Abundance analysis of two extremely metal-poor stars from the Hamburg/ESO Survey

Abstract

We report on the first high spectral resolution analysis of extremely metal-poor halo stars from the Hamburg/ESO objective-prism survey (HES). The spectra were obtained with UVES at VLT-UT2. The two stars under investigation (\object {HE 1303--2708} and \object {HE 1353--2735}) are main-sequence turnoff-stars having metal abundances of [Fe/H]=-2.85 and -3.20, respectively. The stellar parameters derived from the UVES spectra are in very good agreement with those derived from moderate-resolution follow-up spectra. HE 1353--2735 is a double-lined spectroscopic binary. The two stars nicely reproduce the strong scatter in [Sr/Fe] observed for extremely metal-poor stars. While we see a strong Sr II $λ4215$ Å line in the spectrum of HE 1303--2708 ([Sr/Fe]=-0.08), we can only give an upper limit for HE 1353--2735 ([Sr/Fe]<-1.2), since the line is not detected. We report abundances of Mg, Ca, Sc, Ti, Cr for both stars, and Co, Y for respect to known trends for metal-poor stars.Lithium is also detected in these stars, to a level which places them among Lithium-plateau metal-poor dwarfs.