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Detection of the Water Reservoir in a Forming Planetary System

E&ES 471/571. Detection of the Water Reservoir in a Forming Planetary System. Hogerheijde et al. 2011 11/6/2012 Raquel Martinez. TW Hydrae (TW Hya ). Pre-main-sequence (PMS) Star 0.6 M  10 million years old 53.7 pc away. Torsten Bronger 2003. Protoplanetary Disk of TW Hya.

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Detection of the Water Reservoir in a Forming Planetary System

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  1. E&ES 471/571 Detection of the Water Reservoir in a Forming Planetary System Hogerheijde et al. 2011 11/6/2012 Raquel Martinez

  2. TW Hydrae (TW Hya) • Pre-main-sequence (PMS) Star • 0.6 M • 10 million years old • 53.7 pc away TorstenBronger 2003

  3. Protoplanetary Disk of TW Hya • Radius of 196 AU • Disk mass • Dust: 2×10-4 to 6×10-4 M • Gas: between 4×10-5 and 0.06 M NASA-JPL/Caltech

  4. Spin Isomers of Water Detected • Used Heterodyne Instrument for the Far-Infrared (HIFI) spectrometer • 557 GHz (538 μm) • 1113 GHz (269 μm) • Ground-state rotational emission lines • 110-101 from ortho-H2O • 111-000 from para-H2O

  5. Rotational emission lines detected at system’s velocity • Width of emission lines 40% wider than those of cold CO • H2O extends to radius ~115 AU Hogerheijde et al. 2011

  6. Hogerheijde et al. 2011

  7. Method to Determine How Much Water is in the Disk? • Simulated water chemistry using previous observations and disk models • Dust mass: 1.9×10-4 M • Gas-to-Dust mass ratio of 100 • Considered how far UV and X-ray radiation would penetrate into disk • Balanced photodesorption of water ice and photodissociation of water vapor • Results in H2O vapor column in equilibrium throughout the disk

  8. How Much Water is in the Disk? • Maximum water vapor abundance of 0.5×10-7 to 2×10-7 relative to H2 • Model used had outer region of disk dominate the line emission • Discrepant with Herschel’s observations • Possible explanation: location of small, bare grains relative to larger, ice-covered grains • Larger grains would settle lower far from UV radiation

  9. How Much Water is in the Disk? • Ice reservoir in giant planet formation zone • Simulations would have 7.3×1021g of detected H2O vapor from ice reservoir of 9×1027g (That’s thousands of Earth’s oceans!!!)

  10. Hogerheijde et al. 2011

  11. Ortho-to-Para Ratio (OPR) • OPR of observations matched model at 0.77 • Much lower than that found in solar system comets or 2 to 3 • Corresponds to lower Tspin = 13.5 K • CometaryOPRs reflect OPR of its constituents • Stochastic nature of transport and mixing

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