Max Planck Institute for Astronomy - Annual Report 2005

log F /mJy
2
0
– 2
– 4
1
3M � @ 1 AE MgSi0 3
3M � @ 30 AE MgFeSi0 4
1.5
log � / �m
2 2.5
20 AU
MatIssE will extend the astrophysical potential of the
VLTI by overcoming the ambiguities often existing in the
interpretation of simple visibility measurements. It will
be an instrument with unique performance. This is partly
related to the existence of the four large apertures of the
III.2 Radiative Transfer – Link between Simulation and Observation 69
Fig. III.2.5: Top – Possible degeneracy between the grain chemical
composition and the location of a planet clearing the
gap: SED of a dust disk composed of MgSiO 3 grains with a
3 M J planet at 1 AU (solid line) and a dust disk composed of
MgFeSiO 4 grains with a 3 M J planet at 30 AU (dashed line).
Middle – Brightness density distributions at 70 µm (assuming
graybody emission from 12 µm grains) expected from a disk
with a 3 M J planet at 1 AU (shown in arbitrary units). Bottom:
Same as middle, but for 30 AU. High resolution images are
needed to resolve the degeneracy.
VLT (UTs) that permits to push the sensitivity limits up
to values required by selected astrophysical programs
such as the study of Active Galactic Nuclei and extrasolar
planets.
Moreover, the evaluated performance of MatIssE is
linked to the existence of ATs which are relocatable in
position in about 30 different stations allowing the exploration
of the Fourier plane with up to 200 meters baseline
length. Key science programs using the ATs cover for example
the formation and evolution of planetary systems,
the birth of massive stars as well as the observation of the
high-contrast environment of hot and evolved stars.
MatIssE will offer to the European community high
angular resolution imaging and spectroscopic capabilities
in the mid-infrared wavelength domain covering the L,
M, N, and Q band. This wavelength range, in between the
near-infrared domain to which instruments like aMbEr
are sensitive, and the (sub)millimeter domain for which
high angular resolution is foreseen with alMa, is of fundamental
scientific interest. In terms of image capability
MatIssE can be seen as a ground precursor of the future
space interferometer darwIN which is presently studied
as an instrument sensitive to the 6 to 18 µm range.
Radiative transfer simulations are of vital importance
for the identification and analysis of science cases for
MatIssE, and thus for the definition of the instrument
specifications during the MatIssE design phase. For example,
the study of the capability of MatIssE to reconstruct
images is based on model images of selected astrophysical
objects resulting from radiative transfer simulations.
One of the major goals of MatIssE will be the investigation
of the planet formation process. Planets are
expected to form in circumstellar disks, which are considered
as the natural outcome of the protostellar evolution,
at least in the case of low and medium mass stars.
While a detailed picture of the evolution of the circumstellar
environment, in particular of circumstellar disks,
has been developed already, the planet formation process
is mostly still under discussion. The dominant observable
quantity originating from the inner disk region (r � 10
to 20 AU) is the emission of mid-infrared continuum radiation
by hot dust. Given the typical distance of nearby
star-forming regions of about 140 to 200 pc and the spatial
resolution achievable with the Very Large Telescope
Interferometer (VLTI) in the mid-infrared atmospheric
windows (L, M, N, Q band) of up to 3 milliarcseconds