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 GortiNASA 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

Classicaldisks

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


CO sub-mm

CO ro-vib.

(Qi et al. 2006)

(Salyk et al. 2007)

INTRODUCTION


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 ~ 0.7Mo,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

MODELING





MODELING

ApproachApproach: Model inner disk (hole region) first because gas here can shield outer disk and affect its structure.





MODELING


The Two ExtremesThe Two Extremes

Completely gas depleted hole?





MODELING



Completely gas depleted hole? NO Not enough COvib, OH

Full undepleted gas disk?





MODELING



Completely gas depleted hole? NO Not enough COvib, OHFull undepleted gas disk? NO Gas cont. opacity, excess total mid-IR H2 ,Thermal OH, H2O





MODELING



Completely gas depleted hole? NO Not enough COvib

Full undepleted gas disk? NO Gas cont. opacity, excess total mid-IR H2 ,Thermal OH, H2O

Some degree of gas depletion in inner disk

CO rovib. emission (4.7-5um) from r < 4 AUMODELING

(depletion compared to full radial gas disk)

CO rovib. emission (4.7-5um) from r < 4 AU

H2 FluorescenceFrom Inner Disk (Herczeg et al. 2004)

Warm (T>2500K)H2 mass ~ 1019 g

MODELING


CO rovib. emission (4.7-5um) from r < 4 AU

H2 FluorescenceFrom Inner Disk (Herczeg et al. 2004)

Warm (T>2500K)H2 mass ~ 1019 g

MODELING


Model with x100 depletion in gas mass fits data best.

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%)

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

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

NeIIH2, OH

[OI] 63um

CO

OI6300thermal

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 H2O 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 lessGOOD

GOOD

GOOD

GOOD

GOOD

GOODGOOD

MODELING


~ 2 less? - OK

~ 3 lessGOOD

GOOD

GOOD

GOOD

GOOD

GOODGOOD

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

HerschelPACS

~ 1.5 more

MODELING


~ 2 less? - OK

1.2 x 10-5

GOOD

GOOD

GOOD

GOOD

GOOD

GOODGOOD

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

HerschelPACS

Water ice on Td < 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




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

DISCUSSION





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






3. 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...

DISCUSSION






3. 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.

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.

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

Documents

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