A Double-Jet System in the G31.41+0.31 Hot Molecular Core
  This work presents a detailed study of the gas kinematics towards the "Hot
Molecular Core" (HMC) G31.41+0.31 via multi-epoch VLBI observations of the H2O
22 GHz and CH3OH 6.7 GHz masers, and single-epoch VLBI of the OH 1.6 GHz
masers. Water masers present a symmetric spatial distribution with respect to
the HMC center, where two nearby (0.2" apart), compact, VLA sources (labeled
"A" and "B") are previously detected. The spatial distribution of a first group
of water masers, named "J1", is well fit with an elliptical profile, and the
maser proper motions mainly diverge from the ellipse center, with average speed
of 36 km s-1. These findings strongly suggest that the "J1" water maser group
traces the heads of a young (dynamical time of 1.3 10^3 yr), powerful (momentum
rate of ~0.2 M_sun yr-1 km s-1), collimated (semi-opening angle ~10 deg) jet
emerging from a MYSO located close (within 0.15") to the VLA source "B". Most
of the water features not belonging to "J1" present an elongated (about 2" in
size), NE--SW oriented (PA = 70 deg), S-shape distribution, which we denote
with the label "J2". The elongated distribution of the "J2" group and the
direction of motion, approximately parallel to the direction of elongation, of
most "J2" water masers suggests the presence of another collimated outflow,
emitted from a MYSO near the VLA source "A". The orientation of the "J2" jet
agrees well with that (PA = 68 deg) of the well-defined V_LSR gradient across
the HMC revealed by previous interferometric, thermal line observations.
Furthermore, the "J2" jet is powerful enough to sustain the large momentum
rate, 0.3 M_sun yr-1 km s-1, estimated assuming that the V_LSR gradient
represents a collimated outflow. These two facts lead us to favour the
interpretation of the V_LSR gradient across the G31.41+0.31 HMC in terms of a
compact and collimated outflow.
