J. J. Li, L. Moscadelli, R. Cesaroni, R. S. Furuya, Y. Xu, T. Usuda, K. M. Menten, M. Pestalozzi, D. Elia, E. Schisano
We used the Very Long Baseline Array (VLBA) and the European VLBI Network
(EVN) to perform phase-referenced VLBI observations of the three most powerful
maser transitions associated with the high-mass star-forming region
G28.87+0.07: the 22.2 GHz H$_{2}$O, 6.7 GHz CH$_{3}$OH, and 1.665 GHz OH lines.
We also performed VLA observations of the radio continuum emission at 1.3 and
3.6 cm and Subaru observations of the continuum emission at 24.5 $\mu$m. Two
centimeter continuum sources are detected and one of them (named "HMC") is
compact and placed at the center of the observed distribution of H$_{2}$O,
CH$_{3}$OH and OH masers. The bipolar distribution of line-of-sight (l.o.s)
velocities and the pattern of the proper motions suggest that the water masers
are driven by a (proto)stellar jet interacting with the dense circumstellar
gas. The same jet could both excite the centimeter continuum source named "HMC"
(interpreted as free-free emission from shocked gas) and power the molecular
outflow observed at larger scales -- although one cannot exclude that the
free-free continuum is rather originating from a hypercompact \ion{H}{2}
region. At 24.5 $\mu$m, we identify two objects separated along the north-south
direction, whose absolute positions agree with those of the two VLA continuum
sources. We establish that $\sim$90% of the luminosity of the region
($\sim$\times10^{5} L_\sun$) is coming from the radio source "HMC", which
confirms the existence of an embedded massive young stellar object (MYSO)
exciting the masers and possibly still undergoing heavy accretion from the
surrounding envelope.
View original:
http://arxiv.org/abs/1201.3021
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