New white dwarfs in the Hyades

Results from kinematic and photometric studies

Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12-14, 69120 Heidelberg, Germany
e-mail: elena@ari.uni-heidelberg.de; roeser@ari.uni-heidelberg.de

Received: 12 July 2011
Accepted: 14 November 2011

Abstract

Aims. On the basis of the PPMXL catalogue (Röser et al. 2010, AJ, 139, 2440) we searched for white dwarfs that are also member candidates of the Hyades in a region up to 40 pc from the cluster centre.

Methods. We used the proper motions from PPMXL in the convergent point method to determine probable kinematic members. We cross-matched the kinematic candidates with catalogues containing white dwarfs and, finally, checked the kinematic with the photometric distances for consistency.

Results. We found the 10 classical white dwarfs in the Hyades and determined their individual kinematic distances. Additionally, we identified 17 new probable (former) Hyades white dwarfs, i.e. white dwarfs co-moving with the bulk space motion of the Hyades cluster. At present, none of them can be excluded from membership on the basis of the measured radial velocities. For another 10 objects, the kinematic and the photometric distances disagree, which rates them as probable non-members. Among the probable members, five white dwarfs are in binary systems, three are known, two are new. There is good indication for an empirical magnitude-distance (from centre) relation, such that the dimmer white dwarfs are farther away from the cluster centre than the brighter ones. Our sample becomes incomplete close behind the centre of the cluster. Follow-up observations are encouraged to independently confirm the predicted radial velocities and the distances of the candidates.