| Description |
Some pre-main sequence stars exhibit peculiar wavelength-dependence of their
mid-infrared spectral variability. This finding led to the proposal of a
vertically extended obscuring structure in the inner part of the system that
casts time-variable shadow on the outer disk. It is an extra component of
T Tauri disks not considered in most disk models so far. In our previous
optical-to-mid-infrared survey we could directly detect the thermal
emission of this obscuring dust cloud. In order to initiate the physical
characterization of the shadowing material, we propose a 70/160 um 4-epoch
monitoring survey of eight young stars in the Chamaeleon I star forming
region with Herschel. For half of this sample our earlier measurements
already hint for the presence of a shadowing structure. Simultaneously with
the Herschel observations we will also arrange optical-to-mid-infrared
observations from the ground. We will perform a correlation analysis between
the variability patterns observed at different wavelengths, in order to
understand the origin of the obscuring structure. Correlation between optical
and far-infrared light curves would favor an orbiting warp or long-lived dust
cloud in the inner disk, while anticorrelation is interpreted as a signature
of a temporary dust cloud lifted above the disk plane. In both scenarios the
probable driving force behind the origin and the temporal rearrangement of
this structure is time-variable accretion. Through detailed modeling of the
spectral energy distributions and of the wavelength-dependence of the
variability, basic physical parameters of the obscuring structure will be
derived. Together with the timescale on which its structure can change, these
are important entries to learn what kind of dynamical processes occur in the
inner disks of low-mass pre-main sequence stars. For this project we request
7.8 h of Herschel observing time. |
