When Does Gyrochronology Start to Work? Stellar Rotation and Structure of the α Persei Complex by Andrew W. Boyle et al. on Monday 21 November

On the pre-main-sequence, the rotation rates of Sun-like stars are dictated

by the interplay between the protostellar disk and the star's contraction. At

ages exceeding 100 million years (Myr), magnetic spin-down erases the initial

stellar spin rate and enables rotation-based age dating (gyrochronology). The

exact time at which the transition between these two regimes occurs depends on

stellar mass, and has been challenging to empirically resolve due to a lack of

viable calibration clusters. The $\alpha$ Persei open cluster ($t\approx80$

Myr, $d\approx170$ pc) may provide the needed calibrator, but recent analyses

of the Gaia data have provided wildly varying views of its age and spatial

extent. As such, we analyze a combination of TESS, Gaia, and LAMOST data to

calibrate gyrochronology at the age of $\alpha$ Per and to uncover the

cluster's true morphology. By assembling a list of rotationally-confirmed

$\alpha$ Per members, we provide strong evidence that $\alpha$ Per is part of a

larger complex of similarly-aged stars. Through kinematic back-integration, we

show that the most diffuse components of $\alpha$ Per were five times closer

together 50 Myr ago. Finally, we use our stellar rotation periods to derive a

relative gyrochronology age for $\alpha$ Per of 67 $\pm$ 12% the age of the

Pleiades, which yields 86 $\pm$ 16 Myr given current knowledge. We show that by

this age, stars more massive than $\approx$0.8 M$_{\odot}$ have converged to

form a well-defined slow sequence.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.09822v1