Infrared spectroscopy of disks around low-mass stars with Spitzer





          Jacqueline Kessler-Silacci, University of Texas

          Neal Evans, University of Texas

          Geoffrey Blake, Caltech

          Ewine van Dishoeck, Leiden Observatory

          Jean-Charles Augereau, University of Leiden

          Adwin Boogert, Caltech

          Joanna Brown, Caltech

          Vincent Geers, University of Leiden

          Claudia Knez, University of Texas

          Fred Lahuis, MSc Univ.of Groningen

          Klaus Pontoppidan, University of Leiden







          This work is part of the c2d Spitzer legacy program designed to study the evolution of circumstellar matter 'From Molecular Cores to Planet-Forming Disks.'  This program utilizes the improved sensitivity of the Spitzer InfraRed Spectrograph (IRS) to greatly expand the study of infrared emission features in solar-mass stars, which previously were restricted primarily to ground based studies in the 10 micron region. Through the observation of ~5--35 micron spectra toward a variety of solar-type PMS stars, a database analogous to ISO studies of high/intermediate mass stars will be created. To date, near to mid infrared spectra have been obtained for ~50 T Tauri stars with circumstellar disks (class II) with ages up to ~5 Myr.  These spectra probe the changing physical conditions of disks and the chemical structure of silicates and polycyclic aromatic hydrocarbons (PAHs) as grains evolve and grow into planetesimals.  In the spectra observed thus far, PAH emission is observed toward ~10 stars, among which the 11.2 micron feature is most prominent and 6.2 to 8.6 micron features are not frequently observed.  The connection between the observed PAH features and interstellar/circumstellar environment is being explored. Silicate emission is observed at 10 and 20 microns toward a large fraction of the sample and appears to arise from primarily amorphous silicates with grain sizes between 0.1 and 5 microns. The spectral SEDs will be compared to the categories established for intermediate mass Herbig Ae/Be stars to explore the connections between the dust size/composition and disk geometry (Meeus et al. 2001).