The winds of young Suns

The winds of young Suns

Stars produce stellar wind—a tenuous flow of magnetised plasma extending deep into circumstellar space. It is thought that forceful stellar wind can erode the atmospheres of planets lacking strong magnetic fields, and thus reduce the planets' potential habitability. The slowing rotation ofSolar-type stars with increasing age is also caused by the stellar wind. In this Ph. D. project we have mapped the stellar winds of a selection of young, Sunlike stars with well characterised ages. These stars have had their surface magnetic field mapped using Zeeman-Doppler imaging. By driving a state of the art Solar wind code with the stellar surface magnetic fields we have obtained three-dimensional steady-state wind maps of 25 stars aged between 0.1 and 0.6 billion years. Unlike later epochs, this age range is characterised by the absence of single valued relations between stellar age, stellar rate of rotation, and measures of stellar magnetic activity. The resulting collection of wind maps is the largest created to date, and permits the application of robust statistics. We find that the Earth's magnetic field has protected the Earth from atmospheric erosion by strong Solar winds for at least 4 billion years in spite of the more powerful winds of the young Sun. For Solar-type stars younger than about 1/4 billion years, we find that the stellar spin-down resulting from our wind models is insufficient to explain the observed spin-down of stars with increasing age. This suggests that transient phenomena such as coronal mass ejections may account for a large part of these stars' spin-down.

D Evensberget, et al., The winds of young Solar-type stars in the Hyades, Monthly Notices of the Royal Astronomical Society, Volume 506, Issue 2, September 2021, Pages 2309–2335, https://doi.org/10.1093/mnras/stab1696 (This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2021 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.)

D Evensberget, et al., The winds of young Solar-type stars in Coma Berenices and Hercules-Lyra, Monthly Notices of the Royal Astronomical Society, Volume 510, Issue 4, March 2022, Pages 5226–5245, https://doi.org/10.1093/mnras/stab3557 (This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2021 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.)

Daniel V Cotton, et al., The rotationally modulated polarization of ξ Boo A, Monthly Notices of the Royal Astronomical Society, Volume 483, Issue 2, February 2019, Pages 1574–1581, https://doi.org/10.1093/mnras/sty3180 (This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2019 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.)

Jeremy Bailey, et al., Polarization of hot Jupiter systems: a likely detection of stellar activity and a possible detection of planetary polarization, Monthly Notices of the Royal Astronomical Society, Volume 502, Issue 2, April 2021, Pages 2331–2345, https://doi.org/10.1093/mnras/stab172 (This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2021 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.)

Brett C Addison, et al., TOI-257b (HD 19916b): a warm sub-saturn orbiting an evolved F-type star, Monthly Notices of the Royal Astronomical Society, Volume 502, Issue 3, April 2021, Pages 3704–3722, https://doi.org/10.1093/mnras/staa3960 (This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2021 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.)

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