Chemical evolution of the Milky Way: the origin of phosphorus (Research Note)

Context. Recently, the abundance of P was measured for the first time in disk stars. This provides the opportunity of comparing the observed abundances with predictions from theoretical models. Aims. We aim at predicting the chemical evolution of P in the Milky Way and compare our results with the observed P abundances in disk stars to derive constraints on the P nucleosynthesis. Methods. We adopted the two-infall model of galactic chemical evolution, which is a good model for the Milky Way, and computed the evolution of the abundances of P and Fe. We adopted stellar yields for these elements from different sources. The element P is expected to form mainly in type-II supernovae, whereas Fe is mainly produced by type-Ia supernovae. Results. Our results confirm that to reproduce the observed trend of [P/Fe] vs. [Fe/H] in disk stars, P must be formed mainly in massive stars. However, none of the available yields for P can reproduce the solar abundance of this element. In other words, to reproduce the data one needs to assume that massive stars produce three times more P than predicted. Conclusions. We conclude that the entire available yields of P from massive stars are largely underestimated and that nucleosynthesis calculations should be revised. We also predict the [P/Fe] expected in halo stars.