# K2 rotation periods for low-mass Hyads and a quantitative comparison of the distribution of slow rotators in the Hyades and Praesepe

## TL;DR

This study measures rotation periods of low-mass stars in the Hyades cluster, compares them with Praesepe, and uses these data to refine age estimates and understand stellar rotational evolution.

## Contribution

It provides new rotation period measurements for 93 previously unmeasured Hyades stars and introduces a refined comparison of stellar rotation and age between Hyades and Praesepe.

## Key findings

- Hyades stars rotate 0.4 days slower than Praesepe stars on average.
- The age difference between Hyades and Praesepe is approximately 57 million years.
- Rotational differences diminish for lower-mass stars, indicating stalling in rotational evolution.

## Abstract

We analyze K2 light curves for 132 low-mass ($1\ \gtrsim\ M_*\ \gtrsim\ 0.1$~${M_{\odot}}$) members of the 600--800~Myr-old Hyades cluster and measure rotation periods ($P_{rot}$) for 116 of these stars. These include 93 stars with no prior $P_{rot}$ measurement; the total number of Hyads with known $P_{rot}$ is now 232. We then combine literature binary data with Gaia DR2 photometry and astrometry to select single star sequences in the Hyades and its roughly coeval Praesepe open cluster, and derive a new reddening value of $A_V = 0.035$$\pm$$0.011$ for Praesepe. Comparing the effective temperature--$P_{rot}$ distributions for the Hyades and Praesepe, we find that solar-type Hyads rotate, on average, 0.4~d slower than their Praesepe counterparts. This $P_{rot}$ difference indicates that the Hyades is slightly older than Praesepe: we apply a new gyrochronology model tuned with Praesepe and the Sun, and find an age difference between the two clusters of 57~Myr. However, this $P_{rot}$ difference decreases and eventually disappears for lower-mass stars. This provides further evidence for stalling in the rotational evolution of these stars, and highlights the need for more detailed analysis of angular-momentum evolution for stars of different masses and ages.