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Gas Emission From TW Hya: Origin of the Inner Hole Uma Gorti NASA Ames/SETI

Gas Emission From TW Hya: Origin of the Inner Hole Uma Gorti NASA Ames/SETI. (Collaborators: David Hollenbach, Joan Najita, Ilaria Pascucci). OUTLINE: Introduction - TW Hya, Observations Modeling - Comparison with Observations Discussion - Evolution of TW Hya disk. INTRODUCTION.

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Gas Emission From TW Hya: Origin of the Inner Hole Uma Gorti NASA Ames/SETI

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  1. Gas Emission From TW Hya: Origin of the Inner Hole Uma Gorti NASA Ames/SETI (Collaborators: David Hollenbach, Joan Najita, Ilaria Pascucci)

  2. OUTLINE: • Introduction - TW Hya, Observations • Modeling - Comparison with Observations • Discussion - Evolution of TW Hya disk

  3. INTRODUCTION • TW Hya - Nearby (~ 51 pc) in TW Hya association • Very well studied, face-on, transition disk (TD) at interesting age • Dust observations + gas line emission detected from several species (Pascucci & Tachibana 2010) Classical disks Disk Dispersal? Debris Disks Planet Formation? Excellent target for gas disk modeling. Aims: Infer gas conditions & spatial distribution, test disk evolution theories:Grain growth? Planet formation? Photoevaporation?

  4. INTRODUCTION Inner (~ 4 AU) hole inferred from dust continuum modeling. Optically thin inner disk, optically thick outer disk. (Calvet et al. 2002; (also Eisner et al. 2006) flux deficit (Hughes et al. 2007) Calvet et al. Model with hole Data Model: No hole

  5. INTRODUCTION Inner (~ 4 AU) hole inferred from dust continuum modeling. Optically thin inner disk, optically thick outer disk. (Calvet et al. 2002; (also Eisner et al. 2006) But…. flux deficit (Muzerolle et al. 2000) (Hughes et al. 2007) Star accretes! ………gas present. Calvet et al. Model with hole Data Model: No hole

  6. INTRODUCTION • Possible Explanations for TD Morphology: • Grain Growth - Dust has coagulated into larger invisible objects, but gas remains. • Planet Formation - Planet present, interacts with disk dynamically, and creates a hole. • Photoevaporation - Stellar high energy radiation (EUV,FUV, X-rays) causes mass loss at a critical radius, viscous accretion drains inner disk matter. • MRI-induced evacuation - Ionization of gas causes MRI activation at inner disk edge, drives accretion and disk is evacuated “inside-out”. Gas distribution may provide clues to disk evolution

  7. INTRODUCTION Gas Emission Lines detected from TW Hya (Qi et al. 2006) CO sub-mm

  8. INTRODUCTION Gas Emission Lines detected from TW Hya (Qi et al. 2006) CO sub-mm (Salyk et al. 2007) CO ro-vib.

  9. INTRODUCTION Gas Emission Lines detected from TW Hya (Najita et al. 2010) (Qi et al. 2006) Spitzer IRS CO sub-mm (Salyk et al. 2007) NeII CO ro-vib. (Pascucci & Sterzik 2009)

  10. MODELING • Gas Disk Models (Gorti & Hollenbach 2004,2008) • Vertical hydrostatic equilibrium models that solve separately for gas • and dust. • 1+1D dust model, gas non-LTE line radiative transfer, • includes gas opacity. • Heating by FUV, EUV, X-rays, dust-gas collisions, chemical reactions, • cosmic rays. • Cooling by dust, ions, atoms and molecules. • Chemistry includes ~ 84 species, ~ 600 reactions. • [Heating & Cooling] Chemistry solve for n, T structure Model gas emission from TW Hya

  11. MODELING Inputs:Stellar parameters (M ~ 0.7Mo,Sp. Type K7) X-rays (XMM-Newton spectrum) LX ~ 1030 erg s-1 Far UV (IUE spectrum) LFUV ~ 1031 ergs-1 (No EUV assumed) Dust Model(Calvet et al. 2002): Outer disk: Mdust ~ 6 x 10-4 Mo (Mgas ~ 0.06 Mo); 4 < rAU < 200; 0.01 µm< a <1 cm Inner disk: Mdust ~ 2 x 10-8 Mo; 0.06< rAU<4; a ~ 0.9-2 µm

  12. MODELING Inputs:Stellar parameters (M ~ 0.7Mo,Sp. Type K7) X-rays (XMM-Newton spectrum) LX ~ 1030 erg s-1 Far UV (IUE spectrum) LFUV ~ 1031 ergs-1 (No EUV assumed) Dust Model(Calvet et al. 2002): Outer disk: Mdust ~ 6 x 10-4 Mo (Mgas ~ 0.06 Mo); 4 < rAU < 200; 0.01 µm< a <1 cm Inner disk: Mdust ~ 2 x 10-8 Mo; 0.06< rAU<4; a ~ 0.9-2 µm Approach: Model inner disk (hole region) first because gas here can shield outer disk and affect its structure.

