2001/04/30 by I. Neill Reid, Kailash C. Sahu, Suzanne L. Hawley · 6 citations
Physics and Astronomy · Social Sciences · #Astronomy and Astrophysical Research #Educational Leadership and Practices #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/322362
11 pages, 5 figures; accepted for ApJ, 29 May 2001
arxiv created 2001/05/31 · openalex publication_date 2001/10/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
We present an alternative interpretation of the nature of the extremely cool, high-velocity white dwarfs identified by Oppenheimer et al (2001) in a high-latitude astrometric survey. We argue that the velocity distribution of the majority of the sample is more consistent with the high-velocity tail of a rotating population, probably the thick disk, rather than a pressure-supported halo system. Indeed, the observed numbers are well matched by predictions based on the kinematics of a complete sample of nearby M dwarfs. Analysing only stars showing retrograde motion gives a local density close to that expected for white dwarfs in the stellar (R-3.5) halo. Under our interpretation, none of the white dwarfs need be assigned to the dark-matter, heavy halo. However, luminosity functions derived from observations of these stars can set important constraints on the age of the oldest stars in the Galactic Disk.