[GSoC] Add programmatic parser for Seaton opacity tables

[Manivenkat3612]

📝 Description

Type: 🚀 feature

This pull request implements the GSOC 2026 First Objective for the
project idea (Continuum Opacity Source Reader): a programmatic reader for the Seaton continuum opacity data tables from the CDS archive (VI/80).

What was implemented:

• get_seaton_opacity_df(file_name): A simple, reusable function that downloads and parses Seaton opacity data files (gzip-compressed) from the CDS FTP archive
• Parses the Seaton format where block headers define temperature: logT = INDEX/40
• Returns a clean pandas DataFrame with columns: logT, logNe, kappa_planck, kappa_rosseland
• Handles network requests with proper error handling

Key features:

• Downloads directly from CDS archive: https://cdsarc.cds.unistra.fr/ftp/VI/80/{file_name}
• Works with gzip-compressed files (e.g., s92.201.gz)
• Returns data in a standardized format ready for use in TARDIS atomic data workflows
• Minimal, focused implementation suitable for extension to similar Seaton files

Files added:

• carsus/io/literature/seaton.py - Reader function implementation
• carsus/io/literature/__init__.py - Module initialization and exports
• carsus/io/literature/tests/test_seaton.py - Test suite

📌 Resources

• CDS Archive VI/80 (Seaton opacity tables): https://cdsarc.cds.unistra.fr/viz-bin/Cat?cat=VI%2f80&target=brief&msg=redirected%20by%20VizieR
• Seaton et al. 1992 reference: Continuum opacity data for astrophysical models
• Related issue: GSOC 2026 First Objective - Literature Data Tables Reader

🚦 Testing

All changes have been tested using pytest.

• Testing pipeline (pytest carsus/io/literature/tests/test_seaton.py -v returns 1 passed)
• Other method
• My changes can't be tested

Test coverage:

• Validates DataFrame structure and columns
• Verifies data types and column names
• Confirms opacity values are positive
• Uses mock.patch to avoid external network dependencies during testing

☑️ Checklist

• I requested two reviewers for this pull request
• I updated the documentation according to my changes
• I built the documentation by applying the build_docs label

AI Usage Statement
Tool used: GitHub Copilot
How used: Refining code changes and improving PR wording.

Tool used: Gemini
How used: to research on (Opacities from the Opacity Project : VI/80) archive and to know about its formatting.

Confirmation: I confirm that I have read the PR Checklist and the AI and LLM Usage Policy. I fully understand all AI-assisted changes and can explain every modification in this PR.

[github-actions]

*beep* *bop*
Hi human,
I ran ruff on the latest commit (a3195eb).
Here are the outputs produced.
Results can also be downloaded as artifacts here.
Summarised output:

Details

1	F401	[*] unused-import
Found 1 error.
[*] 1 fixable with the `--fix` option.

Complete output(might be large):

Details

carsus/io/literature/tests/test_seaton.py:10:8: F401 [*] `pytest` imported but unused
Found 1 error.
[*] 1 fixable with the `--fix` option.

[Manivenkat3612]

@andrewfullard @jvshields , please take a look when you have a moment. Thanks!

[Manivenkat3612]

Hello @andrewfullard, @afloers, and @jvshields,

I would greatly appreciate your review of my implementation for the GSoC 2026 First Objective under the Continuum Opacity Source Reader project idea.

Your feedback would be very valuable to ensure I am aligned with the project’s expectations and coding standards.

[andrewfullard]

This seems sensible. Does the tardisbase environment have gzip already, or would that need to be installed?

[Manivenkat3612]

@andrewfullard Thanks for checking! It uses Python’s built-in gzip module (import gzip), so no extra package installation is needed in [tardisbase]. I also verified this in tardis-dev environment with: python3 -c 'import gzip; print("Gzip is ready!")'
which runs successfully.