  13. MODELING Inputs:Stellar parameters (M ~ 0.7Mo,Sp. Type K7) X-rays (XMM-Newton spectrum) LX ~ 1030 erg s-1 Far UV (IUE spectrum) LFUV ~ 1031 ergs-1 (No EUV assumed) Dust Model(Calvet et al. 2002): Outer disk: Mdust ~ 6 x 10-4 Mo (Mgas ~ 0.06 Mo); 4 < rAU < 200; 0.01 µm< a <1 cm Inner disk: Mdust ~ 2 x 10-8 Mo; 0.06< rAU<4; a ~ 0.9-2 µm Approach: Model inner disk (hole region) first because gas here can shield outer disk and affect its structure. The Two Extremes Completely gas depleted hole?

  14. MODELING Inputs:Stellar parameters (M ~ 0.7Mo,Sp. Type K7) X-rays (XMM-Newton spectrum) LX ~ 1030 erg s-1 Far UV (IUE spectrum) LFUV ~ 1031 ergs-1 (No EUV assumed) Dust Model(Calvet et al. 2002): Outer disk: Mdust ~ 6 x 10-4 Mo (Mgas ~ 0.06 Mo); 4 < rAU < 200; 0.01 µm< a <1 cm Inner disk: Mdust ~ 2 x 10-8 Mo; 0.06< rAU<4; a ~ 0.9-2 µm Approach: Model inner disk (hole region) first because gas here can shield outer disk and affect its structure. The Two Extremes Completely gas depleted hole? NONot enough COvib, OH Full undepleted gas disk?

  15. MODELING Inputs:Stellar parameters (M ~ 0.7Mo,Sp. Type K7) X-rays (XMM-Newton spectrum) LX ~ 1030 erg s-1 Far UV (IUE spectrum) LFUV ~ 1031 ergs-1 (No EUV assumed) Dust Model(Calvet et al. 2002): Outer disk: Mdust ~ 6 x 10-4 Mo (Mgas ~ 0.06 Mo); 4 < rAU < 200; 0.01 µm< a <1 cm Inner disk: Mdust ~ 2 x 10-8 Mo; 0.06< rAU<4; a ~ 0.9-2 µm Approach: Model inner disk (hole region) first because gas here can shield outer disk and affect its structure. The Two Extremes Completely gas depleted hole? NONot enough COvib, OH Full undepleted gas disk? NOGas cont. opacity, excess total mid-IR H2 ,Thermal OH, H2O

  16. MODELING Inputs:Stellar parameters (M ~ 0.7Mo,Sp. Type K7) X-rays (XMM-Newton spectrum) LX ~ 1030 erg s-1 Far UV (IUE spectrum) LFUV ~ 1031 ergs-1 (No EUV assumed) Dust Model(Calvet et al. 2002): Outer disk: Mdust ~ 6 x 10-4 Mo (Mgas ~ 0.06 Mo); 4 < rAU < 200; 0.01 µm< a <1 cm Inner disk: Mdust ~ 2 x 10-8 Mo; 0.06< rAU<4; a ~ 0.9-2 µm Approach: Model inner disk (hole region) first because gas here can shield outer disk and affect its structure. The Two Extremes Completely gas depleted hole? NONot enough COvib Full undepleted gas disk? NOGas cont. opacity, excess total mid-IR H2 ,Thermal OH, H2O Some degree of gas depletion in inner disk

  17. MODELING CO rovib. emission (4.7-5um) from r < 4 AU (depletion compared to full radial gas disk)

  18. MODELING CO rovib. emission (4.7-5um) from r < 4 AU (depletion compared to full radial gas disk) H2 Fluorescence From Inner Disk (Herczeg et al. 2004) Warm (T>2500K) H2 mass ~ 1019 g

  19. MODELING CO rovib. emission (4.7-5um) from r < 4 AU (depletion compared to full radial gas disk) H2 Fluorescence From Inner Disk (Herczeg et al. 2004) Warm (T>2500K) H2 mass ~ 1019 g Model with x100 depletion in gas mass fits data best.

  20. MODELING Inner Disk: Mgas ~ 1.1 x10-5 Mo (0.06AU < r < 4 AU) Gas/Dust ~ 500 Emission: CO rovib. lines, H2 S(2) S(1) (~ 10% of total) NeII 12.8um (~ 25% of total) OH MIR lines (non-thermal) (~25%) OI 6300A, 5577A (~15%)

  21. MODELING Inner Disk: Mgas ~ 1.1 x10-5 Mo (0.06AU < r < 4 AU) Gas/Dust ~ 500 Emission: CO rovib. lines, H2 S(2) S(1) (~ 10% of total) NeII 12.8um (~ 25% of total) OH MIR lines (non-thermal) (~25%) OI 6300A, 5577A (~15%) Outer Disk: Mgas ~ 0.06 Mo (4 AU < r < 200 AU) Gas/Dust ~ 100 r(AU) 1/r ∑ up by 100 ∑(r) g cm-2 Photoevaporating & Viscous profile

  22. MODELING Heating: X-rays, chemical heating FUV, especially Ly, imp. in chemistry

  23. MODELING OI6300thermal [OI] 63um NeII H2, OH CO OH, OI 6300A non-thermal

  24. MODELING Origin of the OH lines and the OI 6300A line • OH lines originate in a cascade from high J, unlikely to be • thermal. • OI6300/OI5577A line ratio ~ 7, also pointing to non-thermal • origin. (Harich et al. 2000) * (vanDishoeck & Dalgarno 1983) • OH and OI arise from the photodissociation of H2O and OH, • which absorb a large fraction of the Lyman  photons from star.

