K2 Rotation Periods for Low-mass Hyads and a Quantitative Comparison of the Distribution of Slow Rotators in the Hyades and Praesepe

<jats:title>Abstract</jats:title> <jats:p>We analyze <jats:italic>K2</jats:italic> light curves for 132 low-mass (1 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> ≳ <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> ≳ 0.1 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) members of the 600–800 Myr old Hyades cluster and measure rotation periods (<jats:inline-formula> <jats:tex-math> <?CDATA ${P}_{\mathrm{rot}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab2468ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) for 116 of these stars. These include 93 stars with no prior <jats:inline-formula> <jats:tex-math> <?CDATA ${P}_{\mathrm{rot}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab2468ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> measurements; the total number of Hyads with a known <jats:inline-formula> <jats:tex-math> <?CDATA ${P}_{\mathrm{rot}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab2468ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> is now 232. We then combine literature binary data with <jats:italic>Gaia</jats:italic> 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 <jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> = 0.035 ± 0.011 for Praesepe. Comparing the effective temperature–<jats:inline-formula> <jats:tex-math> <?CDATA ${P}_{\mathrm{rot}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab2468ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> distributions for the Hyades and Praesepe, we find that solar-type Hyads rotate, on average, 0.4 day slower than their Praesepe counterparts. This <jats:inline-formula> <jats:tex-math> <?CDATA ${P}_{\mathrm{rot}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab2468ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> 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 <jats:inline-formula> <jats:tex-math> <?CDATA ${P}_{\mathrm{rot}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab2468ieqn6.gif" xlink:type="simple" /> </jats:inline-formula> 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.</jats:p>