Molecular Hydrogen Emission

from Protoplanetary

DisksHideko Nomura (Kobe Univ.), Tom Millar (UMIST)

Modeling the structure, chemistry and appearance of protoplanetary disks

§1 Introduction

106yr 107yr

Obs. of Protoplanetary Disks

SED of TTS + disk

(Chiang & Goldreich 1997)

CentralStar

Disk

StarDisk

(Andre et al. 1994)

CTTS WTTS

Observations of H2 Line Emission

NIR GG Tau, TW Hya, LkCa 15, DoAr25 (v,J)=(1,3)-(0,1) by NOAO (Bary et al. 2003)

MIR GG Tau, GO Tau, LkCa 15 J=2-0, J=3-1 by ISO (Thi et al. 2001)

UV TW Hya 146 Lyman-band H2 lines by HST, FUSE (Herczeg et al. 2002)　　　　　　　　　　　　　　　 etc.

H2 Transition Lines UV pumping

UV fluorescentline emission

Infraredquandrapolar

cascades

v=0

UVpumping

continuousfluorescenc

e(UV)H+H

radiativecascade (IR)

collisionalexcitation,

de-excitation

(Shull & Beckwith 1982)

UV radiation fieldTemperature

profile

Collisional process level populations

Irradiation from central star

H2 level transitions via UV

pumpingHeat gas & dust

in disks

Irradiation from Central Star

(Chiang & Goldreich 1997)

CentralStar

Disk

Radiative transfer process Global physical disk structure (gas & dust temperature, and density profiles) H2 level populations & line emission

§2 Disk Model

Gas Density & TemperatureHydrostatic equilibrium in z-direction

zρΩρgdz

dρc 2

z2s

★

z

xcs

2=2kT/mp

(x)=1.4x10-7 s-1(x/1AU)-3/2 (M*=0.5 Ms )Macc=10-8Ms/yr (=const.)

・

Thermal equilibrium (pe+Lgr-line=0) pe : Grain photoelectric heating by FUV line :Cooling by OI, CII & CO line excitation Lgr : Energy exchange by collisions between gas and dust particles

Dust TemperatureLocal radiative equi. (abs.=reemission)

0 grνν0 νν )(TB κdν4dΩI κdν

2D radiative transfer equationShort characteristic

method in spherical coordinate(Dullemond & Turoulla 2000)

Heating sources:(A) viscous heating at equatorial plane(B) radiation from central star

Stellar blackbody(T*=4000K)

+ Thermal bremsstrahlung

(Tbr=2.5 x 104K)

UV Radiation from Central Star

UV excess

(Costa et al. 2000)

TW Hya

Resulting Temperature Profile

R=0.1AU

1AU

10AU

with UV excess without UV excessR=0.1AU

1AU

10AU

Disk surface　　 heated up by photoelectric heatingMidplane & Outer disk (without UV excess) 　　 gas temp. = dust temp.

§3 H2 Level Populations

H2 Level PopulationsStatistical Equilibrium

lform,lm s

smlmlml2m

ldiss,lm s

slmlm2l

n(H)Rn(s)CβA)(Hn

Rn(s)Cβ)(Hn

u, B1u+ , C1u

m, X1g+

l, X1g+

UVlm

UV ml

Aml CmlClm

H+HRdiss,l

H+H

Rform,lEm>El

Resulting Level Populations

R=0.1AU

10AU

with UV excess without UV excess

with UV excess or Inner disk (hot) : LTE collisional process, nupper: largeOuter disk without UV excess (cold) : non-LTE UV pump. & cascade, nupper: small

R=0.1AU

10AUv=0v=1 v=2 v=3v=4

v=0 v=1 v=2 v=3 v=4

v=1-0 S(1) (@2.12m) Obs.(Bary et al.’03) with UVe without UVe (1.0 - 15) x 10-15 9.3 x 10-15 3.3 x 10-18

ObserverIul

Sul

§4 Resulting H2 Line Emission

IR

)S(Iαdz

dIululul

ul 4π

hνΦAn

α

1S ul

ululuul

ul

[erg/cm-2/s]

e.g., v=1-7 R(3) (@1489.6A) Obs.(Herczeg with with UVe without et al.’02) UVe + LyUVe 4.8 x 10-14 1.4 x 10-14 1.3 x 10-16 4.0 x 10-22

UV with UV excess:UV: nu: Iul:

with UV excess:Tgas: nu: Iul:

[erg/cm-2/s]

§5 Discussion

Dustless Disk ModelPlanet formation

Dustless disk model

ISgas

dust small4

gas

dust small

n

n10

n

n

Dustless disk :no infrared excess

Conserv. of dust mass& dust size growth

amount of small dust

SED

Resulting Temperature Profile

R=0.1AU

1AU

10AU

R=0.1AU

1AU

10AU

Dusty Dustless

Dustless (ndust/ngas: small)　　 grain photoelectric heating Tgas

with UV excess

Resulting Level Populations

R=0.1AU

10AUv=0v=1 v=2 v=3v=4

Dusty Dustlesswith UV excess

Outer region of dustless disk (cold) : non-LTE UV pump. & cascadenupper: large UV radiation fields dust absorption

R=0.1AU

10AU

v=0v=1 v=2 v=3 v=4

Resulting H2 Line Emission

v=1-0 S(1) (@2.12m): Obs.(Bary et al.’03) Dusty Dustless (1.0 - 15) x 10-15 9.3 x 10-15 6.5 x 10-16

S(0) (@28.2m), S(1) (@17.0m): Obs.(Thi et al.’01) Dusty Dustless S(0) (2.5 – 5.7) x 10-14 4.2 x 10-17 9.3 x 10-17

S(1) (2.8 – 8.1) x 10-14 8.5 x 10-16 5.0 x 10-16

UV (@900A-2900A) Obs.(Herczeg et al.’02) Dusty Dustless (1.2 - 73) x 10-15 3.8 x 10-15 1.2 x 10-14

[erg/cm-2/s]

Obs. possibility to detect H2 emission from dustless disks in NIR

& UV

§6 SummaryUV excess + Radiative transfer processGas & dust temperature, density profiles

Gas temperature@disk surface: ~2,000K Grain photoelectric heating

H2 level populations : LTE, nupper: large

Strong NIR H2 lines : consistent with obs. collisional excitation (hot gas) Strong UV H2 lines : consistent with obs. pumping by Ly emission

H2 emission from dustless disks