l 6: circumstellar disks
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L6 - Stellar Evolution II: August-September, 2004 1rene@astro.su.se
L 6: Circumstellar Disks
Background image: HH 30 JHK HST-NICMOS, courtesy Padgett et al. 1999, AJ 117, 1490
L6 - Stellar Evolution II: August-September, 2004 2rene@astro.su.se
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
L6 - Stellar Evolution II: August-September, 2004 3rene@astro.su.se
L 6: Circumstellar Disksand Outflows
L6 - Stellar Evolution II: August-September, 2004 4rene@astro.su.se
Flattened structures - Disks
Inevitable consequence of star formation
Rotation Magnetic Fields
L6 - Stellar Evolution II: August-September, 2004 5rene@astro.su.se
Flattened structures - Disks
Inevitable consequence of star formation
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...
L6 - Stellar Evolution II: August-September, 2004 6rene@astro.su.se
Mass Loss - Outflows
Inevitable consequence of star formation
Angular Momentum Loss - Redistribution
The race between mass accretion & mass loss processses
see review article
L6 - Stellar Evolution II: August-September, 2004 7rene@astro.su.se
Lynden-Bell & Pringle 1974, MNRAS 168, 603:
Keplerian Disk
Differential Rotation + Viscosity
Mass Transport InwardsAngular Momentum Transport Outwards
See also Gösta Gahm’s lecture
L6 - Stellar Evolution II: August-September, 2004 8rene@astro.su.se
`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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When / Where valid ?
L6 - Stellar Evolution II: August-September, 2004 9rene@astro.su.se
Example:
Lin & Papaloizou opacities(1985 PP II)
Icy grains
H-
Moleculesbound-freefree-free(Cox-Stuart-Alexander)
L6 - Stellar Evolution II: August-September, 2004 10rene@astro.su.se
Beckwith et al. 2000, PP IV
Grain Opacities
L6 - Stellar Evolution II: August-September, 2004 11rene@astro.su.se
`standard model´: e.g., Frank, King & Raine Accretion Power in Astrophysicsself-consistent structure of steady, optically thick a-disk
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L6 - Stellar Evolution II: August-September, 2004 12rene@astro.su.se
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
L6 - Stellar Evolution II: August-September, 2004 13rene@astro.su.se
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)
L6 - Stellar Evolution II: August-September, 2004 14rene@astro.su.se
Observations of Keplerian Disks
JE Keeler 1895ApJ 1: 416
The Rings of Saturnspectrum
image
Courtesy Brandeker, Liseau & Ilyn 2002
L6 - Stellar Evolution II: August-September, 2004 15rene@astro.su.se
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
L6 - Stellar Evolution II: August-September, 2004 16rene@astro.su.se
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
L6 - Stellar Evolution II: August-September, 2004 17rene@astro.su.se
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
L6 - Stellar Evolution II: August-September, 2004 18rene@astro.su.se
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
L6 - Stellar Evolution II: August-September, 2004 19rene@astro.su.se
Gas Disks - Masses
H2
GasDirectly
COandDust
L6 - Stellar Evolution II: August-September, 2004 20rene@astro.su.se
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
L6 - Stellar Evolution II: August-September, 2004 21rene@astro.su.se
Gas Disks - Make up
gas disks consist of gas and dust
what components?
what proportions?
L6 - Stellar Evolution II: August-September, 2004 22rene@astro.su.se
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
L6 - Stellar Evolution II: August-September, 2004 23rene@astro.su.se
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
L6 - Stellar Evolution II: August-September, 2004 24rene@astro.su.se
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)
L6 - Stellar Evolution II: August-September, 2004 25rene@astro.su.se
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
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Gas (T Tauri) Disks - Evolution
Disk dispersal and disk lifetimes
Mass accretion evolutionCalvet et al. 2000 PPIV
Average Error Bar
L6 - Stellar Evolution II: August-September, 2004 27rene@astro.su.se
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 ?
L6 - Stellar Evolution II: August-September, 2004 28rene@astro.su.se
Gas Disks to Debris Disks – Evolution ?
Spangler et al. 2001
ClustersIndividual stars
(= 1 zodi)
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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
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http://www.hep.upenn.edu/~davidk/bpic.html
L6 - Stellar Evolution II: August-September, 2004 31rene@astro.su.se
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
L6 - Stellar Evolution II: August-September, 2004 32rene@astro.su.se
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 ?
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