Molecular Hydrogen Emission
from Protoplanetary
DisksHideko Nomura (Kobe Univ.), Tom Millar (UMIST)
Modeling the structure, chemistry and appearance of protoplanetary disks
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
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.
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]
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