Long%20term%20evolution%20of%20circumstellar%20discs:%20DM%20Tau%20and%20GM%20Aur - PowerPoint PPT Presentation

Title: Long%20term%20evolution%20of%20circumstellar%20discs:%20DM%20Tau%20and%20GM%20Aur


1
Long term evolution of circumstellar discs DM
Tau and GM Aur

• Ricardo Hueso () Tristan Guillot
• Laboratoire Cassini, Observatoire de la Côte
  dAzur, Nice, France
• () Now at E.T.S. Ing. Ind. y Telecom. UPV,
  Bilbao, Spain

Circumstellar disks protoplanets, Nice,
February 2003
2
Initial questions

• Are models of star disk formation able to
  compare with observations and give constraints on
  relevant disk physics?

• Numerous Parameterizations.
• How to set up values for the most relevant
  parameters?

• Is it viscous evolution the most important factor
  determining disk properties on the long term?

• Different models of turbulence
• a prescription , b prescription,
• Shear, convection, MRI, surface MRI, waves

• Statistics about protoplanetary disks begin to be
  available.
• Life-span, disk masses, star accretion
• rates with time

• This work

Make simple models of disk formation evolution
and compare with available observations. Set up
model parameters and test turbulence
prescriptions.
Circumstellar disks protoplanets, Nice,
February 2003
3
Models of Disk Formation and Evolution
Fast 1D models
Including gravitational collapse of rotating
isothermal spheres
Viscous evolution source terms
Simplified radiative transfer
Additional equations for disk properties
Photoevaporation (Long term simulations)
Circumstellar disks protoplanets, Nice,
February 2003
4
Two models of turbulence a and b

• na r 3/4 nb r ½ ?
• Are finally both parameterizations so different
  when applied?

Circumstellar disks protoplanets, Nice,
February 2003
5
Observational characteristics of DM Tau and GM Aur
Circumstellar disks protoplanets, Nice,
February 2003
6
Comparing model with DM Tau
PAREMETERS
a 0.005 wcd 3 10-14 s-1 Tcd 10 K M0 0.3 M?
Circumstellar disks protoplanets, Nice,
February 2003
7
Comparing model with DM Tau
PAREMETERS
Circumstellar disks protoplanets, Nice,
February 2003
8
Comparing model with DM Tau
Circumstellar disks protoplanets, Nice,
February 2003
9
Constraining model parameters
Selecting models
All Models
Circumstellar disks protoplanets, Nice,
February 2003
10
Constraining model parameters
Selecting models
All Models CO Star age mass
Circumstellar disks protoplanets, Nice,
February 2003
11
Constraining model parameters
Selecting models
All Models CO Star age mass CO Dust
Circumstellar disks protoplanets, Nice,
February 2003
12
Constraining model parameters
Selecting models
All Models CO Star age mass CO Dust CO
Dust Accretion Rate
Circumstellar disks protoplanets, Nice,
February 2003
13
Constraining model parameters
Selecting models
All Models CO Star age mass CO Dust CO
Dust Accretion Rate
Circumstellar disks protoplanets, Nice,
February 2003
14
Set of model parameters fitting the observational
constraints

• Practically a standard accretion disk.

Circumstellar disks protoplanets, Nice,
February 2003
15
Set of model parameters fitting the observational
constraints

• More mass is needed

• Less Turbulence

• Greater Temperature (15 K)
• (Faster early formation)

• Less dispersion with Temperature

Circumstellar disks protoplanets, Nice,
February 2003
16
a vs. b DM Tau GM Aur
Knowing the data for the disk within an order of
5 doesnt improve these plots. Iincertitudes come
also from the assumed star age and its mass.
Circumstellar disks protoplanets, Nice,
February 2003
17
Conclusions

• Models of purely viscous discs are able to
  explain presently observed characteristics of
  circumstellar disks like DM Tau and GM Aur.
• We can obtain valuable information about the
  relevant parameters governing disk formation and
  evolution.

• Large incertitudes on the determination of
  physical properties.
• Results depends on assumptions such as CO
  depletion or dust abundance.
• Incertitudes give rise to one-two orders of
  magnitude indetermination of disk viscosity.

• Alpha an Beta parameterizations of turbulence
  work equally well (or bad)
• to fit the observations.

• GM Aur requires 10 times less turbulence than DM
  Tau.
• Consequence of a more massive disk
  combined with a lower accretion rate.

Why? Simply more massive system, older, or
... A procative posibility. Can this reduced
accretion be interpreted in terms of an
internal gap in GM Aur? SED of GM Aur seems to
suggest a gap!
Circumstellar disks protoplanets, Nice,
February 2003