Towards a complete stellar mass function of the Hyades. I. Pan-STARRS1
  optical observations of the low-mass stellar content
  The Hyades cluster is an ideal target to study the dynamical evolution of a
star cluster over the entire mass range due to its intermediate age and
proximity to the Sun. We wanted to extend the Hyades mass function towards
lower masses down to 0.1 Msol and to use the full three-dimensional spatial
information to characterize the dynamical evolution of the cluster. We
performed a kinematic and photometric selection using the PPMXL and Pan-STARRS1
sky surveys, to search for cluster members up to 30 pc from the cluster centre.
We determined our detection efficiency and field star contamination rate to
derive the cluster luminosity and mass functions down to masses of 0.1 Msol.
The thorough astrometric and photometric constraints minimized the
contamination. A minimum spanning tree algorithm was used to quantify the mass
segregation. We discovered 43 new Hyades member candidates with velocity
perpendicular to the Hyades motion up to 2 km/s. They have mass estimates
between 0.43 and 0.09 Msol, for a total mass of 10 Msol. This doubles the
number of Hyades candidates with masses smaller than 0.15 Msol. We provide an
additional list of 11 possible candidates with velocity perpendicular to the
Hyades motion up to 4 km/s. The cluster is significantly mass segregated. The
extension of the mass function towards lower masses provided an even clearer
signature than estimated in the past. We also identified as likely Hyades
member an L0 dwarf previously assumed to be a field dwarf. Finally we question
the membership of a number of previously published candidates, including a
L2.5-type dwarf.
