1. The disk of AB Aurigae Dmitry Semenov (MPIA, Heidelberg, Germany)
Yaroslav Pavluchenko (INASAN, Moscow, Russia)
Katharina Schreyer (AIU, Jena, Germany)
Thomas Henning (MPIA, Heidelberg, Germany)
Kees Dullemond (MPA, Garching, Germany)
Aurore Bacmann (Observatoire de Bordeaux, France)
Ringberg April 15

2. The disk of AB Aurigae Chemical modeling Observations Dmitry Semenov
Aurore Bacmann
(Observatoire de Bordeaux, France)
Katharina Schreyer
(AIU Jena)
(MPIA Heidelberg)
Radiative transfer
Lines:
Yaroslav Pavluchenko
(INASAN, Moscow, Russia)
Continuum:
Kees Dullemond
(MPA, Garching,
Germany)
Ringberg April 15

3. Outline Motivation General Properties Observations & Results
a) IRAM 30m & b) PdBI
The Model of the AB Aurigae system
Chemical modeling
Line radiative transfer simulations
Modeling results
Conclusions
3/18

4. Motivation  well suitable object to study the chemistry of the disk
Why AB Aurigae ?
One of the best-studied Herbig Ae(/Be) stars: A0 Ve+sh
D = pc, M = 2.4 ± 0.2 M8, age = 2−5 Myr
(e.g. van den Ancker et al. 1997, Manning & Sargent 1997, Grady et al. 1999,
deWarf et al. 2003, Fukagawa et al. 2004)
circumstellar structure:
compact disk (Rdisk ≈ 450 pc, Mdisk ≈ 0.02 M8,
i,f poorly defined)
(Mannings & Sargent 1997, Henning et al. 1998)
+ extended, low-density envelope
(R > 1000 pc, optically thin, AV = 0.5m
internal structure + extent not well determined) 
-17
 well suitable object to study the chemistry of the disk

5. AB Aur: General Properties The envelope
R-band image,
University of Hawaii
2.2m telescope
(Grady et al. 1999)
AB Aur: General Properties
The envelope
IRAS 60μm 
HST visual image (Grady et al. 1999)
 extended
asymmetrical
nebulosity,
inhomogeneous
spherical
envelope,
Renvelope ≈
1300 AU ( = 10″)
i < 45o
 IRAS 60 μm map
 Renvelope = 4’ ≈ AU
SED Modeling (Miroshnichenko
et al. 1999)  Renvelope ≈ 5000 AU N E
10″

6. AB Aurigae: General Properties - The disk
13CO (10) OVRO
Main velocities
Subaru H-band image
(Fukagawa et al. 2004):
mass supply from the
envelope contributes
to the spiral instability
vLSR (km s-1) 5″
arcsec
(Mannings & Sargent, 1997, OVRO)
Keplerian rotation,
a/b  110 AU / 450 AU
 i  76o 8″ 8″
HST image (Grady et al. 1999)

7. AB Aur - Our observational results: IRAM 30m
Observations:
beamsizes:
10″ − 30″
Results:
detected
species:
HCO+, CS,
CO, C18O,
HCN, HNC,
~3: SiO,
H2CO, CN,
DCO+
CO 21
C18O 1
CS 21
CS 54
HNC 0
HCN 0
HCO 0
HCO 2
Tmb [K]
DCO+ 21
SiO 1
H2CO 31,221,1
CN 10
 non-detections
N2H+, CH3CN,
HDCO, C2H,
SO, SO2
vLSR [km/s]
7/18

8. AB Aur - Our observational results: PdB Interferometer
sum
HCO+ J=1-0
Beam
6.5″ x 5″
Observations:
2002, beams ~ 5″ x 7″
Main velocities
vLSR (km s-1)
Results:
HCO+ map,
~3: 34SO,
SO2, HCN,
C2H, …
HST image: Grady et al. 1999
34SO 3221
C2H 10
3/2-1/2
F=2-1
SO2 73,582,6
S[Jy]
HCN 10
velocity [km/s]

9. The model of the AB Aur system
(Dullemond & Dominik, 2004)
SED
AB Aurigae
2D continuum radiative
transfer code
 passive flared disk model
low-density cones have
the open angle 
shadowed part
of the envelope
is denser and cooler R
9/18

