Modeling galactic Be X-ray binaries with POSYDON*

X-ray binaries (XBRs) are testbeds for modeling binary and stellar evolution. Be XRBs are the most numerous subclass of observed high-mass XRBs, containing Be donors with neutron star (NS) and black hole (BH) companions. While the exact mechanism responsible for the Be phenomenon remains under debate, stellar rotation has been identified as a key ingredient for the formation of the decretion disk. Previous population synthesis studies have used the Be XRB population to constrain binary evolution processes such as mass transfer and common envelope efficiency, but without selection criteria coming from rotational modeling. We use POSYDON, a next generation population synthesis code coupled with binary MESA models, to study galactic Be XRBs. For the first time, we model the rotational evolution of the donor and use prescriptions for the decretion disk to select Be XRB like systems. We can successfully match both the orbital properties of the observed sample of Be XRBs, as well as the relative abundance of NS to BH BeXRBs. Our results demonstrate the necessity of accurately modeling stellar rotation to interpret the Be XRB population.