Chemical composition of two bright extremely metal-poor stars from the SDSS MARVELS pre-survey

TL;DR

This study analyzes the chemical compositions of two extremely metal-poor stars, revealing their neutron-capture element deficiencies, carbon enhancement in one star, and potential binarity, contributing to understanding early supernovae and stellar evolution.

Contribution

First detailed high-resolution chemical abundance analysis of two EMP stars from SDSS-MARVELS, highlighting their neutron-capture deficiencies and carbon enhancement, and comparing them with other metal-poor stars.

Findings

Both stars show neutron-capture element under-abundances.

One star is clearly carbon-enhanced.

Lithium detected at A(Li) = 1.95 in the carbon-enhanced star.

Abstract

\sdsszeroeight\ (V = 11.4; [Fe/H] = $-$3.1) and \sdssonethree\ (V = 12.4; [Fe/H] = $-$3.2) were observed with the SDSS 2.5-m telescope as part of the SDSS-MARVELS spectroscopic pre-survey, and were identified as extremely metal-poor (EMP; [Fe/H] $< -3.0$) stars during high-resolution follow-up with the Hanle Echelle Spectrograph (HESP) on the 2.3-m Himalayan Chandra Telescope. In this paper, the first science results using HESP, we present a detailed analysis of their chemical abundances. Both the stars exhibit under-abundances in their neutron-capture elements, while one of them, \sdssonethree, is clearly enhanced in carbon. Lithium was also detected in this star at a level of about A(Li) = 1.95. The spectra were obtained over a span of 6-24 months, and indicate that both stars could be members of binary systems. We compare the elemental abundances derived for these two stars along with other carbon-enhanced metal-poor (CEMP) and EMP stars, in order to understand the nature of their parent supernovae. We find that CEMP-no stars and EMP dwarfs exhibit very similar trends in their lithium abundances at various metallicities. We also find indications that CEMP-no stars have larger abundances of Cr and Co at a given metallicity, compared to EMP stars.