Background

1
Background
Last review on disk chemistry in Protostars and
Planets Prinn (1993) Kinetic Inhibition
model - (thermo-)chemical timescale vs
(radial) mixing timescale - constraints
and goals composition of solar system materials
Since then

• Spectroscopic observation of disks in mm,
  sub-mm, infrared
• e.g. Dutrey et al., Najita et al.
• Detailed models of disk structure
• e.g. Dullemond et al.

2
Outline

• General Theoretical Picture
• - disk structure
• - key ingredients UV, X-ray, Cosmic-ray
• Observations
• - mm sub-mm
• - infrared
• Chemical-Physical Likns
• - thermal structure
• - grain evolution
• - ionization degree
• - mixing
• Deuterium Chemistry and Comets
• Future

3
General Theoretical Picture
three-layer model (i) photon-dominant layer
UV X-ray irradiation low
density (nHlt 105cm-3) high temperature
(T gt several 10 K)
vertical distribution _at_ r 300 AU
-4
-6
log n(i)/nH
-8
-10
-12
0
100
200
300
400
height from midplane AU
Aikawa Herbst (1999) Willacy Langer
(2000) Aikawa et al. (2002) van Zadelhoff et al.
(2003)
4
General Theoretical Picture
three-layer model (i) photon-dominant layer
UV X-ray irradiation low
density (nHlt 105cm-3) high temperature
(T gt several 10 K) (ii) warm molecular layer
high density (nHgt 105cm-3)
moderate temperature (T gt 20 K)
vertical distribution _at_ r 300 AU
-4
-6
log n(i)/nH
-8
-10
-12
0
100
200
300
400
height from midplane AU
Aikawa Herbst (1999) Willacy Langer
(2000) Aikawa et al. (2002) van Zadelhoff et al.
(2003)
5
General Theoretical Picture
three-layer model (i) photon-dominant layer
UV X-ray irradiation low
density (nHlt 105cm-3) high temperature
(T gt several 10 K) (ii) warm molecular layer
high density (nHgt 105cm-3)
moderate temperature (T gt 20 K) (iii) midplane
freeze-out layer very high density (nHgt
107cm-3) low temperature (T lt 20 K)
vertical distribution _at_ r 300 AU
-4
-6
log n(i)/nH
-8
-10
-12
0
100
200
300
400
height from midplane AU
cf. Observation (Dutrey et al. 1997) - high
CN/HCN ratio - low abundance of gaseous
molecules
Aikawa Herbst (1999) Willacy Langer
(2000) Aikawa et al. (2002) van Zadelhoff et al.
(2003)
6
General Theoretical Picture
three-layer model (i) photon-dominant layer
UV X-ray irradiation low
density (nHlt 105cm-3) high temperature
(T gt several 10 K) (ii) warm molecular layer
high density (nHgt 105cm-3)
moderate temperature (T gt 20 K) (iii) midplane
freeze-out layer very high density (nHgt
107cm-3) low temperature (T lt 20 K)
(iv) inside snow line (r lt 10 AU)
thermal desorption hot core like
chemistry (Najita et al. talk Markwick et al.
2002 Ilgner et al. 2004)
vertical distribution _at_ r 300 AU
-4
-6
log n(i)/nH
-8
-10
-12
0
100
200
300
400
height from midplane AU
Aikawa Herbst (1999) Willacy Langer
(2000) Aikawa et al. (2002) van Zadelhoff et al.
(2003)
7
Key ingredients

• X-rays from central star
• excite molecules (Tine et al. 1997)
• ionization (Glassgold et al. 1997)
• induce UV photons (Bergin et al. 2005)
• non-thermal desorption (Najita et al. 2001)

enhance HCN, CN, HCO (Aikawa Herbst 1999
2001Markwick et al. 2002)
r700AU
10-15
Lx1031 erg/s
1030 erg/s
ionization rate s-1
F? (erg cm-2 s-1 Å-1)
X-ray induced UV ?
10-16
1029 erg/s
1028 erg/s
height from midplane AU
wavelength (Å)
8
Key ingredients

• X-rays from central star
• excite molecules (Tine et al. 1997)
• ionization (Glassgold et al. 1997)
• induce UV photons (Bergin et al. 2005)
• non-thermal desorption (Najita et al. 2001)

enhance HCN, CN, HCO (Aikawa Herbst 1999
2001Markwick et al. 2002)
local hot spot
ejected molecules
-5
CO
X-ray desorption
X-ray
-7
only thermal
HCN
log n(i)/nH
-9
CN
-11
grain aggregate
-13
0
20
40
60
80
height from midplane AU
9
Key ingredients

• Cosmic-rays
• ionization driving force for chemistry in
  molecular clouds
• - attenuation length 96 g cm-2 (Umebayashi
  Nakano 1981)
• - scattered by magnetic field ??
• non-thermal desorption

