Abstract:
We present an elemental-abundance analysis of an extremely metal-poor (EMP; [Fe/H] <−3.0)
star, SDSS J134338.67+484426.6, identified during the course of the Multi-object Apache
Point Observatory Radial Velocity Exoplanet Large-area Survey spectroscopic pre-survey of
some 20 000 stars to identify suitable candidates for exoplanet searches. This star, with an
apparent magnitude V = 12.14, is the lowest metallicity star found in the pre-survey, and
is one of only ∼20 known EMP stars that are this bright or brighter. Our high-resolution
spectroscopic analysis shows that this star is a subgiant with [Fe/H] = −3.42, having ‘normal’
carbon and no enhancement of neutron-capture abundances. Strontium is underabundant,
[Sr/Fe] = −0.47, but the derived lower limit on [Sr/Ba] indicates that Sr is likely enhanced
relative to Ba. This star belongs to the sparsely populated class of α-poor EMP stars that
exhibit low ratios of [Mg/Fe], [Si/Fe], and [Ca/Fe] compared to typical halo stars at similar
metallicity. The observed variations in radial velocity from several epochs of (low- and highresolution) spectroscopic follow-up indicate that SDSS J134338.67+484426.6 is a possible
long-period binary. We also discuss the abundance trends in EMP stars for r-process elements,
and compare with other magnesium-poor stars.
