Herschel PACS observations of 4-10 Myr old Classical T Tauri stars in
  Orion OB1
  We present \emph{Herschel} PACS observations of 8 Classical T Tauri Stars in
the $\sim 7-10$ Myr old OB1a and the $\sim 4-5$ Myr old OB1b Orion
sub-asscociations. Detailed modeling of the broadband spectral energy
distributions, particularly the strong silicate emission at 10 $\mu$m, shows
that these objects are (pre)transitional disks with some amount of small
optically thin dust inside their cavities, ranging from $\sim 4$ AU to $\sim
90$ AU in size. We analyzed \emph{Spitzer} IRS spectra for two objects in the
sample: CVSO-107 and CVSO-109. The IRS spectrum of CVSO-107 indicates the
presence of crystalline material inside its gap while the silicate feature of
CVSO-109 is characterized by a pristine profile produced by amorphous
silicates; the mechanisms creating the optically thin dust seem to depend on
disk local conditions. Using millimeter photometry we estimated dust disk
masses for CVSO-107 and CVSO-109 lower than the minimum mass of solids needed
to form the planets in our Solar System, which suggests that giant planet
formation should be over in these disks. We speculate that the presence and
maintenance of optically thick material in the inner regions of these
pre-transitional disks might point to low-mass planet formation.
