Background Last review on disk chemistry in Protostars and Planets: Prinn (1993) Kinetic Inhibition model - (thermo-)chemical timescale vs (radial) mixing

BackgroundLast 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

• 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.

Since then…

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

General Theoretical Picturethree-layer model (i) photon-dominant layer UV & X-ray irradiation low density (nH< 105cm-3) high temperature (T > several 10 K)

-4

-6

-8

-10

-12

log

n(i)/

n H

height from midplane [AU]0 100 200 300 400

vertical distribution @ r 300 AU

Aikawa & Herbst (1999)Willacy & Langer (2000)Aikawa et al. (2002)van Zadelhoff et al. (2003)


(ii) warm molecular layer high density (nH> 105cm-3) moderate temperature (T > 20 K)

-4

-6

-8

-10

-12

log

n(i)/

n H






(iii) midplane freeze-out layer very high density (nH> 107cm-3) low temperature (T < 20 K)

-4

-6

-8

-10

-12

log

n(i)/

n H



cf. Observation (Dutrey et al. 1997) : - high CN/HCN ratio - low abundance of gaseous molecules




(iii) midplane freeze-out layer very high density (nH> 107cm-3) low temperature (T < 20 K)

(iv) inside snow line (r < 10 AU) thermal desorption “hot core” like chemistry (Najita et al. talk; Markwick et al. 2002; Ilgner et al. 2004)

-4

-6

-8

-10

-12

log

n(i)/

n H




Key ingredientsX-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; 2001;Markwick et al. 2002)

X-ray induced UV ?

wavelength (Å)

F (

erg

cm

-2 s

-1 Å

-1)

height from midplane [AU]

ioniz

ati

on r

ate

[s-

1]

10-15

10-16

r=700AU

Lx=1031 erg/s

1030 erg/s

1029 erg/s

1028 erg/s

Key ingredients

enhance HCN, CN, HCO+

(Aikawa & Herbst 1999; 2001;Markwick et al. 2002)

X-ray

localhot spot

grainaggregate

ejectedmolecules


log

n(i)/

n H -7

-11

-5

-9

-130 20 40 60 80

CO

CN

HCN

X-raydesorption

onlythermal

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)

Key ingredientsCosmic-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

Key ingredients

interstellar UV

stellar UV

scattering

1+1D

2Dscatter


log

n(i)/

n Hlo

g n(

i)/n H

-4

-6

-8

-10

-12

-6

-8

-10

-12

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

Key ingredientsUV 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

0

-2

-4Lo

g1

0 F

(a

t 1

00 A

U)

(erg

cm

-2 s

-1 Å

-1)

C III

Ly

1250wavelength (Å)

1200

CO

H2O

strong L

weak L


log

n(i)/

n H

-4

-6

-8

-5

-7

-9

Observation

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

Detected species:

Solid amorphous & crystalline silicates (Wooden et al.)

PAH

Ice water, CO, CO2, NH4

+

Dutrey et al. (1997), IRAM 30m

- trace r > several 10 AU - high CN/HCN ratio - low abundance of gaseous molecules

Sigle Dish

Observation




Optical: OI

Detected species:


PAH


+ NT(CS) = 1013-1014 cm-2

Upper limits only for H2S,SO,SO2 CS dominant

Interferometer -less dilution - imaging

Observation




Optical: OI

Detected species:

Lahuis et al. (2006), Spitzer

- T > 300 K- r << 100 AU- n(i)/nH=10-6-10-5

cf. Markwick et al. (2001)


PAH


+

Observation




Optical: OI

Detected species:


PAH


+

Acke et al. (2005)

- traces disk surface at r < 1AU

double-peak disk rotation

Observation




Optical: OI

Detected species:


PAH


+

LkHa330PHA

PHA

Silicate

Geers et al. (2006)

- r = 10-100 AU- in 50% of Herbig Ae 15 % of T Tauri stars long timescale for settling and growth

Observation




Optical: OI

Detected species:


PAH

Ice H2O, CO, CO2, NH4

+

Pontoppidan et al. (2005)

edge-on disk

- ice absorption bands against scattered light and warm dust emission- upto 50 % of CO2 and H2O are in disk

Tgas and Tdust are not necessarily equal.

heating coolingdust radiation from thermal radiation star or upper layer gas UV (photo-electric) lines (C+, CI, OI …) gas-dust collision gas-dust collision

- energy balance and chemistry have be solved simultaneously

-Tgas > Tdust at the surface layer extended disk “atmosphere”- no hot finger (?)

