README.md

This repo contains code for evolving double white dwarf systems according to the prescription in Marsh et. al 2004 as implemented in Biscoveanu, Kremer, and Thrane 2022. The script integrate.py contains all the functions governing the evolution of the system, including the effects of tides, mass transfer, and gravitational radiation. This can be run using evolve_nosync.py as follows:

python evolve_nosync.py donor_mass accretor_mass tau0 basedir 

where donor_mass and accretor_mass are in solar masses. tau0 is the initial synchronization time at the onset of mass transfer in years, and basedir is the directory where the output will be written. As an example:

python evolve_nosync 0.25 0.6 10 ./

This will produce an output file called {basedir}/marsh_{tau0}_{donor_mass}_{accretor_mass}_DOP853.dat, where DOP853 is the integration method used by scipy.solve_ivp. The output file containts arrays for the following:

• time (yr)
• fdot_tot (yr^-2): the total gravitational-wave frequency derivative
• fdot_gw: the contribution to the gravitational-wave frequency derivative from gravitational radiation, in yr^-2
• fdot_MT: the contribution to the gravitational-wave frequency derivative from mass transfer, in yr^-2
• fdot_tides: the contribution to the gravitational-wave frequency derivative from tides along, in yr^-2
• Ma (Msun): the accretor mass
• Md (Msun): the donor mass
• accretion_rate (Msun/yr)
• accretor_spin/orbital_spin: the accretor spin in units of the orbital angular frequency
• separation (Rsun)