(pre-ALMA) The size scales are too small even for the largest current & near-term arrays. Spectroscopy to the rescue? How can we probe gas in the planet-forming region? Theory Observation? Jupiter (5 AU): V_doppler = 13 m/s V_orbit = 13 km/s H 2 is difficult, what other gas tracers can be studied?

High Resolution IR Spectroscopy & Disks CO M-band fundamental Keck NIRSPEC R=25000 R=10, ,000 (30-3 km/s) echelles (ISAAC,NIRSPEC, PHOENIX,TEXES) on 8-10 m telescopes can now probe “typical” T Tauri/Herbig Ae stars: AB Aur HD

L1489: Gas/Ice~10/1, accretion. CRBR2422.8: Gas/Ice~1/1, velocity field? Elias 18 Gas/Ice<1/10 (Shuping et al.) Edge-on absorption. As Ewine notes, orientation is pivotal to IR spectra: H 2, H 3 + in absorption? 12Aug2004

CO lines give distances slightly larger than K-band interferometry, broad H I traces gas much closer to star (see also Brittain & Rettig 2002, ApJ, 588, 535; Najita et al. 2003, ApJ, 589, 931). Can do ~30-40 objects/night. In older systems, CO disk emission is common: Herbig Ae stars, from ~face-on (AB Aur) to highly inclined (HD ). CO lines correlated with inclination and much narrower than those of H I Disk! Pf 

CO and 13 CO rotation diagrams show curvature as a result of  >1. Still, small amounts of gas since N(H 2 )~5 x leads to dust opacities near unity. Collisional excitation important, but cannot explain line widths at low J values (too broad). Resonant IR scattering at larger radii! The vibrational excitation is highly variable, likely due to variations in the UV field. Disk shadowing? How is the CO excited in these disks? 12Aug2004 CO 13 CO

Explanation: Dust sublimation near the star exposes the inner disk to direct stellar radiation, heating the dust and “puffing up” the disk. Flared disk models often possess 2-5 micron deficiency in model SEDs, where a “bump” is often observed for Herbig Ae stars. Where does the CO emission come from? Dullemond et al Aug2004

Step 1: Take your favorite description of the physical structure of the disk. Step 2: From this description along with your favorite grain opacity model and abundance for CO, calculate the optical depth in the gas and in the dust as you go into the disk. Step 3: For now, we simply use thermal blackbody and v = 0 LTE models to calculate the gas/dust emission and resonant scattering. How to model the CO emission?

Systematic Line Width Trends: Objects thought to be ~face on have the narrowest line widths, highly inclined systems the largest. As the excitation energy increases, so does the line width (small effect). Consistent with disk emission, radii range from AU at high J. Low J lines also resonantly scatter 5  m photons to much larger distances. Asymmetries (VV Ser)? 12Aug2004 Blake & Boogert 2004, ApJL 606, L73.

This model can now be directly tested via YSO size determinations with K-band interferometry. Intense dust emission pumps CO, rim “shadowing” can produce moderate T rot. Fits to AB Aur SED yield an inner radius of ~0.5 AU (and 0.06 AU for T Tau). SED Fits versus IR Interferometry (Monnier & Millan-Gabet 2002, ApJ) Dullemond et al. 2002

Calvet et al For dust sublimation alone, the lines from T Tauri disks should be broader than those from Herbig Ae stars+disks. Often observed, but… CO Emission from Disks around T Tauri Stars The TW Hya lines are extremely narrow, even for a disk with i~7 degrees, imply R>1 AU. Gap tracer?

For NIRSPEC at R~25,000; limit is M~8-9. Does CO follow dust? (Inner holes & TW Hya) Can CO be seen toward wTTs? We have tried a few observations toward Ophiuchus, but K stars have very complex M-band spectra! Thus, we must be much more careful about standards. Are there other tracers we should be looking for? (esp. Gemini and VLT) Future work, Spitzer follow up: