Thermonuclear Reaction Rates for the $^2^4$Mg(p,\gamma)$^2^5$Al Reaction
Abstract
There is substantial evidence that most of the material in the envelopes of some globular cluster giants is mixed so deeply into the interior that the abundances of many of the light elements, including magnesium and aluminum, are reshuffled by proton capture before the material is returned to the envelope above. In order to understand these abundance changes we must know all of the appropriate proton capture rates. We have recalculated the thermonuclear reaction rates, N_A <sigma v>_T, for the ^2^4Mg(p gamma) ^2^5Al reaction using the canonical 57 temperatures from Caughlan and Fowler (1988) in the range from T9 = 0.004 to T9 = 10.0, where T9 is the temperature in units of 10^9 Kelvins. We have done these calculations using a range of values for the unmeasured total width, Gamma_1, of the lowest resonance, (1/2)^+, in the p + ^2^4Mg system. This resonance is located at 2486 keV excitation in ^2^5Al and there is a large uncertainty in the value of Gamma_1. The rates currently used are based upon a value of Gamma_1 = 75 meV, whereas the most recently accepted experimental value is an upper limit for Gamma_1 of 32 eV. For values of T9 < 0.07 the rates are quite sensitive to this uncertain width. We discuss the consequences of this uncertainty and the need for experimental data to determine Gamma_1. We have also found that for T9 > 5.0, the recalculated rates are somewhat higher than those in Caughlan and Fowler (1988). We present our rates in tabular form.
- Publication:
-
Publications of the Astronomical Society of the Pacific
- Pub Date:
- March 1997
- DOI:
- 10.1086/133881
- Bibcode:
- 1997PASP..109..252Z
- Keywords:
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- GLOBULAR CLUSTERS: GENERAL;
- ATOMIC PROCESSES