twirl

twirl (formerly SpyDust) is a Python package for modeling spinning dust radiation in astrophysical environments. Building upon the IDL SPDUST, it offers enhanced capabilities and corrections for astrophysical research.

For details on the underlying model, see SpyDust: an improved and extended implementation for modeling spinning dust radiation.

Features

• Grain-shape modeling, rotational dynamics, and directional radiation.
• Updated treatments of electric-dipole radiation back-reaction and plasma drag.
• Parallel execution using MPI.
• The retained legacy model at twirl.legacy.spdust_as_is.

Package layout

• twirl.physics: grain properties and physical processes.
• twirl.model: spinning-dust calculations and SED generation.
• twirl.analysis: SED fitting, moment expansion, and Stokes analysis.
• twirl.core: shared numerical and parallel-computing utilities.
• twirl.legacy.spdust_as_is: the legacy implementation retained for comparison.
• twirl.data: bundled tables, grouped by physical process.

Requirements

The project requires Python 3.12 or newer. Its declared dependencies are NumPy, SciPy, and Matplotlib. MPI support uses mpi4py; free-free emission also uses Pandas.

Installation

Install the project with pip:

pip install .

Or clone this repository and install its dependencies in your environment.

Usage

The following example computes a spectrum for a sample CNM environment:

from twirl.model.spinning_dust import SpyDust

cnm_params = {
    "nh": 30,
    "T": 100.0,
    "Chi": 1,
    "xh": 1.2e-3,
    "xC": 3e-4,
    "y": 0,
    "gamma": 0,
    "dipole": 9.3,
    "line": 7,
}

spectrum = SpyDust(
    cnm_params,
    min_freq=1,
    max_freq=400,
    n_freq=200,
    single_beta=True,
)

The individual physics, model, and analysis modules can also be imported directly from their corresponding packages.

Bundled data

Reference tables and generated lookup tables are stored under src/twirl/data/, separated into charge/, collisions/, free_free/, grains/, infrared/, and plasma/.

Resources

• SpyDust paper
• SPDUST documentation
• SpyDust GitHub collaboration