Towards a complete stellar mass function of the Hyades

Abstract

The Hyades cluster is an ideal target to study the dynamical evolution of a\nstar cluster over the entire mass range due to its intermediate age and\nproximity to the Sun. We wanted to extend the Hyades mass function towards\nlower masses down to 0.1 Msol and to use the full three-dimensional spatial\ninformation to characterize the dynamical evolution of the cluster. We\nperformed a kinematic and photometric selection using the PPMXL and Pan-STARRS1\nsky surveys, to search for cluster members up to 30 pc from the cluster centre.\nWe determined our detection efficiency and field star contamination rate to\nderive the cluster luminosity and mass functions down to masses of 0.1 Msol.\nThe thorough astrometric and photometric constraints minimized the\ncontamination. A minimum spanning tree algorithm was used to quantify the mass\nsegregation. We discovered 43 new Hyades member candidates with velocity\nperpendicular to the Hyades motion up to 2 km/s. They have mass estimates\nbetween 0.43 and 0.09 Msol, for a total mass of 10 Msol. This doubles the\nnumber of Hyades candidates with masses smaller than 0.15 Msol. We provide an\nadditional list of 11 possible candidates with velocity perpendicular to the\nHyades motion up to 4 km/s. The cluster is significantly mass segregated. The\nextension of the mass function towards lower masses provided an even clearer\nsignature than estimated in the past. We also identified as likely Hyades\nmember an L0 dwarf previously assumed to be a field dwarf. Finally we question\nthe membership of a number of previously published candidates, including a\nL2.5-type dwarf.\n