10
Key ingredients

• UV from central star and interstellar field
• photo-dissociation and ionization
• - require 2D radiation transfer with scattering
  (van Zadelhoff et al. 2003)
• - contribution of Lya line (Bergin et al. 2003
  2006)
• photo-desorption

-4
11D
interstellar UV
-6
stellar UV
log n(i)/nH
-8
-10
-12
2D scatter
-6
scattering
-8
log n(i)/nH
-10
-12
height from midplane AU
11
Key ingredients

• UV from central star and interstellar field
• photo-dissociation and ionization
• - require 2D radiation transfer with scattering
  (van Zadelhoff et al. 2003)
• - contribution of Lya line (Bergin et al. 2003
  2006)
• photo-desorption

-4
CO
-5
strong La
log n(i)/nH
-6
-7
H2O
-8
weak La
-9
height from midplane AU
12
Observation
Sigle Dish
Detected species
Gas-Phase radio - neutral H2, CO, CN,
HCN, CS, H2CO, C2H, - ion HCO, N2H,
H2D, - deuterated HDO, H2D, DCN
mid-IR C2H2, HCN, CO2 NIR CO, H2O (Najita et
al.) Optical OI
Solid amorphous crystalline silicates
(Wooden et al.) PAH Ice water, CO, CO2, NH4

Dutrey et al. (1997), IRAM 30m - trace r gt
several 10 AU - high CN/HCN ratio - low
abundance of gaseous molecules
13
Observation
Interferometer -less dilution - imaging
Detected species
Gas-Phase radio - neutral H2, CO, CN,
HCN, CS, H2CO, C2H, - ion HCO, N2H,
H2D, - deuterated HDO, H2D, DCN
mid-IR C2H2, HCN, CO2 NIR CO, H2O (Najita et
al.) Optical OI
Solid amorphous crystalline silicates
(Wooden et al.) PAH Ice water, CO, CO2, NH4

NT(CS) 1013-1014 cm-2 Upper limits only for
H2S,SO,SO2 CS dominant
14
Observation
Detected species
Gas-Phase radio - neutral H2, CO, CN,
HCN, CS, H2CO, C2H, - ion HCO, N2H,
H2D, - deuterated HDO, H2D, DCN
mid-IR C2H2, HCN, CO2 NIR CO, H2O (Najita et
al.) Optical OI
Solid amorphous crystalline silicates
(Wooden et al.) PAH Ice water, CO, CO2, NH4
Lahuis et al. (2006), Spitzer
- T gt 300 K - r ltlt 100 AU - n(i)/nH10-6-10-5
cf. Markwick et al. (2001)

15
Observation
Detected species
Gas-Phase radio - neutral H2, CO, CN,
HCN, CS, H2CO, C2H, - ion HCO, N2H,
H2D, - deuterated HDO, H2D, DCN
mid-IR C2H2, HCN, CO2 NIR CO, H2O (Najita et
al.) Optical OI
double-peak ? disk rotation
Solid amorphous crystalline silicates
(Wooden et al.) PAH Ice water, CO, CO2, NH4

Acke et al. (2005)
- traces disk surface at r lt 1AU

16
Observation
Detected species
Gas-Phase radio - neutral H2, CO, CN,
HCN, CS, H2CO, C2H, - ion HCO, N2H,
H2D, - deuterated HDO, H2D, DCN
mid-IR C2H2, HCN, CO2 NIR CO, H2O (Najita et
al.) Optical OI
LkHa330
PHA
PHA
Silicate
Solid amorphous crystalline silicates
(Wooden et al.) PAH Ice water, CO, CO2, NH4
Geers et al. (2006)
- r 10-100 AU - in 50 of Herbig Ae 15
of T Tauri stars ? long timescale for
settling and growth

17
Observation
Detected species
Gas-Phase radio - neutral H2, CO, CN,
HCN, CS, H2CO, C2H, - ion HCO, N2H,
H2D, - deuterated HDO, H2D, DCN
mid-IR C2H2, HCN, CO2 NIR CO, H2O (Najita et
al.) Optical OI
Pontoppidan et al. (2005)
Solid amorphous crystalline silicates
(Wooden et al.) PAH Ice H2O, CO, CO2, NH4
edge-on disk

- ice absorption bands against scattered light
and warm dust emission - upto 50 of CO2 and H2O
are in disk
18
Chemical-Physical Links gas thermal structure
Tgas and Tdust are not necessarily equal.
heating
cooling dust radiation from thermal
radiation star or upper layer gas
UV (photo-electric) lines (C, CI, OI )
gas-dust collision gas-dust collision
(Dullemond et al. Inga Dullemond
2004 Junkheid et al. 2004)

• energy balance and chemistry have be solved
  simultaneously

• density distribution is determined by Tgas

? Self-consistent calc of Tgas, Tdust, and
density distribution (Nomura Millar 2005)

• Tgas gt Tdust at the surface layer ? extended disk
  atmosphere
• no hot finger (?)

