63rd International Symposium on Molecular Spectroscopy
June 16-20, 2008
Circumstellar 12C/13C Ratios Derived from
Millimeter Observations of CO and CN:
Insight into Nucleosynthesis on the Giant Branches
S.N. Milam, N.J. Woolf, and L.M. Ziurys
Steward Observatory
University of Arizona
Arizona
Radio
Observatory
63rd International Symposium on Molecular Spectroscopy
June 16-20, 2008
Importance of 12C/13C Ratio
• Ratio significant tracer of Galactic Chemical Evolution
• 12C formed in triple alpha process (Helium-burning)
- 2 4He → 8Be
- 8Be + 4He → 12C
• Such He-burning occurs in 1 -10 M stars on Giant Branches, also in SN
• 13C reaction intermediate in CNO cycle
- 2H → 4He with 12C as a catalyst
- CNO competes with p-p chain for M > 1.2 M
• 13C should be destroyed..
 survives because of convective mixing
• Subsequent Mass Loss from Stars
 brings 12C and 13C to ISM
 ratio an indicator of IMF, SFR
CNO Cycle
63rd International Symposium on Molecular Spectroscopy
June 16-20, 2008
Ratio measured from molecules
250
H2CO
CO
AVG
120
Primary/Secondary
200
Local ISM and Solar
System Values disagree
60
Secondary
150
CN
AVG
C/13C
Solar System
0
12
0
4
8
12
16
100
Gradient in
Interstellar 12C/13C
Ratio vs. DGC
50
0
0
2
4
6
Understand Origins of this Ratio
8
10
Dgc (kpc)
12
14
16
63rd International Symposium on Molecular Spectroscopy
June 16-20, 2008
Stellar Evolution
PLANETARY NEBULA PROTO-PLANETARY
NEBULA (PPN)
Stellar envelope completely
•
ratios influenced by
Nucleosynthesis stops
detached HELIX
stellar convection & “dredge-up”
CRL2688
ASYMPTOTIC
GIANT
To
• Convection starts in Red Giant
BRANCH (AGB)
White
3.25
—
He & H Shell
Dwarf
Branch (C < O)
Burning Envelope
- H-burning shell & He Core
IRC+10216
- CNO cycle: excess 13C
• Brought to surface in FIRST
DREDGE-UP
• Continue to AGB Branch
- He-burning shell
- 3 α produces excess 12C
• THIRD DREDGE-UP
 C > O at surface
12C/13C
Log (L)
3.40 —
12C/13C
Triple -Process
H Shell
3.10 — Burning
He Core
Burning
H Shell
Narrows
RED
GIANT
BRANCH
2.95 —
2.80 —
ratio vary with C/O ratio
4.30
MAIN SEQUENCE
Hydrogen Core
Burning
Sun
4.15
First Dredge-up:
Surface Abundances Change
4.00
Log (Te)
3.85
3.60
63rd International Symposium on Molecular Spectroscopy
June 16-20, 2008
ARO Survey of Circumstellar 12C/13C Ratios
• Such surveys conducted in past (e.g. Schoier & Olofsson 2000)
• Focused on C-rich (AGB) stars using CO
• ARO Survey: sample of O and C-rich circumstellar shells
• Both CO and CN at 1 and 3 mm wavelengths
 J = 1→0 and 2→1 lines of 12CO, 13CO, 12CN, 13CN
• Observations with 12 m (3 mm) and SMT (ALMA Band 6 Receiver)
• CN: check on CO ratios (opacity effects)
Kitt Peak 12 m
Arizona
Radio
Observatory
SMT
63rd International Symposium on Molecular Spectroscopy
June 16-20, 2008
Type
C/Oa)
Distance (pc)
L (L)
Teff (K)
R* (cm)
(M yr-1)
