The power of binaries on stripped-envelope supernovae across metallicity: uniform progenitor parameter space and persistently low ejecta masses, but subtype diversity

ABSTRACT Stripped-envelope supernovae (SESNe) originate from massive stars that lose their envelopes through binary interactions or stellar winds. The connection between SESN subtypes and their progenitors remains poorly understood, as does the influence of initial mass, binarity, explodability, and metallicity on their evolutionary pathways, relative rates, ejecta masses, and progenitor ages. Here, we investigate these properties across a wide metallicity range (0.01–2 $Z_{\odot }$) using POSYDON, a state-of-the-art population synthesis code that incorporates detailed single- and binary-star model grids. We find that the common-envelope channel contributes less than 6 per cent of SESNe, since unstable mass transfer is found less frequent than previously thought and rarely leads to common envelope survival when envelope binding energies are computed from detailed stellar models. The secondary channel accounts for less than 11 per cent, while the vast majority of SESNe originate from primary stars in binaries undergoing stable mass-transfer episodes. These interactions maintain a largely metallicity-independent SESN parameter space, making the overall SESN rate almost insensitive to metallicity. In contrast, subtype fractions exhibit strong metallicity dependence, though their exact values remain affected by classification thresholds. The age distributions and therefore the progenitor masses of different SESN types also vary significantly with metallicity, revealing metallicity-dependent trends that can be tested observationally. Predicted SESN ejecta masses remain nearly constant across metallicity, in contrast to single-star models, and fall within observed ranges. Future transient surveys, combined with statistical environmental studies that constrain metallicity dependence, will provide decisive tests of these predictions and of the dominant role of binary interactions in shaping SESNe.