Identification of Emission-Line Stars in 30 Doradus Using HST Observations

Abstract

Using broadband (F439W) and narrowband (F469N) Hubble Space Telescope archive images of the R136 central cluster of 30 Doradus, we have identified candidate Wolf-Rayet stars from the strength of their He II λ4686 emission lines. The number ratio of Wolf-Rayet to O stars found in our data is 0.11±0.03. Our results are more consistent with an instantaneous burst with an age of about 3 × 10⁶ yr than with a continuous star formation scenario. However, even in the starburst scenario, evolutionary model predictions for low-metallicity stellar evolution agree with our observations only if we also assume enhanced mass loss and/or a relatively flat slope (Γ > -1.35) for the initial mass function with an upper mass limit of more than 80 M_sun.