IRAS 19520+2759: a 10^5 Lsun massive young stellar object driving a
  collimated outflow
  The theory of massive star formation currently suffers from a scarce
observational base of massive young stellar objects to compare with. In this
paper, we present OVRO CO(1-0), 13CO(1-0), C18O(1-0), and 2.6 mm continuum
images of the infrared source IRAS 19520+2759 together with complementary
single-dish observations of CS(1-0), obtained with the 34m antenna DSS-54 at
the Madrid Deep Space Communications Complex, as well as archive images at
different wavelengths. As a result from our work, IRAS 19520+2759, with a
controversial nature in the past, is firmly established as a massive young
stellar object associated with a strong and compact millimetre source and
driving a collimated outflow. In addition, a second fainter millimetre source
is discovered about 4 arcsec to the south, which is also driving an outflow.
Furthermore, the two millimetre sources are associated with C18O clumps
elongated perpendicularly to the outflows, which may be related to rotating
toroids. The masses of gas and dust of the millimetre sources are estimated to
be around 100 and 50 Msun. MM1, the dominant source at all wavelengths, with a
total luminosity of (1-2)x10^5 Lsun at 9 kpc, is however not associated with 6
cm emission down to a rms noise level of 0.1 mJy. We propose that IRAS
19520+2759 could be an example of the recent theoretical prediction of
`bloated' or `swollen' star, i.e., a massive young stellar object whose radius
has increased due to effects of accretion at a high-mass accretion rate.
