Dust Envelopes around
Oxygen-rich AGB stars
Kyung-Won Suh
Dept. of Astronomy & Space Science
Chungbuk National University, Korea
E-mail: kwsuh@chungbuk.ac.kr
 Introduction
 Radiative transfer models - Models and comparison with the observations
★
Pulsation Phase-Dependent Dust Shell Models for O-rich AGB stars
1) Low mass-loss rate O-rich AGB (LMOA) stars
2) High mass-loss rate O-rich AGB (HMOA) stars
★ Axi-symmetric dust envelope Models for O-rich AGB stars (tentative results)
 Summary
AGB stars
 Large amplitude, long period pulsation.
 Strong stellar winds with high mass-loss rates.
- Pulsation driven shock & Radiation pressure on dust grains
 Thick dust envelopes – Main sources of dust grains in galaxies
Optical depth (10 m)
mB
Low mass-loss rate O-rich Carbon stars
High mass-loss rate O-rich
AGB (LMOA) stars
AGB (HMOA) stars
0.001 - 3
0.1 - 1
3- 40
0.3 - 1
1
1-3
300 - 700
500 - 2000
Pulsation Period (days) 100 - 500
-8
Mass Loss Rate (Mo/yr) 10
Dust grains (Main)
-6
- 10
-7
10 - 10
-5
-6
10 - 10
-4
Silicates
Amorphous
Silicates
(emission features)
Carbon
(absorption features)
Radiative Transfer Models for AGB stars
 Stellar Parameters
The flux from the central star ( core: degenerate C,N,O shell: H, He burning )
Usually, blackbody model is enough for AGB stars
T*, R*, (L*)
 Dust Envelope Parameters
Opacity, Envelope structure (Shape, Location, Optical depth,,,)
For Spherically symmetric dust shell models:
Dust opacity functions (silicate, uniform 0.1 m spheres) , The optical depth,
r(r) : dust density distribution,
Rc : dust shell inner radius, and the outer radius (10000 Rc)
 Tc : Inner shell dust temperature
(may not be same as the dust formation temperature)
For Axi-symmetric dust envelope models:
+ Shape parameters (degree of flattening, viewing angle, etc.)
Optical properties of dust grains
– amorphous and crystalline silicates
100
Suh 1999 (cool dust)
Suh 1999 (warm dust)
Mixed (Crystal 10%)
Mixed (Crystal 10%)
Qabs
10-1
10-2
Crystal Enstatite (Jager et al. 1998)
Crystal Forsterite (Jager et al. 1998)
10-3
10
20
30
40
Wavelength (m)
50
60
70
80
AGB stars on IR 2-color diagrams
5.0
3.0
Oxygen-rich stars
Carbon-rich stars
Silicate carbon stars
2.5
Oxygen-rich stars
Carbon stars
Silicate carbon stars
4.5
4.0
2.0
3.5
3.0
[12-25]
[25 - 60]
1.5
1.0
OS
2.5
2.0
0.5
IRCS
1.5
0.0
1.0
Silicate (1000 K)
-0.5
AMC (1000 K)
0.5
AMC
Silicate
VCS
0.0
-1.0
0.0
0.5
1.0
1.5
[12 - 25]
2.0
2.5
3.0
3.5
0
2
4
6
8
10
K - 12
12
14
16
18
20
Low mass-loss rate O-rich AGB stars (LMOA stars)
Mass-loss Rate: 1×10-8∼1×10-6 M/yr
Envelope ( 10 = 0.1,  = 0)
10-8
Envelope ( 10 = 0.1,  = 0.1)
No Evident Crystalline
Silicate features
-2
F(W m )
10-9
10-10
Mira (o Ceti)
ISO
IRAS LRS
IRAS PSC
10-11
10
Wavelength (m)
100
High mass-loss rate O-rich AGB stars (HMOA stars)
Mass-loss Rate: 1×10-6∼1×10-4 M/yr
Envelope ( = 30,  = 0.2)
Envelope and disk ( = 30,  = 0.2,  = 0.1)
F(W m-2)
10-11
Prominent Crystalline
Silicate features at
33.3, 40.6, 43.3 m
10-12
OH21.5+0.5
ISO SWS
IRAS LRS
IRAS PSC
10-13
10
Wavelength (m)
100
Mass-loss rates of O-rich AGB stars
Mass-loss Rate: 5.0×10-8∼1.0×10-4 M/yr
Models for AGB stars (LMOA stars)
L*=1.0E4 Lo, T*=2900 K, Tc=553 K, 10=0.04
F
L*=1.0E4 Lo, T*=2900 K, Tc=1000 K, 10=0.04
L*=4.5E3 Lo, T*=2500 K, Tc=420 K, 10=0.027
L*=4.5E3 Lo, T*=2900 K, Tc=420 K, 10=0.027
Models for typical LMOA stars
1
10 Wavelength (m)
100
Models for AGB stars (LMOA stars)
small grains (0.01m) vs. large grains (0.1 m)
L*=1.0E4 Lo, T*=2900 K, Tc=553 K, 10=0.04
L*=1.0E4 Lo, T*=2900 K, Tc=1000 K, 10=0.04
F
L*=1.0E4 Lo, T*=2900 K, Tc=1000 K, 10=0.04 (small)
L*=4.5E3 Lo, T*=2500 K, Tc=420 K, 10=0.027
L*=4.5E3 Lo, T*=2500 K, Tc=1000 K, 10=0.027
L*=4.5E3 Lo, T*=2500 K, Tc=1000 K, 10=0.027 (small)
Models for typical LMOA stars
1
10 Wavelength (m)
100
Dust Shell Models for AGB stars
1.Continuous model: Dust shell is continuous (r(r)  r-2) from the dust
shell inner radius (Rc) up to 10000 Rc.
