Emily M. Boudreaux -- sdOB12 Presentation

Towards 3D Stellar Structure and Evolution Models

of Stars; or,

New Dimensions in Stellar Structure and Evolution

Emily M. Boudreaux & 4D-STAR Collaboration

The 12th International Meeting on Hot Subdwarfs & Related Objects
4D-STAR is funded by European Research Council (ERC) under the Horizon Europe programme
(Synergy Grant agreement No. 101071505: 4D-STAR)
Work for this project is funded by the European Union.
Views and opinions expressed are however those of the author(s) only and do not necessarily
reflect those of the European Union or the European Research Council

Overview

Current state of stellar modeling
4D-STAR project
Audience feedback

What assumptions do current generation stellar structure and evolution models make which prevent you from answering open questions about hot subdwarfs?

Current state of stellar modeling

Name	Equation
Mass Continuity	\[\frac{dM_{r}}{dr} = 4\pi r^{2}\rho\]
Hydrostatic Equilibrium	\[\frac{dP}{dr} = -\rho g\]
Energy Continuity	\[\frac{dL_{r}}{dr} = 4\pi r^{2}\rho\varepsilon\]
Energy Transport	\[\frac{dT}{dr} = \frac{3}{16\pi a}\frac{\kappa}{c}\frac{L_{r}}{r^{2}}\]

Equations of stellar structure for a star in hydrostatic equilibrium
Opacities, energy generation, equation of states...

Current state of stellar modeling

Stellar modeling has been incredibly successful.
However, models* are limited to a single dimension

* ESTER is an example of a current 2D code (radius and co-latiude); however, almost all models are 1D and almost all work has been done with 1D models.

Radial Models

Simple discritization
Lagrangian formulation ($r\rightarrow M_{r}$)
Well understood

Radial Models

Easy(ish) To Implement*

Radial Models

MESA
STAREVOL
DSEP
Geneva
CESTAM
PARSEC

Radial Models

Limitations

Rotation
Magnetic fields
Convection

4D-STAR

Theoretical advances in stellar modeling
Extension of ESTER into 3D
New SSE codebase (SERiF)

4D-STAR

Theoretical advances in stellar modeling
Extension of ESTER into 3D
New SSE codebase (SERiF)

SERiF

Stellar Evolution and Rotation in Four dimensions

SERiF

Design Goals

High performance
Scalable
Easy to use for non-computationalists

SERiF

Current State

Microphysics
Infrastructure

Discritization
3D polytrope

Started Work February 2025

What assumptions do current generation stellar structure and evolution models make which prevent you from answering open questions about hot subdwarfs?

Feedback Form

Appendicies

Module Name	Status	Description	Current Assignee
config	Complete	This module handles all configuration files. It is responsible for parsing the YAML files	N/A
composition	MVS	This module tracks a general composition object, allowing for arbitrary species tracking and mixing	N/A
const	Complete	This module contains all physical constants from the CODATA 2022 data release as well as some astronomical constants from IAU 2015	N/A
eos	MVS	This module implements both a general interface for equation of states as well as specific equations of states. Currently the helmholtz equation of state is the only one implemented.	N/A
meshIO	Complete	This module handles all I/O for the mesh. It is responsible for reading and writing the mesh to disk. This is used to interface with the resource manager which allows for easier configuration on the user end.	N/A
misc	WIP	This is a catch-all module for miscellaneous things. Generally we should avoid putting stuff in here but sometimes (such as for debugging macros) it is useful.	N/A
network	MVS	This module handles the nuclear network and burning calculations. Currently only Frank Timmes’ Approx8 network is implemented. It also implements a general interface for nuclear networks so that other networks can be added.	N/A
opac	WIP	This module handles opacity calculation / interpolation.	A.D.
poly	WIP	This module computes polytropic models which are used as initial states for solving the structure equations.	E.B.
probe	Complete	This module implements the `probe` namespace which is used to hold functions for probing the current state of the code (stuff like `whydt` in MESA).	N/A
python	WIP	This module contains all code relevant to the Python interface. All interface code is then organized in submodules within this (such as python/config).	E.B.
resource	Complete	This module handles loading resources from disk in a clean fashion. The key justification here is to avoid users having to explicitly set environmental variables but also to make loading of resources anywhere in the code easier to handle.	N/A
types	Complete	This module implements custom datatypes for SERiF which do not cleanly fall into any other module (i.e. `__datatypes` should not go in `misc`).	N/A

opat-core