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A New Wolf-Rayet Transition Star: A WC with Nitrogen

Presentation #330.02 in the session “Stellar Abundances and Ages”.

Published onJan 11, 2021
A New Wolf-Rayet Transition Star: A WC with Nitrogen

We announce the discovery of a new “transition” Wolf-Rayet (WR) star, BAT99-9. WR stars are classified into two different classes, based on their optical spectra: the nitrogen sequence WN-type (show strong emission lines of helium and nitrogen) and the carbon sequence WC-type (show strong emission lines of carbon). WR stars are the evolved He-burning descendants of the most massive O-type stars, with the products of their nuclear fusion brought to the surface. The Large Magellanic Cloud (LMC) WC BAT99-9 is unique as it still has nitrogen in its spectrum, which is unheard of in WC stars! There is a group of stars called WN/C stars, whose spectra are that of WN-type WR stars with the exception of a single carbon line, C IV λ5812. It is unclear whether these stars have a higher abundance of carbon than the WNs, as the strength of this line is heavily influenced by other parameters. The model analysis is presented as part of an analysis of three other WC-type stars in the LMC. We found that the WCs’ chemical abundances are in agreement with both binary and single-star evolutionary models. However, for BAT99-9, binary evolution models may better explain the timescales with nitrogen still being on the surface. This work is supported through the NASA Astrophysics Data Analysis Program80NSSC18K0729 as well as a grant from the Space Telescope Science Institute (GO-13781).

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