Stellar Systems Group

Dinescu, D. I., Martínez-Delgado, D., Girard, T. M., Peñarrubia, J., Rix, H.-W., Butler, D., and van Altena, W. F.
The Astrophysical Journal, Volume 631, Issue 1, pp. L49-L52 (2005).
09/2005

ABSTRACT

We have measured the absolute proper motion of the candidate Canis Major dwarf galaxy (CMa), at (l,b)=(240°,-8°). Likely main-sequence stars in CMa have been selected from a region in the color-magnitude diagram that has very little contamination from known Milky Way components. We obtain μlcosb=-1.47+/-0.37 and μb=-1.07+/-0.38 mas yr-1, on the International Celestial Reference System by means of Hipparcos stars. Together with the radial velocity of 109 km s-1 and the assumed distance of 8 kpc, these results imply a space motion of (Π,Θ,W)=(-5+/-12, 188+/-10, -49+/-15) km s-1. While CMa has in-plane rotation similar to the mean of thick-disk stars, it shows significant (3 σ) motion perpendicular to the disk and differs even more (7 σ) from that expected for the Galactic warp. The W-velocity lends support to the argument that the CMa overdensity is part of a satellite-galaxy remnant.