Tuesday 15 Jan 2019[Journal Club] Stellar Wind Braking: The Sun During the last nine millennia

Adam Finley - University of Exeter

4th Floor Interaction Area 11:15-11:45

The magnetic fields of Sun-like stars are observed to vary significantly on timescales of years to decades. Variation on longer timescales is presumed to occur, but is unconstrained. During the main sequence, magnetised stellar winds remove angular momentum from these stars. This braking torque is coupled to the stellar magnetic field, such that changes in the strength and/or geometry of the field should modify the efficiency of this process. We can explore the solar wind on a longer timescale than for any other star. Since the space-age, we have been able to directly measure the solar wind using in-situ spacecraft. Furthermore, indirect proxies such as sunspot number, geomagnetic indices, and cosmogenic radionuclides, are available to constrain the variation of the heliospheric magnetic field on centennial, and millennial timescales. In this talk, I will show the time-varying braking torque on the Sun, due to the solar wind, on timescales ranging from months to millennia. Firstly, using near-Earth measurements to calculate the torque on the Sun throughout the space-age. Then, by using reconstructions of the solar open magnetic flux to estimate the solar wind torque during the last four centuries, and then the last nine millennia.

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