Be X-ray binaries in the SMC as indicators of mass transfer efficiency

Understand

Be X-ray binaries (BeXRBs) consist of rapidly rotating Be stars with neutron star companions accreting from the circumstellar emission disk.

• We compare the observed population of BeXRBs in the Small Magellanic Cloud with simulated populations of BeXRB-like systems produced with the COMPAS population synthesis code.
• We focus on the apparently higher minimal mass of Be stars in BeXRBs than in the Be population at large.
• Assuming that BeXRBs experienced only dynamically stable mass transfer, their mass distribution suggests that at least 30% of the mass donated by the progenitor of the neutron star is typically accreted by the B-star companion.