Exploring the Sagittarius Stream with SEKBO Survey RR Lyrae Stars
  A sample of RR Lyrae (RRL) variables from the Southern Edgeworth-Kuiper Belt
Object survey in regions overlapping the expected position of debris from the
interaction of the Sagittarius (Sgr) dwarf galaxy with the Milky Way (RA ~ 20
and 21.5 h; distance 16-21 kpc) has been followed up spectroscopically and
photometrically. The 21 photometrically confirmed type ab RRLs have mean [Fe/H]
= -1.79 +/- 0.08, consistent with the abundances found for RRLs in a different
portion of the Sgr tidal debris stream. The distribution of velocities in the
Galactic standard of rest frame (V_GSR) of the 26 RRLs in the region is not
consistent with a smooth halo population. Upon comparison with the Sgr
disruption models of Law et al (2005), a prominent group of five stars having
highly negative radial velocities (V_GSR ~ -175 kms-1) is consistent with
predictions for old trailing debris when the Galactic halo is modeled as
oblate. The observations also require that the recent trailing debris stream
has a broader spread perpendicular to the Sgr plane than predicted by the
models. We have also investigated the possible association of the Virgo Stellar
Stream (VSS) with Sgr debris by comparing radial velocities for RRLs in the
region with the same models, finding similarities in the velocity-position
trends. As suggested by our earlier work, the stars in the VSS region with
large negative V_GSR values are likely to be old leading Sgr debris, but we
find that while old trailing Sgr debris may well make a contribution at
positive V_GSR values, it is unlikely to fully account for the VSS feature.
Overall we find that further modeling is needed, as trailing arm data generally
favors oblate models while leading arm data favors prolate models, with no
single potential fitting all the observed data.