AFGL 190
Carbon-AGB
1.1
2300
10000
2500b)
3.7 x 1013
6.8 x 10-5
AFGL 809
Carbon-AGB
1.1
1450
9400
2500b)
3.6 x 1013
1.7 x 10-5
AFGL 865
Carbon-AGB
1.1
1760
9200
2500b)
3.6 x 1013
2.3 x 10-5
IRC +40540
Carbon-AGB
1.1
630
9000
2000
3.5 x 1013
1.5 x 10-5
CRL 2688
Proto-PN (C)
1.1
1000
20000
6500
9.0 x 1012
1.7 x 10-4
CRL 618
Proto-PN (C)
1.1
1700
30000
30000
4.5 x 1011
2.0 x 10-4
CIT 6
Carbon-AGB
1.1
410
10000
2445
4.0 x 1013
6.5 x10-6
IRC +10216
Carbon-AGB
1.4c)
150
18000
2320
6.5 x 1013
1.0 x 10-5
V Hya
Carbon-AGB
1.05c)
330
14000
2650
4.0 x 1013
2.5 x 10-6
Y CVn
Carbon-J-type
1.09c)
220
4400
2700
2.0 x 1013
2.0 x 10-7
S Cep
Carbon-AGB
1.1
400
7300
1500
1.1 x 1014
2.5 x 10-6
F-Supergiant (O)
0.6
5000
700000
6200
7.5 x 1013
3.0 x 10-4
 Ori
Supergiant (O)
0.6
190
100000
3650
4.0 x 1013
1.0 x 10-6
VY CMa
Supergiant (O)
0.6
1500
500000
3368
1.4 x 1014
2.0 x 10-4
IRC +00365
Carbon-AGB
1.1
960
10400
2500b)
4.0 x 1013
2.2 x 10-5
UU Aur
Carbon-AGB
1.06c)
260
6900
3000
3.0 x 1013
3.5 x 10-7
89 Her
F-Supergiant (O)
0.6
1000
9000
7000
3.0 x 1012
4.0 x 10-6
c Cyg
S-type (C=O)
0.95d)
150
9300
2000
3.0 x 1013
5.0 x 10-7
OH231.8+4.2
Proto-PN (O)
0.6
1500
10000
2900
4.6 x 1013
2.3 x 10-4
TX Cam
Oxygen-AGB
0.6
317
8400
2600
2.0 x 1013
4.0 x 10-6
Oxygen-RG
0.6
115
11050
2500
4.0 x 1013
2.3 x 10-6
NML Cyg
Supergiant (O)
0.6
2000
500000
2500
2.6 x 1014
1.6 x 10-4
IK Tau
Oxygen-AGB
0.6
270
2000
2100
2.1 x 1013
4.5 x 10-6
Source
IRC +10420
W Hya
• 23 stars
observed
• C and O
Rich
• AGB, Miras,
Supergiants,
PPN
63rd International Symposium on Molecular Spectroscopy
June 16-20, 2008
CN Observations: Hyperfine structure to evaluate opacities
C
63rd International Symposium on Molecular Spectroscopy
Representative Data: CO and CN in CIT6
June 16-20, 2008
63rd International Symposium on Molecular Spectroscopy
CO and CN in YCVn (C-Rich)
June 16-20, 2008
63rd International Symposium on Molecular Spectroscopy
June 16-20, 2008
Spectra in NML Cyg:
O-Rich Supergiant
Note Galactic contamination
CN weak:
Only N = 2→1 line
63rd International Symposium on Molecular Spectroscopy
June 16-20, 2008
Spectra from TX Cam:
O-Rich AGB Star
63rd International Symposium on Molecular Spectroscopy
Source
IRC +40540
f(12CO)
f(13CO)
8.0 x 10-4
2.0 x 10-5
10-3
CIT 6
~ 1.5 x
IRC +10216
~ 1.5 x 10-3
6.0 x 10-5
V Hya
5.0 x 10-4 a)
7.0 x 10-6 a)
3.8 x 10-4 b)
5.3 x 10-6 b)
Y CVn
5.0 x 10-4
2.0 x 10-4
IRC +10420
5.0 x 10-4
3.5 x 10-5
 Ori
8.0 x 10-4
1.0 x 10-4
4.6 x 10-5 c)
1.0 x 10-6 c)
IRC +00365
7.0 x 10-4
1.0 x 10-5
UU Aur
9.0 x 10-4
1.0 x 10-5
c Cyg
5.0 x 10-4
1.5 x 10-5
TX Cam
4.0 x 10-4
1.3 x 10-5
W Hya
7.0 x 10-5
2.0 x 10-6
NML Cyg
4.0 x 10-4
3.0 x 10-5
IK Tau
8.0 x 10-5
8.0 x 10-6
VY CMa
5.0 x
10-5
June 16-20, 2008
Representative Results
• CO spectra modeled using
circumstellar radiative transfer code
