The discovery and analysis of a new type of Wolf-Rayet star

Neugent, K.F. (2017) The discovery and analysis of a new type of Wolf-Rayet star. Masters thesis, Northern Arizona University.

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Abstract

We’ve recently completed searches for Wolf-Rayet (WR) stars in the Local Group galaxies including M31, M33, and the Magellanic Clouds using a combination of image subtraction techniques and photometry for candidate discovery and spectrophotometric follow-up for candidate confirmation. As part of these surveys, we’ve discovered a new type of WR star in the Large Magellanic Cloud (LMC). These stars have both strong emission lines as well as He II and Balmer absorption lines and spectroscopically resemble a WN3 and O3V binary pair. However, they are visually too faint to be WN3+O3V binaries. So far we have found nine of these WN3/O3s, making up ~6% of the population of LMC WRs. Using CMFGEN, a spectral modeling program, we have successfully modeled their spectra as single stars and have compared the physical parameters with those of more typical LMC WNs. Their temperatures are around 100,000 K, a bit hotter than average LMC WNs (by around 10,000 K), and abundances are what you would expect for a WR star in CNO equilibrium. However, most anomalous are their mass-loss rates which are more like that of an O-type star than a WN. While we are still learning more about their evolutionary status, their low mass-loss rates and wind velocities suggest that they are not products of homogeneous evolution. It is possible instead that these stars represent some sort of intermediate stage between O stars and WNs. There is some indication that there may be a metallicity dependence in their formation environment so we have recently started a survey searching for these WN3/O3s in M33, which has a strong metallicity gradient. By either confirming or denying their existence in other metallicity regimes we hope to gain further insight into their evolution.

Item Type:	Thesis (Masters)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	Massive stars; Wolf-Rayet
Subjects:	Q Science > QC Physics
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of Engineering, Forestry, and Natural Science > Physics and Astronomy
Date Deposited:	28 Feb 2018 23:02
URI:	http://openknowledge.nau.edu/id/eprint/5128

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