Chemical Fingerprinting the Milky Way's Accretion Past

Chou, M.-Y., Majewski, S. R., Smith, V. V., Cunha, K., Patterson, R. J., Crane, J. D., and Martinez-Delgado, D.
American Astronomical Society Meeting 207, #133.10; Bulletin of the American Astronomical Society, Vol. 37, p.1384


Stars have distinctive abundance patterns that reflect the unique chemical history of their parent system. In principle, therefore, ``chemical fingerprinting" can help identify groups of stars in the Milky Way halo that have been tidally stripped from the same parent satellite. Recently, M giant stars moving in apparent tidal streams or moving groups have been discovered in the Galactic halo using the Two Micron All-Sky Survey (2MASS). The majority of the M giants can be associated with the tidal disruption of the Sagittarius (Sgr) dSph galaxy, but others have positions and velocities that are not clearly consistent with an origin as Sgr debris. We have begun a program of high resolution spectroscopy of these M giants in order to: (1) determine whether the tidal stream M giant stars that are almost certainly associated with Sgr maintain the peculiar s-process abundance ratios that is the hallmark of K giant stars observed in the Sgr core, (2) establish other fingerprint characteristics of Sgr tidal debris stars, and (3) check whether halo M giants in more peculiar parts of phase space can be chemically fingerprinted as Sgr in origin as well. If so, some refinements in the Sgr destruction models may be required. Initial results show that we find similarly high [La/Y] ratios among leading arm Sgr stream M giants and in another moving group of M giants having similar positions to the leading Sgr debris in the northern Galactic hemisphere but with opposite radial velocity. This suggests that the latter moving group may represent older debris from the Sgr trailing arm overlapping the well known leading arm in the northern Galactic hemisphere.

Acknowledgements: This work was supported by NSF grants AST-0307851 as well as a SIM Key Project grant, NASA/JPL contract 1228235. This work was also partially supported by the F.H. Levinson Fund of the Peninsula Community Foundation.