10. The model of the AB Aur system
Disk: 2D passive disk with vertical temperature gradient,
(r) = o·(r / Ro)p, p = −1.5, Mdisk = 3 (± 0.5) 10-2 M8,
Rin = Ro = 0.7 AU, Rout = 400 AU, vertical hight = 0.3 … 350 AU
i = 17˚±3˚,  = 80˚ +10˚, Tdisk = K
ndisk = g cm-3,
Keplerian rotation, Vturb = 0.2 km/s
Envelope: Rin = 0 / 400 AU, Rout = 2100 AU,
 (r) = o·(r / Rin )p, p = −1.0,
low-density cones:  = 25˚, olobe = g cm-3, Tenv = 100 K
shadowed torus: olobe = g cm-3, Tenv = 35 K
Menv  4 · 10-3 M8, ad = 0.1 μm, AV ≈ 0.5m, Vturb = 0.2 km/s,
stationary accretion, V(r)  1 / r (0.2 km/s at r = Rin),
dynamical timescale is ~ 107 yrs
ad = 0.3 μm
−30˚
T = 35 K
T = 100 K
400 AU
10/18

11. AB Aur – Chemical Modeling
(Semenov et al., 2004)
 a gas-phase chemistry (UMIST95) with a surface reaction set
(Hasegawa et al. 1992)
 a deuterated chemical network from Bergin et al. 1999
 self- & mutual-shielding of H2 (Draine & Bertoldi 1996) and
CO (Lee et al. 1996)
 the 1D slab model to compute UV- and CR-dissociation and
ionization rates depending on vertical height
 ionization by the decay of radionuclides (disk)
 thermal, photo-, and CR-desorption of surface species back
in the gas-phase
 initial abundances: chemical evolution of a molecular cloud (low-metal
set, T = 10 K, n = 2·104 cm-3, time span = 1Myr, Wiebe et al. 2003)
11/18

12. AB Aur – Chemical Modeling
Modeling of the chemistry  with reduced chemical network
(in total 560 species made of 13 elements, involved in 5335 reactions)
On the basis of the fractional ionisation, disk  divided into
three layers:
dark dense mid-plane
(chemical network of ~ ten species & reactions)
(ii) intermediate layer
(chemistry of the fractional ionization driven
by the stellar X-rays)
(iii) unshielded low-density surface layer
(photoionisation-recombination processes)
Results :
2D-distribution of column densities and
molecular abundances for 3 Myr
evolutionary time span
12/18

13. AB Aur - Line radiative transfer
(Pavluchenkov & Shustov, 2004)
2D URAN NLTE code: further development
of the public 1D code by Hogerheijde
& van der Tak (2000)
solution of the system of radiative transfer equations
using the Accelerated –Iteration (ALI) method
the mean intensities are calculated with the
Accelerated Monte Carlo algorithm
the same model as obtained by the continuum radiative
transfer
synthetic line profiles, beam-convolved
Results:
13/18

14. Modeling Results: НСО+(1-0) disk map
AB Aurigae 4 3 2 1 -1 -2 -3 -4
Inverse P Cygni profile
a possible evidence
for the accretion at distances ~ 600 AU
Disk model:
R = 400 AU
arcsec
14/18

15. Modeling Results: НСО+(1-0) disk map
AB Aurigae
Subaru H-band image
disk model
Fukagawa et al. 2004 4 3 2 1 -1 -2 -3 -4
 sub-component
structures possibly
stem from the
spirals
arcsec
15/18

16. Modeling Results: Estimate of i and 
i = 10o i = 15o i = 20o
AB Aurigae
 inclination
angle of
the disk 
i = 17˚± 3˚
 position
angle 
 = 80˚+10˚
 = 40o  = 80o  = 120o
−30˚
arcsec
16/18

17. AB Aur -Modeling Results: Line profiles of different species
Fit for three cases:
Left:
Middle:
Right:
Tmb [K]
only the disk
only the
envelope
disk +
 
 
(J=2−1)
17/18

18. AB Aurigae - Conclusions
Based on observational data  a suitable model of the
AB Aurigae system is acquired
 mass, size, geometry and dynamical structure
 temperature and density distribution
There is an evidence for the accretion at distances of
about 600 AU from the star
It is shown that the IRAM single-dish spectra can be adequately described by the «disk-in-envelope» model
The coupled dynamical, chemical, and radiative transfer
simulation is an effective tool to find a consistent model
18/18

21. AB Aur - Our observations
IRAM 30m:
, beam sizes 10″ - 30″
detected different transitions of
HCO+, CS, CO, C18O, HCN, HNC,
~3: SiO, H2CO, CN, DCO+
non-detections:
N2H+, CH3CN, HDCO, C2H, SO, SO2
IRAM
Plateau de Bure Interferometer:
2002, synthezied beam sizes 5″×7″
detected HCO+ (& ~ 3: 34SO, SO2,
HCN, C2H, …)
PdBI
7/19

22. AB Aurigae - Conclusions
About a dozen molecular spectra as well as the HCO+(1-0) interferometric map of AB Aurigae are acquired
There is an evidence for the accretion at distances of about 600 AU from the star
The mass, size, geometry and dynamical structure of the disk are constrained
The temperature and density distribution of the envelope are estimated
It is shown that the IRAM single-dish spectra can be adequately described by the «disk-in-envelope» model
Further investigations are needed
18/18