2. Superwind model: There is a density-enhanced region for the overall
continuous dust shell.
Dust Number Density
R1
R2
1
10
100
R ( RC )
1000
10000
Pulsating AGB stars (LMOA stars)
Continuous vs. Superwind models
Continuous dust shell models for typical LMOA stars
L*=1.0E4 Lo, T*=2900 K, Tc=553 K, 10=0.04, Rc=36.8 R*
F
L*=1.0E4 Lo, T*=2900 K, Tc=1000 K, 10=0.04, Rc=10.9 R*
Superwind models for typical LMOA stars
L*=1.0E4 Lo, T*=2900 K, Tc=1000 K, 10=0.04 (SW 10-110)
Rc=10.8 R* ; density is 10 times enhanced at 10 - 110 RC
L*=1.0E4 Lo, T*=2900 K, Tc=1000 K, 10=0.04 (SW 30-130)
Rc=10.8 R* ; density is 10 times enhanced at 30 - 130 RC
1
10 Wavelength (m)
100
Pulsating AGB stars (LMOA stars)
Mass-loss Rate: 7.6×10-8∼1.1×10-7 M/yr
L*=1.0E4 Lo, T*=2900 K, Tc=553 K, 10=0.04
L*=6.0E3 Lo, T*=2650 K, Tc=463 K, 10=0.03
10
-10
L*=4.5E3 Lo, T*=2500 K, Tc=420 K, 10=0.027
-2
F(W m )
10-11
10-12
10-13
Z Cyg (IRAS 20000+4954)
ISO SWS01_03 (1996-08-05T18:18:37)= 0.55
ISO SWS01_04 (1996-10-08T04:30:57)= 0.79
ISO SWS01_02 (1996-11-24T11:29:59)= 0.97
ISO SWS01_01 (1997-01-24T00:26:47)= 1.20
ISO SWS01_06 (1997-03-21T05:11:56)= 1.42
ISO SWS01_05 (1997-05-15T02:16:42)= 1.63
IRAS PSC
IRAS LRS
10-14
10
Wavelength (m)
100
Pulsating AGB stars (LMOA stars)
Mass-loss Rate: 8.6×10-8∼1.6×10-7 M/yr
L*=1.0E4 Lo, T*=2900 K, Tc=654 K, 10=0.020
L*=7.0E3 Lo, T*=2670 K, Tc=578 K, 10=0.015
L*=4.0E3 Lo, T*=2500 K, Tc=484 K, 10=0.010
10-8
-2
F(W m )
10-9
10-10
o Ceti (IRAS 02168-0312)
10-11
ISO (SWS: 1997-02-09, LWS: 1997-07-04)
IRAS LRS
IRAS PSC
Epchtein et al. 1980 (1979. 07. 13.)
10 Wavelength (m)
100
Pulsating AGB stars (LMOA stars)
Continuous vs. Superwind models
L*=1.0E4 Lo, T*=2900 K, Tc=1000 K, 10=0.020 (SW 5-205)
L*=1.0E4 Lo, T*=2900 K, Tc=654 K, 10=0.020
L*=1.0E4 Lo, T*=2900 K, Tc=1000 K, 10=0.020
10-8
-2
F(W m )
10-9
10-10
o Ceti (IRAS 02168-0312)
10-11
ISO (SWS: 1997-02-09, LWS: 1997-07-04)
IRAS LRS
IRAS PSC
Epchtein et al. 1980 (1979. 07. 13.)