19
Chemical-Physical Links Grain Growth

• Grains must coagulate sediment to make planets
• calculation of coagulation equation
• (Weidenschiling_at_PPII, Dullemond Dominik
  2005, Tanaka et al. 2005)
• SEDs and disk images are better reproduced with
  amax 1 mm
• (Miyake Nakagawa 1995 DAlessio et al.
  2001 Chiang et al. 2001)
• ? dust opacity decreases at UV wavelength

20
Chemical-Physical Links Grain Growth

• As dust grows
• UV penetrates deeper into the disk
• ? T _at_intermediate height increases
• Photoelectric heating becomes less efficient
• ? T _at_disk surface decreases
• ? disk is less flared-up
• Molecular layer is pushed down to lower heights

Junkheid et al. (2004) Aikawa Nomura (2006)
21
Chemical-Physical Links ion fraction

• Angular momentum transport by Magneto-Rotational
  Instability
• - magnetic field decouples if ionization
  degree (xe) is too low
• - accretion and turbulence may be active only
  on disk surface

Gammie (1996)
22
Chemical-Physical Links ion fraction

• Angular momentum transport by Magneto-Rotational
  Instability
• - magnetic field decouples if ionization
  degree (xe) is too low
• - accretion and turbulence may be active only
  on disk surface

photoionization of H xe gt 104
photoionization of C xe 104
Cosmic-ray and X-ray ionization xe 10-11
- 10-6 HCO, H3
Cosmic-ray and Radionucleide r lt 3AU 3
AU lt r lt 60 AU r gt 60 AU xe lt 10-12
xe 10-12 xe gt 10-11
Metal/grain HCO/grain H3 D3
(Sano et al. 2000 Semenov et al. 2004)
agreement with simple chemistry ?? -gt TED
23
Chemical-Physical Links mixing

• Three must be some mixing in the disks, because
• - angular mom. transport by turbulent
  viscosity
• - crystalline silicate in disks and comets
• - refractory inclusions in meteorites

• Chemistry is modified if tmix lt tchem

tmix tvis ? (cf. Carballido et al.
2005)
Stationary z-mixing Advection r-mixing
1.0
Z/Zmax
Semenov et al. (2006) in prep

• Three-layer structure is preserved
• because tchem is small in the surface
• and midplane
• Species formed on grains (ex. H2CO)
• are enhanced by vertical mixing
• Ionization fraction is not modified

CS
0.1
NH3
H2CO
electron
see also Willay et al. and Ilgner et al.
10
100
R AU
24
Deuterium chemistry in disks

• Isotopic fractionations in comets and meteorites
• D/H enrichment in low temperature
• - D-H exchange reactions
• H3 HD ? H2D H2 230K
• H2D CO ? HCO HD
• H2D e ? H2 D
• - Further enhancement by CO depletion

survival of interstellar matter ? nebula process ?
25
Deuterium chemistry in disks
Detection of deuterated species in disks !
species col cm-2 D/H object DCO
3x1011 0.035 TW Hya HDO
(0.064) LkCa15 8x1012
(1x10-3) DM Tau DCN (lt
2x10-3) LkCa15 o-H2D 4x1012
DM Tau 6x1013
TW Hya
H2D
TW Hya
van Dishoeck et al. (2003), Kessler et al.
(2003), Caccarelli. et al. (2004 2005),
DM Tau
TW Hya
HDO
26
Deuterium chemistry in disks
Detection of deuterated species in disks !
species col cm-2 D/H object DCO
3x1011 0.035 TW Hya HDO
(0.064) LkCa15 8x1012
(1x10-3) DM Tau DCN (lt
2x10-3) LkCa15 o-H2D 4x1012
DM Tau 6x1013
TW Hya
van Dishoeck et al. (2003), Kessler et al.
(2003), Caccarelli. et al. (2004 2005),
Model - High D/H right above the midplane -
Midplane is traced by H3, H2D, HD2,
D3 ? grain size ionization rate
Ceccarelli Dominik (2005)
27
Deuterium Chemistry Links to Comets
D/H in comets HDO 3x10-4
(2x10-3) DCN 2x10-3
Comet ice _at_ r 5-30 AU cf. radio obs gas
beam size gt 100 AU

• D/H changes while fluid parcel migrates
• towards the inner radius (Aikawa Herbst 1999)
• mixing is not considered
• D/H is determined by radial mixing (Hersant et
  al. 2001)
• only thermal reactions

D/H model with mixing (radial vertical)
and full chemistry is highly desirable !
28
future