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The magnetic fields of low-mass stars are observed to be variable on decadaltimescales, ranging in behaviour from cyclic to stochastic. The changingstrength and geometry of the magnetic field should modify the efficiency ofangular momentum loss by stellar winds, but this has not been well quantified.In Finley et al. (2018) we investigated the variability of the Sun, andcalculated the time-varying angular momentum loss rate in the solar wind. Inthis work, we focus on four low-mass stars that have all had their surfacemagnetic fields mapped for multiple epochs. Using mass loss rates determinedfrom astrospheric Lyman-$\alpha$ absorption, in conjunction with scalingrelations from the MHD simulations of Finley & Matt (2018), we calculate thetorque applied to each star by their magnetised stellar winds. The variabilityof the braking torque can be significant. For example, the largest torque for$\epsilon$ Eri is twice its decadal averaged value. This variation iscomparable to that observed in the solar wind, when sparsely sampled. Onaverage, the torques in our sample range from 0.5-1.5 times their averagevalue. We compare these results to the torques of Matt et al. (2015), which useobserved stellar rotation rates to infer the long-time averaged torque onstars. We find that our stellar wind torques are systematically lower than thelong-time average values, by a factor of ~3-30. Stellar wind variabilityappears unable to resolve this discrepancy, implying that there remain someproblems with observed wind parameters, stellar wind models, or the long-termevolution models, which have yet to be understood.

The Effect of Magnetic Variability on Stellar Angular Momentum Loss II: The Sun, 61 Cygni A, $\epsilon$ Eridani, $\xi$ Bootis A and $\tau$ Bootis A