Binaries

At the moment, NBODY6 and NBODY6++GPU are the only supported codes that have a separate treatment for binary stars. In both cases, the main array of stars contain the centre of mass position and velocity of each binary. The masses are then the total mass of the binary star. Separate parameters are used that contain properties of the individual binaries themselves. These include, but are not limited to:

  • ids i_d1 and i_d2

  • kwtypes kw1 and kw2

  • eccentricity ecc

  • orbital period pb

  • semi-major axis semi

  • masses m1 and m2

  • luminosities logl1 and logl2

It is possible to add binary star properties manually using StarCluster.add_bse, however clustertools will always assume the binary’s centre of mass positions and velocities, total mass, and primary star ID were added via StarCluster.add_stars.

Generally speaking, unit and coordinate transformations do not act on these parameters. They are saved in the event an experienced NBODY6 user would like to view these parameters (see StarCluster.add_bse for the full list of saved parameters). The only functions designed specifically designed for binaries are to_audays and to_sudays. These unit conversion function convert orbital period pb to units days, semi-major axis semi to units of solar units (su) or astronomical units (au). When these are called, the masses of individual binary stars (m1 and m2) are converted to solar masses. When to_nbody is called, all of these values are returned to nbody units.

More support for binary stars is planned for future releases.