10
Wavelength (m)
100
Pulsating AGB stars (LMOA stars)
The superwind model results compared with continuous dust shell models. With
Tc=1000 K, the 10 times density-enhanced region from 5 to 205 Rc produces a similar
SED to the ISO spectra of the both stars. Namely, the superwind dust shell with the
density enhancement mimics a continuous shell with a lower inner shell dust
temperature. If the superwind model is right, the dust formation temperature can be
as high as 1000 K for LMOA stars.
AGB stars (HMOA stars) – Pulsations
1.5
OH26.5+0.6 (L Band)
Forrest et al. 1978
Werner et al. 1980
Grasdalen et al. 1983
Jones et al. 1990
Ney & Merrill 1980
Evans II & Beckwith 1977
Lebofsky et al. 1978
Engels 1982
Period : 1559 ± 7.20 (day)
Amplitude : 0.55± 0.03 (5 10-10 Wm-2)
Lepine et al. 1995
Olivier et al. 2001
ISO SWS01
-2
F( 5 10-10 Wm )
1.0
0.5
IRAS
0.0
2000
3000
4000
5000
6000
7000
8000
9000
10000
11000
12000
JD 2440000+
OH127.8+0.0 (M Band)
Gehrz et al. 1985
Ney & Merrill 1980
Grasdalen et al. 1983
Persi et al. 1990
Period : 1541 ± 16.51 (day)
Amplitude : 0.61 ± 0.07 (5 10-10 Wm-2)
Jones et al. 1990
ISO SWS01
ISO PHT40
-10
-2
F( 5 10 Wm )
1.5
1.0
0.5
IRAS
2000
3000
4000
5000
6000
7000
JD 2440000+
8000
9000
10000
11000
12000
Dust shell models for HMOA stars
L*=3.6E4 Lo, T*=2000 K, Tc=1379 K, 10=19
L*=3.6E4 Lo, T*=2000 K, Tc=1000 K, 10=19
L*=3.6E4 Lo, T*=2300 K, Tc=1000 K, 10=19
F
L*=3.6E4 Lo, T*=2000 K, Tc=1000 K, 10=10
Models for typical HMOA stars
10
Wavelength (m)
100
Pulsating AGB stars (HMOA stars)
Mass-loss Rate: 4.1×10-5∼4.3×10-5 M/yr
10-9
Dust Model One (=0)
Dust Model Two (=0)
Dust Model Three (=0)
L*=3.6x10 Lo , Tc=1000 K, 10 = 10
L*=3.6x10 Lo , Tc=1200 K, 10 = 13.6
L*=3.6x104 Lo , Tc=1365 K, 10 = 17.3
L*=2.7x104 Lo , Tc=1000 K, 10 = 11
L*=2.7x104 Lo , Tc=1182 K, 10 = 15
L*=2.7x104 Lo , Tc=1270 K, 10 = 17.2
4
4
Crystalline Silicate
features at 33.3, 40.6,
43.3 m
-2
F ( W m )
10-10
10-11
OH127.8+0.0 (IRAS 01304+6211)
10-12
ISO (SWS: 1998-01-11, LWS: 1997-07-21)
IRAS LRS
IRAS PSC
Jones et al. 1990 (1987-09-13 ~ 1988-12-07)
Jones et al. 1990 (1988-5-22)
Ney & Merrill 1980 (1976-09-08)
10 Wavelength (m)
Minimum phase for all dust models
L*=1.0x104 Lo , Tc=1000 K, 10 = 17, =0
L*=1.0x104 Lo , Tc=1000 K, 10 = 17, =0.2
100
Pulsating AGB stars (HMOA stars)
Mass-loss Rate: 6.1×10-5∼6.8×10-5 M/yr
Dust Model One (=0)
-9
10
Dust Model Three (=0)
Dust Model Two (=0)
L*=3.6x10 Lo , Tc=1000 K, 10 = 15
L*=3.6x10 Lo , Tc=1139 K, 10 = 17.3
L*=3.6x104 Lo , Tc=1328 K, 10 = 24
L*=2.7x104 Lo , Tc=1000 K, 10 = 17
L*=2.7x104 Lo , Tc=1121 K, 10 = 20
L*=2.7x104 Lo , Tc=1191 K, 10 = 23
4
4
Crystalline Silicate
features at 33.3, 40.6,
43.3 m
-2
F ( W m )
10-10
10-11
Minimum phase for all dust models
OH26.5+0.6 (IRAS 18348-0526)
10-12
ISO (SWS, LWS: 1996-10-11)
Forrest et al. 1978 (1976-05 ~ 1976-06)
Forrest et al. 1978 (1975-04 ~ 1975-05)
Engels 1982 (1976-02-28 ~ 1980-10-20)
Engels 1982 (1977-08-23)
IRAS PSC
L*=1.0x104 Lo , Tc= 1000 K, 10 = 22,  = 0
L*=1.0x104 Lo , Tc= 1000 K, 10 = 22,  = 0.2
10-13
10 Wavelength (m)
100
Dust shell models for Pulsating HMOA stars (from Suh 2004)
Dust Model One
Dust grains form at 1000 K and instantaneously evaporate at T > 1000 K.
