Sternentstehung - Star FormationSommersemester 2006

Henrik Beuther & Thomas Henning24.4 Today: Introduction & Overview1.5 Public Holiday: Tag der Arbeit8.5 ---15.5 Physical processes, heating & cooling, cloud thermal structure22.5 Physical processes, heating & cooling, cloud thermal structure (H. Linz)29.5 Basic gravitational collapse models I5.6 Public Holiday: Pfingstmontag12.6 Basic gravitational collapse models II19.6 Accretion disks26.6 Molecular outflow and jets3.7 Protostellar evolution, the stellar birthline10.7 Cluster formation and the Initial Mass Function17.7 Massive star formation, summary and outlook24.7 Extragalactic star formation

More Information and the current lecture files: http://www.mpia.de/homes/beuther/lecture_ss06.html beuther@mpia.de

Summary last week

- Ambipolar diffusion- Magnetic reconnection- Turbulence- Cloud collapse of singular isothermal sphere and Bonnor-Ebert sphere- Inside out collapse, rarefaction wave, density profiles, accretion rates- Accretion shock and accretion luminosity- Observational features: SEDs, Infall signatures- Rotational effects: - magnetic locking of “outer” dense core to cloud. - further inside it causes the formation of accretion disks

Star Formation Paradigm

Rotational effects IIIn dense core centers magnetic bracking fails because neutral matter and magnetic field decouple with decreasing ionization fraction. matter within central region can conserve angular momentum.Since Fcen grows faster than Fgrav each fluid element veers away fromgeometrical center. --> Formation of disk

The larger the initial angular momentum j of a fluid element, the further away from the center it ends up --> centrifugal radius cencen = 0

2R4/GM = m03at0

2t3/16 = 0.3AU (T/10K)1/2 (0/10-14s-1)2 (t/105yr)3

cen can be identified with disk radius. Increasing with time because in inside-out collapse rarefaction wave moves out --> increase of initial j.

Early disk indications and evidence Early single-dish observations toward T-Tauri stars revealed cold dust emission. In spherical symmetry this would not be possible since the corresponding gas and dust would extinct any emission from the central protostar.--> Disk symmetry necessary!

Beckwith et al. 1990

1.3mm IRAS NIR 1.3mm IRAS NIR

Full line: no inner wholeDashed line: Inner whole

HH30, one of the first imaged disks

Optical disk examples

Schmetterlingsstern

The Butterfly star

Wolf et al. 2003

1016 m

7 104 AU

Molecular cloud core

5 1013 m

300 AU

Circumstellar dust disk

Approximate disk size-scales

Disk masses

Beckwith et al. 1990, Andre et al. 1994

- Theories of early solar system require disk masses between 0.01 and 0.1Msun. --> Typical disk systems apparently have enough disk mass to produce planetary systems.

Disk ages

Haisch et al. 2001

Simple case: flat, black diskT ~ r-3/4, Ldisk ~ 1/4 L*

Model SEDs

Beckwith et al. 1996, 1999

Effects of gaps on disk SED

Full line: no gapLong-dashed: gap 0.75 to 1.25 AUShort-dashed: gap 0.5 to 2.5 AUDotted: gap 0.3 to 3 AU

To become detectable gap has tocut out at least a decade of disksize.

Additional FIR excess

- Larger inner or smaller outer disk radii even increase the discrepancy.- Data indicate that outer disk region is hotter than expected from flat, black disk model --> Disk flaring

Disk flaring

The scale height h of a disk increases with radius r because the thermal Energy decreases more slowly with increasing radius r than the verticalComponent of the gravitational energy: Evert, grav ~ h/r * GM*/r ~ Etherm ~ kT(r) with T(r) ~ r-3/4

--> h ~ k/GM* r5/4

Hydrostatic equilibrium, radiative transfer models for flared disks I

Chiang & Goldreich 1997

Hydrostatic equilibrium , radiative transfer models for flared disks II

Chiang & Goldreich 1997

h nvert ~ exp(z2/2h2)

Hydrostatic equlibrium, radiative transfer models for flared disks III

Chiang & Goldreich 1997

Flat spectrum disks

Class I protostar

Class II T Tauri star

Outflow cavity

Infallingenvelope

disk

- Flat-spectrum sources have too much flux to be explained by heating of protostar only.- In very young sources, they are still embedded infalling envelope --> this can scatter light and cause additional heating of outer disk. Flat spectrum sources younger than typical class II T Tauri stars.

