ltesti kes jun2017 for webrvanderb/kes/leonardo/ltesti_kes.pdf · 2019. 7. 10. · simple theory of...
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Protoplanetary disksLeonardo Testiltesti@eso.org
• Origins of disks, overview and timescales• Disk structure and evolution• Observations: properties from continuum observations • Molecular gas properties from CO and isotopologues• Most likely not cover: Transition Disks and photo evaporation• Definitely not cover: dust evolution and planet formation(Warning: very selective material and focused mostly on submm)
mailto:ltesti@eso.org
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Stars form in molecular clouds
molecular core
Molecular gas on the Galactic plane
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Jeans criterion
M jeans ∝ T 3/2 n -1/2 → 2 Μsun for T=10 K, n=104 cm-3
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As an order of magnitude
estimate, a star has
~one free-fall time
to reach its final mass
~ 105 y n5-1/2
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From an observational perspective …
• Molecular cores are cold• T ~ 10 K
• and dense• n ~ 10 5 - 10 6 cm -3
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The (once) elusive protostars
“an interstellar cloud undergoing inexorable gravitational contraction to form a single star”
—L. Spitzer (1948)
“Protostars are the Holy Grail of infrared astronomy”
—C.G. Wynn-Williams (1982)
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Where is the disk coming from?Cores are rotating:
Centrifugal radius:(angular momentum conservation)
DensityStreamlines
angular momentum conservation r2Ω
Increase
s with
time fo
r
the dur
ation o
f the
collapse
phase
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Rotation of coresMeasuring rotation
Goodman et al. (1993)
� = Erot
/Egrav
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ALMAcaniden+fyacompactrota+ngcomponentaroundclass0protostar!
SMA
280AU
Ohashietal.2015
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L1527Rota+onCurvemeasuredbyALMAOhashietal.2015
N
S
-
(UV excess)
Classical TTauri star
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YSO SED classification
• Original classification I-II-II based on IR spectral index
• Class 0 based on FIR-submm• Many caveats, but still a useful
classification scheme
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IR SED slope
Meyer+1997
Photospheres
Infrared excess
Extincted photospheres
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Statistics and timescales
Evans et al. 2009
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Statistics and timescales
Evans et al. 2009
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Statistics and timescales
Evans et al. 2009
• In nearby star forming regions, we can estimate:• very roughly tII ~ 5-10 tI ~ 5-10 t0 or ~106 yr : ~105 yr : ~104 yr
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From Cores to Planetary Systems
LCore
Disk
Debris Disk
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From Cores to Planetary Systems
Core
Disk
Debris Disk
Inner disk clearing:e-folding time t~2-3 Myr
(Her
nand
ez e
t al.
2007
)
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Our own Solar System
• CAI• Formed early
• Condrules• After 1-2 Myr• Spread ~3Myr
• Matrix• Sub-um particles• Cement the body
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Our own Solar SystemThe accepted view has recently been challenged by recent measurements of isotopic abundances in CAIs and Condrules
(Con
nelly
et a
l. 20
12)
• CAI• Formed early
• Condrules• After 1-2 Myr• Spread ~3Myr
• Matrix• Sub-um particles• Cement the body
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Protoplanetary disks
100 AU
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Vertical structure
• Hydrostatic equilibrium: pressure vs gravity
€
ddz
ρ(z)kT(z)µmp
#
$ % %
&
' ( ( = −ρ(z)ΩK
2 z
€
kTµmp
dρ(z)dz
= −ρ(z)ΩK2 z
€
ρ(z) = ρ0 exp −z2
2h2$
% &
'
( )
€
h = kTr3
µmpGM*
• Using an isothermal approximation, we can find a gaussian solution for the density
