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A radio census of the young massive stellar cluster Westerlund 1

Andrews, Holly Maddra; (2020) A radio census of the young massive stellar cluster Westerlund 1. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Observations were made of the massive stellar cluster Westerlund 1 (Wd1) using the Australia Telescope Compact Array (ATCA), with a total on source integration time of ~ 16 hours, collected over the autumn and winter of 2015, with follow up observations carried out in the summer of 2016. This thesis presents a full radio census of the massive stellar cluster. This thesis aims to investigate in full the dataset of radio observations, looking at the radio emission detected from the most massive stars in the cluster, as well as the majority of the post-main sequence massive stars present, including several Wolf-Rayet stars, yellow hypergiants, red supergiants, and a luminous blue variable. A full description outlining the data reduction process and the analysis carried out showcases current methods for handling radio interferometric data from ATCA when considering a crowded field full of extended and complex sources. The scientific results gained provide a follow-up to previous ATCA observations taken in the late 1990s and early 2000s. The more recent observations that are the focus of this thesis demonstrate an increase in both the sensitivity and resolution possible with the use of ATCA. New radio detections are made for ten members of the known stellar population of Wd1. The radio observations could be compared to complementary observations at millimetre wavelengths to determine spectral indices and index limits, which allowed for the nature of the radio emission to be constrained. Conclusions could be made from the spectral indices and index limits about the potential binarity of the stellar sources. For all stars where the radio emission could be validly approximated to a thermally emitting stellar wind, updated constraints could be found for the mass-loss rates of these sources. Comparisons between radio and millimetre wavebands allowed for a consideration of clumping factors.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: A radio census of the young massive stellar cluster Westerlund 1
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2020. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
Keywords: stellar winds, massive stars, radio astronomy
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10091579
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