ERIC HERBST DEPARTMENTS OF PHYSICS AND ASTRONOMY THE OHIO STATE UNIVERSITY Chemistry in Protoplanetary Disks

 CLASSIFICATIONS OF PROTOSTARS  

Dust particles contain 1% of interstellar matter.

Cosmic rays produce ions some radical-stable reactions

“Primary” Fractionation Reaction (i)H HD H 2 D + + H K H 2 D + /H 3 + >> HD/H 2 Other deuterated species Signature of depletion!!!

Successes for quiescent cores: (1)Reproduces 80% of abundances including ions, radicals, isomers (2)Predicts strong deuterium fractionation

(diffusion)

TYPES OF SURFACE REACTIONS REACTANTS: MAINLY MOBILE ATOMS AND RADICALS A + B  AB association H + H  H 2 H + X  XH (X = O, C, N, CO, etc.) WHICH CONVERTS O  OH  H 2 O C  CH  CH 2  CH 3  CH 4 N  NH  NH 2  NH 3 CO  HCO  H 2 CO  H 3 CO  CH 3 OH X + Y  XY ?????????? H + HX  H 2 + X abstraction

Diffusive Surface Chemistry Rate equations (non-discrete) Rate equations (non-discrete) Modified rate equations Modified rate equations Stochastic approaches Stochastic approaches a) Monte Carlo a) Monte Carlo b) Master equation b) Master equation

Some Star-forming Regions quiescent cores (TMC-1; gas-grain) quiescent cores (TMC-1; gas-grain) pre-stellar cores (L1544; gas-grain) pre-stellar cores (L1544; gas-grain) low mass protostars (IRAS ) low mass protostars (IRAS ) protoplanetary disks (DM Tau; gas + accret./desorp.) protoplanetary disks (DM Tau; gas + accret./desorp.) hot cores (Orion KL; gas-grain) hot cores (Orion KL; gas-grain)

Protoplanetary Disk (Proplyd) M AU Cosmic rays X-ray UV Keplerian rotation T Tauri star – 10 6 yr old midplane Column density UV

Temperature and Density Distribution (D’Alessio et al. 1998, 1999) A. MIDPLANE Radius (AU) n(cm -3 ) T (K) 1 10(14) (12) (9) (7) 10 Heavy species condensed onto grains

Calculated Major Icy Species at 30 AU from Star (Aikawa and Herbst 1999) Cloud  Disk  migration inwards Cloud  Disk  migration inwards can be compared with solid cometary material in solar system can be compared with solid cometary material in solar system H 2 O**, CO, NH 3, CO 2, HCN ices H 2 O**, CO, NH 3, CO 2, HCN ices Deuterated species HDO, DCN Deuterated species HDO, DCN Deuterium fractionation in reasonable agreement with several comets Deuterium fractionation in reasonable agreement with several comets

Species Disk(DMTau) Cloud(TMC1) CO 1.4 × × HCN 5.5 × × CN 3.2 × × CS 3.3 × × H 2 CO 2.0 × × HCO+ 7.4 × × C 2 H 1.1 × × ● Molecular Line Survey at IRAM30m telescope (Dutrey et al. 1997) Gaseous molecular abundances in disks are different from those in clouds, typically lower, but these are averages in outer disk. Abundance relative to H 2 Gaseous Molecular Abundances

Chemical Models of Gas in Outer Disk Performed by 3-4 different groups Chemistry dependent on physical model chosen and on radial and vertical distances Models start with dense cloud abundances and run for 10(6) yr at fixed physical conditions and with various sources of radiation through an inhomogeneous region. Collaborators: Aikawa, van Dishoeck, van Zadelhof

Divide outer disk into elements of space; each with density and temperature Details of Models

Vertical Distribution PDR Icy Layer Molecular Layer Ｒ＝１０５ＡＵ densiy [cm -3 ] temperature density T [K] R = 105 AU Z(AU) K cm accretion photodissociation Too detailed for observers

Column Density 2D rad. trans previous 1Dcalc. Still, too detailed for most observations!

Aikawa et al. (2002); physical model of D’Alessio; theoretical results at 373 AU and 10(6) yr

Line Profile from Model Disk CO J=6-5 CO 3-2CO 2-1 HCO HCN 4-3 CN 3-2 Line profiles are calculated using non-LTE 2D radiation code. Comparison with LkCa15 (JCMT) (R out =400AU, incl.=60 o )