• h
-
viscosity and radial structure• The vertical timescale (h/cs) is much shorter than the
radial evolution timescale (can decouple the two processes)
• Assumption: vr
-
• Alpha-disk after Shakura & Sunyaev (1973)viscosity and radial structure
• Self similar solution after Linden-Bell & Pringle (1973) • if T~r-q then n~r(3-2q)/2 (assuming alpha~const)
€
ν =αcsh
€
α = 0.001...0.1
€
ν =αcs2
ΩK
Viscous disc similarity solution
�(R, t) =Md(0)(2� �)
2⇥R20r�
⇤�(5/2��)
2�� exp
✓�r
2��
⇤
◆
Lynden-Bell & Pringle (1974)
t⌫ =R20
3(2� �)2⇥0r = R/R0 � = t/t⌫ + 1
Ṁacc =Md(0)
2(2� �)t�⇥
�(5/2��)2��
� / R�
Viscous disc similarity solution
�(R, t) =Md(0)(2� �)
2⇥R20r�
⇤�(5/2��)
2�� exp
✓�r
2��
⇤
◆
Lynden-Bell & Pringle (1974)
t⌫ =R20
3(2� �)2⇥0r = R/R0 � = t/t⌫ + 1
Ṁacc =Md(0)
2(2� �)t�⇥
�(5/2��)2��
� / R�
Viscous disc similarity solution
�(R, t) =Md(0)(2� �)
2⇥R20r�
⇤�(5/2��)
2�� exp
✓�r
2��
⇤
◆
Lynden-Bell & Pringle (1974)
t⌫ =R20
3(2� �)2⇥0r = R/R0 � = t/t⌫ + 1
Ṁacc =Md(0)
2(2� �)t�⇥
�(5/2��)2��
� / R�
Viscous disc similarity solution
�(R, t) =Md(0)(2� �)
2⇥R20r�
⇤�(5/2��)
2�� exp
✓�r
2��
⇤
◆
Lynden-Bell & Pringle (1974)
t⌫ =R20
3(2� �)2⇥0r = R/R0 � = t/t⌫ + 1
Ṁacc =Md(0)
2(2� �)t�⇥
�(5/2��)2��
� / R�
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• evolution of a thin annulus (gamma=1.0)viscosity and radial structure
Log(R)
Log(
Sigm
a)
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• full disk evolution (gamma=1.0)viscosity and radial structure
Log(R)
Log(
Sigm
a)
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• Data generally consistent with viscous evolution and Macc
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Mass accretion rate
A more realistic picture
• Data generally consistent with viscous evolution and Macc
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• Very slow!
Viscous evolution
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Disk photoevaporation
• Energetic stellar radiation heats the disk surface• Unbound material flows away from the system
(Arm
itage
)
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Photoevaporation cartoonSimple Theory of Photoevaporation from internal EUV radiation1. EUV radiation ionises and heats the disc atmosphere: bound atmosphere at r < rg; mass loss in thermal wind at r > rg. Ioniaing flux dominated by scattered stellar photons from the wind atmosphere (diffuse field)
2. Accretion rates drop below the mass-loss rates and a gap opens in the disc close to rg. The outer and the inner disc become decoupled. The inner disc is starved.
3.The inner disc drains rapidly on to the star an inner hole (transition disc is produced and the direct EUV flux from the star quickly photoevaporates the outer region.
Monday, 7 May 2012
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• Consistent with disk evolution timescales• (… need to add planet formation …)
Evolution of Mdisk
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Observations
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Spectral Energy Distributions (SEDs)The SED shows the energy emitted per logarithmic wavelength
interval. Plotting just the flux may be misleading:
Energy:
€
Fν dν = Fν Δν
erg cm-2 Hz-1
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Spectral Energy Distribution
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• Balance energy losses Q- and source Q+:viscous heating
Q-=2sTeff4 (two sides, each radiate as a BlackBody)
Q+=(3/4p)Macc(WK)2 (viscous heating)Q-=Q+
Teff4=3/(8sp)Macc(WK)2Teff~r-3/4
Tmid4=tRossTeff4 tRoss=SkRoss/2
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Wien
Intermediate region
Rayleigh-Jeans
τν∝Σ(r)κν Σ(r)∝r-p κν∝κoνβ
SED for a locally isothermal disk
λ
νFν
-
ν(4q-2)/qνFν
λ
τν∝Σ(r)κν Σ(r)∝r-p κν∝κoνβ
SED for a locally isothermal disk
ν3+β
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τν∝Σ(r)κν Σ(r)∝r-p κν∝κoνβ
SED for a locally isothermal disk
Beckwith et al. (1991)
Viscous heating provides a poor fit of protoplanetary disc temperature:real disks are warmer than expected in the outer regions!
