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

Figure 6.3: Contribution of heating processes in a T Tauri disk: radial profile of these contributions to the temperature
of the disk. Left: mid-plane temperature, middle: effective temperature, right: surface temperature.
One sees that in the inner 2 AUs the mid-plane temperature is dominated by the viscous dissipation. From
Lachaume et al. (2003).
IOTA and VLTI/VINCI.
Figure 6.4: FU Orionis disk-spot model. Lines corresponds to the best model fit and markers to visibilities in
binned form. Top-left panel: spectral energy distribution and best fit model. The solid line stands for the whole
model and the dashed one for the spot. Right panel: visibility data vs. hour angle for each baseline in H and
K. The contribution of the disk is displayed in dashed lines. Bottom-left panel: synthetic image in logarithmic
scale. East is left and North is up. From Malbet et al. (2005).
FU Ori was observed on 42 nights over a period of 6 years, from 1998 to 2003. 287 independent measurements
of the fringe visibility with 6 different baselines ranging from 20 to 110m, in the H- and K-bands, were obtained,
see Fig. 6.4. Our data resolve FU Ori at the AU scale, and provides new constraints at shorter baselines and
shorter wavelengths. Our extensive (u,v)-plane coverage, coupled with the published spectral energy distribution
data shows that FU Ori hosts an active accretion disk whose temperature law is consistent with standard
models. A 10% peak-to-peak oscillation is detected in the longest baseline data. It is interpreted as a possible
disk hot-spot or companion. Although this bright spot on the surface of the disk could be tracing some thermal
instabilities in the disk, we have proposed to interpret this spot as the signature of a companion of the central FU
Ori system on an extremely eccentric orbit. We speculate that the close encounter of this putative companion
and the central star could be the explanation of the initial photometric rise of the luminosity of this object.
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