(Bieging and Tafalla 1993)
• Account for opacities
• Derived 13CO and 12CO
abundances
 12C/13C ratios
• 12CN and 13CN abundances
derived from line intensities and
ratios of hyperfine components
 independent 12C/13C values
63rd International Symposium on Molecular Spectroscopy
12CO/13CO
12CN/13CN
Previous Values
AFGL 190
≥ 20
>5
> 22a
AFGL 809
≥ 28
>5
-
AFGL 865
≥ 13
> 14
> 15a
40
15-20
55f
-
57-66
32d, 20h
CIT 6
30
11-37
12-35c, 17-31a, d
V Hya
71*, 72**
> 16
33e, 69i
Y CVn
3
2-8
2.5f, 3.4e, 3.5i
S Cep
37
> 16
> 15a
IRC +10420
14
-
7l
 Ori
8
-
7g, 4k
VY CMa
46†,
> 3†
36l
IRC +00365
70
>7
~ 57b
UU Aur
90
-
~ 45f, 52i
89 Her
3-4
-
-
c Cyg
33
> 11
25g, 35-63h
TX Cam
31
>3
-
W Hya
35
-
-
NML Cyg
13
>1
10l
IK Tau
10
>1
10l
Source
IRC +40540
CRL 2688
June 16-20, 2008
12C/13C
Ratios
• CO and CN ratios
in good agreement
(also with photospheric)
• all 12C/13C < 89 (solar)
• C-Rich:
12C/13C ~ 25-90
• O-Rich:
12C/13C ~ 3-35
• Supergiants:
12C/13C ~ 3-14
except VYCMa (26-46)
• S Stars (C~O):
12C/13C = 33
63rd International Symposium on Molecular Spectroscopy
June 16-20, 2008
Qualitative Dredge-Up Calculations
FIRST DREDGE-UP
THIRD DREDGE-UP
H Ashes:
Unprocessed matter
12C/13C
C/O
He Ashes:
H-shell products
12C/13C
C/O
0:1
68
0.5
0:100
3
0.69
1:1
32
0.55
1:99
15
0.95
2:1
22
0.57
2:98
27
1.05
10:1
10
0.67
5:95
53
1.1
100:1
3
0.7
99:1
> 100
1.15
Unprocessed: 12C/13C ~ 68, C/O ~0.5
H Ashes: 12C/13C ~ 3, C/O ~0.7
H-shell products: 100:1 mixture
He ashes: C/O ~ 1.8; 12C/13C >>1
• Substantial mixing of H-burning products for low 12C/13C ratios (O-rich)
• 5 -10 % mixing of He-burning products raises 12C/13C and C/O ratios
63rd International Symposium on Molecular Spectroscopy
June 16-20, 2008
100
Observations
vs.
Calculations
UU Aur
Solar
V Hya
Local ISM
IRC +00365
60
G
CRL 2688
VY CMa (S)
12
CO/13CO
80
40
W Hya
A
IRC +40540
S Cep
c Cyg
TX Cam
F
VY CMa (O)
B
20
AFGL 190
NML Cyg
C
OH231.8+4.2
0
0.4
CRL 618 CIT 6
AFGL 809
E
IRC +10420
IK Tau
 Ori
89 HerD
0.6
AFGL 865
• Stars with C < O:
12C/13C ratios
lower
IRC +10216
• As stars evolve to
C > O:
12C/13C increases
Y CVn
0.8
1.0
C/O
1.2
1.4
1.6
63rd International Symposium on Molecular Spectroscopy
June 16-20, 2008
Conclusions and Future Directions
• 12C/13C ratios measured via CO and CN in circumstellar gas
• Ratios on average lower for O-rich than C-rich
•12C/13C ratios increase with C/O ratio
• Trends explained by mixing in First and Third Dredge-Up
• Ratios from other molecules
 Test theory (HCN, CS, etc)
 Higher sensitivity
• Possible with ALMA technology
• New Band 3 sideband-separating
mixers
 At least a factor of 2 improvement
from new 12 m: ALMA Band 3 receiver
63rd International Symposium on Molecular Spectroscopy
June 16-20, 2008
Acknowledgements
Nick
Woolf
Stefanie
Milam
NASA
Arizona
Astrobiology
Radio
Observatory NSF
Astronomy