Survey of the astrophysical conditions that produce light heavy elements in metal-poor stars

Thanassis Psaltis (@psaltistha)
TU Darmstadt, Institut für Kernphysik Theoriezentrum

26.10.2022
OMEG16

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

How I see nuclear astrophysics


 

 

 

 

 

 

 
HD 122563 (DSS2/ Aladin Sky Atlas)

What do the old stars reveal to us?

See also: C. Sneden, J. J. Cowan and R. Gallino, Annu. Rev. Astron. Astrophys. 46, 241 (2008)
Talks by M. Mumpower, T. Kajino & W. Aoki • ⚠️ Solar r-process = Solar total - Solar s-process - Solar p-process

How many "r-processes" contribute to the production of elements between Sr and Ag?

Nucleosynthesis
in neutrino-driven ejecta

Image Credit: NASA/CXC/DSS/Rutgers/K.Eriksen et al.

How I see nuclear astrophysics

$\nu p$-process and weak $r$-process

A. Psaltis et al., Phys. Rev. C 106, 045805 (2022)

$\nu p$-process and weak $r$-process

We need isotopic abundances!

Nuclear Data Needs


 

weak $r$-process

Mainly $(\alpha, xn)$ and $(n,\gamma)$ reaction rates for $T \approx 2-5$ GK.

R. Surman et al. AIP Advances 4 041008 (2014)
J. Bliss et al., Phys. Rev. C 101 055807 (2020)
A. Psaltis et al., Astrophys. J 935 27 (2022)

$\nu p$-process

3$\alpha$, $\mathrm{^{56}Ni(n,p)}$, $(p,\gamma), (n,p)$ rates and the $pp$-chain breakout reactions.

S. Wanajo, H.-T. Janka and S. Kubono Astrophys. J. 729 46 (2011) • N. Nishimura et al. MNRAS 489 1379 (2019)

These studies have motivated many nuclear astrophysics experiments!
More in the next slides!

Take-home message #1


Elements between Sr and Ag can be produced in $\nu$-driven ejecta

Which are the most favourable astrophysical conditions?

How I see nuclear astrophysics

Methods

J. Bliss et al., Astrophys. J. 855, 135 (2018)
M. Jacobi, M.Sc. Thesis, TU Darmstadt (2018)

We used a large set of neutron-rich and proton-rich astrophysical conditions.
$0.40 \leq Y_e \leq 0.63$

Methods

We created linear combinations from the different conditions to compare with observations.

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

Total number of unique combinations: $C_r = N! / r! (N - r)!$
for example 2 conditions out of 36 yields 630 unique combinations

Methods

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

Least-squares problem solved using $\texttt{sklearn}$

Results: 2 neutron-rich conditions for
HD 122563

Results: 2 neutron-rich conditions for
HD 122563

2 neutron-rich conditions for the whole sample

Only combinations with the lowest $\chi^2$ are shown.

Proton-rich conditions

We find a very narrow window of number ratio $\Delta_n$ that better reproduces the abundance pattern ($\Delta_n \approx 16\pm 2$).

Which are the most suitable conditions?

Combination of proton-rich and neutron-rich conditions provide the best fit

Results for HD122563

Take-home message #2


We used a large library of astrophysical conditions to find combinations that match the observed abundances in metal-poor stars.

How I see nuclear astrophysics

$\nu$-driven explosions in the lab 💥

Measurement of the $\boldsymbol{\mathrm{^{7}Be}(\alpha,\gamma)\mathrm{^{11}C}}$ reaction

$\mathrm{^{7}Be}(\alpha,\gamma)\mathrm{^{11}C}$ at TRIUMF with DRAGON

A. Psaltis et al., Phys. Rev. Lett. 129, 162701 (2022)
A. Psaltis et al., Phys. Rev. C 106, 045805 (2022)

  • Was proposed to affect $\Delta_n$ in the $\nu p$-process ($pp-$chain breakout).
    • S. Wanajo, H.-T. Janka and S. Kubono Astrophys. J. 729, 46 (2011)
  • Two newly measured resonance strengths.
  • Decreased the reaction rate uncertainty to $\approx 10\%$.
  • The new constrained rate does not affect the $\nu p$-process.

First measurement of the $\boldsymbol{\mathrm{^{93}Sr}(\alpha,xn)\mathrm{^{96-x}Zr}}$ reaction

$\mathrm{^{93}Sr}(\alpha,xn)\mathrm{^{96}Zr}$ at Argonne with MUSIC

M. L. Avila et al., Nucl. Instrum. Methods Phys. Res A 859, 63 (2017)

  • It affects the production of Rb, Mo, Ru and Pd in the weak $r$-process.
    A. Psaltis et al., Astrophys. J 935 27 (2022)
  • Re-accelerated $\mathrm{^{93}Sr}$ beam from nuCARIBU.
  • Close to 100% efficiency.
  • Measure a large range of excitation functions of angle and energy integrated cross sections using single beam energy.
Proposal #1923, PI: Psaltis, co-PI: Ong

Acknowledgements

Almudena Arcones   Camilla Juul Hansen   Max Jacobi   Fernando Montes   Hendrik Schatz

Summary and future plans

  1. Elements between Sr and Ag can be produced
    in neutrino-driven ejecta (weak $r$-process or $\nu p$-process).

  2. We used a large library of astrophysical conditions to find combinations that match the observed abundances in metal-poor stars.

  3. Future nuclear physics experiments using rare isotope beams (RIBs)
    will shed light on the production of elements between Sr and Ag.