2025/10/15 by Lévesque, Michaël, Charbonneau, Paul
#Computational Physics (physics.comp-ph) #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR)
paper · doi:10.48550/arxiv.2510.14164
Gyrochronology, a method for dating aged field stars (\gtrsim a few Gyr) based on their rotation rate, has recently been shown to fail for many stars older than the sun. The explanation most often put forth is that a shutdown or mode change in the stellar dynamo leads to a sharp decrease in angular momentum loss in magnetized coronal winds. In this paper, we explore an alternate possibility, namely a collapse of the wind itself through a reduction of coronal heating. We show that in the low coronal temperature (T0) limit, even at solar-like low rotation rates (Ω) and coronal magnetic field strength (Br0), magnetocentrifugal effects are important and preclude expression of the mass and angular momentum loss rates as power-laws of T0 or Ω when T0 drops below ≃ 1.5 MK. Mass loss is found to scale linearly with power input into the wind at all coronal temperatures. Introducing an ad hoc power law relationship T0∝ Br0σ while retaining the ``standard'' dynamo relationship Br0∝Ω, we show that reproducing the observed break in gyrochronology requires an exponent σ\gtrsim 1.5, with which is associated a drop by over 3 orders of magnitude in power input into the quiet corona. This appears physically unrealistic, given current observations of chromospheric and coronal non-thermal emission in aged solar-type stars.