The X-ray view of the Hyades cluster: updated
  We revisit the X-ray properties of the main-sequence Hyades members and the
relation between X-ray emission and stellar rotation. As input catalog for
Hyades members, we combined three recent membership lists derived from Gaia DR2
data including the Hyades core and its tidal tails. We searched for X-ray
detections from the ROSAT all-sky survey (RASS) and pointings from ROSAT,
Chandra, and XMM-Newton of the Hyades members and adopted rotation periods
derived from Kepler's K2 mission and other resources. We find an X-ray
detection for 281 of 1066 bona fide main-sequence Hyades members and provide
statistical upper limits for the undetected sources. F- and G-type stars have
the highest detection fraction (72 %), while K- and M-type dwarfs have lower
detection rates (22 %). The X-ray luminosities of the detected members range
from ~$2\times10^{27}$ for late M-type dwarfs to ~$2\times10^{30}$ erg s$^{-1}$
for active binaries. The X-ray luminosity distribution functions formally
differ for the members in the core and tidal tails, which is likely caused by a
larger fraction of field stars in our Hyades tails sample. Compared to previous
studies, our sample is slightly fainter in X-rays due to differences in the
used Hyades membership list, furthermore, we extend the X-ray luminosity
distribution to fainter luminosities. The X-ray activity of F- and G-type stars
is well defined at $F_X/F_bol=10^{-5}$ and increases to later spectral types
reaching the saturation limit for members later than spectral type M3. The
X-ray flux varies by less than a factor of three between epochs for the 104
Hyades members with multiple epoch data. Rotation periods are found for 204
Hyades members, with about half of them being detected in X-rays. The
activity-rotation-relation derived for the coeval Hyades members has properties
very similar to those obtained by other authors investigating stars of
different ages.
