The Impact of Interacting Binary Stars on Core-collapse Supernovae and Emission Nebulae

Abstract

The evolution of binary-star systems vary from that of single stars as they can interact with their companions. This leads to mass loss, mass gain, or stellar mergers. We now know that most massive stars are binary stars. In nearby galactic open clusters as many as 70% of massive stars interact with a binary companion (Sana et al., 2012, 2014). Therefore, in observed stellar populations their properties will be largely determined by past and ongoing binary interactions. In this thesis, we use the results of the Binary Population and Spectral Synthesis (BPASS) code to investigate the impact of accounting for all the possible binary interactions on the properties of stellar populations. Our focus is on core-collapse supernovae and emission nebulae. First, we constructed synthetic galaxy population models for nearby galaxies within 11Mpc, modelling their Hα flux, FUV flux and CCSN rate. We found that the interacting binaries produce low-mass helium stars that evolve to explode as type Ibc SNe, increasing the rate of these events at the expense of type II SNe. This increases the relative ratio of type Ibc to type II, closer to the observed rate while having little effect on the total CCSN rate. In addition, we investigated how star formation history (SFH), ionizing photon leakage and allowing for missing supernovae impact on these galaxy populations. We then modelled nebular emission from young HII regions in great detail by combining bpass with the photoionization code cloudy (Ferland et al., 1998, 2013). We have compared these models to two different samples of observed HII region samples. For each observed HII region we determined which of our models provided a best fit and obtained a constraint on the gas properties and underlying stellar populations. We have found that binary interactions must be considered as they can provide harder ionizing photons at later population ages beyond 10 Myr. These harder photons arise due to the production of less-massive helium stars which are not possible from single-star populations. These are the stars that go on to explode as type Ibc CCSNe. The existence of stellar populations with these helium stars means that we must reexamine the emission line diagnostics of HII regions. We nd that some HII regions could be substantially older, beyond ~ 10 Myrs, than the canonical 3 to 5 Myr due to the helium stars producing ionizing photons when single star populations produce none. Finally by studying the HII regions that have hosted a recent CCSN, we have been able to determine the oxygen abundance and age distributions for type II and type Ibc CCSNe. We find that both most likely arise from stars with masses ≤ 20M Θ .