Neutrino-Driven Outflows and
the Origin of Light Heavy Elements

 

Thanassis Psaltis
Triangle Universities Nuclear Laboratory & North Carolina State University
 

September 22, 2023
Nuclei in the Cosmos (NIC-XVII)


 

Image Credit: NASA/CXC/SAO


 

 

 

 

 

 

 

HD 122563 (DSS2/ Aladin Sky Atlas)

What do the ancient stars show us?


See also: C. Sneden, J. J. Cowan and R. Gallino, Annu. Rev. Astron. Astrophys. 46, 241 (2008)
See talks by G. Martínez-Pinedo, G. McLaughlin and S. Honda • ‼️ r-process = total solar - s-process - γ-process

How many processes contribute to the production of elements between
strontium and silver?

What is the impact of the $\mathbf{(\alpha,xn)}$ reactions in the weak $r$-process?

How much do we know the $(\alpha,xn)$ reaction rates?

The $(\alpha,xn)$ reaction rates are sensitive to the $\alpha$-nucleus potential
and their uncertainties can be up to two orders of magnitude.


 
J. Pereira and F. Montes, Phys. Rev. C 93, 034611 (2016) • P. Mohr, Phys. Rev. C 94, 35801 (2016)

Framework of the sensitivity study

J. Bliss et al., Astrophys. J 855, 135 (2018) • P. Mohr et al., At. Data Nucl. Data Tables 132, 101453 (2021)

The impact of updated $(\alpha,n)$ reaction rates to elemental abundances

Same model, but different $(\alpha, xn)$ reaction rates!

A. Psaltis et al., Astrophys. J 935, 27 (2022)

Which are the most important
$\mathbf{(\alpha,xn)}$ reactions
for the weak $r$-process?

The most important $(\alpha,n)$ reactions for the weak $r$-process

N=50 shell closure is a bottleneck for T= 4-5 GK due to the $(n,\gamma) \leftrightarrow (\gamma,n)$ equilibrium

Can we study the most important
$\mathbf{(\alpha,xn)}$ reactions in the lab?

Most of the relevant beams are accessible!



Expected FRIB ultimate beam rates

First measurement of the $\boldsymbol{\mathrm{^{93}Sr}(\alpha,xn)}$ reaction at Argonne with MUSIC



Proposal #1923, PI: A. Psaltis, co-PI: W.J. Ong

If you are interested in participating, contact me! 😁

Which are the most favourable
conditions to produce the light heavy elements in neutrino-driven outflows?

We formed linear combinations using trajectories of various astrophysical conditions to compare with observations of metal-poor stars.

The case of HD122563

Results for HD122563 using two trajectories

Results using two trajectories for our star sample

Colored lines have $\chi^2_n<1$

Proton-rich conditions are more favourable than neutron-rich

High entropy and short expansion timescale is preferred

Can isotopic abundances from meteorites reveal neutrino-driven nucleosynthesis signatures?

Secrets in the stardust?

A. Psaltis, W.J. Ong et al. (in preparation)

What is on the horizon?


New experimental measurements of the key $(\alpha, xn)$ reactions and multi-messenger observations will help us constrain the contribution of neutrino-driven outflows to the production elements between strontium and silver.

Acknowledgements


Almudena Arcones   Melina Avila   Camilla Juul Hansen  

Peter Mohr   Fernando Montes   Wei Jia Ong Hendrik Schatz


Summary

  1. The weak $r$-process in neutrino-driven outflows can contribute to the production of elements between strontium and silver that are observed in Galactic metal-poor stars.

  2. We explored the impact of $(\alpha,xn)$ reactions to the weak $r$-process and identified the most important of them to motivate future experiments in stable and radioactive ion beam facilities.

  3. We investigated which are the most common astrophysical conditions of the neutrino-driven outflows that fit the observational patterns of metal-poor stars.

  4. Experiments in the current and next-generation RIB facilities, multimessenger observations and theoretical modeling will enhance our understanding of the origin of the light heavy elements.

Thank you!

Slides available at http://psaltisa.github.io/talks

Extra slides

Combine observations, astrophysical modeling and nuclear physics uncertainties

$\mathrm{^{93}Sr}(\alpha,xn)$ at Argonne with MUSIC

M. L. Avila et al., NIM A 859, 63 (2017)

  • Re-accelerated $\mathrm{^{93}Sr}$ beam from $\nu$CARIBU.

  • MUSIC has close to 100% efficiency due to its segmented anode structure.

  • Use a single beam energy to measure a large range of excitation functions of angle integrated cross sections.

Methods

We formed linear combinations using various astrophysical conditions ($Y_e, s, \tau$)
to compare with observations of metal-poor stars.

\[ P = \sum_{i=1}^N w_i Y_i \]

where $w_i>0$ is a multiplication factor and $Y_i$ is the abundance pattern of the $i^{th}$ trajectory.

Total number of unique combinations: $C_r = N! / r! (N - r)!$
for example 2 trajectories out of 46 yields 1035 unique combinations

Methods

\[ \mathrm{minimize}~ ||A w - O||^2 \] where $O$ is the observational pattern and \[ A = \begin{bmatrix} Y_{11} & \cdots & Y_{1k}\\ \vdots & \ddots & \vdots \\ Y_{N1} & \cdots & Y_{Nk} \end{bmatrix} , w = \begin{bmatrix} w_1 \\ \vdots \\ w_k \end{bmatrix} \]

Goal: solve the least-squares problem using $\texttt{sklearn}$