Chemical evolution of the Milky Way: the origin of phosphorus

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.