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

§1 Introduction

10 6 yr10 7 yr Obs. of Protoplanetary Disks SED of TTS + disk (Chiang & Goldreich 1997) Central Star Disk Star Disk (Andre et al. 1994) CTTS WTTS

Observations of H 2 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 H 2 lines by HST, FUSE (Herczeg et al. 2002) etc.

H 2 Transition Lines UV pumping UV fluorescent line emission Infrared quandrapolar cascades v=0 UV pumping continuous fluorescence (UV) H+H radiative cascade (IR) collisional excitation, de-excitation (Shull & Beckwith 1982) UV radiation field Temperature profile Collisional process level populations

Irradiation from central star H 2 level transitions via UV pumping Heat gas & dust in disks Irradiation from Central Star (Chiang & Goldreich 1997) Central Star Disk Radiative transfer process Global physical disk structure (gas & dust temperature, and density profiles) H 2 level populations & line emission

§2 Disk Model

Gas Density & Temperature Hydrostatic equilibrium in z-direction ★ z x c s 2 =2kT/  m p  (x)=1.4x10 -7 s -1 (x/1AU) -3/2 (M * =0.5 M s ) M acc =10 -8 M s /yr (=const.) ・ Thermal equilibrium (  pe +L gr -  line =0)  pe : Grain photoelectric heating by FUV  line : Cooling by OI, CII & CO line excitation L gr : Energy exchange by collisions between gas and dust particles

Dust Temperature Local radiative equi. (abs.=reemission) 2D radiative transfer equation Short 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 (T br =2.5 x 10 4 K) UV Radiation from Central Star UV excess (Costa et al. 2000) TW Hya

Resulting Temperature Profile R=0.1AU 1AU 10AU with UV excesswithout UV excess R=0.1AU 1AU 10AU Disk surface heated up by photoelectric heating Midplane & Outer disk (without UV excess) gas temp. = dust temp.

§3 H 2 Level Populations

H 2 Level Populations Statistical Equilibrium u, B 1  u +, C 1  u m, X 1  g + l, X 1  g + UV  lm UV  ml A ml C ml C lm H+H R diss,l H+H R form,l E m >E l

Resulting Level Populations R=0.1AU 10AU with UV excesswithout UV excess with UV excess or Inner disk (hot) : LTE collisional process, n upper : large Outer disk without UV excess (cold) : non-LTE UV pump. & cascade, n upper : small R=0.1AU 10AU v=0 v=1 v=2 v=3 v=4 v=0 v=1 v=2 v=3 v=4

v=1-0 S(1)  m) Obs.(Bary et al.’03) with UVe without UVe ( ) x x x Observer I ul S ul §4 Resulting H 2 Line Emission IR [ erg/cm -2 /s ] e.g., v=1-7 R(3) Obs.(Herczeg with with UVe without et al.’02) UVe + Ly  UVe 4.8 x x x x UV with UV excess:UV: n u : I ul : with UV excess:T gas : n u : I ul : [ erg/cm -2 /s ]

§5 Discussion

Dustless Disk Model Planet formation Dustless disk model 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 DustyDustless Dustless (n dust /n gas : small) grain photoelectric heating T gas with UV excess

Resulting Level Populations R=0.1AU 10AU v=0 v=1 v=2 v=3 v=4 DustyDustless with UV excess Outer region of dustless disk (cold) : non-LTE UV pump. & cascade n upper : large UV radiation fields dust absorption R=0.1AU 10AU v=0 v=1 v=2 v=3 v=4

Resulting H 2 Line Emission v=1-0 S(1)  m): Obs.(Bary et al.’03) Dusty Dustless ( ) x x x S(0)  m), S(1)  m): Obs.(Thi et al.’01) Dusty Dustless S(0) (2.5 – 5.7) x x x S(1) (2.8 – 8.1) x x x UV Obs.(Herczeg et al.’02) Dusty Dustless ( ) x x x [ erg/cm -2 /s ] Obs. possibility to detect H 2 emission from dustless disks in NIR & UV

§6 Summary UV excess + Radiative transfer process Gas & dust temperature, density profiles Gas surface: ~2,000K Grain photoelectric heating H 2 level populations : LTE, n upper : large Strong NIR H 2 lines : consistent with obs. collisional excitation (hot gas) Strong UV H 2 lines : consistent with obs. pumping by Ly  emission H 2 emission from dustless disks