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Title:
Millimeter/radio
Gas Observations of Disks
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Authors:
C. Ceccarelli, Grenoble
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Abstract:
Available radio to sub-millimeter line observations of disks
allow to reconstruct
the physical, kinematic and chemical structure of the outer (>100AU)
disk, and
are, therefore, powerful diagnostics in the studies of disk evolution.
From a chemical point of view, the outer disks of low to intermediate
mass
stars are composed by three regions : i) the upper disk atmosphere
(where all
molecules are photo-dissociated), ii) the intermediate layer, and iii)
the disk
midplane (where all molecules freeze-out onto the grains).
In relatively massive disks (0.01Mo) around T Tau stars, most of the
observed
molecular emission (CO, HCO+...) originates in the warm intermediate
layer,
whereas in warmer disks, around AeBe stars, the dust can be warm enough
to
prevent the condensation of molecules even in the midplane.
Lines from molecules like CO or HCO+ provide, therefore, key
informations on
the disk structure and kinematics: density, temperature and, possibly
ionization
degree, along with the velocity field.
In addition, other less abundant molecules have been detected in
some cases,
providing unique information on the disk molecular composition.
Finally, a few
observations of deuterated molecules have been reported so far. These
observations probe the midplane of cold disks, and provide estimates of
the
ionization degree.
In this contribution I will review the radio to sub-millimeter single
dish and
interferometric observations of gas lines, and I will discuss how they
help in
understanding the disk structure and evolution.
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