Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...21113110l&link_type=abstract
American Astronomical Society, AAS Meeting #211, #131.10; Bulletin of the American Astronomical Society, Vol. 39, p.960
Astronomy and Astrophysics
Astrophysics
Scientific paper
We have developed techniques for the estimation of [α/Fe] ratios for moderate- to high- S/N medium-resolution spectra obtained with the SDSS, and tested by these estimates by comparison with external libraries (ELODIE and MILES) of high- and medium-resolution spectra with available [Mg/Fe], [Si/Fe], [Ca/Fe], or [Ti/Fe] measurements, based on averages of these elements, when available. Our tests indicate that, for sufficiently high-quality spectra, we are able to obtain estimates of [α/Fe] with a precision of about 0.06 dex. We apply these procedures to the sample of the SDSS DR-5 calibration stars used by Carollo et al. (2007, Nature, in press) to argue for the existence of a dichotomy in the spatial distribution, orbital properties, and metallicities of the halo populations of the Milky Way. Our initial investigation of the [α/Fe] patterns in the halo populations concentrates on the contrast in the observed behavior for stars with prograde and retrograde orbits. Stars with prograde orbits are assumed to be dominated by inner-halo stars, while those with retrograde orbits should include a larger fraction of stars that are members of the outer-halo population. We also compare the observed distribution of [α/Fe] for halo stars with that observed for stars that are members of dwarf spheroidal galaxies surrounding the Milky Way.
We would like to acknowledge support from grant PHY 02-16783; Physics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA), awarded by the U.S. National Science Foundation.
Beers Timothy C.
Carollo Daniela
Lee Young Sam
Sivarani Thirupathi
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