l 6: circumstellar disks

L6 - Stellar Evolution II: August-September, 2004 [email protected]

L 6: Circumstellar Disks

Background image: HH 30 JHK HST-NICMOS, courtesy Padgett et al. 1999, AJ 117, 1490


L 6: Circumstellar Disks

Recent reviews include:

Protostars & Planets IV, Mannings, Boss & Russell (eds.) 12 Articles on Disks 5 Articles on Outflows

Zuckerman, ARAA 2001, 39: 549

Zuckerman & Song (?), ARAA 2004, in press


L 6: Circumstellar Disksand Outflows


Flattened structures - Disks

Inevitable consequence of star formation

Rotation Magnetic Fields


Flattened structures - Disks


Rotation

P.S. Laplace 1796, 1799

Exposition du systeme du mondeMechanique celeste

I. Kant 1755

Allgemeine Naturgeschichte und Theorie des Himmels

Planetary System Formation

...another lecture – another time...


Mass Loss - Outflows


Angular Momentum Loss - Redistribution

The race between mass accretion & mass loss processses

see review article


Lynden-Bell & Pringle 1974, MNRAS 168, 603:

Keplerian Disk

Differential Rotation + Viscosity

Mass Transport InwardsAngular Momentum Transport Outwards

See also Gösta Gahm’s lecture


`standard model´: e.g., Frank, King & Raine Accretion Power in Astrophysicsself-consistent structure of steady, optically thick -disk

blackbody radiation and thin disk approximation

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Lin & Papaloizou opacities(1985 PP II)

Icy grains

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Beckwith et al. 2000, PP IV

Grain Opacities


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40 observed SEDs of T Tauri Stars & `mean model´ of star+disk

D´Alessio et al. 1999

HABE Disk Structure:

Dullemond & Dominik 2004

includes vertical

Temperaturedistribution


Gas Disks – Structure Models

Steady Disks around Single Stars

Boundary Conditions Rin : boundary layer, magnetosphere?Rout: ? , interstellar turbulence?

Viscosity MHD/rotation (Hawley & Balbus 1995)

Opacity , T, …, XYZ, ..., ,..., ...)

Models Adams & Shu 1986 (flat)[examples] Kenyon & Hartmann 1987 (flared)

Malbet & Bertout 1991 (vertical structure)D´Allessio et al. 1998,... 2003Aikawa & Herbst 1998 (chemistry)Nomura 2002 (2D)Wolf 2003 (3D)


Observations of Keplerian Disks

JE Keeler 1895ApJ 1: 416

The Rings of Saturnspectrum

image

Courtesy Brandeker, Liseau & Ilyn 2002


2 Categories of Disks

T Tauri Disks: around young stars (0.1 - 10 Myr) of half a solar mass (0.1 - 1 Msun) at 150 pc distance (50 - 450 pc) in and/or near molecular clouds Accretion Disks

Debris Disks: around young ms-stars (10 - 400 Myr) of about a solar mass (1 - 2 Msun) at 20 pc distance (3 - 70 pc) in the general field Vega-excess stellar disks

gas rich

gas poor


Frequency of Disks

High Rate of occurence around young stars

NGC 2024 86% Trapezium cluster 80% IC 348 65% Haisch et al. 2001

and around

BDs in Trapezium cluster 65% Muench et al. 2001

see also G. Gahm’s lecture


Gas Disks - Sizes

Size scale (AU) Tracer (mode)* Reference

20000 CS (1- 0) (S) Kaifu et al. 19845000 - 10000 13CO (1- 0) (S) Fridlund et al. 1989 1400 C18O (1- 0) (I) Sargent et al. 1988 <500 1.4 mm (I) Woody et al. 1989 45 + 1600 mm, cm (I) Keene & Masson 1990 200 0.8 mm (I) Lay et al. 1994 7000 H13CO+ (1- 0) (S) Mizuno et al. 1994 5000 0.7 - 1 mm (S) Ladd et al. 1995 4000 - 6000 C18, 17O (2- 1) (S) Fuller et al. 1995 1200 13CO (1- 0) (I) Ohashi et al. 1996 4000 H13CO+ (1- 0) (I)Saito et al. 1996 5000 H12, 13CO+ (1- 0) (S, I) Hogerheijde et al.1997, 98 2500 C18O+ (1- 0) (I) Momose et al. 1998

