Galactic restrictions on iron production by various types of supernovae

We propose a statistical method for decomposition of contributions to iron production from various sources: Type II supernovae and the subpopulations of Type Ia supernovae, prompt (their progenitors are short-lived stars with ages lower than ∼100 Myr) and tardy (their progenitors are long-lived stars with ages >100 Myr). To do that, we develop a theory of oxygen and iron synthesis that takes into account the influence of the spiral arms on the amount of the above elements synthesized by both Type II supernovae and prompt Type Ia supernovae. In the framework of the theory, we processed statistically the new, more precise, observational data on Cepheid abundances, which, as is well known, demonstrate non-trivial radial distributions of oxygen and iron in the Galactic disc with bends in the gradients. In our opinion, such fine structure in the distribution of elements along the Galactic disc enables one to decompose the amount of iron unambiguously into three components produced by the above three sources. In addition, by means of our statistical methods we solve this task without any preliminary suppositions about the ratios between the proportions of iron synthesized by the above sources. The total mass supplied to the Galactic disc during its life by all types of supernovae is ∼(4.0 ± 0.4) × 10 7 M� , while the mass of iron occurring in the present interstellar medium (ISM) is ∼(1.20 ± 0.05) × 10 7 M� , i.e. about two thirds of iron is contained in stars and