Presolar grain analysis: Hands-on astrophysics...

... or astronomy with a microscope

xkcd.com

Acknowledgement

	Brett Isselhardt, Wei Jia Ong, Mike Savina, Ziva Shulaker
	Andy Davis, Mike Pellin, Philipp Heck, Thomas Stephan