Origin and Status of Low-Mass Candidate Hypervelocity Stars
  We present an analysis of the chemical abundances and kinematics of six
low-mass dwarf stars, previously claimed to be candidate hypervelocity stars
(HVSs). We obtained moderate-resolution ($R\sim$ 6000) spectra of these stars
to estimate their abundances of several chemical elements (Mg, Si, Ca, Ti, Cr,
Fe, and Ni), and derived their space velocity components and orbital parameters
using proper motions from \gaia\ Data Release 2. All six stars are shown to be
bound to the Milky Way, and in fact are not even considered high-velocity stars
with respect to the Galactic rest frame. Nevertheless, we attempt to
characterize their parent Galactic stellar components by simultaneously
comparing their abundance patterns and orbital parameters with those expected
from various Galactic stellar components. We find that two of our program stars
are typical disk stars. For four of the program stars, even though their
kinematic probabilistic membership assignment suggests membership in the
Galactic disk, based on their distinct orbital properties and chemical
characteristics, we cannot rule out the exotic origins of these objects, as
follows. Two stars appear to be runaway stars from the Galactic disk. One
program star has possibly been accreted from a disrupted dwarf galaxy or
dynamically heated from a birthplace in the Galactic bulge. The last object may
be either a runaway disk star or has been dynamically heated. Spectroscopic
follow-up observations with higher resolution for these curious objects will
provide a better understanding of their origin.
