The inner gaseous accretion disk around a Herbig Be star revealed by near- and mid-infrared spectro-interferometry

摘要

Herbig Ae/Be stars are pre-main-sequence stars of intermediate mass, which are stillaccreting material from their environment, probably via a disk composed of gas and dust. Herewe present a recent study of the geometry of the inner (AU-scale) circumstellar region aroundthe Herbig Be star MWC 147 using long-baseline interferometry. By combining for the firsttime near- and mid-infrared spectro-interferometry on a Herbig star, our VLTI/AMBER andVLTI/MIDI data constrain not only the geometry of the brightness distribution, but also theradial temperature distribution in the disk. The emission from MWC 147 is clearly resolved andhas a characteristic physical size of~1.3 AU and 9~ at 2.2 μmand 11 μm respectively. Thisincrease in apparent size towards longer wavelengths is much steeper than predicted by analyticdisk models assuming power-law radial temperature distributions. For a detailed modeling ofthe interferometric data and the spectral energy distribution of MWC 147, we employ 2-Dfrequency-dependent radiation transfer simulations. Tins analysis shows that passive irradiatedKeplerian dust disks can easily fit the SED, but predict much lower visibilities than observed, sothese models can clearly be ruled out. Models of a Keplerian disk with emission from an opticallythick inner gaseous accretion disk (inside the dust sublimation zone), however, yield a good fitof the SED and simultaneously reproduce the observed near- and mid-infrared visibilities. Weconclude that the near-infrared continuum emission from MWC 147 is dominated by accretionluminosity emerging from an optically thick inner gaseous disk, while the mid-infrared emissionalso contains strong contributions from the passive irradiated dust disk.