The inner gaseous accretion disk around a
Herbig Be star revealed by near- and mid-infrared spectro-interferometry
Kraus, S., Preibisch, T., Ohnaka, K.
"Star-disk interaction in young stars"
Proceedings of IAU Symposium 243
held from 21-25 May, 2007 in Grenoble, France
Proceedings of the International Astronomical Union, IAU Symposium, Volume 243, p. 337-344 (2007)
Abstract
Herbig Ae/Be stars are pre-main-sequence stars of intermediate mass,
which are still
accreting material from their environment, probably via a disk composed
of gas and dust. Here
we present a recent study of the geometry of the inner (AU-scale)
circumstellar region around
the Herbig Be star MWC 147 using long-baseline interferometry. By
combining for the first
time near- and mid-infrared spectro-interferometry on a Herbig star,
our VLTI/AMBER and
VLTI/MIDI data constrain not only the geometry of the brightness
distribution, but also the
radial temperature distribution in the disk. The emission from MWC 147
is clearly resolved and
has a characteristic physical size of 1.3 AU and 9 AU at 2.2 µm and
11 µm respectively. This
increase in apparent size towards longer wavelengths is much steeper
than predicted by analytic
disk models assuming power-law radial temperature distributions. For a
detailed modeling of
the interferometric data and the spectral energy distribution of MWC
147, we employ 2-D
frequency-dependent radiation transfer simulations. This analysis shows
that passive irradiated
Keplerian dust disks can easily fit the SED, but predict much lower
visibilities than observed, so
these models can clearly be ruled out. Models of a Keplerian disk with
emission from an optically
thick inner gaseous accretion disk (inside the dust sublimation zone),
however, yield a good fit
of the SED and simultaneously reproduce the observed near- and
mid-infrared visibilities. We
conclude that the near-infrared continuum emission from MWC 147 is
dominated by accretion
luminosity emerging from an optically thick inner gaseous disk, while
the mid-infrared emission
also contains strong contributions from the passive irradiated dust
disk.
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