Volume 629, September 2019
|Number of page(s)||10|
|Section||Stellar structure and evolution|
|Published online||16 September 2019|
The s process in rotating low-mass AGB stars
Nucleosynthesis calculations in models matching asteroseismic constraints⋆
Konkoly Observatory, MTA CSFK, Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary
2 Astrophysics Group, Lennard-Jones Laboratories, Keele University, Keele ST5 5BG, UK
3 Kavli Institute for the Physics and Mathematics of the Universe (WPI), University of Tokyo, 5-1-5 Kashiwanoha, 277-8583 Kashiwa, Japan
4 Monash Centre for Astrophysics (MoCA), School of Physics and Astronomy, Monash University, Victoria 3800, Australia
5 School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, UK
6 Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P5C2, Canada
7 JINA-CEE, Michigan State University, East Lansing, MI 48823, USA
8 E. A. Milne Centre for Astrophysics, Department of Physics and Mathematics, University of Hull, Hull HU6 7RX, UK
9 Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
Accepted: 20 August 2019
Aims. We investigate the s-process during the AGB phase of stellar models whose cores are enforced to rotate at rates consistent with asteroseismology observations of their progenitors and successors.
Methods. We calculated new 2 M⊙, Z = 0.01 models, rotating at 0, 125, and 250 km s−1 at the start of main sequence. An artificial, additional viscosity was added to enhance the transport of angular momentum in order to reduce the core rotation rates to be in agreement with asteroseismology observations. We compared rotation rates of our models with observed rotation rates during the MS up to the end of core He burning, and the white dwarf phase.
Results. We present nucleosynthesis calculations for these rotating AGB models that were enforced to match the asteroseismic constraints on rotation rates of MS, RGB, He-burning, and WD stars. In particular, we calculated one model that matches the upper limit of observed rotation rates of core He-burning stars and we also included a model that rotates one order of magnitude faster than the upper limit of the observations. The s-process production in both of these models is comparable to that of non-rotating models.
Conclusions. Slowing down the core rotation rate in stars to match the above mentioned asteroseismic constraints reduces the rotationally induced mixing processes to the point that they have no effect on the s-process nucleosynthesis. This result is independent of the initial rotation rate of the stellar evolution model. However, there are uncertainties remaining in the treatment of rotation in stellar evolution, which need to be reduced in order to confirm our conclusions, including the physical nature of our approach to reduce the core rotation rates of our models, and magnetic processes.
Key words: stars: rotation / stars: evolution / stars: AGB and post-AGB
This paper is dedicated to the celebration of the 100th birthday of Prof. Dr. Margaret Burbidge, in recognition of the outstanding contributions she has made to nuclear astrophysics.
NuGrid Collaboration, http://www.NuGridstars.org
© ESO 2019
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