Solar Angular Momentum Loss Over the Past Several Millennia
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Citations
Accounting for differential rotation in calculations of the Sun's angular momentum-loss rate
The magnetic field and stellar wind of the mature late-F star χ Draconis A
References
Magnetic Braking by a Stellar Wind—I
Revisiting the Sunspot Number. A 400-Year Perspective on the Solar Cycle
Measuring the rotation period distribution of field M dwarfs with Kepler
Revisiting the Sunspot Number
Grand minima and maxima of solar activity: new observational constraints
Related Papers (5)
The Effect of Magnetic Variability on Stellar Angular Momentum Loss I: The Solar Wind Torque During Sunspot Cycles 23 & 24
Frequently Asked Questions (14)
Q2. Why is the torque in the solar wind so variable?
Due to the nonlinear dependence of Equation (11) on the open magnetic flux in the solar wind, short-term variability in the open magnetic flux, even around a fixed average value, will increase the long-term average torques.
Q3. What is the effect of the cosmogenic radionuclides on the solar flux?
Reconstructions of solar activity based on the concentrations of cosmogenic radionuclides incur smoothing effects from the transport and deposition timescales of each radionuclide.
Q4. What is the effect of CMEs on the solar wind?
CMEs carry only afew percent of the total solar mass-loss rate (Cranmer et al. 2017), however, at solar maximum they can provide a significant fraction of the average mass flux in the equatorial solar wind (Webb & Howard 1994).
Q5. How did they calculate the torque on the Sun due to the solar wind?
By applying a braking law derived from magnetohydrodynamic (MHD) simulations by Finley & Matt (2018), they calculated the time-varying torque on the Sun due to the solar wind.
Q6. Why is the open magnetic flux an upper limit?
Due to kinematic effects that occur between the Alfvén surface and the measurements taken at 1 au, their estimate of the open magnetic flux is likely an upper limit (Owens et al. 2017a).
Q7. What is the effect of the magnetic field on the rotation of low-mass stars?
The resulting strong dependence of torque on rotation rate leads to a convergence of rotation periods with age, as initially fast rotating stars generate strong magnetic fields and experience a larger braking torque than the initially slowly rotating stars.
Q8. What are the fit constants for the wind torques?
These fit constants also account for the multiplicative factor of (4π)2, and any effects introduced by the flow being multi-dimensional in nature.
Q9. How do the authors estimate the open magnetic flux?
The authors use measurements of the solar wind to estimate the open magnetic flux usingf p= á ñR B R4 , 8Ropen 2 1 hr 27 days∣ ( )∣ ( )where the authors average the radial magnetic field BR, (taken from a single observing location) at a distance R from the Sun, over a full solar rotation (27 days), and assume that the solar wind is roughly isotropic on their averaging timescale, in order to estimate the open magnetic flux.
Q10. How do the authors calculate the braking torque of the Sun?
The authors then utilize reconstructions of the solar open magnetic flux, based on geomagnetic indices (Lockwood et al. 2014a), sunspot number records (Owens & Lockwood 2012), and concentrations of cosmogenic radionuclides (Wu et al. 2018b), to estimate the braking torque over the last four centuries, and then the last nine millennia.
Q11. What is the simplest way to estimate the mass loss rate for the open magnetic flux?
When the authors estimate the mass-loss rate for the historical estimates of the open magnetic flux in Sections 4.3, the authors will use both Equation (10) and the 2σ bounds.
Q12. What is the reason why the original data sets have a larger torque than their smoothed?
By comparing the average torques from the smoothed reconstructions of Lockwood et al. (2014a) and Owens et al. (2017b) to their original data sets, the authors find the original data sets have alarger torque by ∼4% than their smoothed counterparts; a result of the nonlinearity of the torque on open magnetic flux.
Q13. How have previous authors removed these events?
Previous authors have removed these events through the use of CME catalogs (Cane & Richardson 2003) or clipping anomalous spikes (Cohen 2011).
Q14. How did Finley and Matt determine the solar wind torque?
In Finley et al. (2018), the short timescale variability (from ∼27 days up to a few decades) of the solar wind was examined using in situ observations of the solar wind plasma and magnetic field.