Proton-Capture Rates on Carbon Isotopes and Their Impact on the Astrophysical ^{12}C/^{13}C Ratio

Area of Science:

• Nuclear Astrophysics
• Stellar Evolution
• Nucleosynthesis

Background:

• The Carbon isotope ratio (¹²C/¹³C) is a key tracer for stellar nucleosynthesis and mixing processes.
• Accurate determination of this ratio requires precise measurements of the ^{12}C(p,γ)^{13}N and ^{13}C(p,γ)^{14}N reaction rates.

Purpose of the Study:

• To measure the cross sections of the ^{12}C(p,γ)^{13}N and ^{13}C(p,γ)^{14}N reactions at astrophysically relevant energies.
• To determine the lowest possible ^{12}C/^{13}C ratio produced during hydrogen burning in giant stars.

Main Methods:

• Experiments conducted at the Laboratory for Underground Nuclear Astrophysics (LUNA) in Italy.
• Measurements performed down to E_{c.m.}=60 keV, probing the high-energy tail of hydrogen burning.
• Utilized both prompt gamma-ray detection and activation measurements for cross-section determination.

Main Results:

• Achieved the most precise cross-section measurements to date for both reactions, with 7%-8% systematic uncertainties.
• Results are systematically lower than most literature values: 25% lower for ^{12}C(p,γ)^{13}N and 30% lower for ^{13}C(p,γ)^{14}N.
• Provided the most precise value for the lowest ^{12}C/^{13}C ratio (3.6±0.4) in the 20-140 MK range for giant stars.

Conclusions:

• The new cross-section data refine our understanding of nucleosynthesis in giant stars.
• The determined ^{12}C/^{13}C ratio has significant implications for stellar models and the interpretation of stellar observations.