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Imaging the CO Snow Line in the TW Hya Disk *

Imaging the CO Snow Line in the TW Hya Disk *. C. Qi (SAO) K. Oberg (Harvard) P. D’Alessio (UNAM) E. Bergin (U. Michigan) S. Andrews (SAO) G. Blake (Caltech) M. Hogerheijde (Leiden) E. Van Dishoeck (Leiden). David J. Wilner Harvard-Smithsonian CfA.

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Imaging the CO Snow Line in the TW Hya Disk *

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  1. Imaging the CO Snow Line in the TW Hya Disk* C. Qi (SAO) K. Oberg (Harvard) P. D’Alessio (UNAM) E. Bergin (U. Michigan) S. Andrews (SAO) G. Blake (Caltech) M. Hogerheijde (Leiden) E. Van Dishoeck (Leiden) David J. Wilner Harvard-Smithsonian CfA *Qi et al. 2013, Science, 341, 630 Exoplanets and Disks: Their Formation and Diversity II, December 9, 2013, Kona, Hawaii

  2. Snow Lines and Planet Formation “snow line” = boundary where volatiles condense out of gas phase • enhance planetesimal formation • dramatically increase available solids • increase grain stickiness (icy mantles) • influence bulk composition e.g. C/O Oberg et al. 2011 Hayashi 1981

  3. radial and vertical gradients CO “snow line” = CO “snow surface” impossible to discern in (optically thick) CO emission may be teased out with a disk structure model and extensive analysis of resolved multi-transition, multi-isotope CO data (Qi et al. 2011) Disks are 3D Objects

  4. CO Snow Line and N2H+ Chemistry • use chemical selectivity to advantage • N2H+ is abundant only where CO highly depleted • CO inhibits N2H+ formation • CO speeds up N2H+ destruction • CO freezes out at about 20 K • observed in pre-stellar cores Tafalla et al. 2004 L1498

  5. The TW Hya System • closest gas-rich circumstellar disk (54 pc) • M* ~ 0.8 M,age 3-10 Myr, • southern, isolated, viewed nearly face-on • many studies with SMA • good model of (outer) disk physical structure HST Weinberger et al. 2002 Qi et al. 2008 Andrews et al. 2012 Hugheset al. 2011

  6. TW Hya SMA N2H+ Data and Model

  7. N2H+ SMA Data  ALMA Imaging 2011.0.00340.S PI Qi • ALMA Cycle 0 • 2012 November 18 • l= 0.8 mm (band 7) • 26 antennas, 2 hours • beam 0.6 x 0.6 arcsec • rms 25 mJy (0.1 km/s)

  8. Quantifying the N2H+ Ring Structure • adoptfiducialdisk structure (SED, resolved mm continuum) • assume N2H+ power-law radial abundance profile • RATRAN: fit for Rin, Rout, index • Rin= 30 AUCO snow line • TCOfreeze-out ~18 K

  9. ALMA N2H+ Channel Maps Data Model Residual

  10. Consistent with SMA CO Isotope Data SMA observations of 13CO and C18O J=2-1 CO freeze-out

  11. Concluding Remarks disks present a series of “snow lines” that impact planetesimal formation and composition enhanced N2H+ abundance reflects CO freeze-out ALMA Cycle 0 imaging of TW Hya CO snow line at 30 AU validates concept easy to extend to more disks, anchor temperature structure, test theories of thermal effects and chemistry, e.g. do complex organics emerge from CO-ice? NRAO

  12. END

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