ATCA millimetre observations of young dusty disks

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ATCA millimetre observations of young dusty disks

• Chris Wright, ARC ARF, UNSW_at_ADFA
• Dave Lommen, Leiden University
• Tyler Bourke, Michael Burton, Annie Hughes, Jes
  Jorgensen, Sarah Maddison, Ewine van Dishoeck,
  David Wilner, Tony Wong

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Aims

• Through 3 and 12 mm continuum observations to
  investigate disk evolution and grain growth
  around a sample of young stars (T Tauri, Herbig
  AeBe) in southern molecular clouds
• Through molecular emission to investigate the
  chemistry and dynamics of such disks

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Results 1

• TW Hya and HD100546 observed in 2001 and 2002 at
  3 mm, published 2003 (Wilner et al., ApJ, 596,
  597)
• TW Hya detected in both continuum and HCO
• Closest known T Tauri star
• Spatially resolved in HCO 1?0 line
• Narrow line width implies almost face-on disk
• Substantial gas depletion
• Herbig Be HD100546 detected in continuum only
• Comet-like dust detected by ISO
• Compact 3 mm source provides direct evidence of
  disk
• Likely even more extreme gas depletion,
  consistent with highly processed nature of the
  dust, inference of planet(s)

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Results 1a TW Hya HCO, HD100546 continuum
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Results 2

• Survey conducted of T Tauri stars in Lupus (4)
  and Chamaeleon (10) 2003-2005
• Merging of two programs C996 and C1173
• 9 of 14 sources detected
• Disk masses calculated
• Millimetre slopes and dust opacity indices
  derived
• Grain growth, up to mm sizes, is inferred
• Presented at Protostars and Planets 2005 (Lommen
  et al.)

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Results 2a 4 Lupus, 5 Cham
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Results 2b Fluxes, a, ß, mass
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Results 3

• During bad 3 mm weather attempted 12 mm
  observation of HD100546 and HD135344
• A clear detection of HD100546
• 1.65 mJy with rms of 0.12 mJy/beam
• Consistent with falling SED from 31 mJy at 3 mm
• But what is emission mechanism?
• Large dust grains, e.g. cm sized pebbles?
• Or free-free?
• HD135344 not detected at 0.3 mJy level (rms)
• Difference in molecular emission toward the two
  sources, CO seen toward HD135344, not for
  HD100546
• Difference in dust species toward the two
  sources, crystalline silicates in HD100546, PAHs
  in HD135344

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Results 3a HD100546 at 18.5 GHz
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Results 3b HD135344 at 23.5 GHz
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Future observations 1 HD100546

• 12 mm monitoring of HD100546 to look for time
  variation
• If stable, then stronger case for pebbles
• If not, then likely stellar magnetic activity
• 3 and 6 cm observations of HD100546 to determine
  spectral index
• So potentially determine emission mechanism, e.g.
  free-free from a wind or otherwise
• Attempt to resolve HD100546 at 3 and/or 12 mm
• 12 mm observations of the best disk survey targets

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Future observations 2 - Survey

• Determine flux at 3 points between 85 and 105 GHz
  to potentially better constrain the spectral
  index and so dust particle sizes
• Consistent set of instrument and flux calibrators
• Observe more chemical species to better determine
  disk chemistry and/or dynamics
• Abundances, rotation, correlation with continuum
  (gas depletion with grain growth?)
• Extend sample to include more targets observed by
  Spitzer
• Independent measures of grain sizes
• Spatially resolve best targets
• Better constrain disk physics (surface density,
  irradiated accretion models)