  25. MODELING Best Fit Model Comparisons ~ 2 less? - OK GOOD ~ 3 less GOOD GOOD GOOD GOOD GOOD GOOD

  26. MODELING Best Fit Model Comparisons ~ 2 less? - OK GOOD ~ 3 less GOOD GOOD GOOD GOOD GOOD GOOD OI 63µm 3.4 x 10-6 5.1 x 10-6 OI 145µm <5.1 x 10-7 2.0 x 10-7 CII 157µm <6.0 x 10-7 3.1 x 10-7 ~ 1.5 more Herschel PACS

  27. MODELING Best Fit Model Comparisons Water ice on Td < 80K ~ 2 less? - OK GOOD 1.2 x 10-5 GOOD GOOD GOOD GOOD GOOD GOOD OI 63µm 3.4 x 10-6 5.1 x 10-6 OI 145µm <5.1 x 10-7 2.0 x 10-7 CII 157µm <6.0 x 10-7 3.1 x 10-7 3.1 x 10-6 Herschel PACS

  28. DISCUSSION TW Hya Disk Evolutionary Status • At radii smaller than r ~ 4 AU, dust depleted by ~ 1000, • gas is depleted by ~ 100. • Outer disk is massive with gas and dust, optically thick.

  29. DISCUSSION TW Hya Disk Evolutionary Status • At radii smaller than r ~ 4 AU, dust depleted by ~ 1000, • gas is depleted by ~ 100. • Outer disk is massive with gas and dust, optically thick. Grain Growth: Can be ruled out, Gasdepletion mechanism needed

  30. DISCUSSION TW Hya Disk Evolutionary Status • At radii smaller than r ~ 4 AU, dust depleted by ~ 1000, • gas is depleted by ~ 100. • Outer disk is massive with gas and dust, optically thick. Grain Growth: Can be ruled out, Gasdepletion mechanism needed Planet formation: Likely explanation. Perhaps Jovian mass planet or larger, from the large surface density contrast. Gas streams past planet to accrete onto star.

  31. DISCUSSION TW Hya Disk Evolutionary Status • At radii smaller than r ~ 4 AU, dust depleted by ~ 1000, • gas is depleted by ~ 100. • Outer disk is massive with gas and dust, optically thick. Grain Growth: Can be ruled out, Gasdepletion mechanism needed Planet formation: Likely explanation. Perhaps Jovian mass planet or larger, from the large surface density contrast. Gas streams past planet to accrete onto star. Photoevaporation: Disk is massive, FUV/X-ray photoevaporation. Depletion factor of 100 implies ~ 5 e-folding times for viscous clearing, or 105 years since gap opening. Short timescale for complete gas hole. BUT [NeII] profile indicates flow (Pascucci & Sterzik 2009) Gas in photoevaporating flow may be re-captured...

  32. DISCUSSION TW Hya Disk Evolutionary Status • At radii smaller than r ~ 4 AU, dust depleted by ~ 1000, • gas is depleted by ~ 100. • Outer disk is massive with gas and dust, optically thick. Grain Growth: Can be ruled out, Gasdepletion mechanism needed Planet formation: Likely explanation. Perhaps Jovian mass planet or larger, from the large surface density contrast. Gas streams past planet to accrete onto star. Photoevaporation: Disk is massive, FUV/X-ray photoevaporation. Depletion factor of 100 implies ~ 5 e-folding times for viscous clearing, or 105 years since gap opening. Short timescale for complete gas hole. BUT [NeII] profile indicates flow (Pascucci & Sterzik 2009) Re-capture of gas in photoevaporating flow? Planet opens gap at 4 AU, and photoevaporation is ongoing. Mass loss rate ~ 5 10-9 Mo/yr, disk lifetime estimate ~ 10 Myrs.

  33. Summary • Observed CO rovibrational emission constrains gas in inner disk. • Gas present in inner opacity hole of TW Hya disk, but depleted • by a factor of ~ 100. • Pure grain growth is not a likely cause of the dust hole. • Gas disk models reproduce observed line emission. • OH MIR lines and OI 6300A line are produced by photodissociation • of H2O and OH by FUV photons. • Gas giant planet is the best explanation for the surface density • jump at ~ 4AU. • Photoevaporation also acts, mass loss is enhanced at the 4 AU rim, • disk may survive for < 10 Myrs at current mass loss rate.

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