The Hyades Cluster: Identification of a Planetary System and Escaping White Dwarfs

TL;DR

This study confirms the membership of several white dwarfs in the Hyades cluster, identifies calcium pollution indicating planetary systems, and discusses the potential first case of an older Hyades white dwarf.

Contribution

It provides new radial velocity measurements confirming cluster membership and reports the detection of planetary system signatures in white dwarf atmospheres within the Hyades.

Findings

Confirmed Hyades membership for several white dwarfs

Detected calcium pollution indicating planetary systems

Identified a potentially older Hyades white dwarf

Abstract

Recently, some hot DA-type white dwarfs have been proposed to plausibly be escaping members of the Hyades. We used hydrogen Balmer lines to measure the radial velocities of seven such stars and confirm that three, and perhaps two others, are/were indeed cluster members and one is not. The other candidate Hyad is strongly magnetic and its membership status remains uncertain. The photospheres of at least one quarter of field white dwarf stars are "polluted" by elements heavier than helium that have been accreted. These stars are orbited by extended planetary systems that contain both debris belts and major planets. We surveyed the seven classical single Hyades white dwarfs and the newly identified (escaping) Hyades white dwarfs and found calcium in the photosphere of LP 475-242 of type DBA (now DBAZ), thus implying the presence of an orbiting planetary system. The spectrum of white dwarf GD 31, which may be, but probably is not, an escaping member of the Hyades, displays calcium absorption lines; these originate either from the interstellar medium or, less likely, from a gaseous circumstellar disk. If GD 31 was once a Hyades member, then it would be the first identified white dwarf Hyad with a cooling age >340 Myr.