Title : High mass star formation in an Infrared dark cloud
Authors : T. Pillai, F. Wyrowski, K.M. Menten, E. Kruegel
Abstract :
We report the first detection of moderate to high-mass star formation
in an Infrared dark cloud (G11.11-0.12) where we detected a class II methanol
maser and water maser at 6.7 GHz and 22.2 GHz, respectively. Such masers are
unambiguous tracers of massive star formation and usually associated with
ultra--compact HII regions. We observed the object also in ammonia inversion
transitions. We find two components the hotter of which with a rotation
temperature T_rot=60K is smaller than 4' and has a column density
N_NH_3= 8times 10^14 cm{-2}. The line width of the hot component
(4 km/s) is also indicative of high mass star formation. To further constrain
the physical parameters of the source, we derive the spectral energy
distribution (SED) of the dust continuum by analyzing the data from the 2MASS
survey, HIRAS, MSX and by providing a new 3mm point. The SED was modeled in a
radiative transfer program. The interpretation of the disk
is not unique, however, the models agree in their
estimates on the main parameters. a) The stellar luminosity equals
1500 L_\odot corresponding to a ZAMS star of 8 M$_\odot$. {\it b)} The
bulk of the envelope is at a temperature of 19 K. {\it c)} The mass of the
remnant protostellar cloud in an area $8\times 10^{17}$ cm or 15$''$ across
amounts to 500\,M$_\odot$ assuming standard dust of the diffuse medium, and to
about 60 M$_\odot$ should the grains be fluffy and have ice mantles.