Francesco Trotta YERAC, Manchester - 2011 Using mm observations to constrain variations of dust...
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Transcript of Francesco Trotta YERAC, Manchester - 2011 Using mm observations to constrain variations of dust...
Francesco Trotta
YERAC, Manchester - 2011
Using mm observations to constrain variations of dust
propertiesin circumstellar disks
Advised by:
Leonardo Testi
Planet Formation in circumstellar disks
Observational evidence of dust grain growth
Constrain the radial variation of dust properties with
high-resolution mm-observation
Future prospective with ALMA
Outline
1
2
3
4
What are the circumstellar disks and why do we study them?
• Disks are presumed to be the birthplace of planetary system
Forming star
Rotating disk Massaccretion
• Central forming star accretes most of its mass throught the disk
dominates the mass
the dynamics of the disk
dominates the opacity
thermal and gemetrical structure of the disk
the emission properties of the disk
GAS99%
DUST1%
Angular Momentumtransported outward
Circumstellar disks play a fundamental role in the process of star and planet formation
TurbulenceTransport angular
momentum
Mass accretion onto the star
with time: (1) Mstar↗ Mdisk↘ (2) Disk spreads out
1mm 1m 1km 103km Log a1mm
ISMdust
grains
coupled to the gas gravitycoupled to the gas + gravity
Early growth Mid-life growth Late growth
Gas sweeping
Gravitational interactionAereodynamic interaction
Core accretion
model
weakwell
Growth of 12 order of magn. in size in a few Myr
From dust to planet
1mm 1m 1km 103km Log a1mm
ISMdust
grains
coupled to the gas gravitycoupled to the gas + gravity
Early growth Mid-life growth Late growth
Gas sweeping
Gravitational interactionAereodynamic interaction
weakwell
From dust to planet
Directly observable
Exo-Planets
Growth of 12 order of magn. in size in a few Myr
Core accretion
model
Which observations do we need?
)1))((()( )(ReRTBRI
)()()( RRR
The dust thermal emission (at each radius)
withOpticaldepth
Optical depth is very high (at least at short l) LIMITATION:
Which observations do we need?
)1))((()( )(ReRTBRI
)()()( RRR
The dust thermal emission (at each radius)
withOpticaldepth
Optical depth is very high (at least at short l) LIMITATION:
Probe the bulk of the dust mass in the disk mid-plane
Information only on grain located in the surface layer (tiny fraction of dust mass)
Limited to the outer regions of the disks
V
IR
R
Longer ,l bigger fraction of the dust optically
thin
How to observe dust grain size at mm-l?
Small (compact) grain (a<<l)(es. ISM dust b ~ 1.7)
For a optically thin disk and in RJ regime the dust thermal emission at mm-l
b=2
Solid bodies with a>> /2l p(es. Rocks)
b=0
mm-size particles
0< <2b
Optically thick inner region
Deviation from RJ regime
+ b > a - 2
(diagnostic of dust size,shape,composition)
We are observing b
Fn ~n4
)2(F
Fn ~n2
Fn ~ n2:4
Draine & Lee (1984)
Gray opacity
)1( e2)( TB
Log
F
Log l
Grain growth evidence from mm spectral index
If b < bISM ~ 1.7DUST GRAIN
GROWTH
Resolved (large) disks make (2) improbable
Need of Spatially Resolved Disk at mm l
(hi-res interferometry)
Twopossibility
Testi & al. (2003)
CQ Tau
VLA 7mm res~0.8’’(~100 AU)
Observational
evidence
Shallow SED(a mesured are small
)
(1) Optically thin disk & low b(2) Optically thick disk & any b
Disk models(with radial variation
of the grain size distrib)
High-resolution observ (at more l)
How to constrain the radial variation of dust properties?
Dust evolution models predict grain growth different dust properties in function the position on the
disk
kdust(x)
We are trying tho constrain the radial
opacity profile
Surface layer
Interior
Surface DensitySimilari
tySolution
qaRan ),()(005.0 max Raam
Grain size distribution
PowerLawapproximati
on
max)/()( 0max0max
bRRaRa
starsurface
interior
total
SURFACE LAYERDominate the flux ~ 60 mm (mid-IR)
STARBB emission picco a l - 1 mm (near-IR)
INTERIOR LAYERDominate the flux a l > 100 mm (sub-
mm/mm)
Disk models
How to constrain the radial variation of dust properties?
Isella & al. (2010)
1.3mm 2.8mm
6.92mm
res~0.5’’(~70 AU)
res~0.3’’(~40 AU)
res~0.15’’(~20 AU)
CARMA
VLA
High angular resolution observations at 3 different mm-l of RY Tau
new data
High-res observation
CARMA
VLA
How to constrain the radial variation of dust properties?
Disk around RYTau
We use c2 fitting procedure (directly on visibility)
Choose the grid models (n free-param with a wide range of value)
• Produce disk images
• Fourier trasform it and sampled at the (u,v) points corrisponding to the observed samples
• Computed the c2 value
Calculate the best fitting model (minimum of the c2 hypercube_sum)
2/2)Im(Im2ReRe2 toto
Costruct the c2 hypercube(for each l)
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2
3
Free parameter
Str Rtr g a0max bmax inc P.A.
How to constrain the disk parameters?
First resultsRtr = 30 [AU]Str = 3.4 [g/cm^2]g = -0.53
Rtr = 34 [AU]Str = 2.3 [g/cm^2]g = -0.35
Rtr = 36 [AU]Str = 1.8 [g/cm^2]g = -0.9
The best fit values we found are ~ in agreement with the Isella result
a0max=0.03cm bmax= 0P.A. = 24°Inclination = 66°
Compare with Isella & al. 2010
1.3mm
2.8mm
6.92mm
But large error-bars
Evidence of radial variation of dust
properties
BEST FIT VALUE
Future prospects
ALMA
To place more stringent constrains on the radial variation of the dust opacity we need of observations with:
higher angular resolution
higher sensitivity
At least 50X12m Antennasmax resolution <0.01’’
at 870 mm
Will be able to resolve structure of
few AU
(at near star forming region)
Should be possible detect spiral structure
of few AU
Simulated observations of massive self-graviting circumstellar disk with ALMA
Should be possible detect spiral
structure of few AU
Cossin,Lodato,Testi (2010)
Intensity maps at sub-mm l from SPH simulation of disk
Image maps at that sub-mm l with various
array conf.
CASA ALMA simulator
(Taurus-Auriga star-forming
region)
Conclusions
• mm spectral slopes indicate presence of mm-size dust grains in the disk (dust grain growth)
• To study the radial variation of the dust properties we need of observations with higher angular resolution and sensitivity
• High angular resolution observation show us radial variation of dust property in circumstellar disk
ALMA will play a crucial role in the next future
However
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