For a sample of metal-poor stars (-3.3< [Fe/H] <-2.2) that have
high-resolution spectroscopic abundance determinations, we have measured
equivalent widths (EW) of the Ca II K, Mg I b and near-infrared (NIR) Ca II
triplet lines using low-resolution spectra of the Sloan Digital Sky Survey
(SDSS), calculated effective temperatures from (g-z)0 color, deduced stellar
surface gravities by fitting stellar isochrones, and determined metallicities
based on the aforementioned quantities. Metallicities thus derived from the Ca
II K line are in much better agreement with the results determined from
high-resolution spectra than the values given in the SDSS Data Release 7 (DR7).
The metallicities derived from the Mg I b lines have a large dispersion owing
to the large measurement errors, whereas those deduced from the Ca II triplet
lines are too high due to both non-local thermodynamical equilibrium (NLTE)
effects and measurement errors. Abundances after corrected for the NLTE effect
for the Mg I b lines and Ca II triplet lines are also presented. Following this
method, we have identified six candidates of ultra-metal-poor stars with [Fe/H]
<-4.0 from a sample of 166 metal-poor star candidates. One of them, SDSS
J102915+172927, was recently confirmed to be an ultra-metal-poor ([Fe/H] <
-4.0) star with the lowest metallicity ever measured. Follow-up high-resolution
spectroscopy for the other five ultra-metal-poor stars in our sample will
therefore be of great interest.Comment: 12 pages, 3 figures, to be published in Research in Astronomy and
Astrophysics (RAA
