Mid-infrared interferometry towards the massive young stellar object CRL
  2136: inside the dust rim
  We apply mid-infrared spectro-interferometry to the massive young stellar
object CRL2136. The observations were performed with the Very Large Telescope
Interferometer and the MIDI instrument at a 42m baseline probing angular scales
of 50 milli-arcseconds. We model the observed visibilities in parallel with
diffraction-limited images at both 24.5micron and in the N-band (with
resolutions of 0.6" and 0.3", respectively), as well as the spectral energy
distribution. The arcsec-scale spatial information reveals the well-resolved
emission from the dusty envelope. By simultaneously modelling the spatial and
spectral data, we find that the bulk of the dust emission occurs at several
dust sublimation radii (approximately 170 AU). This reproduces the high
mid-infrared fluxes and at the same time the low visibilities observed in the
MIDI data for wavelengths longward of 8.5micron. However, shortward of this
wavelength the visibility data show a sharp up-turn indicative of compact
emission. We discuss various potential sources of this emission. We exclude a
dust disk being responsible for the observed spectral imprint on the
visibilities. A cool supergiant star and an accretion disk are considered and
both shown to be viable origins of the compact mid-infrared emission. We
propose that CRL2136 is embedded in a dusty envelope, which truncates at
several times the dust sublimation radius. A dust torus is manifest in the
equatorial region. We find that the spectro-interferometric N-band signal can
be reproduced by either a gaseous disk or a bloated central star. If the disk
extends to the stellar surface, it accretes at a rate of 3.0 10^(-3) Msun/yr.
