Abstract
Wolf–Rayet stars (WRs) represent the end of a massive star’s life as it is about to turn into a supernova. Obtaining complete samples of such stars across a large range of metallicities poses observational challenges, but presents us with an exacting way to test current stellar evolutionary theories. A technique we have developed and refined involves interference filter imaging combined with image subtraction and crowded-field photometry. This helps us address one of the most controversial topics in current massive star research: the relative importance of binarity in the evolution of massive stars and formation of WRs. Here, we discuss the current state of the field, including how the observed WR populations match with the predictions of both single and binary star evolutionary models. We end with what we believe are the most important next steps in WR research.
Highlights
Wolf–Rayet Star PrimerWolf–Rayet (WR) stars are hot, luminous stars whose spectra are dominated by strong emission lines, either of helium and nitrogen (WN-type) or helium, carbon, and oxygen (WC and WO type)
Observing a complete set of both the nitrogen and carbon rich Wolf–Rayet stars (WRs) within a galaxy allows for important comparisons between the observed WC/WN ratio and that predicted by the evolutionary models
Because the evolution of WRs is highly dependent on the metallicity of the surrounding environment, it is important to do these comparisons across a wide range of galaxies with different metallicities, such as the galaxies in the Local Group
Summary
Wolf–Rayet (WR) stars are hot, luminous stars whose spectra are dominated by strong emission lines, either of helium and nitrogen (WN-type) or helium, carbon, and oxygen (WC and WO type). In the Conti Scenario, stars with initial masses greater than ∼30M will form on the main-sequence as massive O-type stars As they evolve, the stellar winds will continue to strip more and more material from their surfaces until they first turn into WNs, and (depending on the strength of the stellar winds), WCs and possibly WOs. Variable (LBV) phase, shedding material that way. Single-star evolution is highly dependent on the strength of the stellar-wind mass-loss rates, which are in turn dependent on the metallicity of the birth environment. Magellanic Cloud (SMC) [11] to 1.7× solar in M31 [12] This allows us to compare the observations against the model predictions across a large range of metallicities, which is important given the strong dependence on stellar evolution to mass-loss rate. We’ll describe how to obtain the physical parameters of such stars using spectral modeling programs before ending with a discussion of how the evolutionary models compare to our observed number of WRs
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