W Ursae Majoris binaries for Celestia

This repository contains scripts to generate W Ursae Majoris binaries for Celestia, based on the WUMaCat database. Each binary is represented as a single star in Celestia, with a custom mesh giving it the shape of the common envelope.

Spectral types, apparent magnitudes and cross-matching of identifiers to the Hipparcos, Tycho and Gaia DR2 catalogues are obtained from SIMBAD. Where V-magnitudes are not available, this is estimated using the relationships given in Evans et al. (2018). Distances for stars not included in Celestia's stars.dat file are taken from the Gaia DR2 geometric distance catalogue (Bailer-Jones et al., 2018).

Pre-built releases for given versions of the CelestiaContent repository are available. The below instructions are provided for re-generating the files in case of updates to Celestia.

Prerequisites

• Celestia
• Python 3.8 or higher
• Internet connection

How to use

1. Clone or download this repository.

2. Open a command window in the repository directory.

3. Set up a Python 3 virtual environment

   python3 -m venv myenv

4. Switch to the virtual environment.

   source myenv/bin/activate (Linux) .\myenv\Scripts\Activate.ps1 (Windows Powershell)

5. Install the requirements.

   python -m pip install -r requirements.txt

6. Run the script, supplying the path to the Celestia directory (this is used for star names and positions).

   python wuma -c (path to Celestia)

7. The output is generated in the archive wuma.zip.

Generating custom contact binary meshes

Custom contact binary meshes can be generated using the classes in the wuma_model.py. For example:

from celestia_wuma.model import make_geometry, write_cmod

q = 0.3  # mass ratio M2/M1, in the range (0,1)
f = 0.6  # fillout factor, in the range [0,1]

geometry = make_geometry(q, f)
print(f'Radius factor {g.radius}')

with open('output.cmod', 'wb') as f:
    write_cmod(f, geometry)

The "radius factor" is a value which should be multiplied by the binary's semimajor axis and used as the Radius parameter in the .stc file.

In order to produce an orientation with a given inclination, use the convert_orientation function in wuma_frame.py:

from celestia_wuma.frame import convert_orientation

ra = 123.45  # in degrees
dec = -67.8  # in degrees
inc = 90.12  # in degrees

inc_ecl, node_ecl = convert_orientation(ra, dec, inc)

The values in inc_ecl and node_ecl can be used as the Inclination and AscendingNode parameters in the UniformRotation block in the .stc file.

References

• Astropy Collaboration et al. (2013), A&A 558, id.A33 "Astropy: A community Python package for astronomy"
• Bailer-Jones et al. (2018), AJ 156(2), id.58 "Estimating distances from parallaxes. IV. Distances to 1.33 billion stars in Gaia data release 2"
• Evans et al. (2018), A&A 616, id. A4 "Gaia Data Release 2: Photometric content and validation"
• Gaia Collaboration et al. (2016), A&A 595, id.A1, "The Gaia mission"
• Gaia Collaboration et al. (2018), A&A 616, id.A1, "Gaia Data Release 2. Summary of the contents and survey properties"
• Harris et al. (2020), Nature 585, 357–362 "Array programming with NumPy"
• Latković et al. (2021), "Statistics of 700 individually studied W UMa stars"
• Virtanen et al. (2020), Nature Methods 17(3), 261–272 "SciPy 1.0: Fundamental Algorithms for Scientific Computing in Python"

Acknowledgements

This work has made use of data from the European Space Agency (ESA) mission Gaia, processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.

This work has made use of the SIMBAD database, operated at CDS, Strasbourg, France.

This work made use of Astropy, a community-developed core Python package for Astronomy.