EXPLOSIVE HYDROGEN BURNING OF P-31

Proton threshold states in S-32 have been studied via the reactions P- 31(p, gamma)S-32, P-31(p, alpha)Si-28 and Si-28(alpha, gamma)S-32 to i nvestigate their influence on a possible SiP cycle in explosive hydrog en burning. One new resonance at E(p) = 200 +/- 2 keV has been found i n the (p, gamma) reaction channel, but only upper limits could be dedu ced for the corresponding (p, alpha) and (alpha, gamma) resonance stre ngths. The stellar reaction rates for P-31(p, gamma)S-32 are now exper imentally determined for stellar temperatures T9 greater-than-or-equal -to 0.05, whereas the stellar rates for P-31(p, alpha )Si-28 still car ry large uncertainties for T9 < 0.4. The results of the present work s uggest only weak cycling in the Si P mass range at all stellar tempera tures of interest.