The Effect of Magnetic Variability on Stellar Angular Momentum Loss I: The Solar Wind Torque During Sunspot Cycles 23 & 24
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Citations
Alfvénic velocity spikes and rotational flows in the near-Sun solar wind
First grids of low-mass stellar models and isochrones with self-consistent treatment of rotation: From 0.2 to 1.5 Mo at 7 metallicities from PMS to TAMS
First grids of low-mass stellar models and isochrones with self-consistent treatment of rotation : From 0.2 to 1.5 M_\odot at 7 metallicities from PMS to TAMS
Mass loss in pre-main sequence stars via coronal mass ejections and implications for angular momentum loss
Do Non-dipolar Magnetic Fields Contribute to Spin-down Torques?
References
The open flux problem.
The rise and fall of open solar flux during the current grand solar maximum
Bulk properties of the slow and fast solar wind and interplanetary coronal mass ejections measured by Ulysses: Three polar orbits of observations
Rotating models of young solar-type stars Exploring braking laws and angular momentum transport processes
Stellar evidence that the solar dynamo may be in transition
Related Papers (5)
Frequently Asked Questions (15)
Q2. What future works have the authors mentioned in the paper "The effect of magnetic variability on stellar angular momentum loss i: the solar wind torque during sunspot cycles 23 & 24" ?
The authors need additional information to discriminate between these possibilities. The required variability of ( a ) suggests the authors should observe stars like the Sun that are on average significantly more active ( i. e., that they have larger torques ) such that the average is correct. From the dynamical models, ( b ), uncertainties remain in the wind acceleration and effects of non-axisymmetric field components which both require further study to disentangle. Using the FM18 formula, predictions of the angular momentum loss rates for these stars based on their surface measurements may be smaller than in reality.
Q3. What is the reason for the differences in the modelled torque?
As the mass loss rate is typically evolved self consistently in these models, differences in the modelled torque value is often due to discrepant mass loss rates when compared to observations (as this is a challenging problem).
Q4. What is the way to measure the wind properties of distant stars?
In order to gain information about the mass loss rate and wind properties of these distant stars, the authors rely on proxies such as the strength of Lyman-α absorption at their astropauses (Wood 2004) and more recently the observed erosion of exoplanet atmospheres (Vidotto et al. 2011; Vidotto & Bourrier 2017).
Q5. What is the impact of the wind temperature on the torque formulas?
In general, variability in thewind temperature over the cycle will affect both torque formulas from FM18 and so represents an uncertainty on their results, i.e. for a fixed Ṁ , a faster wind will open more flux with a weaker resulting torque.
Q6. How many different observations can lead to the estimation of the angular momentum loss?
Magnetic variability can lead to estimates of the angular momentum loss which are, in the solar case, up to a factor of ∼ 10 different from one observation to another.
Q7. What is the PLUTO code used to generate a torque in the bottom panel of Figure?
The PLUTO code is used to construct 3D wind solutions for each WSO magnetogram, this produces global values for the mass loss rate and open magnetic flux (Réville, private communication), which are used to generate a torque in the bottom panel of Figure 1.
Q8. What is the effect of the long-term variability on the predictions of the stellar wind torques?
3. Long-time variability may also play a role, and with the difficultly ascertaining the true magnetic behaviour of other Sun-stars, i.e. if they are cyclic or stochastic, the corresponding estimate of their angular momentum loss rate may be discrepant from rotation evolution model predictions.
Q9. What is the impact of the non-axisymmetric components on the solar torque?
In their calculation of the solar torque, based on surface magnetogram observations, the authors include the strength of the non-axisymmetric components through equation (8)which adds the components in quadrature to produce a combined strength for each mode l.
Q10. How did the authors determine the impact of the non-axisymmetric components?
In order to assess the impact of including the nonaxisymmetric components with equation (8), the authors performed the torque analysis using both, only the axisymmetric components, and the combined strength approach of equation (8).
Q11. What is the average of the Alfvén radii predicted from the open flux method?
The averages of the Alfvén radii predicted from the open flux method are nearly constant between cycles, but as cycle 24 is currently moving into a minimum the average is expected to move lower as it becomes complete.
Q12. What is the reason for the difference in the dynamical torque estimates for the current Sun?
Differences in the dynamical torque estimates for the current Sun and the long-time-average value may then be due to magnetic variation on longer timescales than the 22 year magnetic cycle.
Q13. What is the torque controlled by the combined dipole field strength?
The torque calculated in Section 4.1 is controlled largely by the combined dipole field strength, which appears to be out of phase with solar activity, displayed in the top left panel of Figure 1 (note the use of absolute magnitude field strengths).
Q14. What is the difference between the present-day torques and the spin-evolution torques?
Differences in the average present-day torques to the spin-evolution torques, could be due to, (a) variability on a longer timescale than probed by the presentday variability presented here (but less than a spin-down time), (b) errors in using the dynamical models inferring present-day torque, or (c) that stars spin-down significantly different than Skumanich at ages of a few to several Gyr.
Q15. What is the effect of the angular momentum loss rate on the observations of other stars?
Observations of other Sunlike stars will therefore suffer from considerable uncertainty in their derived angular momentum loss rates based on a single or small number of observations.