Fridlund et al. 2002for

One Object

Size depends on frequency/mode of observation*S=single dish, I=Interferometer


Gas Disks - Sizes

T Tauri/HABE disks

50 - 100 AU Dust: mm-continuum interferometry

100 - 300 AU Dust: scattered stellar light

300 AU Gas: CO lines (evidence for Kepler rotation)

Silhouettte disks (``proplyds´´)

up to 1000 AU Dust: scattered stellar light

generally


Gas Disks - Masses

H2

GasDirectly

COandDust


Gas Disks - Masses

Lower limit: 0.001 to 1 MSun (based on mm / submm continuum)

How good are these numbers ?

Do we understand disks ?

? Why ?

dust

gas+dust

Solar Minimum Mass Nebula = 0.002 MSun


Gas Disks - Make up

gas disks consist of gas and dust

what components?

what proportions?


2 T Tauri Disks - Make up

van Zadelhoff 2002

13CO (1)*

HCO+ (5)

HCN (5)

CO (200)

HCO+ (200)

HCN (200)

LkCa 15 TW Hya*(N) = depletion factor


2 T Tauri Disks - Chemistry

Molecular abundances (rel. H2)

Species LkCa 15 TW Hya

CO 3.4 ( - 7) 5.7 ( - 8)HCO+ 5.6 (-12) 2.2 (-11)H13CO+ < 2.6(-12) 3.6 (-13)DCO+ …. 7.8 (-13)CN 2.4 (-10) 1.2 (-10)HCN 3.1 (-11) 1.6 (-11)H13CN …. < 8.4(-13)HNC …. < 2.6(-12)DCN …. < 7.1(-14)CS 8.5 (-11) ….H2CO 4.1 (-11) < 7.1(-13)CH3OH < 3.7(-10) < 1.9(-11)N2H+ < 2.3(-11) < 1.8(-11)H2D+ < 1.5(-11) < 7.8(-12)

Thi 2002


Gas Disks - Evolution

Time scales (viscous accretion disk)

tdyn ~ ttherm ~ (H/R)2 tvisc

tdyn ~ 1/Kepler

~ 10-3 - 10-2

H/R << 1

if T ~ R-1/2 , tvisc ~ R

tvisc ~ 105 yr (/0.01)-1 (R/10 AU)


Gas Disks - Evolution

Disk dispersal and disk lifetimes

Physical MechanismsHollenbach et al. 2000 PPIV

SE = Stellar Encounter (tidal stripping) WS = Stellar wind stripping evap E = photoevaporation external starevap c = photoevaporation central star

All for Trapezium conditions


Gas (T Tauri) Disks - Evolution

Disk dispersal and disk lifetimes

Mass accretion evolutionCalvet et al. 2000 PPIV

Average Error Bar


Gas Disks to Debris Disks – Evolution ?

See also lecture by G. Gahm

fdust = LIR/L vs stellar age

(F)IR - excess

Stellar luminosity(bolometric)

How ?


Gas Disks to Debris Disks – Evolution ?

Spangler et al. 2001

ClustersIndividual stars

(= 1 zodi)


Debris Disks - Properties

debris (collision products) or particulate (gas free)

percentage of Main Sequence stars (15%?)(observationally) biased towards Spectral Type Afor (detectable) ages <400 Myr Habing et al. 1999, 2001

disk sizes 100 to 2000 AUdisk masses >1 to 100 MMoon (small grains)

Pre-IRAS

Solar system Zodi US Navy Chaplain G. Jones 1855 AJ 4, 94

Vega Blackwell et al. 1983


http://www.hep.upenn.edu/~davidk/bpic.html


How much Gas in Dusty Debris Disks ?

Disk evolution hypothesis: gas rich to gas poor

Census of material (mgas/mdust): planet formation

planet formation: enough gas for GPs ?

planet formation: time scales ?

planet formation: seeds of Life ?

See review


L 6: conclusions• circumstellar disks are a consequence of star formation• disks and bipolar outflows/jets are connected• disks form potentially planetray systems

L 6: open questions• what are the physics of disks and their outflows ?• how do disks evolve ?• what fraction forms planetary systems ?• when and how ?

l 6: circumstellar disks

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