2006A&A...447..929P

We report detection of moderate to high-mass star formation in an infrared dark cloud (G11.11-0.12) where we discovered class II methanol and water maser emission at 6.7GHz and 22.2GHz, respectively. We also observed the object in ammonia inversion transitions. Strong emission from the (3,3) line indicates a hot (60K) compact component associated with the maser emission. The line width of the hot component (4km/s), as well as the methanol maser detection, are indicative of high mass star formation. To further constrain the physical parameters of the source, we derived the spectral energy distribution (SED) of the dust continuum by analysing data from the 2MASS survey, HIRAS, MSX, the Spitzer Space Telescope, and interferometric 3mm observations. The SED was modelled in a radiative transfer program: a) the stellar luminosity equals ∼1200L_☉ corresponding to a ZAMS star of 8M_☉; b) the bulk of the envelope has a temperature of 19 K; c) the mass of the remnant protostellar cloud in an area 8x10¹⁷cm or 15'' across amounts to 500M_☉, if assuming standard dust of the diffuse medium, and to about 60M_☉, should the grains be fluffy and have ice mantles; d) the corresponding visual extinction towards the star, A_V, is a few hundred magnitudes. The near IR data can be explained by scattering from tenuous material above a hypothetical disk. The class II methanol maser lines are spread out in velocity over 11km/s. To explain the kinematics of the masing spots, we propose that they are located in a Kepler disk at a distance of about 250AU. The dust temperatures there are around 150K, high enough to evaporate methanol-containing ice mantles.