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

- density distribution is determined by Tgas

Chemical-Physical Links: gas thermal structure

(Dullemond et al.;Inga & Dullemond 2004;Junkheid et al. 2004)

Chemical-Physical Links: Grain GrowthGrains must coagulate & sediment to make planets- calculation of coagulation equation (Weidenschiling@PPII, Dullemond & Dominik 2005, Tanaka et al. 2005)

- SEDs and disk images are better reproduced with amax 1 mm (Miyake & Nakagawa 1995; D’Alessio et al. 2001; Chiang et al. 2001)

dust opacity decreases at UV wavelength

>

D’Alessio et al. (2001)

ISM dust

amax=1mm

Chemical-Physical Links: Grain GrowthAs dust grows…- UV penetrates deeper into the disk T @intermediate height increases

- Photoelectric heating becomes less efficient T @disk surface decreases disk is less flared-up

- Molecular layer is pushed down to lower heights

Junkheid et al. (2004)Aikawa & Nomura (2006)

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)

photoionization of H: xe > 104

photoionization of C: xe 104

Cosmic-ray and X-ray ionization: xe 10-11 - 10-6

HCO+, H3+

Cosmic-ray and Radionucleide:r < 3AU 3 AU < r < 60 AU r > 60 AUxe 10-12 xe 10-12 xe 10-11

Metal+/grain HCO+/grain H3+ & D3

+

(Sano et al. 2000; Semenov et al. 2004)

agreement with simple chemistry ?? -> TED

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

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

tmix ~ tvis ? (cf. Carballido et al. 2005)

• Chemistry is modified if tmix < tchem:

• 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

10 100

NH3

CS

R [AU]

Stationary z-mixing Advection & r-mixing

H2CO

electron

Semenov et al. (2006) in prep

2/1sun*

2/11124 /AU1/K10/10/yr10 MMrTvis

Z/Z

max

0.1

1.0

see also Willay et al. and Ilgner et al.

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

e)()CO(

HD)(

)H(

)DH(

32

1

3

2

nknk

nk

n

n

survival of interstellar matter ?nebula process ?

Deuterium chemistry in disksDetection of deuterated species in disks !

species col [cm-2] D/H objectDCO+ 3x1011 0.035 TW HyaHDO (0.064) LkCa15 8x1012 (1x10-3) DM TauDCN (< 2x10-3) LkCa15o-H2D+ 4x1012 DM Tau 6x1013 TW Hya van Dishoeck et al. (2003), Kessler et al. (2003), Caccarelli. et al. (2004; 2005),

DM TauHDO

H2D+ TW Hya

TW Hya

Deuterium chemistry in disks

species col [cm-2] D/H objectDCO+ 3x1011 0.035 TW HyaHDO (0.064) LkCa15 8x1012 (1x10-3) DM TauDCN (< 2x10-3) LkCa15o-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)

Detection of deuterated species in disks !

Deuterium Chemistry: Links to Comets

Comet: ice @ r= 5-30 AU cf. radio obs: gas beam size > 100 AU

D/H in comets

HDO 3x10-4 (2x10-3)DCN 2x10-3

-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) andfull chemistry is highly desirable !

species col [cm-2] D/H objectDCO+ 3x1011 0.035 TW HyaHDO (0.064) LkCa15 8x1012 (1x10-3) DM TauDCN (< 2x10-3) LkCa15o-H2D+ 4x1012 DM Tau 6x1013 TW Hya

future

Documents

Background Last review on disk chemistry in Protostars and Planets: Prinn (1993) Kinetic Inhibition model - (thermo-)chemical timescale vs (radial) mixing