NGTS Clusters Survey VI. Stellar rotation in seven young open clusters within the PLATO LOPS2 field

The first billion years represents a critical phase of stellar evolution. Stars spin up as they evolve through the Pre-main sequence (PMS) until contraction is halted by the onset of fusion at the zero-age main sequence (ZAMS), whereby stars move from a spin up regime to a spin down regime as magnetised stellar winds carry away angular momentum. Disk lifetime affects for how long a star spins up during the PMS, leading to a spread of rotational velocities at a given mass on the ZAMS. As a result age dating processes such as gyrochronology; which leverages the relationship between a stars age, mass and rotation period, are poorly constrained at young ages. Thus further observations are required to constrain the spread of rotation periods at a given age and mass in order to calibrate empirical models.

We present here NGTS measurements of seven young open clusters, spanning ages ~40–700Myr that reside within the upcoming PLATO LOPS2 field. These are the first comprehensive rotation period distributions for Trumpler 10, NGC 2451 B and Alessi 3, while extending existing distributions for NGC 2451 A, NGC 2516, Collinder 135 and IC 2391. In total, we report 1063 rotation periods across all seven clusters whilst also identifying 285 likely binary or higher order systems from these results. We find that solar-mass stars in the ~40Myr NGC 2451 B have distinctly faster rotation periods than their counterparts in clusters at the canonically accepted lower gyrochronal age anchor of ~70–80Myr, thereby halving the minimum age at which open clusters can be distinguished via gyrochronology. We also observe stalled spin down from ~70Myr to at least 150Myr, supporting previous predictions that angular momentum redistribution and removal by stellar winds should result in a wave of stalled spin down that propagates as a function of mass and age. Finally, we use the rotation period distribution of Alessi 3 to calculate a differential gyrochronology age of 687 ± 106 Myr.