The Stars of the HETDEX Survey. I. Radial Velocities and Metal-Poor
  Stars from Low-Resolution Stellar Spectra
  The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is an unbiased,
massively multiplexed spectroscopic survey, designed to measure the expansion
history of the universe through low-resolution ($R\sim750$) spectra of
Lyman-Alpha Emitters. In its search for these galaxies, HETDEX will also
observe a few 10$^{5}$ stars. In this paper, we present the first stellar
value-added catalog within the internal second data release of the HETDEX
Survey (HDR2). The new catalog contains 120,571 low-resolution spectra for
98,736 unique stars between $10 < G < 22$ spread across the HETDEX footprint at
relatively high ($b\sim60^\circ$) Galactic latitudes. With these spectra, we
measure radial velocities (RVs) for $\sim$42,000 unique FGK-type stars in the
catalog and show that the HETDEX spectra are sufficient to constrain these RVs
with a 1$\sigma$ precision of 28.0 km/s and bias of 3.5 km/s with respect to
the LAMOST surveys and 1$\sigma$ precision of 27.5 km/s and bias of 14.0 km/s
compared to the SEGUE survey. Since these RVs are for faint ($G\geq16$) stars,
they will be complementary to Gaia. Using t-Distributed Stochastic Neighbor
Embedding (t-SNE), we also demonstrate that the HETDEX spectra can be used to
determine a star's T${\rm{eff}}$, and log g and its [Fe/H]. With the t-SNE
projection of the FGK-type stars with HETDEX spectra we also identify 416 new
candidate metal-poor ([Fe/H] $< -1$~dex) stars for future study. These
encouraging results illustrate the utility of future low-resolution stellar
spectroscopic surveys.
