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Gaspard Duchêne University of California Berkeley Observatoire de Grenoble. Circumstellar Disks and young stars. 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
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Gaspard Duchêne University of California Berkeley Observatoire de Grenoble Circumstellar Disks and young stars G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010
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 star’s dynamical evolution • Influence of companions, environment G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010
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 star’s dynamical evolution • Influence of companions, environment A critical ‘boundary condition’ for star formation theories and simulations G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010
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
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 Very few stars are born with no circumstellar disk Hernández et al. (2007) G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010
Disks as a function of M★ • Proportion of disks varies very little with central stellar mass (from 0.05 to ~5 M) Luhman et al. (2010) Taurus Hillenbrand et al. (1998) Orion Cha I IC 348 mass mass G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010
Disks and environment • Presence of nearby high-mass stars has little influence on initial disk proportion 100% θ1C Ori Hillenbrand et al. (1998) Hernández et al. (2007) G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010
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? random Ménard & Duchêne (2004) |PAsystem – PAB field| G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010
Disks in binary/multiple systems • Relative orientation between angular momentum vectors may be primordial • General but imperfect alignment Circumbinary disk parallel to inner orbit JprimaryvsJsecondary Monin et al. (2007) Simon et al. (2000) G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010
Total disk mass and size • Disks are generally gravitationally stable • Major selection bias! mass Natta et al. (2000) Natta et al. (2000) G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010
Total disk mass and size • Disks are generally gravitationally stable • Major selection bias! • Disk sizes show no trend • … with age • … with stellar mass • However… mass Natta et al. (2000) Natta et al. (2000) G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010
Total disk mass and size • Disks are generally gravitationally stable • Major selection bias! • Disk sizes show no trend • … with age • … with stellar mass • However… These disks are not representative of star formation (too old)! mass Natta et al. (2000) Natta et al. (2000) G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010
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
Disks and embedded protostars • Disks are assumed to be prevalent in earlier phases of stellar evolution • Issue: contamination by massive envelope • Disks around protostarsmay bequite massive and large (150-300 AU) • Handful of sources • Selection bias? • Topic under debate! Class I Class 0 Jörgensen et al. (2005, 2009); see also Enoch et al. (2009), Maury et al. (2009) G. Duchêne - Circumstellar disks and young stars - IAUS 270 - Barcelona, June 1st 2010
Summary • Disks are prevalent around young stars, from brown dwarfs to intermediate-mass stars • Disks around embedded protostarsare 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
