  Aims: We search for PAH features towards T Tauri stars and compare them with
surveys of Herbig Ae/Be stars. The presence and strength of the PAH features
are interpreted with disk radiative transfer models exploring the PAH feature
dependence on the incident UV radiation, PAH abundance and disk parameters.
  Methods: Spitzer Space Telescope 5-35 micron spectra of 54 pre-main sequence
stars with disks were obtained, consisting of 38 T Tauri, 7 Herbig Ae/Be and 9
stars with unknown spectral type.
  Results: Compact PAH emission is detected towards at least 8 sources of which
5 are Herbig Ae/Be stars. The 11.2 micron PAH feature is detected in all of
these sources, as is the 6.2 micron PAH feature where short wavelength data are
available. However, the 7.7 and 8.6 micron features appear strongly in only 1
of these 4 sources. PAH emission is observed towards at least 3 T Tauri stars
(8% detection rate). The lowest mass source with PAHs in our sample is T Cha
(G8). All 4 sources in our sample with evidence for dust holes in their inner
disk show PAH emission, increasing the feature/continuum ratio. Typical 11.2
micron line intensities are an order of magnitude lower than those observed for
the more massive Herbig Ae/Be stars. Measured line fluxes indicate PAH
abundances that are factors of 10-100 lower than standard interstellar values.
Conversely, PAH features from disks exposed to stars with Teff<=4200K without
enhanced UV are predicted to be below the current detection limit, even for
high PAH abundances. Disk modeling shows that the 6.2 and 11.2 micron features
are the best PAH tracers for T Tauri stars, whereas the 7.7 and 8.6 micron
bands have low feature over continuum ratios due to the strongly rising
silicate emission.
