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 (R.A. ∼ 20 and 21.5 hr; distance = 16-21 kpc) has been followed up spectroscopically and photometrically. The 21 photometrically confirmed type ab RRLs in this region have ([Fe/H]) = -1.79 ± 0.08 on our system, 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., a prominent group of five stars having highly negative radial velocities (V GSR ∼-175 km s-1) is consistent with predictions for old trailing debris when the Galactic halo potential is modeled as oblate. In contrast, the prolate model does not predict any significant number of Sgr stars at the locations of the observed sample. 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 favor oblate models while leading arm data favor prolate models, with no single potential fitting all the observed data.