A direct measurement of the distance to the Galactic center using the
  kinematics of bar stars
  The distance to the Galactic center $R_0$ is a fundamental parameter for
understanding the Milky Way, because all observations of our Galaxy are made
from our heliocentric reference point. The uncertainty in $R_0$ limits our
knowledge of many aspects of the Milky Way, including its total mass and the
relative mass of its major components, and any orbital parameters of stars
employed in chemo-dynamical analyses. While measurements of $R_0$ have been
improving over a century, measurements in the past few years from a variety of
methods still find a wide range of $R_0$ being somewhere within $8.0$ to
$8.5\,\mathrm{kpc}$. The most precise measurements to date have to assume that
Sgr A$^*$ is at rest at the Galactic center, which may not be the case. In this
paper, we use maps of the kinematics of stars in the Galactic bar derived from
APOGEE DR17 and Gaia EDR3 data augmented with spectro-photometric distances
from the \texttt{astroNN} neural-network method. These maps clearly display the
minimum in the rotational velocity $v_T$ and the quadrupolar signature in
radial velocity $v_R$ expected for stars orbiting in a bar. From the minimum in
$v_T$, we measure $R_0 = 8.23 \pm 0.12\,\mathrm{kpc}$. We validate our
measurement using realistic $N$-body simulations of the Milky Way. We further
measure the pattern speed of the bar to be $\Omega_\mathrm{bar} =
40.08\pm1.78\,\mathrm{km\,s}^{-1}\mathrm{kpc}^{-1}$. Because the bar forms out
of the disk, its center is manifestly the barycenter of the bar+disc system and
our measurement is therefore the most robust and accurate measurement of $R_0$
to date.
