On high proper motion white dwarfs from photographic surveys

Free access article

Issue		A&A Volume 378, Number 3, November II 2001


Page(s)		L53 - L56
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20011296

A&A 378, L53-L56 (2001)
DOI: 10.1051/0004-6361:20011296

On high proper motion white dwarfs from photographic surveys

C. Reylé¹, A. C. Robin¹ and M. Crézé²

¹ CNRS UMR6091, Observatoire de Besançon, BP1615, 25010 Besançon Cedex, France
² Université de Bretagne-Sud, BP 573, 56017 Vannes Cedex, France

(Received 13 August 2001 / Accepted 15 September 2001)

Abstract
The interpretation of high proper motion white dwarfs detected by Oppenheimer et al. ([CITE]) was the start of a lively controversy. While the discoverers identify a large fraction of their findings as dark halo members, others interpret the same sample as essentially made of disc and/or thick disc stars. We use the comprehensive description of Galactic stellar populations provided by the "Besançon" model to produce a realistic simulation of Oppenheimer et al. data, including all observational selections and calibration biases. The conclusion is unambiguous: Thick disc white dwarfs resulting from ordinary hypotheses on the local density and kinematics are sufficient to explain the observed objects, there is no need for halo white dwarfs. This conclusion is robust to reasonable changes in model ingredients. The main cause of the misinterpretation seems to be that the velocity distribution of a proper motion selected star sample is severely biased in favour of high velocities. This has been neglected in previous analyses. Obviously this does not prove that no such objects like halo white dwarfs can exist, but Oppenheimer et al. observations drive their possible contribution in the dark matter halo down to an extremely low fraction.

Key words: cosmology: dark matter -- Galaxy: structure -- Galaxy: stellar content -- Galaxy: general

Offprint request: C. Reylé, celine@obs-besancon.fr

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