2021ApJ...922..158L

The maximum mass of neutron stars (NSs) is of great importance for constraining equations of state of NSs and understanding the mass gap between NSs and stellar-mass black holes. NSs in X-ray binaries increase in mass by accreting material from their companions (known as the recycling process), and the uncertainties in the accretion process make studying the NS mass at birth a challenge. In this work, we investigate the NS accreted mass while considering the effect of NS spin evolution and provide the maximum accreted mass for NSs in the recycling process. By exploring a series of binary evolution calculations, we obtain the final NS mass and the maximum accreted mass for a given birth mass of an NS and a mass transfer efficiency. Our results show that NSs can accrete relatively more material for binary systems with donor masses in the range of 1.8 ∼ 2.4 M_☉, NSs accrete relatively more mass when the remnant WD mass is in the range of ∼ 0.25-0.30 M_☉, and the maximum accreted mass is positively correlated with the initial NS mass. For a 1.4 M_☉ NS at birth with a moderate mass transfer efficiency of 0.3, the maximum accreted mass could be 0.27 M_☉. The results can be used to estimate the minimum birth mass for systems with massive NSs in observations.