Mid-infrared interferometry of massive young stellar objects^*

I. VLTI and Subaru observations of the enigmatic object M8E-IR

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: [linz;henning;feldt;leinert;boekel;quanz]@mpia-hd.mpg.de
² Department of Physics and Astronomy, Johns Hopkins University, 403 Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218, USA e-mail: pascucci@pha.jhu.edu
³ CEA, IRFU, SAp, Centre de Saclay, 91191 Gif-sur-Yvette, France e-mail: alexander.menshchikov@cea.fr
⁴ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany e-mail: stecklum@tls-tautenburg.de
⁵ UMR 6525, Univ. Nice, CNRS, Obs. de la Côte d'Azur, Av. Copernic, 06130 Grasse, France 
e-mail: chesneau@obs-azur.fr
⁶ Astrophysikalisches Institut Potsdam, Sternwarte 16, 14482 Potsdam, Germany e-mail: [tratzka;hzinnecker]@aip.de
⁷ Astronomical Institute “Anton Pannekoek”, Universiteit van Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands e-mail: rensw@science.uva.nl

Received: 30 November 2007
Accepted: 2 July 2009

Abstract

Context. Our knowledge of the inner structure of embedded massive young stellar objects is still quite limited. Thus, it is difficult to decide to what extent the mass accumulation onto forming massive stars differs from the process of low-mass star formation.

Aims. We attempt to overcome the spatial resolution limitations of conventional thermal infrared imaging.

Methods. We employed mid-infrared interferometry using the MIDI instrument on the ESO/VLTI facility to investigate M8E-IR, a well-known massive young stellar object suspected of containing a circumstellar disk. Spectrally dispersed visibilities in the 8–13 μm range have been obtained at seven interferometric baselines.

Results. We resolve the mid-infrared emission of M8E-IR and find typical sizes of the emission regions of the order of 30 milliarcseconds (45 AU). Radiative transfer simulations were performed to interpret the data. The fitting of the spectral energy distribution, in combination with the measured visibilities, does not provide evidence for an extended circumstellar disk with sizes 100 AU but requires the presence of an extended envelope. The data are not able to constrain the presence of a small-scale disk in addition to an envelope. In either case, the interferometry measurements indicate the existence of a strongly bloated, relatively cool central object, possibly tracing the recent accretion history of M8E-IR. In addition, we present 24.5 μm images that clearly distinguish between M8E-IR and the neighbouring ultracompact Hii region and which show the cometary-shaped infrared morphology of the latter source.

Conclusions. Our results show that IR interferometry, combined with radiative transfer modelling, can be a viable tool to reveal crucial structure information on embedded massive young stellar objects and to resolve ambiguities arising from fitting the SED.