We report on a pilot study on identifying metal-poor stars pre-enriched by
Pair-Instability Supernovae (PISNe). Very massive, first generation (Population
III) stars (140M\odot \leq M \leq 260M\odot) end their lives as PISNe, which
have been predicted by theories, but no relics of PISNe have been observed yet.
Among the distinct characteristics of the yields of PISN, as predicted by
theoretical calculations, are a strong odd-even effect, and a strong
overabundance of Ca with respect to iron and the Solar ratio. We use the latter
characteristic to identify metal-poor stars in the Galactic halo that have been
pre-enriched by PISN, by comparing metallicites derived from strong, co-added
Fe lines detected in low-resolution (i.e., R \sim 2000) spectra of the Sloan
Digital Sky Survey (SDSS), with metallicities determined by the SDSS Stellar
Parameters Pipeline (SSPP). The latter are based on the strength of the Ca II K
line and assumptions on the Ca/Fe abundance ratio. Stars are selected as
candidates if their metallicity derived from Fe lines is significantly lower
than the SSPP metallicities. In a sample of 12,300 stars for which SDSS
spectroscopy is available, we have identified 18 candidate stars. Higher
resolution and signal-to-noise ratio spectra of these candidates are being
obtained with the Very Large Telescope of the European Southern Observatory and
the XSHOOTER spectrograph, to determine their abundance patterns, and to verify
our selection method. We plan to apply our method to the data base of several
million stellar spectra to be acquired with the LAMOST telescope in the next
five years.Comment: Accepted by RA