2004ApJ...605L..25K

Newberg et al., Yanny et al., Ibata et al., Rocha-Pinto et al., and Martin et al. have reported overdensities of stars that form a ring with a galactocentric distance (R_gal) of ≲18 kpc. Martin et al. and Frinchaboy et al. have found star clusters associated with these overdensities; Martin et al. found what seems to be the central overdensity in Canis Major, so we shall refer to it as the CMa ring. The stars in the CMa ring have a small velocity dispersion and [Fe/H] of about -0.4 and -1.6, respectively. Zinn et al. found a small RR Lyrae overdensity in the more populous southern arc of the CMa ring. We do not find any overdensity of RR Lyrae stars in a 65 deg² field that covers a more tenuous part of the ring in the anticenter. Existing evidence suggests that the halo component of the CMa ring has a horizontal-branch (HB) morphology that does not favor RR Lyrae stars; the evidence from the associated clusters suggests that it may be richer in blue HB stars. Our RR Lyrae sample in the anticenter contains three groups (each containing three stars that have a high probability of physical association). These groups account for half of the RR Lyrae stars with 17 kpc≤R_gal≤28 kpc in this field; all of these RR Lyrae stars are of Oosterhoff I type. It is suggested that they may be globular cluster remnants.