Direct Detection of Solar Angular Momentum Loss with the Wind Spacecraft

Abstract

The rate at which the solar wind extracts angular momentum from the Sun has been predicted by theoretical models for many decades, and yet we lack a conclusive measurement from in-situ observations. In this letter we present a new estimate of the time-varying angular momentum flux in the equatorial solar wind, as observed by the \textit{Wind} spacecraft from 1994-2019. We separate the angular momentum flux into contributions from the protons, alpha particles, and magnetic stresses, showing that the mechanical flux in the protons is $\sim$3 times larger than the magnetic field stresses. We observe the tendency for the angular momentum flux of fast wind streams to be oppositely signed to the slow wind streams, as noted by previous authors. From the average total flux, we estimate the global angular momentum loss rate of the Sun to be $3.3\times 10^{30}$erg, which lies within the range of various MHD wind models in the literature. This angular momentum loss rate is a factor of $\sim$2 weaker than required for a Skumanich-like rotation period evolution (${\Omega }_{\ast }\propto$ stellar age${}^{-1/2}$), which should be considered in studies of the rotation period evolution of Sun-like stars.

10 pages + 2 figures, accepted for publication to ApJL

References in corpus (14)

• The Mass-Dependence of Angular Momentum Evolution in Sun-Like Stars
• The effect of magnetic topology on thermally-driven winds: towards a general formulation of the braking law
• Improved angular momentum evolution model for solar-like stars II. Exploring the mass dependence
• Stellar Winds on the Main-Sequence I: Wind Model
• The Metastable Dynamo Model of Stellar Rotational Evolution
• Simulating the environment around planet-hosting stars - II. Stellar winds and inner astrospheres
• Do non-dipolar magnetic fields contribute to spin-down torques?
• The Effect of Combined Magnetic Geometries on Thermally Driven Winds I: Interaction of Dipolar and Quadrupolar Fields
• Global solar magnetic field organization in the outer corona: influence on the solar wind speed and mass flux over the cycle
• Magnetic braking of Sun-like and low-mass stars: Dependence on coronal temperature
• A semi-empirical model for magnetic braking of solar-type stars
• The open flux evolution of a solar-mass star on the main sequence
• Mass Loss via Solar Wind and Coronal Mass Ejections During Solar Cycle 23 and 24
• 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

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• Transition of latitudinal differential rotation as a possible cause of weakened magnetic braking of solar-type stars
• Accounting for Differential Rotation in Calculations of the Sun's Angular Momentum-loss Rate
• Catching the wisps: Stellar mass-loss limits from low-frequency radio observations
• Reconstructing the Sun's Alfvén surface and wind braking torque with Parker Solar Probe
• Comment on "The Sun is less active than other solar-like stars"
• Testing the Alfvén-wave model of the solar wind with interplanetary scintillation