Effect of orbital trapping by bar resonances in the local U-V velocity
  field
  The effects in the local U-V velocity field due to orbital trapping by bar
resonances have been studied computing fifteen resonant families in a
non-axisymmetric Galactic potential, considering the bar's angular velocity
between 35 and 57.5 ${\rm\,km\,s^{-1}{kpc}^{-1}}$. Only cases in the low, 37.5,
40 ${\rm\,km\,s^{-1}{kpc}^{-1}}$, and high, 55, 57.5
${\rm\,km\,s^{-1}{kpc}^{-1}}$, velocity ranges give trapping structures that
have some similarity with observed features in the velocity distribution. The
resulting structures in the local U-V plane form resonant bands appearing at
various levels in velocity V. Cases with angular velocity 40 and 55
${\rm\,km\,s^{-1}{kpc}^{-1}}$ show the greatest similarity with observed
branches. Our best approximation to the local velocity field by orbital
trapping is obtained with a bar angular velocity of 40
${\rm\,km\,s^{-1}{kpc}^{-1}}$ and a bar angle of 40${^\circ}$. With this
solution, three main observed features can be approximated: i) the Hercules
branch at V=$-50$ ${\rm\,km\,s^{-1}}$ produced by the resonance 8/1 outside
corotation, and the close features produced by resonances 5/1 and 6/1, ii) the
newly detected low-density arch at V $\simeq$ 40 ${\rm\,km\,s^{-1}}$ produced
approximately by the resonance 4/3, iii) the inclined structure below the
Hercules branch, also observed in the $\textit{Gaia}$ DR2 data, produced by
tube orbits around Lagrange point $L_5$ at corotation. Some predicted
contributions due to orbital trapping in regions of the U-V plane corresponding
to the Galactic halo are given, which could help to further restrict the value
of the angular velocity of the Galactic bar. No support by orbital trapping is
found for the Arcturus stream at V $\approx$ $-100$ ${\rm\,km\,s^{-1}}$.
