Program: GS-2006B-Q-37

The spatial distribution of 2MASS M giants points to two low-latitude stellar overdensities (Canis Major and Argo) as candidate cores of a putative satellite galaxy responsible for the Monoceros tidal stream seen at 8 to 14 kpc away from the Sun in the antigalactic center direction. While the tidal stream status of Monoceros seems to be pretty much undisputed in the literature, a noisy controversy arose on the nature of both Argo and Canis Major: some authors claim that at least one or both of these overdensities are the stellar counterpart of the gas warp or part of an external spiral arm. In order to address the nature of these structures, we propose to look for chemical signatures in six M giants, (two in each stellar structure) measured by the abundances of Fe, Ti and O. We expect to address whether these three stellar overdensities have had a similar chemical history, that would argue for its common origin, or whether some of them could be considered disk stars, as the warp and spiral arm hypotheses propose.