Transcript Document 7811610

Protoplanetary disks as seen by the
IRAM array
Vincent Pietu (LAOG)
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A few important points in the observations and
analysis related to the survey we have performed
with the IRAM array on TTauri and Herbig HA
stars in Taurus-Auriga cloud
Main collaborators:
A. Dutrey (L3AB), S. Guilloteau(L3AB), E. Dartois (IAS)
Protoplanetary disks as seen by
the IRAM array
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Collapse of a prestellar
condensation
The conservation of angular
momentum gives raise to a
flattened structure : disk
Evolutionary sequence :
Class 0, I, II, III
Also holds for intermediate-mass
stars : Herbig HAe stars (3 <
Msun)
Planet formation ?
Disks emission in mm range
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Thermalized lines
CO optically thin lines :
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J=1-0: Tb a S/T
J=2-1: Tb a S
CO optically thick lines :
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Tb= Tk
Brightness temperatures
from a few mK to a few 10
K (12CO J=2-1)
Continuum optically thin :
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Tb a  M.T
 =  0 (ν/ν0)
D= 150 pc
Res = 1’
Observations and reduction :
strategy
 12CO
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Snapshot observations (better calibration)
Other molecules : SNR is an issue. Can only image
brightest disks and strongest lines.
Final error bars on parameters depend on the SNR.
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: (u,v) coverage is the limiting factor.
PdBI CO observations : physical structure.
30-m : line detection.
PdBI : imaging of molecular lines other than CO
Data reduction : flux calibration is an issue !
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Error on Tk proportionnal to flux errors.
Method of analysis : parametric
modelling and inversion
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Quite complex observations : direct analysis is not possible. Rather use a parametric
model.
Need to account for tranfert function of the interferometer for a non-biased analysis.
Since deconvolution is non-linear, comparison performed in the (u,v) plane
2 = Si Sn [ Re(modi,n) - Re(obsi,n)]2 *Wi + Si Sn [ Im(modi,n) - Im(obsi,n)]2 *Wi
Weight : Wi = 1 / i2 where i is the thermal noise associated with visibility i
Standard disk model (Pringle 1981):
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Power-law parametrisation :
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Vertical distribution derived from (isothermal) hydrostatic equilibrium
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T ( r ) = T0 . (r / r0) -q
S ( r) = S 0 . (r / r0) -p
n(r,z ) = n(r,0 ) . exp[ - (z / h) 2 ]
Where the scaleheight is : h ( r ) ~ cs / v q
Disk in rotation : v ( r ) = v 0 . (r / r 0) –v
(Keplerian case (v=0.5) : dynamical masses measurement : v0 =√ G.M/r0)
Line width : quadratic sum of thernal width and a turburlent width
Level population : Local Thermodynamic Equilibrium (LTE)
CO isotopes analysis : MWC 480
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MWC 480 is a isolated
Herbig A4 star.
Observed in 12CO (2-1)
13CO (2-1) and 13CO (1-0)
The modeling reveals a
vertical temperature
gradient between the plane
of the disk (30 K) and
above (50 K) at r = 100 AU
Contrary to TTauri stars,
CO isotopes are not
depleted with respect to
TMC-1
Analysis : the (relative) importance
of line contamination by continuum
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MWC 480 possesses a strong (220 mJy @ 230 GHz) and compact
(0.8”) continuum emission (therefore used as an internal flux
calibrator).
Can contaminate line wings  bias on kinematic properties !
Solution : simultaneous fitting of line and continuum data (the
latter are less noisy thanks to a larger bandwidth)
Indeed, such a procedure provides an better fit to the data.
For example in MWC 480,
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12CO(2-1)
:M*= 1.65±0.07 Msol (Simon et al. 2000)
Small difference with prestellar evolution models ? Distance problem ?
 Same data : M*= 1.97±0.02 Msol (with continum fitting).
 Perfect agreement with models at the nominal distance
Sub-arcsecond imaging of the
Herbig A0e star AB Auriga
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Continuum assymetry
also present in 13CO
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Fukagawa et al. 2004
Density effect
Spiral arm ?
AB Aur : modelling and analysis
CO lines modelling reveal that
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The disk is quite hot, and there is a vertical
temperature between the disk plane (30 K)
and “atmosphere” (80-100 K) at 100 AU
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Contrary to TTauri disks, CO isotopes in
HAe disks are not significantly depleted
compared to TMC-1 CO abundance .
 But some difficulties remain :
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The rotation is not Keplerian:
v(r) = 2.44 (r/ro) 0.4 +\- 0.01
(as derived from 13 CO 2-1, 1-0)
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Spiral pattern in the disk
 Origin of these disturbances ?
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Companion ? Quite unlikely.
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Massive disk ? Stable according to
Toomre’s criterion
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Youth remnant ? (Cassen et al. 1981, 1983,
Stahler et al. 1994)
From Grady et al. 1999
Conclusion and perspective
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Millimeter interferometry is a powerful way to study protoplanetary disks, but SNR is
an issue
With respect to this concern, the IRAM array is actually the best instrument in use.
Whenever using a model and inversion techniques, it is very useful to compare with
observations in the (u,v) plane
mm interferometry provides a reliable and robust access to unique insight onto
protoplanetary disks.
In the long term, ALMA will
cause a revolution because of
 Higher angular resolution
(5 AU @ 230 GHz @ 150 pc)
 Greater sensitivity
In that perspective, PdBI should
be used to prepare ALMA