Towards a complete stellar mass function of the Hyades. I. Pan-STARRS1 optical observations of the low-mass stellar content

TL;DR

This study extends the Hyades cluster's stellar mass function down to 0.1 solar masses using Pan-STARRS1 data, revealing significant mass segregation and identifying new low-mass members, thereby improving understanding of cluster evolution.

Contribution

The paper presents a comprehensive method combining kinematic and photometric data to identify low-mass Hyades members, doubling the known candidates below 0.15 solar masses and analyzing mass segregation.

Findings

Discovered 43 new low-mass Hyades candidates

Extended the mass function to 0.1 Msol, showing clear mass segregation

Questioned membership of some previously identified candidates

Abstract

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.