Deciphering the ionized gas content in the massive star forming complex
  G75.78+0.34
  We present sub-arcsecond observations toward the massive star forming region
G75.78+0.34. We used the Very Large Array to study the centimeter continuum and
H2O and CH3OH maser emission, and the Owens Valley Radio Observatory and
Submillimeter Array to study the millimeter continuum and recombination lines
(H40alpha and H30alpha). We found radio continuum emission at all wavelengths,
coming from three components: (1) a cometary ultracompact (UC) HII region with
an electron density 3.7x10^4 cm^{-3}, excited by a B0 type star, and with no
associated dust emission; (2) an almost unresolved UCHII region (EAST), located
6 arcsec to the east of the cometary UCHII region, with an electron density
1.3x10^5 cm^{-3}, and associated with a compact dust clump detected at
millimeter and mid-infrared wavelengths; and (3) a compact source (CORE),
located 2 arcsec to the southwest of the cometary arc, with a flux density
increasing with frequency, and embedded in a dust condensation of 30 Msun. The
CORE source is resolved into two compact and unresolved sources which can be
well-fit by two homogeneous hypercompact HII regions each one photo-ionized by
a B0.5 ZAMS star, or by free-free radiation from shock-ionized gas resulting
from the interaction of a jet/outflow system with the surrounding environment.
The spatial distribution and kinematics of water masers close to the CORE-N and
S sources, together with excess emission at 4.5 mum and the detected dust
emission, suggest that the CORE source is a massive protostar driving a
jet/outflow.