Calvet et al. 1994, Natta et al. 1993

Disk accretion rates

The centrifugal radius cen is:cen = 0

2R4/GMcore = GMcore/2at2 with break = 2√2 at

3/GMcore larger mass cores form larger disks accretion rate spread is dominated by initial rotation of cores, imprint of initial core properties

Dullemond et al. 2006

Macc M*1.8+-0.2

Dimensionlessrotation rate ofinitial core:break

.

Disk dynamics: Keplerian motionSimon et al.2000

For a Keplerian supported disk, centrifugal force should equal grav. force. Fcen = mv2/r = Fgrav = Gm*m/r2

--> v = (Gm*/r)1/2

Velocity

Offse

tOhashi et al. 1997

Guilloteau et al. 1998DM Tau

Non-Keplerian motion: AB Aur

PdBI, Pietu et al. 2005

SMA, Lin et al. 2006

345GHz continuum

SMA, Lin et al. 2006CO(3-2)

- Central depression in cold dust and gas emission.- Non-Keplerian velo- city profile vr -0.4+-0.01

- Possible explanations Formation of low- mass companion or planet in inner disk. Early evolutionary phase where Keplerian motion is not established yet (large envelope).

Disk chemistry

Bergin et al. 2006

Accretion and mass transport

Equilibrium between Fcen and Fgrav: mr2 = Gmm*/r2 => = (Gm*/r3)1/2

--> no solid body rotation but a sheared flow --> viscous forces --> mass transport inward, angular momentum transport outward, heating

The inner disk is warm enough for large ionization: matter and magnetic fieldare coupled well --> accretion columns transport gas from disk to protostar

Strassmeier et al. 2005

Particle growth in disks- At (sub)mm wavelength the flux F BT) () with the dust absorption coefficient () proportional to --> In the Rayleigh-Jeans limit we get F

- For typical interstellar grains = 2. Rocks are opaque at mm wavelengths --> = 0.--> Grain growth could be witnessed by decreasing .

Tempting to interpret as grain growth. However, there are caveats,e.g., the temperature dependence not considered.

Disks in massive star formation

IRAS20126+4104, Cesaroni et al. 1997, 1997, 2005Keplerians disk around central protostar of ~7Msun

- Still deeply embedded, large distances, clustered environment --> confusion- Current obs. status largely “Velocity gradient perpendicular to outflow”.- (Sub)mm interferometry important to disentangle the spatial confusion.- The right spectral line tracer still missing which can distinguish the disk emission from the surrounding envelope emission.

IRS5 in M17, Chini et al. 200626Msun mass star with 0.5MJup dust

Summary- Disks are expected from angular momentum considerations.- The SEDs of disk sources show strong FIR excess.- SEDs allow to analyze various disk aspects: Radial and vertical disk morphology, flaring of disks Evolutionary stages Inner holes Gaps maybe due to planets- Observable in NIR in absorption and in (sub)mm line and continuum emission.- Disk lifetimes a few million years.- T Tauri disks usually in Keplerian motion.- Younger disks like AB Aur deviate from Keplerian motion- In young sources, the outer disks can also be irradiated by scatter light from the surrounding envelope- Strong vertical and radial chemical evolution.- Sites of grain growth and later planet formation.- Massive disks far less understood.

Zodiacal light

Bob Shobbrook, Siding spring, 2 hoursafter sunset.Etienne Leopold Trouvelot (1827-1895)

Sternentstehung - Star FormationSommersemester 2006

Henrik Beuther & Thomas Henning24.4 Today: Introduction & Overview1.5 Public Holiday: Tag der Arbeit8.5 ---15.5 Physical processes, heating & cooling, cloud thermal structure22.5 Physical processes, heating & cooling, cloud thermal structure (H. Linz)29.5 Basic gravitational collapse models I5.6 Public Holiday: Pfingstmontag12.6 Basic gravitational collapse models II19.6 Accretion disks26.6 Molecular outflow and jets3.7 Protostellar evolution, the stellar birthline10.7 Cluster formation and the Initial Mass Function17.7 Massive star formation, summary and outlook24.7 Extragalactic star formation

More Information and the current lecture files: http://www.mpia.de/homes/beuther/lecture_ss06.htmlbeuther@mpia.de