Untitled - Laboratoire d'Astrophysique de l'Observatoire de Grenoble

disks. At these wavelength, the bulk of the emission comes from the midplane of the outer disk, a region that is
not probed by scattered light images which are sensitive to grains in the disk surface. By attempting to model
simultaneously the millimeter thermal emission and the scattered light images, we are constraining the vertical
structure of disks and the possible presence of mm-sized particles in the disk midplane. In our first millimeter
study of the edge-on disk around HK Tau B, based on data collected at IRAM’s Plateau de Bure Interferometer,
we have shown that the disk must have layered structure, with a physical disconnection between the midplane
and disk surface in order to explain all observations of that disk (Duchêne et al. 2003).
To complement the various types of images descrived above, we are also involved in the ”Core To Disk”
Spitzer Legacy Survey, from which we hope to construct complete SEDs over the entire infrared range (from 3
to 170µm). Combined with the constraints obtained from the analyses of the disk images, this will allow us to
probe the parts of the disk that are not well sampled by current imaging techniques.
Our efforts in the observation (and models) of protoplanetary disks are well received and lead to several
invitations for review talks at international conferences, including a full review chapter awarded (with Ménard
PI) at the prestigious Protostar & Planets V conference (Hawaii, Oct.2005).
To wrap-up this section, it is our hope that models of numerous protoplanetray disks will help us identify
systematic trends and characterise important physical mechanisms like setlling, or show the presence of asymmetries
and complex dust properties, to understand the processes by which disks evolve, a mid-term goal, and
ultimately form planets, a long term-goal.
The inner dust disk
While the section above dealt mostly with the outer parts of disks, say 30AU and outwards, i.e., the resolution
available with HST and ground based adaptive optics at 150pc, the distance of nearby star forming regions,
other members of team FOST focus their attention on the inner disk by using another high angular resolution
technique, namely infrared interferometry. The goal of these efforts is to investigate the physical conditions in
the disk close to central star and to better understand the different evolution stages of these disks.
To reach these goals, data is obtained from most existing interferometers (PTI, IOTA, VINCI, MIDI). We
have also improved our interpretation capacities by developing a code dealing with the vertical structure of disks
and other radiative transfer tools based lambda iteration and Monte Carlo techniques to extract predictions
from the vertical structure code.
Finally, a part of the team is involved, through GRIL, in the development of new instruments like IONIC
on IOTA and AMBER on the VLTI. Thanks to this instrumental involvement, we have access to a large part
of observing time at IOTA and part of the AMBER guaranteed time but also a privileged access to the VLTI
Science Demonstration Time on objects not observable by the existing instruments.
The staff involved over the period 2001-2005 include Jean-Philippe Berger, Fabien Malbet, Jean-Louis Monin,
together with PhD students Regis Lachaume, Carla Gil, Eric Tatulli, and Myriam Benisty and undergraduate
students F. Millour (Master 2 student) and E. Herwats (Master 2 student).
Models of vertical structure To analyse the interferometric observations our models of the vertical structure
of disks have been improved following the initial work by Malbet & Bertout, 1991, ApJ, 383, 814), as part of
the PhD thesis work of R. Lachaume. Influenced by the approach of Chiang & Goldreich (1997, ApJ, 490, 368),
Lachaume developped a two layer model that provides an adequate analytical solution to the more complex
numerical simulations (Lachaume et al. 2003). This model successfully reproduces the observations of T Tauri
disks: both the SED and the visibilities. It also predicts that in the inner zone where the viscous dissipation
is the main heating source, the flaring angle of the disk surface is driven by the accretion and the opacity
contrarily to the outer disks where it is driven by the direct stellar radition heating. Lachaume et al. (2003)
further showed that at the same radius, the outgoing flux can be dominated by the stellar flux reprocessing
whereas the vertical structure of the central layers are regulated by the accretion rate, see Fig. 6.3.
FU Orionis under scrutiny Malbet & Berger conducted the largest interferometric campaign to date on
the young stellar object FU Orionis, as part of an international collaboration including observations on PTI,
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