Vanadium Abundance Derivations in 255 Metal-poor Stars
  We present vanadium (V) abundances for 255 metal-poor stars, derived from
high-resolution optical spectra from the Magellan Inamori Kyocera Echelle
spectrograph on the Magellan Telescopes at Las Campanas Observatory, the Robert
G. Tull Coud\'{e} Spectrograph on the Harlan J. Smith Telescope at McDonald
Observatory, and the High Resolution Spectrograph on the Hobby-Eberly Telescope
at McDonald Observatory. We use updated V I and V II atomic transition data
from recent laboratory studies, and we increase the number of lines examined
(from 1 to 4 lines of V I, and from 2 to 7 lines of V II). As a result, we
reduce the V abundance uncertainties for most stars by more than 20% and expand
the number of stars with V detections from 204 to 255. In the metallicity range
$-$4.0 $<$ [Fe/H] $< -$1.0, we calculate the mean ratios [V I/Fe I]$ = -0.10
\pm 0.01 (\sigma = 0.16)$ from 128 stars with $\geq$ 2 V I lines detected, [V
II/Fe II] $= +0.13 \pm 0.01 (\sigma = 0.16)$ from 220 stars with $\geq$ 2 V II
lines detected, and [V II/V I] $= +0.25 \pm 0.01 (\sigma = 0.15)$ from 119
stars. We suspect this offset is due to non-LTE effects, and we recommend using
[V II/Fe II], which is enhanced relative to the solar ratio, as a better
representation of [V/Fe]. We provide more extensive evidence for abundance
correlations detected previously among scandium, titanium, and vanadium, and we
identify no systematic effects in the analysis that can explain these
correlations.
