Investigation of the Contamination of the Gould (2003) Halo Sample

Understand

A recent astroph posting argued that the Gould (2003a) halo sample is substantially contaminated with thick-disk stars, which would then ``wash out'' any signature of granularity in the halo velocity distribution due to streams.

• If correct, this would imply that the limits placed by Gould (2003b) on streams are not valid.
• Here I investigate such contamination using six different indicators: (1) morphology of the underlying reduced proper motion diagram used to select halo stars; (2) comparison of kinematic and parallax-based distance scales; (3) comparison of derived halo parameters for the Gould (2003a) sample with other determinations; (4) a precision color-color diagram for a random subsample; (5) the 3-dimensional velocity distribution of a random subsample; (6) metallicity distribution versus kinematic cuts on a random subsample.
• I estimate that the contamination is of order 2%.