The Most Metal-Poor Stars. I. Discovery, Data, and Atmospheric
  Parameters
  We report the discovery of 34 stars in the Hamburg/ESO Survey for metal-poor
stars and the Sloan Digital Sky Survey that have [Fe/H] < -3.0. Their median
and minimum abundances are [Fe/H] = -3.1 and -4.1, respectively, while 10 stars
have [Fe/H] < -3.5. High-resolution, high-S/N spectroscopic data - equivalent
widths and radial velocities - are presented for these stars, together with an
additional four objects previously reported or currently being investigated
elsewhere. We have determined the atmospheric parameters, effective temperature
(Teff) and surface gravity (logg), which are critical in the determination of
the chemical abundances and the evolutionary status of these stars. Three
techniques were used to derive these parameters. Spectrophotometric fits to
model atmosphere fluxes were used to derive Teff, logg, and an estimate of
E(B-V); Halpha, Hbeta, and Hgamma profile fitting to model atmosphere results
provided the second determination of Teff and logg; and finally, we used an
empirical Teff-calibrated Hdelta index, for the third, independent Teff
determination. The three values of Teff are in good agreement, although the
profile fitting may yield systematically cooler Teff values, by ~100K. This
collective data set will be analyzed in future papers in the present series to
utilize the most metal-poor stars as probes of conditions in the early
Universe.
