Signatures of i-process nucleosynthesis

Womack, Kate Alice

September 2021

Thesis or dissertation

© 2021 Kate Alice Womack. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

Neutron capture nucleosynthesis is responsible for the production of heavy elements. Three neutron capture processes are currently known, each occurring at their own characteristic neutron density and operating in different ways. The slow neutron capture process operates at neutron densities of n ≈ 10⁷ 10¹⁰ cm⁻³, the rapid at neutron densities of = & 10²⁰ cm⁻³ and the intermediate at neutron densities of n ≥ 10¹² - 10¹⁵ cm⁻³. The intermediate neutron capture process (i process) is the focus of this work.

The i process is now widely accepted to be the process that produces the unusual abundances of carbon-enhanced metal-poor (CEMP) -r/s stars. A challenge in recent years has been constraining a site for the i process. Given the large range in potential neutron densities, many astrophysical sites have the potential to host i-process conditions. Two of the most promising sites for the i process are: the intershell regions of low-mass, low-metallicity asymptotic giant branch stars and on rapidly accreting white dwarfs. This work provides abundance analyses of models of the two different scenarios.

I first look at comparing both models to a sample of CEMP-r/s stars using j2 fitting. From this I was able to determine the abundance signatures that can make one model fit an i-process pattern more closely than another. I used this fitting technique to fit i-process models to other objects in the literature, including to phosphorus-rich stars. j2 fitting is also used to show that stellar models can be used to make predictions of the Th and U we would expect to see from the i process.

I move on to investigating elemental abundance ratios that may help us distinguish an s process from an i process by using three-element plots. From this, I came up with four abundance ratios that have the potential to be useful as an i-process signature.

Department of Physics, The University of Hull
Stancliffe, Richard; Pignatari, Marco
Qualification level
Qualification name
14 MB
QR Code