Constraining TW Hydra Disk Properties

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Constraining TW Hydra Disk Properties

• Chunhua Qi
• Harvard-Smithsonian Center for Astrophysics

Collaborators D.J. Wilner, P.T.P. Ho, T.L.
Bourke, N. Calvet (CfA)
G.A. Blake(Caltech), M. Hogerheijde(Leiden),
N. Ohashi(ASIAA),
E. Bergin (U. Michigan)
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TW Hya disk in scattered light
Weinberger et al. 2002

• Closest classical T Tauri star, 56 pc in
  distance
• Nearly face on disk around.
• Strong X-ray, UV radiation
• Age variable from 6 -20 Myr, highly evolved
  system

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Outline

• SMA observations
• Dust continuum emission (220-355 GHz)
• Molecular line emission (cool gas 20-40 K)
• 2D radiative transfer calculation and Chi-square
  analysis on disk properties
• Temperature profile (surface heating)
• Outer radius
• Vsini at 100 AU
• Depletion
• Summary

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SMA Observations
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TW Hya Continuum

• The SMA continuum measurements agree well with
  the predictions of the physically self-consistent
  irradiated accretion disk model for TW Hya
  (Calvet et al. 2002)
• The radial brightness distribution of the disk
  observed at 345 GHz is also consistent with the
  Calvet model.

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TW Hya Images I
CO 2-1
CO 3-2
13CO 2-1
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TW Hya Images II
HCN 3-2
HCO 3-2
CN 2-1
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Aikawa et al. 2002 Van Zadelhoff et al. 2003

• (Sub)mm molecular emission typically from cool
  gas 20-40 k
• Some common lines are optically thick like CO
• Physical and chemical processes ( freeze out,
  photodissociation etc.) add the complexity of
  analysis.

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Data Analysis

• We use a 2-D accelerated Monte Carlo model
  (Hogerheijde van der Tak 2000) to calculate the
  radiative transfer and molecular excitation.
• Chi-square analysis

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CO 2-1
CO 3-2
Blue Canonical Model (Calvet et al. 2002, Qi et
al. 2004 ) Black SMA data
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The Effects of X-Rays
Mean heating energy per ionization

• The heating by X-rays

• The dust-gas cooling

Glassgold Najita 2001
Mean dust radius
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CO 2-1
CO 3-2
CO 6-5
Blue Canonical Model (Calvet et al.
2002, Qi et al. 2004 ) Black SMA
data Red Model with X ray heating
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Constaining Outer Radius

• Rout 172 2 AU
• Vsini at 100 AU 0.27 0.01km/s
• Turbulence velocity 0.12 0.01 km/s
• Uncertainty can be limited by the velocity
  resolution.

CO
CO
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Smaller outer radius photochemical effect ?
CO/13CO60

• Rout 110 5 AU
• Isotope-selective photodissociation of CO

• Rout 120 10 AU
• HCN large cross sections which absorb Lya
  radiation

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13CO 2-1
Model (Rout 110 AU)
Model (Rout 172 AU)
Data
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Depletion

• Dc constant depletion factor
• Dj jump depletion factor where the kinetic
  temperature falls below 22K
• Dc 10-1.2 Dj 10-2.2

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Summary

• Dust emission follows closely the predictions of
  the irradiated accretion disk model of Calvet et
  al. 2002.
• Higher gas temperature vs dust temperature on the
  disk surface is needed to explain the line
  intensity, probably due to X-ray heating.
• Outer radius can be well constrained, given the
  resolution small enough. We have the first clear
  evidence of the isotope-selective
  photodissociation of CO in the disk.
• Substantial CO depletion, by an order of
  magnitude or more, is required to explain the
  line emission.

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Constraining inclination
(Vsini)0.27 km/s

• We can resolve the disk at radii where most of
  the disk mass resides. Can place strong
  constraints on vsini at 100AU.
• Very hard to use the kinematics to disentangle M
  from inclination. Better spectral resolution is
  needed.

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CO 2-1
Model vsini 0.273 (i6o)
Model vsini0.273, (i13.5o)
Data