Detection of an Inner Gaseous Component in a Herbig Be Star Accretion Disk: Near‐ and Mid‐Infrared Spectrointerferometry and Radiative Transfer modeling of MWC 147

Abstract

Westudythegeometryandthephysicalconditionsintheinner(AU-scale)circumstellarregionaroundtheyoung HerbigBestarMWC147usinglong-baselinespectrointerferometryinthenear-infrared(NIR)K-band,VLTI/AMBER observations, and PTI archive data, as well as the mid-infrared (MIR) N-band, VLTI/MIDI observations. The emission from MWC 147 is clearly resolved and has a characteristic physical size of � 1.3 and � 9 AU at 2.2 and 11 � m, respectively (Gaussian diameter). The MIR emission reveals asymmetry consistent with a disk structure seen under intermediate inclination. The spectrally dispersed AMBER and MIDI interferograms both show a strong increase in the characteristic size toward longer wavelengths, much steeper than predicted by analytic disk models assuming power-law radial temperature distributions. We model the interferometric data and the spectral energy distribution of MWC 147 withtwo-dimensional, frequency-dependent radiationtransfer simulations. Thisanalysis showsthat models of spherical envelopes or passive irradiated Keplerian disks (with vertical or curved puffed-up inner rim) can easily fit the SED, but predict much lower visibilities than observed; the angular size predicted by such models is 2Y4 times larger than the size derived from the interferometric data, so these models can clearly be ruled out. Models of a Keplerian disk with optically thick gas emission from an active gaseous disk (inside the dust sublimation zone), however, yield a good fit of the SED and simultaneously reproduce the absolute level and the spectral dependence of the NIR and MIR visibilities. We conclude that the NIR continuum emission from MWC 147 is dominated by accretion luminosity emerging from an optically thick inner gaseous disk, while the MIR emission also contains contributions from the outer, irradiated dust disk. Subject headingg accretion, accretion disks — stars: formation — stars: individual (MWC 147) — stars: preYmain-sequence — techniques: interferometric