Speaker
Timothy Beers
(Michigan State University and JINA)
Description
Recent large surveys of metal-poor stars in the Galaxy have revealed that a
surprising fraction of them are enhanced in their carbon-to-iron ratios by
factors of from 10-10,000 relative to the solar ratio. Although most of the
stars in the metallicity interval -2.7 < [Fe/H] < -2.0 are likely to have arisen
from Asymptotic Giant Branch processing (and subsequent dumping via mass
transfer to a surviving companion), there exist many stars with [Fe/H] < -3.0
(including the two lowest [Fe/H] stars known, with [Fe/H] < -5.0) that cannot be
accounted for by this process. Rather, primordial (or nearly primordial)
progenitors are implicated.
We report on the existing information from present surveys, including cool
giants from the recently completed HERES (Hamburg/ESO R-process Enhanced Star)
survey, and from warm turnoff stars from SDSS-I. We will also describe the
results that will come from the recently-funded extension of the SDSS, which
includes the program SEGUE = Sloan Extension for Galactic Understanding and
Exploration. SEGUE will identify some 20,000 stars with [Fe/H] < -2.0, several
thousand of which are expected to be carbon enhanced. New carbon-enhanced models
have been used in the analyses of these spectra, and we consider the impact of
these models on the derived [Fe/H], [C/Fe], and in some cases, [N/Fe], that are
derived.
Author
Timothy Beers
(Michigan State University and JINA)
Co-authors
Mr
Brian Marsteller
(Michigan State University and JINA)
Prof.
Gillian Knapp
(Princeton University)
Prof.
Norbert Christlieb
(Uppsala University, Sweden)
Prof.
Paul Barklem
(Uppsala University, Sweden)
Dr
Sara Lucatello
(University of Padova, Italy)
Prof.
Silvia Rossi
(IAG, University of Sao Paulo, Brazil)
Dr
Thirupathi Sivarani
(Michigan State University and JINA)
Mr
Thomas Masseron
(University of Montpelier, France)
