Forum Springer Astron. Astrophys.
Forum Whats New Search Orders

Astron. Astrophys. 358, L67-L70 (2000)

Previous Section Next Section Title Page Table of Contents

3. Results and discussion

The various seed abundances of Fig. 2 are used to compute the production of the p-nuclides in the PPLs of the [FORMULA] 25 [FORMULA] star considered here. As in RAHPN, the abundance of a p-nuclide i is characterized by its mean overproduction factor [FORMULA], where [FORMULA] is its solar mass fraction (Anders & Grevesse 1989), and


where [FORMULA] is the mass fraction of isotope i at the mass coordinate [FORMULA], [FORMULA] is the total mass of the PPLs, the sum running over all the PPLs ([FORMULA] corresponds to the bottom layer). An overproduction factor averaged over all 35 p-nuclei is calculated as [FORMULA], and is a measure of the global p-nuclide enrichment in the PPLs. So, if the computed p-nuclei abundance distribution were exactly solar, the normalized mean overproduction factor [FORMULA] would be equal to unity for all i.

Fig. 3 shows the normalised p-nuclide overproduction factors derived from the seed abundance distributions calculated with the [FORMULA] rates R1, R3 and R5. Changes in the shape of the p-nuclide abundance distribution are clearly noticeable, at least for [FORMULA]. The use of R1 leads to a more or less substantial underproduction of not only [FORMULA], [FORMULA], [FORMULA] and [FORMULA], a `classical' result in p-process studies (see RAHPN), but also of [FORMULA] and [FORMULA], which was not predicted in previous calculations. This new feature directly relates to the larger abundances around [FORMULA] used by RAHPN (dashed curve in Fig. 2), in contrast to the much flatter seed distribution obtained with R1. This Kr-Sr-Mo-Ru trough is gradually reduced, and in fact essentially disappears, for [FORMULA] rates of the order or in excess of R3. This situation is most clearly illustrated by Fig. 4. In these very same conditions, [FORMULA] for [FORMULA] and [FORMULA] comes much closer to unity as well. It has to be noticed that this situation does not result from a stronger production of these two nuclides by the p-process, but instead from their increased initial abundances associated with a more efficient s-process when going from R1 to R5. In contrast, the [FORMULA] pattern does not depend on the adopted [FORMULA] rate for [FORMULA]. This is expected from a mere inspection of the s-nuclide seed distributions displayed in Fig. 2. In particular, [FORMULA] and [FORMULA] remain underproduced. This cannot be considered as an embarassment as these two nuclides can emerge from the s-process in low- or intermediate-mass stars.

[FIGURE] Fig. 3. Values of [FORMULA] and of [FORMULA] derived from the seed abundances calculated with the [FORMULA] rate R1 (upper panel), R3 (middle panel) and R5 (lower panel). Lines connect different isotopes of the same element. The dotted horizontal lines delineate the [FORMULA] range

[FIGURE] Fig. 4. Values of the normalized overproduction factors of the Kr, Sr, Mo and Ru p-isotopes as a function of the [FORMULA] rate

In addition, the overall efficiency of the p-nuclide production substantially increases with increasing [FORMULA] burning rates. More specifically, [FORMULA] is multiplied by a factor of about 15 when going from R1 to R5. This could largely ease, and even solve, the problem of the relative underproduction of the p-nuclides with respect to oxygen identified by RAHPN. For their considered 25 [FORMULA] model star calculated with the [FORMULA] rate from Caughlan et al. (1985), they obtain [FORMULA] and report a value of 4.4 for the ratio of the oxygen to p-process yields. This value would come close to unity for [FORMULA] rates in the vicinity of R3-R4, as the p-nuclides would be about 3 to 6 times more produced than in RAHPN.

Previous Section Next Section Title Page Table of Contents

© European Southern Observatory (ESO) 2000

Online publication: June 20, 2000