1. Gaspard Duchêne University of California Berkeley Observatoire de Grenoble G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010

2. On the importance of disks An inescapable outcome of star formation The main angular momentum depository Birthsite of planetary systems And driver of subsequent evolution Tracer of a stars dynamical evolution Influence of companions, environment G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010

3. On the importance of disks An inescapable outcome of star formation The main angular momentum depository Birthsite of planetary systems And driver of subsequent evolution Tracer of a stars dynamical evolution Influence of companions, environment G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010 A critical boundary condition for star formation theories and simulations

4. Disks in the T Tauri phase Over the first few Myr, disk proportion declines around T Tauri stars Relates/informs planet formation and disk dissipation

5. Disks in the T Tauri phase Over the first few Myr, disk proportion declines around T Tauri stars Relates/informs planet formation and disk dissipation 90% at the very beginning G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010 Hernández et al. (2007) Very few stars are born with no circumstellar disk

6. Disks as a function of M Proportion of disks varies very little with central stellar mass (from 0.05 to ~5 M ) G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010 Orion Taurus Cha IIC 348 mass Hillenbrand et al. (1998) Luhman et al. (2010)

7. Disks and environment Presence of nearby high-mass stars has little influence on initial disk proportion G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010 Hillenbrand et al. (1998) Hernández et al. (2007) θ 1 C Ori 100%

8. Disks orientation The angular momentum of disks is randomly oriented w.r.t. local B field In Taurus Is it representative … of all SFRs? … of earlier phases? G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010 |PA system – PA B field | random Ménard & Duchêne (2004)

9. Disks in binary/multiple systems Relative orientation between angular momentum vectors may be primordial General but imperfect alignment G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010 Simon et al. (2000) Monin et al. (2007) J primary vs J secondary Circumbinary disk parallel to inner orbit

10. Total disk mass and size Disks are generally gravitationally stable Major selection bias! G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010 mass Natta et al. (2000)

11. Total disk mass and size Disks are generally gravitationally stable Major selection bias! Disk sizes show no trend … with age … with stellar mass However… G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010 mass Natta et al. (2000)

12. Total disk mass and size Disks are generally gravitationally stable Major selection bias! Disk sizes show no trend … with age … with stellar mass However… G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010 mass Natta et al. (2000) These disks are not representative of star formation (too old)! Natta et al. (2000)

13. Disks and embedded protostars Disks are assumed to be prevalent in earlier phases of stellar evolution Issue: contamination by massive envelope G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010

14. Disks and embedded protostars Disks are assumed to be prevalent in earlier phases of stellar evolution Issue: contamination by massive envelope Disks around protostars may be quite massive and large (150-300 AU) Handful of sources Selection bias? Topic under debate! G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010 Class 0 Class I Jörgensen et al. (2005, 2009); see also Enoch et al. (2009), Maury et al. (2009)

15. Summary Disks are prevalent around young stars, from brown dwarfs to intermediate-mass stars Disks around embedded protostars are the best probes/tests of star formation theory Among young stars, the disk presence and orientation are the easiest to assess Disk mass, radius, …, are model-dependent and generally biased Difficult to compare observations and models G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010