Title: The most-metal poor dwarfs of the binary CS 22876--032: Abundances and 3D effects
Author(s): Jonay I. Gonzalez Hernandez
Abstract:
Unevolved extremely metal-poor stars offer us a unique tool to infer
knowledge of the first generation of stars. We have analysed the UVES
high-resolution spectra of the double-lined spectroscopic
binary CS 22876--032 which comprises the two most metal-poor
dwarfs known. In particular, we determine the oxygen (from OH lines in
the near-UV) and lithium abundances taking into account 3D effects.
The long-time baseline radial velocity measurements and
photometric data available allowed us to determine the orbital
elements as well as stellar parameters of both components. We
use OSMARCS 1D models and the {\scshape turbospectrum} spectral
synthesis code to determine the abundances of Li, O, Na, Mg, Al, Si,
Ca, Sc, Ti, Cr, Mn, Fe, Co and Ni. We also use the CO$^5$BOLD
code to predict the 3D abundance corrections, mainly for Li, O and Fe.
We find a metallicity of [Fe/H]$\sim -3.6$ for both stars
using 1D models with 3D corrections from horizontal and temporal
average 3D models around -0.1 dex. We find $\alpha-$elements
consistent with those found for metal-poor giants with similar
iron content although Ca and Si show rather low values [X/Fe]$\simeq
0$. A significantly high 1D abundance ratio [O/Fe]$\sim 2$ has been
obtained for both stars although 3D models predict large abundance
corrections of roughly -1 dex and -1.5 dex for the secondary and
primary stars, respectively. The Li abundance seems to be consistent
with the Spite plateau although the secondary star shows a slightly
lower abundance. These abundances have been discussed in the context
of the chemical evolution of the Galaxy at the lowest metallicities in
comparison with the most recent results.
Online version of poster
Conference proceedings (pdf)
