Binary system and jet precession and expansion in G35.20-0.74N
  Context. ALMA observations of the high-mass star-forming region G35.20-0.74N
have revealed the presence of a Keplerian disk in core B rotating about a
massive object of 18 Msun, as computed from the velocity field. The luminosity
of such a massive star would be comparable to (or higher than) the luminosity
of the whole star-forming region. To solve this problem it has been proposed
that core B could harbor a binary system. This could also explain the possible
precession of the radio jet associated with this core, which has been suggested
by its S-shaped morphology. Aims. To establish the origin of the free-free
emission from core B and investigate the existence of a binary system at the
center of this massive core and the possible precession of the radio jet.
Methods. We carried out VLA continuum observations of G35.20-0.74N at 2 cm in
the B configuration and at 1.3 cm and 7 mm in the A and B configurations. The
bandwidth at 7 mm covers the CH3OH maser line at 44.069 GHz. Continuum images
at 6 and 3.6 cm in the A configuration were obtained from the VLA archive. We
also carried out VERA observations of the H2O maser line at 22.235 GHz.
Results. The observations have revealed the presence of a binary system of
UC/HC HII regions at the geometrical center of the radio jet in G35.20-0.74N.
This binary system, which is associated with a Keplerian rotating disk,
consists of two B-type stars of 11 and 6 Msun. The S-shaped morphology of the
radio jet has been successfully explained as due to precession produced by the
binary system. The analysis of the precession of the radio jet has allowed us
to better interpret the IR emission in the region, which would be not tracing a
wide-angle cavity open by a single outflow with a position angle of ~55 deg but
two different flows: a precessing one in the NE-SW direction associated with
the radio jet, and a second one in an almost E--W direction ...