Dust Model Two
Dust grains form only at 1000 K and there is no dust evaporation at any phase (because the
dust evaporation requires much higher temperature than 1000 K).
Dust Model Three
Dust formation temperature is higher than 1000 K at higher luminosity (or mass-loss rate).
The dust formation process does not cease at any phase and there is no dust evaporation.
Dust shell models for Pulsating HMOA stars
Dust Model One
Dust Model Two
Dust Model Three
Dust shell models for Pulsating HMOA stars
 The 3 different dust models produce similar
fitting with the observations.
2.0
Max
Dust Model Two for OH26.5+0.6 (a HMOA star)
Dust shell inner radius (Rc)
Dust formation radius (1000 K)
Rc formed at minimum phase
1.8
Dust Model One
-4
r (x10 pc)
1.6
Dust Model Two
1.4
1139 K
1.2
Min
1.0
0.00
0.25
0.50
0.75
Pulsation Phase
1.00
1.25
1.50
Dust formation and Crystallization in Pulsating
AGB stars
Crystallization
Dust grains may spend enough
time for annealing after their
formation in AGB stars.
 A HMOA star with a higher
inner shell dust temperature
provides better conditions for
crystallization.
 Only HMOA stars show
crystalline features.
The IR two-color diagram
4.0
LMOA stars
3.5
HMOA stars (using Dust Model Three)
Z Cyg
OH127.8+0.0
o Ceti
OH26.5+0.6
3.0
[25 - 60]
2.5
2.0
1.5
Min
Min
Max
1.0
Max
0.5
Min
Min
0.0
Max
Max
-0.5
-1.0
0.0
0.5
1.0
1.5
[12 - 25]
2.0
2.5
3.0
3.5
The IR two-color diagram
3.5
3.0
2.5
Min
[12-25]
Min
Max
Max
2.0
Max
Min
1.5
Max
1.0
LMOA stars
Min
HMOA stars (using Dust Model Three)
Z Cyg
OH127.8+0.0
o Ceti
OH26.5+0.6
0.5
0
1
2
3
4
K-L
5
6
7
8
9
Axi-symmetric dust envelope models for
AGB stars – The Model SEDs
(using 2-Dust with multi dust components;
Suh 2005 in preparation)
Axi-symmetric dust envelope Model for HMOA stars
- The model SEDs
L*=1.0E4 Lo, T*=2000 K, Tc=1131 K, 10=30 (Shell)
L*=1.0E4 Lo, T*=2000 K, Tc=1131 K, 10=30 (0d)
L*=1.0E4 Lo, T*=2000 K, Tc=1131 K, 10=30 (45d)
10-9
L*=1.0E4 Lo, T*=2000 K, Tc=1131 K, 10=30 (90d)
-2
F(W m )
10-10
10-11
2-dust models (A=9, F=1)
10-12
10-13
1
Wavelength (m)
10
100
Axi-symmetric dust envelope
Model for HMOA stars
- Model Images
(equ)=30=10*(pol)
0.8 m
25 m
10 m
60 m
Edge-on views of an axi-symmetric
dust envelope model (disk-like shape)
at different wavelengths
AGB stars and Planetary Nebulae
Summary
O-rich AGB stars at their last stage of stellar evolution lose their mass to ISM by large
amplitude pulsation and dust formation in outer envelopes. We find that the dust shell
structures (e.g., the inner shell dust temperatures) change as well as the central stars
depending on the phase of pulsation.
1. LMOA stars with thin dust shells :
Tc ~ 400 K (min) – 700 K (max) ; Rc ~ 30 - 40 R* (too large?)
 Superwind models: Tc ~ 1000 K ; Rc ~ 10 R*
2. HMOA stars with thick dust shells :
Tc~ 1000 K (min) – 1300 K (max) ; Rc ~ 4 - 6 R* (depending on the dust model)
3. We expect that the dust annealing process (T > 1000K) driven by pulsation could be a
mechanism for crystallizing the dust grains in inner regions of the dust shells around
HMOA stars with thick dust shells.
4. New axi-symmetric dust envelope models are necessary. New IR observations (Spitzer,
SOFIA, Astro-F) will provide better data for understanding the dust grains and the
envelope structure.