1. Imaging gaps in disks at mid-IR VLT VISIR image 8.6 PAH 11.3 PAH 19.8  m large grains => gap! Geers et al. 2007 IRS48 -Gap seen in large grains, but NOT in PAHs => separation small and large grains

2. A big surprise: Gas-phase lines toward IRS46 disk Low-mass: IRS46 Lahuis et al., 2006 - Spitzer can detect gas-phase lines in spite of low spectral resolution - Gas is hot: 400-700 K - Abundances factor 1000 larger than in cold clouds - Must arise within inner 11 AU => inner disk - Potential blue-shift by 20 km/s => disk wind? IRS46 IRS44 IRS43 CRBR2422.8 T ex ~400-700 K 10’’

3. Hot chemistry in inner 10 AU of disks - Line of sight through puffed-up inner rim produces large enough column and T - HCN and C 2 H 2 abundances ~10 -5 w.r.t. H 2 consistent with high-T models=> First probe of organic chemistry in planet-forming zones

4. Silicate line profiles (continuum subtracted) Bouwman et al. 2001 Van Boekel et al. 2003 Przygodda et al. 2003 0.1  m 2.0  m - Ratio of 11.3/9.7  m fluxes is measure of flatness of profile

5. Large fraction of T Tauri disks shows evidence for grain growth Models Data Kessler-Silacci et al. 2006,2007 10  m band20  m band Obs Model - No correlation grain growth with age, Ha (accretion rate) - Trend for more grain growth around M-type stars

6. Statistical analysis 10  m band - Large fraction of disks shows evidence for grain growth to a few  m (first step in planet formation process) - Similar conclusion from 20  m data Kessler-Siliacci et al. 2006, 2007 Van Boekel et al. 2003, 2005 Przygodda et al. 2003 Large Small

7. Evidence for grain growth– edge-on disks Shape and depth of mid-IR “valley” very sensitive to grain size. For this source, grains at least ten  m in size are inferred. “Flying Saucer” in Oph Pontoppidan et al. 2007 i~85 o => Very weak at mid-IR Scattered radiation Thermal radiation

8. Crystallinity ISO: Herbig stars Spitzer: T Tauri stars and Brown Dwarfs - Crystallinity seen in large fraction of T Tauri + BD disks (>50%) - Interstellar silicates amorphous => crystallization at > 800 K must have occurred in inner disk => provides constraints on efficiency of heating and mixing processes - Also seen in comets => mixing in our solar system was more significant than thought before Malfait, Waelkens et al. 1998 Crovisier et al. 1997 Merin et al. 2007 Apai et al. 2005

9. Spitzer results on PAHs  3/ 37 T Tauri stars show PAH  Mostly G stars detected, not K  PAHs as tracers of stellar radiation and disk shape  Enhanced UV compared with stellar BB for some objects => accretion? chromosphere?  Absence in majority objects due to low PAH abundance  7.7 and 8.6  m bands sometimes masked by silicate emission RR Tau Optical, UV PAH Geers et al. 2006

10. [Ne II] in disks: tracer of X-ray/EUV radiation? Geers et al. 2006 Lahuis et al. 2007 Pascucci et al. 2007 T Cha - Detected in at least 20% of sources - Fluxes consistent with recent models of X-ray irradiated disks