Mid-infrared interferometry of massive young stellar objects. I. VLTI and Subaru observations of the enigmatic object M8E-IR

摘要

[abridged] Our knowledge of the inner structure of embedded massive youngstellar objects is still quite limited. We attempt here to overcome the spatialresolution limitations of conventional thermal infrared imaging. We employedmid-infrared interferometry using the MIDI instrument on the ESO/VLTI facilityto investigate M8E-IR, a well-known massive young stellar object suspected ofcontaining a circumstellar disk. Spectrally dispersed visibilities in the 8-13micron range were obtained at seven interferometric baselines. We resolve themid-infrared emission of M8E-IR and find typical sizes of the emission regionsof the order of 30 milli-arcseconds (~45 AU). Radiative transfer simulationshave been performed to interpret the data. The fitting of the spectral energydistribution, in combination with the measured visibilities, does not provideevidence for an extended circumstellar disk with sizes > 100 AU but requiresthe presence of an extended envelope. The data are not able to constrain thepresence of a small-scale disk in addition to an envelope. In either case, theinterferometry measurements indicate the existence of a strongly bloated,relatively cool central object, possibly tracing the recent accretion historyof M8E-IR. In addition, we present 24.5 micron images that clearly distinguishbetween M8E-IR and the neighbouring ultracompact HII region and which show thecometary-shaped infrared morphology of the latter source. Our results show thatIR interferometry, combined with radiative transfer modelling, can be a viabletool to reveal crucial structure information on embedded massive young stellarobjects and to resolve ambiguities arising from fitting the SED.