Younger disks -- HL Tau
T-Tauri star about 106 y old
- Early phase, star still contracting
- i.e. phase d) in vu-graph
- Dust in disk evident through Infrared excess
- IRAS satellite and ground-based observations
- Gas in disk evident through CO molecule Fig.20-3
- CO is quite abundant and much easier to detect than dominant H2 molecules and He atoms.
- Gas motion detected via Doppler shifts
- Velocities higher near star
- Velocities “Keplerian” i.e. V ~ 1/sqroot(R)
- same pattern as planets orbiting the sun
- Gas is in circular orbits around central star
- phase just before planet formation