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τν∝Σ(r)κν Σ(r)∝r-p κν∝κoνβ
“flat” passive diskIrradiation flux:
€
Firr =αL*4π r2
Coincidentally, same profile: no good!
The flaring angle:
€
α ≅0.4 r*r
€
T = 0.4 r*L*4πσ r3
$
% &
'
( )
1/ 4
€
T ∝ r−3 / 4
-
τν∝Σ(r)κν Σ(r)∝r-p κν∝κoνβ
“flared” passive diskIrradiation flux:
€
Firr =αL*4π r2
Can work……depending on hs(r)
The flaring angle:
€
α = r ∂∂r
hsr
$
% &
'
( ) →ξ
hsr
€
T 4 = ξσhsL*4π r3
€
hs = χ h
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Flared disks: detailed models
Global disk model...
... consists of vertical slices, each forming a 1D problem. All slices are independent from each other.
[K. Dullemond]
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Including viscous heating
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Including viscous heating
(Macc~10-8 Msun/yr @ 1 Myr)
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“flared” disk emission
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Flared disks: which observations probe what?
Mid-IR imaging
Scattered light
IR SpectroscopyPAH
Emission
[C. Dominic]
Submm/radio: Entire Disk
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Disk masses: (sub)mm continuum• MD ~ 0.01-0.1 Msun• MD/Mstar ~ 0.03
• F1mm ~ Bn(T) k1mm MD
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Disk masses - Taurus
• Full Taurus survey, pre-ALMA: low detection rate M*
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Disk masses: ALMA
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Disk masses: ALMA
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LTesti | ALMA Development | STC Apr 23, 2017
Forming the TRAPPIST-1 system
Young Brown Dwarf disks ➢Where is the material to form
TRAPPIST-1? ➢Planet formation much faster
than we think or TRAPPIST-1 unreasonably rare…
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Examples of pre-ALMA results
• Data generally well described, note limited angular resolution
Isella+2009
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Examples of pre-ALMA results
Isella+2009 Williams&Cieza 2011 Andrews+2010
• Extract N random samples from “Taurus” applying the same selection biases as expected in the other region. Method first applied by Andrew+2013
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Examples of pre-ALMA results
Isella+2009 Williams&Cieza 2011 Andrews+2010
• Extract N random samples from “Taurus” applying the same selection biases as expected in the other region. Method first applied by Andrew+2013
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Accretion
• Direct measurement of accretion: energy released in the collision
• Indirect measurement: emission lines from accretion columns
(UV excess)
L. Hartmann
Manara+2014
Gullbring+2000
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Accretion
• Lacc measured directly from the UV excess luminosity (with a correction factor for FUV/EUV
(UV excess)
L. Hartmann
Gullbring 1998
Rm ~ 5 Rstar
Rigliaco 2011
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ALMA - Md
XSho
oter
- M
acc
Man
ara+
2016
ALMA - Md
XSho
oter
- M
acc
Mul
ders
+201
7
Accretion-Md connection
• Almost, but not quite…
Dul
lem
ond,
Nat
ta, T
esti
2006
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30 au
100 =1
3600degree
1 au = Sun-Earth distance
orbit of neptune = 30 au
gaps
thermal emission of solid particles ≲ 1 cm Kwon et al. 2011
thermal emission of solid particles ≲ 1 cm ALMA Partnership 2015
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Disks with ALMA
• Not as smooth and simple as advertised so far: dust evolution and dust-gas-planets interaction rule (another KES, sometime)
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Summary• Disk formation and initial properties
• Process is understood in broad terms• Details are tricky: gas and dust initial content and
properties? Amount of L-loss during collapse?
• Disk properties• angular momentum loss drives early evolution:
viscosity (origin? properties?) and/or winds?
• photoevaporation and/or planet formation drives disk dissipation
• Observing dust is easy, gas a bit more tricky, understanding what observations tell us requires models!
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