sternentstehung - star formation - mpia.de · · 2009-06-12sternentstehung - star formation...

Sternentstehung - Star Formation Sommersemester 2009

Henrik Beuther

3.4 Today: Introduction & Overview 10.4 Karfreitag 17.4 Physical processes I 24.4 Physcial processes II 1.5 Tag der Arbeit 8.5 Collapse models I 15.5 Collapse models II 22.5 Observations of outflows and jets 29.5 No lecture 5.6 Jet theory (Christian Fendt) 12.6 Accretion disks 19.6 Protostellar evolution, stellar birthline, pre-main sequence evolution 26.6 High-mass star formation, clusters and the IMF 3.7 Extragalactic star formation (Eva Schinnerer) 10.7 Summary

More Information and the current lecture files: http://www.mpia.de/homes/beuther/lecture_ss09.html [email protected]

Topics today

- Principal disk observations and characteristics

- Disk models

- More observational constraints

- Inner disk and accretion

- Disks in massive star formation and grain growth & planet formation

Star Formation Paradigm

Rotational effects II In 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= j2/ω3 grows faster than Fgrav=Gm/ω2

each fluid element veers away from geometrical 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 ωcen ωcen = Ω0

2R4/GM = m03atΩ0

2t3/16 = 0.3AU (T/10K)1/2 (Ω0/10-14s-1)2 (t/105yr)3

ωcen 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 whole Dashed 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

Topics today


- Disk models




Simple case: flat, black disk

T ~ r-3/4, Ldisk ~ 1/4 L*

Model SEDs

Beckwith et al. 1996, 1999

Effects of gaps on disk SED

Full line: no gap Long-dashed: gap 0.75 to 1.25 AU Short-dashed: gap 0.5 to 2.5 AU Dotted: gap 0.3 to 3 AU

To become detectable gap has to cut out at least a decade of disk size.

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 vertical component 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


h nvert ~ exp(z2/2h2)

Hydrostatic equlibrium, radiative transfer models for flared disks III


Flat spectrum disks

Class I protostar

Class II T Tauri star

Outflow cavity

Infalling envelope

disk

- Flat-spectrum sources have too much flux to be explained by heating of protostar only. - Very young sources are still embedded in 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

Topics today


- Disk models




Disk dynamics: Keplerian motion Simon 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 O

ffse

t

Ohashi et al. 1997

Guilloteau et al. 1998 DM Tau

Non-Keplerian motion: AB Aur

PdBI, Pietu et al. 2005

SMA, Lin et al. 2006

345GHz continuum

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

- Central depression in cold dust and gas emission. - Non-Keplerian velocity profile v∝r -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-jet co-rotation in DG Tau

Bacciotti et al. 2002

blue

red

Testi et al. 2002

Corotation of disk and jet

Disk structure

Pietu et al. 2007

Different lines trace different optical depth.

Disk accretion rates

The centrifugal radius ωcen is: ωcen = Ω0

2R4/GMcore = GMcore/(2at2) ω2 with Ωbreak = 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

Dimensionless rotation rate of initial core: ω = Ω0/Ωbreak

.

Relatively robust results

- Disk sizes between 200 and 2000AU.

- Most disks are in Keplerian rotation.

- Temperature structure consistent with flared disk models and T at CO disk surface (τ=1) goes like T(r) ~ r-0.6.

- Vertical temperature gradients with cooler disk mid-plane.

- Disk temperature increase with increasing central stellar mass.

- Beyond 150AU, disks around low-mass stars have T<17K, therefore, CO can freeze out on dusk grains.

Topics today


- Disk models




Inner disk regions

Squares: gaseous inner disk radii (CO fundamental) Circles: dust inner disk radii (interferometry and SEDs)

- Mid-infrared emission lines of vibrationally excited CO traces gas > 1000K. - The gas rotates at Keplerian velocity --> line-widths converts to inner disk radii. - Inner gas disk extends beyond disk sublimation radius and is close to and within co-rotation radius (coupling of stellar magnetic field to disk).

Najita et al. 2007

Accretion and mass transport

Equilibrium between Fcen and Fgrav: mrω2 = Gmm*/r2 => ω = (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 field are coupled well --> accretion columns transport gas from disk to protostar

Accretion and mass transport

Equilibrium between Fcen and Fgrav: mrω2 = Gmm*/r2 => ω = (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 field are coupled well --> accretion columns transport gas from disk to protostar

Strassmeier et al. 2005

Topics today


- Disk models




Disks in massive star formation

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

- Still deeply embedded, large distances, clustered environment --> confusion - Keplerian motion possible but not necessirily observed on large scales. - (Sub)mm interferometry important to disentangle the spatial confusion. - The right spectral line tracer still difficult to identify which can distinguish the disk emission from the surrounding envelope emission.

IRAS18089-1732 (Beuther & Walsh 2008) Hot rotating structure not in Keplerian motion.

