The Wolf-Rayet stars of the carbon sequence in the Andromeda Galaxy

Gruner, David

Context: Wolf-Rayet stars are among the most outstanding examples for extreme stellar physics. With their strong stellar winds they shape galaxies, their nucleosynthesis produce the heavy elements all life is made of, and at the end of their life, they create another example for extreme physics: a neutron star or a black hole. In this thesis, we shed light on a subgroup of those exciting stars: the WR stars of the carbon sequence, also denoted as WC stars.

Motivation: Little is understood of the evolution of those key objects in galaxies. The quantication of their mass-loss rate and the interplay and dependency with other stellar parameter is of great interest for the elds of stellar physics and evolution, galaxy evolution and gravitational wave astronomy.

Aims: In this work, we perform a spectroscopic analysis on the sample of WC stars in the Andromeda Galaxy (M 31). The advantage of stars not located in our own Galaxy is that distance uncertainties can be widely eliminated. Furthermore, M31 is a galaxy with similar metalicity to the Milky Way. This fact makes it ideal for a comparison to the Galactic sample of WC stars.

Methods: The spectroscopic analysis is performed utilizing the PotsdamWolf-Rayet model atmosphere code (PoWR). We calculate model atmospheres and synthetic spectra which are then compared to optical spectra and photometry of the M31 WC stars. The model parameter are adjusted in order to obtain the best spectral fit.

Results: Stellar parameter are derived for 23 stars whose spectra do not show a sign of contamination by other sources. A detailed analysis was carried out for each star accounting for temperature, mass-loss rate, luminosity, abundances, terminal velocity and clumping.

Conclusions: We find that the spectral classication of WC stars into subtypes solely based on the standard line characteristics is not meaningful. We show that a combination of temperature and abundance effects is required for spectral classication. Furthermore, we find signs of fast rotation in the majority of stars analyzed here. The analyzed stars populate the same parameter regime that is also found for Galactic WC stars.

Main Part (dgruner-thesis-mainpart.pdf, 42MB)

Main Part (dgruner-thesis-appendix.pdf, 41MB)

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