Breaking gyrochronology through the collapse of coronal winds

Michaël Lévesque; Paul Charbonneau

doi:10.3847/1538-4357/ae03b0

paper

Breaking gyrochronology through the collapse of coronal winds

arXiv:2510.14164 · doi:10.3847/1538-4357/ae03b0

Abstract

Gyrochronology, a method for dating aged field stars ( $≳$ 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 ( $T_{0}$ ) limit, even at solar-like low rotation rates ( $Ω$ ) and coronal magnetic field strength ( $B_{r 0}$ ), magnetocentrifugal effects are important and preclude expression of the mass and angular momentum loss rates as power-laws of $T_{0}$ or $Ω$ when $T_{0}$ 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 $T_{0} \propto B_{r 0}^{σ}$ while retaining the ``standard'' dynamo relationship $B_{r 0} \propto Ω$ , we show that reproducing the observed break in gyrochronology requires an exponent $σ ≳ 1.5$ , 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.

15 pages, 9 figures, published in ApJ

Breaking gyrochronology through the collapse of coronal winds

Abstract

References in corpus (33)