Particle growth in disks - At (sub)mm wavelength the flux Fν ∝ B(ν,T) κ(ν) with the dust absorption coefficient κ(ν) proportional to νβ. --> In the Rayleigh-Jeans limit we get Fν ∝ ν2+β - For typical interstellar grains β = 2. Rocks are opaque at mm wavelengths --> β = 0. --> Grain growth could be witnessed by decreasing β.

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

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 and gaps maybe due to planets

- Observable in NIR absorption and in (sub)mm line & continuum emission.

- Disk lifetimes a few million years.

- T Tauri disks usually in Keplerian motion. Younger disks like AB Aur deviate from Keplerian motion.

- Sites of grain growth and later planet formation.

- Massive disks far less understood.

Zodiacal light

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

Sternentstehung - Star Formation Sommersemester 2009

Henrik Beuther 3.4 Today: Introduction & Overview 10.4 Karfreitag 17.4 Physical processes I 24.4 Physcial processes II 1.5 Tag der Arbeit 8.5 Collapse models I 15.5 Collapse models II 22.5 Observations of outflows and jets 29.5 No lecture 5.6 Jet theory (Christian Fendt) 12.6 Accretion disks 19.6 Protostellar evolution, stellar birthline, pre-main sequence evolution 26.6 High-mass star formation, clusters and the IMF 3.7 Extragalactic star formation (Eva Schinnerer) 10.7 Summary

More Information and the current lecture files: http://www.mpia.de/homes/beuther/lecture_ss09.html [email protected]

Disk chemistry

Bergin et al. 2006

Molecules in Space 2 3 4 5 6 7 8 9 10 11 12 13 atoms -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- H2 C3 c-C3H C5 C5H C6H CH3C3N CH3C4H CH3C5N? HC9N CH3OC2H5 HC11N AlF C2H l-C3H C4H l-H2C4 CH2CHCN HCOOCH3 CH3CH2CN (CH3)2CO AlCl C2O C3N C4Si C2H4 CH3C2H CH3COOH? (CH3)2O NH2CH2COOH? C2 C2S C3O l-C3H2 CH3CN HC5N C7H CH3CH2OH CH3CH2CHO CH CH2 C3S c-C3H2 CH3NC HCOCH3 H2C6 HC7N CH+ HCN C2H2 CH2CN CH3OH NH2CH3 CH2OHCHO C8H CN HCO CH2D+? CH4 CH3SH c-C2H4O CH2CHCHO CO HCO+ HCCN HC3N HC3NH+ CH2CHOH CO+ HCS+ HCNH+ HC2NC HC2CHO CP HOC+ HNCO HCOOH NH2CHO CSi H2O HNCS H2CHN C5N HCl H2S HOCO+ H2C2O HC4N KCl HNC H2CO H2NCN NH HNO H2CN HNC3 NO MgCN H2CS SiH4 NS MgNC H3O+ H2COH+ NaCl N2H+ NH3 OH N2O SiC3 PN NaCN C4 SO OCS SO+ SO2 SiN c-SiC2 SiO CO2 SiS NH2 CS H3+ HF SiCN SH AlNC FeO(?) SiNC

About 150 detected interstellar molecules as of April 2009 (www.cdms.de). 36 (+2 tentative) molecular detection in extragalactic systems.

Molecules in disks 2 3 4 5 6 7 8 9 10 11 12 13 atoms -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- H2 C3 c-C3H C5 C5H C6H CH3C3N CH3C4H CH3C5N? HC9N CH3OC2H5 HC11N AlF C2H l-C3H C4H l-H2C4 CH2CHCN HCOOCH3 CH3CH2CN (CH3)2CO AlCl C2O C3N C4Si C2H4 CH3C2H CH3COOH? (CH3)2O NH2CH2COOH? C2 C2S C3O l-C3H2 CH3CN HC5N C7H CH3CH2OH CH3CH2CHO CH CH2 C3S c-C3H2 CH3NC HCOCH3 H2C6 HC7N CH+ HCN C2H2 CH2CN CH3OH NH2CH3 CH2OHCHO C8H CN HCO CH2D+? CH4 CH3SH c-C2H4O CH2CHCHO CO HCO+ HCCN HC3N HC3NH+ CH2CHOH CO+ HCS+ HCNH+ HC2NC HC2CHO CP HOC+ HNCO HCOOH NH2CHO CSi H2O HNCS H2CHN C5N HCl H2S HOCO+ H2C2O HC4N KCl HNC H2CO H2NCN NH HNO H2CN HNC3 NO MgCN H2CS SiH4 NS MgNC H3O+ H2COH+ NaCl N2H+ NH3 OH N2O SiC3 PN NaCN C4 SO OCS SO+ SO2 SiN c-SiC2 SiO CO2 SiS NH2 CS H3+ HF SiCN SH AlNC FeO(?) SiNC DCO+

About 150 detected interstellar molecules as of April 2009 (www.cdms.de). 36 (+2 tentative) molecular detection in extragalactic systems.

sternentstehung - star formation - mpia.de · · 2009-06-12sternentstehung - star formation...

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