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

OUTLINE: I.Introduction - TW Hya, Observations II.Modeling - Comparison with Observations III.Discussion - Evolution of TW Hya disk

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) Debris Disks Classical disks Disk Dispersal? Planet Formation? INTRODUCTION Excellent target for gas disk modeling. Aims: Infer gas conditions & spatial distribution, test disk evolution theories: Grain growth? Planet formation? Photoevaporation?

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

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

Possible Explanations for TD Morphology: 1.Grain Growth - Dust has coagulated into larger invisible objects, but gas remains. 2.Planet Formation - Planet present, interacts with disk dynamically, and creates a hole. 3.Photoevaporation - Stellar high energy radiation (EUV,FUV, X-rays) causes mass loss at a critical radius, viscous accretion drains inner disk matter. 4.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 INTRODUCTION

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

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

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

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 MODELING

Inputs: Stellar parameters (M ~ 0.7M o,Sp. Type K7) X-rays (XMM-Newton spectrum) L X ~ erg s -1 Far UV (IUE spectrum) L FUV ~ ergs -1 (No EUV assumed) Dust Model (Calvet et al. 2002): Outer disk: M dust ~ 6 x M o (M gas ~ 0.06 M o ); 4 < r AU < 200; 0.01 µm< a <1 cm Inner disk: M dust ~ 2 x M o ; 0.06< r AU <4; a ~ µm MODELING

Inputs: Stellar parameters (M ~ 0.7M o,Sp. Type K7) X-rays (XMM-Newton spectrum) L X ~ erg s -1 Far UV (IUE spectrum) L FUV ~ ergs -1 (No EUV assumed) Dust Model (Calvet et al. 2002): Outer disk: M dust ~ 6 x M o (M gas ~ 0.06 M o ); 4 < r AU < 200; 0.01 µm< a <1 cm Inner disk: M dust ~ 2 x M o ; 0.06< r AU <4; a ~ µm MODELING Approach Approach: Model inner disk (hole region) first because gas here can shield outer disk and affect its structure.

Inputs: Stellar parameters (M ~ 0.7M o,Sp. Type K7) X-rays (XMM-Newton spectrum) L X ~ erg s -1 Far UV (IUE spectrum) L FUV ~ ergs -1 (No EUV assumed) Dust Model (Calvet et al. 2002): Outer disk: M dust ~ 6 x M o (M gas ~ 0.06 M o ); 4 < r AU < 200; 0.01 µm< a <1 cm Inner disk: M dust ~ 2 x M o ; 0.06< r AU <4; a ~ µm MODELING Approach 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?

Inputs: Stellar parameters (M ~ 0.7M o,Sp. Type K7) X-rays (XMM-Newton spectrum) L X ~ erg s -1 Far UV (IUE spectrum) L FUV ~ ergs -1 (No EUV assumed) Dust Model (Calvet et al. 2002): Outer disk: M dust ~ 6 x M o (M gas ~ 0.06 M o ); 4 < r AU < 200; 0.01 µm< a <1 cm Inner disk: M dust ~ 2 x M o ; 0.06< r AU <4; a ~ µm MODELING Approach 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?NO Not enough CO vib, OH Full undepleted gas disk?

Inputs: Stellar parameters (M ~ 0.7M o,Sp. Type K7) X-rays (XMM-Newton spectrum) L X ~ erg s -1 Far UV (IUE spectrum) L FUV ~ ergs -1 (No EUV assumed) Dust Model (Calvet et al. 2002): Outer disk: M dust ~ 6 x M o (M gas ~ 0.06 M o ); 4 < r AU < 200; 0.01 µm< a <1 cm Inner disk: M dust ~ 2 x M o ; 0.06< r AU <4; a ~ µm MODELING Approach 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?NO Not enough CO vib, OH Full undepleted gas disk? NO Gas cont. opacity, excess total mid-IR H 2,Thermal OH, H 2 O

Inputs: Stellar parameters (M ~ 0.7M o,Sp. Type K7) X-rays (XMM-Newton spectrum) L X ~ erg s -1 Far UV (IUE spectrum) L FUV ~ ergs -1 (No EUV assumed) Dust Model (Calvet et al. 2002): Outer disk: M dust ~ 6 x M o (M gas ~ 0.06 M o ); 4 < r AU < 200; 0.01 µm< a <1 cm Inner disk: M dust ~ 2 x M o ; 0.06< r AU <4; a ~ µm MODELING Approach 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?NO Not enough CO vib Full undepleted gas disk? NO Gas cont. opacity, excess total mid-IR H 2,Thermal OH, H 2 O Some degree of gas depletion in inner disk

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

CO rovib. emission (4.7-5um) from r < 4 AU H 2 Fluorescence From Inner Disk (Herczeg et al. 2004) Warm (T>2500K) H 2 mass ~ g MODELING (depletion compared to full radial gas disk)

CO rovib. emission (4.7-5um) from r < 4 AU H 2 Fluorescence From Inner Disk (Herczeg et al. 2004) Warm (T>2500K) H 2 mass ~ g MODELING (depletion compared to full radial gas disk) Model with x100 depletion in gas mass fits data best.

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

Inner Disk: M gas ~ 1.1 x10 -5 M o (0.06AU < r < 4 AU) Gas/Dust ~ 500 Emission: CO rovib. lines, H 2 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: M gas ~ 0.06 M o (4 AU < r < 200 AU) Gas/Dust ~ 100 MODELING r(AU) ∑(r) g cm -2 1/r Photoevaporating & Viscous profile ∑ up by 100

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

MODELING NeII H 2, OH [OI] 63um CO OI6300 thermal OH, OI 6300A non-thermal

Origin of the OH lines and the OI 6300A line MODELING OH lines originate in a cascade from high J, unlikely to be thermal. OI6300/OI5577A line ratio ~ 7, also pointing to non-thermal origin. OH and OI arise from the photodissociation of H 2 O and OH, which absorb a large fraction of the Lyman  photons from star. * (Harich et al. 2000) (vanDishoeck & Dalgarno 1983)

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

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

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

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.

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. 1.Grain Growth: Can be ruled out, Gas depletion mechanism needed

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. 1.Grain Growth: Can be ruled out, Gas depletion mechanism needed 2.Planet formation: Likely explanation. Perhaps Jovian mass planet or larger, from the large surface density contrast. Gas streams past planet to accrete onto star.

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. 1.Grain Growth: Can be ruled out, Gas depletion mechanism needed 2.Planet formation: Likely explanation. Perhaps Jovian mass planet or larger, from the large surface density contrast. Gas streams past planet to accrete onto star. 3.Photoevaporation: Disk is massive, FUV/X-ray photoevaporation. Depletion factor of 100 implies ~ 5 e-folding times for viscous clearing, or 10 5 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...

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. 1.Grain Growth: Can be ruled out, Gas depletion mechanism needed 2.Planet formation: Likely explanation. Perhaps Jovian mass planet or larger, from the large surface density contrast. Gas streams past planet to accrete onto star. 3.Photoevaporation: Disk is massive, FUV/X-ray photoevaporation. Depletion factor of 100 implies ~ 5 e-folding times for viscous clearing, or 10 5 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 ~ M o /yr, disk lifetime estimate ~ 10 Myrs.

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 H 2 O 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.