On the Need for the Light Elements Primary Process (LEPP)

Journal
Date Issued
2015
Author(s)
•
Abia, C.
•
•
DOI
Description
We thank the referee for valuable comments and suggestions that improved the quality of this paper. This work was supported by Italian grants RBFR08549F-002 (FIRB 2008 program), PRIN-MIUR 2012 “Nucleosynthesis in AGB stars: An integrated approach” project (20128PCN59), and from Spanish grants AYA2008-04211-C02-02 and AYA-2011-22460.
Abstract
Extant chemical evolution models underestimate the galactic production of Sr, Y, and Zr as well as the solar system abundances of s-only isotopes with 90 \lt A \lt 130. To solve this problem, an additional (unknown) process has been invoked, the so-called light element primary process (LEPP). In this paper we investigate possible alternative solutions. Based on Full Network Stellar evolutionary calculations, we investigate the effects on the solar system s-only distribution induced by the inclusion of some commonly ignored physical processes (e.g., rotation) or by the variation of the treatment of convective overshoot, mass loss, and the efficiency of nuclear processes. Our main findings are (1) at the epoch of the formation of the solar system, our reference model produces supersolar abundances for the whole s-only distribution, even in the range 90 \lt A \lt 130, (2) within errors, the s-only distribution relative to 150Sm is flat, (3) the s-process contribution of the less massive AGB stars (M \lt 1.5 M ☉ ) as well as of the more massive ones (M \gt 4.0 M ☉ ) are negligible, (4) the inclusion of rotation implies a downward shift of the whole distribution with a higher efficiency for the heavy s-only isotopes, leading to a flatter s-only distribution, (5) different prescriptions on convection or mass loss produce nearly rigid shifts of the whole distribution. In summary, a variation of the standard paradigm of AGB nucleosynthesis would allow reconciliation of model predictions with solar system s-only abundances. Nonetheless, the LEPP cannot be definitely ruled out because of the uncertainties still affecting stellar and galactic chemical evolution models.
Volume
801
Issue
1
Start page
53
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...801...53C
Rights
open.access
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