Contents of: VI/111/./abstract/GSTRINGF_EXORS.abs

The following document lists the file abstract/GSTRINGF_EXORS.abs from catalogue VI/111.
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EXORs, named after the prototype EX Lup, are a very small subclass of classical
T Tauri stars (CTTSs) which experience rather major optical outbursts. Outbursts
of the EXORs are intermediate between the long lived and more energetic FU Ori
type outbursts (FUORs) and the more modest accretion variability of the CTTSs.
EXORs undergo large amplitude outbursts as a direct result of enhanced mass
accretion from their circumstellar disk. The accretional energy liberated
results in a brightening of 3--5 magnitudes in the UV and optical. Direct
accretion to the stellar surface can be via a boundary layer or magnetic
coupling between the disk and star.  The outbursts play a major role in
modifying the circumstellar environment, and initiate the formation of winds,
jets, and H-H objects, and dispersal of the disk. The large physical changes in
the circumstellar environment during such outbursts likely influence the
formation and evolution of giant planets and brown dwarfs.  EXOR, and the
related FUOR, outbursts frequently occur over the disk-accretion lifetime of
young stellar objects. However, the characteristics of the EXORs are poorly
understood due to the paucity of observational data during both quiescence and
in outburst; the PI has ongoing ground-based programs in the optical and near-IR
to rectify this. The (variable?) near-IR colors of the EXORs indicate a range
of properties, some being optically thin while others are massive and optically
thick. Exactly how the disk replenishes itself between outbursts and the
underlying mechanism that triggers the outbursts remains a mystery. We propose
to obtain the necessary ISO data that will (1) determine the spectral energy
distribution of the extended disk, (2) deduce the temperature distribution of
the disk and it's composition, (3) determine how rapidly the disk is being
replenished and how the temperature structure and composition respond to the
infall of matter onto the disk, and (4) gain insight into the trigger mechanism
of the outburst and how this affects the outer disk.




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