2004A&A...414..299F

We present the results of a multi-line and continuum study towards the source IRAS23385+6053 performed with the IRAM-30 m telescope, the Plateau de Bure Interferometer, the Very Large Array Interferometer and the James Clerk Maxwell Telescope. We have obtained single-dish maps in the C¹⁸O (1-0), C¹⁷O (1-0) and (2-1) rotational lines, interferometric maps in the CH₃C₂H (13-12) line, NH₃(1,1) and (2,2) inversion transitions, and single-pointing observations of the CH₃C₂H (6-5), (8-7) and (13-12) rotational lines. The new results confirm our earlier findings, namely that IRAS23385+6053 is a good candidate high-mass protostellar object, precursor of an ultracompact HII region. The source is roughly composed of two regions: a molecular core ∼0.03/0.04pc in size, with a temperature of ∼40K and an H₂ volume density of the order of 10⁷cm^–3, and an extended halo of diameter ≤0.4pc, with an average kinetic temperature of ∼15K and H₂ volume density of the order of 10⁵cm^–3. The core temperature is much smaller than what is typically found in molecular cores of the same diameter surrounding massive ZAMS stars. From the continuum spectrum we deduce that the core luminosity is between 150 and 1.6x10⁴L_☉, and we believe that the upper limit is near the ``true'' source luminosity. Moreover, by comparing the H₂ volume density obtained at different radii from the IRAS source, we find that the halo has a density profile of the type n_H2∝r^–2.3. This suggests that the source is gravitationally unstable. The latter hypothesis is also supported by a low virial-to-gas mass ratio (M_VIR/M_gas≤0.3). Finally, we demonstrate that the temperature at the core surface is consistent with a core luminosity of 10³L_☉ and conclude that we might be observing a protostar still accreting material from its parental cloud, the mass of which is at present ∼6M_☉.