Modelling motions of binary star system

[henrysky]

I have added support to model motions of binary star system as seen on the sky and their 6D astrometry (RA, DEC, PMRA, PMDEC, PLX, RV).

So far I have only manually added Alpha Centauri A/B, Sirius A/B and 61 Cygni A/B. In order to model a binary system we need:

• $e$ - Eccentricity
• $a$ - Semi-major axis
• $\Omega$ - Longitude of the ascending node
• $\omega$ - Argument of periapsis
• $i$ - Inclination
• $P$ - Period
• $T$ - Periastron epoch
• Barycenter RA/DEC, PMRA/PMDEC, PLX, RV
• Barycenter data epoch
• HIP or Gaia ID of primary and secondary stars
• Primary and secondary star masses

At least for Alpha Centauri A/B and Sirius A/B, the motion on the sky as well as radial velocity matched really well to past observations (https://iopscience.iop.org/article/10.3847/1538-3881/abfaff/pdf, https://arxiv.org/pdf/1703.10625).

If there are other binary systems you want to model, I can try to find all the required orbital parameters and add them manually before we figure it out a way to model a large amount of binary stars if possible.

Fixes #353

Screenshots (if appropriate):

An example of Sirius A/B with parallax disabled to avoid confusion:

Untitled.mov

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• This change requires a documentation update
• Housekeeping

How Has This Been Tested?

Test Configuration:

• Operating system: MacOS 15.2
• Graphics Card: Apple M3

Checklist:

• My code follows the code style of this project.
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (header file)
• I have updated the respective chapter in the Stellarium User Guide
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[github-actions]

Great PR! Please pay attention to the following items before merging:

Files matching src/**/*.cpp:

• Are possibly unused includes removed?

This is an automatically generated QA checklist based on modified files.

[gzotti]

Great stuff! But probably #4076 should be 100% fixed before adding this.

γ Vir is another nice double. For a catalog, this looks promising: http://www.astro.gsu.edu/wds/orb6.html

[alex-w]

Great stuff! But probably #4076 should be 100% fixed before adding this.

γ Vir is another nice double. For a catalog, this looks promising: http://www.astro.gsu.edu/wds/orb6.html

Damn, I don't have access to WDS catalog anymore O_o

Yes, adding full support WDS catalog is possible now and probably it should be adding via 2 files - one file for known orbital elements of binaries (multiple systems) and one file for cross identification and informational data (likewise a currect HIP subset of WDS).

[Atque]

Great work! However, proper motions seem odd now (possibly not calculated for the barycenter of the star system). Compare 61 Cyg in 21,000 AD between this branch and master:

henrysky:binary

Stellarium:master

[henrysky]

Great work! However, proper motions seem odd now (possibly not calculated for the barycenter of the star system). Compare 61 Cyg in 21,000 AD between this branch and master:

Thanks for noticing the inconsistency! Motion of the barycenter is taken into account already but a problem on normalized vector caused the error in position. Now I have fixed the issue and added γ Vir.

[Atque]

I see some discrepancies with 61 Cyg. Compare the HiPS layer, with the plate in question probably taken around 1990-01-01 (based on the position of 61 Cyg in master):

henrysky-binary

stellarium-master

Maybe weird parameters for the stellar orbits?