On the formation history of Galactic double neutron stars

Double neutron stars (DNSs) have been observed as Galactic radio pulsars, and the recent discovery of gravitational waves from the DN merger GW170817 adds to the known DNS population. We perform rapi population synthesis of massive binary stars and discuss mode predictions, including DNS formation rates, mass distributions, an delay time distributions. We vary assumptions and parameters of physica processes such as mass transfer stability criteria, supernova natal kic distributions, remnant mass prescriptions, and common-envelop eccentricity distribution of the Galactic DNS population under each o our population synthesis models, allowing us to quantitatively compar burning secondary (case BB) on to a neutron star is most likel dynamically stable. We also find that a natal kick distribution compose of both low (Maxwellian σ =30 km s^{-1}) and high (σ =265 km s^{-1} components is preferred over a single high-kick component. We conclud that the observed DNS mass distribution can place strong constraints o model assumption

Wind Mass-loss Rates of Stripped Stars Inferred from Cygnus X-1

Recent observations of the high-mass X-ray binary Cygnus X-1 have shown that both the companion star (41 solar masses) and the black hole (21 solar masses) are more massive than previously estimated. Furthermore, the black hole appears to be nearly maximally spinning. Here we present a possible formation channel for the Cygnus X-1 system that matches the observed system properties. In this formation channel, we find that the orbital parameters of Cygnus X-1, combined with the observed metallicity of the companion, imply a significant reduction in mass loss through winds relative to commonly used prescriptions for stripped stars