Current hot questions on the s process in AGB stars

6th Nuclear Physics in Astrophysics

物理学;天文学

Lugaro, M.^1,2 ; Campbell, S.W.^2,3 ; D'Orazi, V.^2,4,5 ; Karakas, A.I.^6 ; Garcia-Hernandez, D.A.^7 ; Stancliffe, R.J.^8 ; Tagliente, G.^9 ; Iliadis, C.^10 ; Rauscher, T.^11,12

Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Konkoly Thege Miklós út 15-17, Budapest

H-1121, Hungary^1

Monash Centre for Astrophysics (MoCA), School of Mathematical Sciences, Monash University, Clayton

VIC

3800, Australia^2

Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, Garching bei München

D-85741, Germany^3

INAF, Osservatorio Astronomico di Padova, vicolo dell'Osservatorio 5, Padova

I-35122, Italy^4

Department of Physics and Astronomy, Macquarie University, Balaclava Rd, North Ryde

NSW

2109, Australia^5

Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, Weston Creek

ACT

2611, Australia^6

Instituto de Astrofisica de Canarias, C/ Via Lactea s/n, La Laguna (Tenerife)

38200, Spain^7

Argelander-Institut für Astronomie, Auf dem Hugel 71, Bonn

D-53121, Germany^8

Istituto Nazionale di Fisica Nucleare (INFN), Bari, Italy

(10) Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill

NC

27695-8202, United States

(11) Centre for Astrophysics Research, School of Physics, Astronomy, and Mathematics, University of Hertfordshire, Hatfield

AL10 9AB, United Kingdom

(12) Department of Physics, University of Basel, Basel

4056, Switzerland^9

关键词: Asteroseismology;    Asymptotic giant branch stars;    Effects of rotation;    Globular clusters;    Metal-poor star;    Neutron capture cross section;    Rotational velocity;    Second generation;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/665/1/012021/pdf
DOI  :  10.1088/1742-6596/665/1/012021

学科分类：天文学(综合)

来源: IOP

【 摘 要 】

Asymptotic giant branch (AGB) stars are a main site of production of nuclei heavier than iron via the s process. In massive (>4 Mo) AGB stars the operation of the22Ne neutron source appears to be confirmed by observations of high Rb enhancements, while the lack of Tc in these stars rules out13C as a main source of neutrons. The problem is that the Rb enhancements are not accompanied by Zr enhancements, as expected by s-process models. This discrepancy may be solved via a better understanding of the complex atmospheres of AGB stars. Second- generation stars in globular clusters (GCs), on the other hand, do not show enhancements in any s-process elements, not even Rb. If massive AGB stars are responsible for the composition of these GC stars, they may have evolved differently in GCs than in the field. In AGB stars of lower masses,13C is the main source of neutrons and we can potentially constrain the effects of rotation and proton-ingestion episodes using the observed composition of post-AGB stars and of stardust SiC grains. Furthermore, independent asteroseismology observations of the rotational velocities of the cores of red giants and of white dwarves will play a fundamental role in helping us to better constrain the effect of rotation. Observations of carbon-enhanced metal-poor stars enriched in both Ba and Eu may require a neutron flux in-between the s and the r process, while the puzzling increase of Ba as function of the age in open clusters, not accompanied by increase in any other element heavier than iron, require further observational efforts. Finally, stardust SiC provides us high-precision constraints to test nuclear inputs such as neutron-capture cross sections of stable and unstable isotopes and the impact of excited nuclear states in stellar environments.