23. AB Aur - Line radiative transfer
(Pavluchenkov & Shustov, 2004)
• 2D URAN NLTE code: further development of the public
1D code by Hogerheijde & van der Tak (2000)
System of equations including the equation of radiative transfer and statistical equations for the level populations
Mean intensity in every cell is calculated by the accelerated Monte-Carlo technique (AMC)
Level populations are iteratively calculated using the Accelerated Lambda Iteration (ALI) scheme
Global iterations are finished after a requested accuracy in level populations is achieved
13/18

24. 2. Integration of transfer equation
1. Geometry
1D model
2D model
Grid
cell er e e
Back-up integration:
First calculation
Second calculation
Comparison of the level populations for each cell to
estimate Monte-Carlo error
3. Estimation of the error in level populations
2. Integration of transfer equation
ray
cell boundaries N

25. Modeling Results: НСО+(1-0) disk map
AB Aurigae
Subaru R-band image
Fukagawa
et al. 2004 4 3 2 1 -1 -2 -3 -4
 sub-component
structures possibly
stem from the
spirals
arcsec
15/18

26. HCO+(1-0) [29’’] Disk Envelope Both
Line wings  disk, central peak  envelope 24
Friday-seminar talk at AIU Jena

27. HCO+(3-2) [9.3’’] Disk Envelope Both
Beam is smaller  contribution from the disk is larger 25
Friday-seminar talk at AIU Jena

28. Friday-seminar talk at AIU Jena
CO(2-1) [11’’]
Disk Envelope Both
Line is optically thick, 26
Friday-seminar talk at AIU Jena

29. Friday-seminar talk at AIU Jena
C18O(2-1) [11’’]
Disk Envelope Both
Line is optically thin, 27
Friday-seminar talk at AIU Jena

30. Friday-seminar talk at AIU Jena
CS(2-1) [26’’]
Disk Envelope Both 28
Friday-seminar talk at AIU Jena

31. Friday-seminar talk at AIU Jena
Mass of the disk
HCO+(1-0) is optically thin  21
Friday-seminar talk at AIU Jena

32. Friday-seminar talk at AIU Jena
Mass of the disk
Dependence on the grain size:
Dependence on the chemical network:
Dependence on the gas-to-dust ratio: ?
Dependence on the disk structure: ? 22
Friday-seminar talk at AIU Jena

33. AB Aurigae: General properties
Star:
Disk:
Envelope: 3
Friday-seminar talk at AIU Jena

34. The AB Aurigae system: IR
IRAS 60m map  radius of the envelope ~ AU 4
Friday-seminar talk at AIU Jena

35. The AB Aurigae system: visual
(Grady et al. ApJ, 523, 151, 1999)
Scattered light image  extended asymmetrical nebulosity 5
Friday-seminar talk at AIU Jena

36. AB Aur: General Properties - The envelope
HST K-band image (Grady et al. 1999):
inhomogeneous spherical envelope, Rdisk  1300 AU  i < 45o

37. The AB Aurigae system: 10m
The shape of the 10m-silicate band implies that ad<1m (Bouwman et al. A&A, 375, 950, 2001) 8
Friday-seminar talk at AIU Jena

38. Results: PdB Interferometer
Keplerian rotation, positional angle   90 ?

39. Chemical processes in space
Desorption
Accretion
Surface reaction
Gas-phase reaction
UV, CR, X-ray
Mantle
Grain
Grain 15
Friday-seminar talk at AIU Jena

40. Disk positional angle  = 40o  = 80o  = 120o
Positional angle of the disk  20
Friday-seminar talk at AIU Jena

41. Line wings  disk, central peak  envelope
HCO+(1-0) [29’’]
Line wings  disk, central peak  envelope

42. Temperature of the envelope
T = 15K T = 25K T = 35K
 Envelope temperature (r  800 AU)  35K

43. AB Aurigae: General Properties - The disk
Main velocities
13CO (1-0) OVRO 5″
arcsec
vLSR (km s-1)
Subaru H-band image
(Fukagawa et al. 2004):
mass supply from the
envelope contributes
to the spiral instability
(Mannings & Sargent, 1997)
Keplerian rotation,
a/b  110 AU / 450 AU
 i  76o 8″ 8″
HST image (Grady et al. 1999)

44. AB Aur - Our observational results: PdB Interferometer
sum
HST image: Grady et al. 1999
HCO+ J=1-0
Beam
6.5″ x 5″
Main velocities
vLSR (km s-1)
Keplerian rotation,
position angle   90 ?
34SO 3221
SO2
73,582,6
S[Jy]
HCN 10

45. The model of the AB Aur system
(Dullemond & Dominik, 2004)
SED
AB Aurigae
2D continuum radiative
transfer code
 passive flared disk model
low-density cones have
the open angle 
shadowed part
of the envelope
is denser and cooler R
9/18