FU Orionis: The MIDI VLTI Perspective

We present the first mid-infrared interferometric measurements of FU Orionis.We clearly resolve structures that are best explained with an optically thickaccretion disk. A simple accretion disk model fits the observed SED andvisibilities reasonably well and does not require the presence of anyadditional structure such as a dusty envelope. The inclination and also theposition angle of the disk can be constrained from the multibaselineinterferometric observations. Our disk model is in general agreement with mostpublished near-infrared interferometric measurements. From the shape andstrength of the 8-13 micrometer spectrum the dust composition of the accretiondisk is derived for the first time. We conclude that most dust particles areamorphous and already much larger than those typically observed in the ISM.Although the high accretion rate of the system provides both, high temperaturesout to large radii and an effective transport mechanism to distributecrystalline grains, we do not see any evidence for crystalline silicatesneither in the total spectrum nor in the correlated flux spectra from the innerdisk regions. Possible reasons for this non-detection are mentioned. Allresults are discussed in context with other high-spatial resolutionobservations of FU Ori and other FU Ori objects. We also address the questionwhether FU Ori is in a younger evolutionary stage than a classical TTauri star.Comment: 41 pages (aastex style), 11 figures, 8 tables, accepted by Ap