Molecular Evolution from AGB Stars to Planetary Nebulae
October 30, 2017 | Author: Anonymous | Category: N/A
Short Description
molecules .. Other features at 15.8., 16.4, 17.4, 17.8, and. kwok kwok_toledo2.ppt [Compatibility Mode] 17.4 ......
Description
31/5/2011
Molecular Evolution from AGB Stars to Planetary Nebulae Sun Kwok June 2011: IAU Symposium 280, Toledo
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Evolution of intermediate mass (1-8 M⊙) stars • Triple- reaction (HeC) • Slow neutron capture (s-process) (Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, etc)
• Thermal pulse and dredge up • Mass loss manifested in both IR continuum and molecular emissions 3 M⊙ track
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Cirucmstellar dust envelope completely obscures the central star 21318+5631 SWS
F(10-10 erg cm-2s-1 )
100
2500 BB
LWS
10
1
Model
0
0.1
1.0
10.0
100.0
Wavelength (m)
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Molecules in the gas phase • Rotational transitions of over 60 molecules have been detected in the circumstellar envelopes of AGB stars • Inorganics: CO, SiO, SiS, NH3, AlCl, .. • Organics: C2H2, CH4, H2CO, CH3CN, .. • Radicals: CN, C2H, C3, HCO+ • Rings (C3H2), chains (HC9N) AGB stars are prolific molecular factories
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Remnant AGB dust envelope in PN 10000
BD +30 3639
Flux (10-10 erg s-1 cm-2)
1000
100
Dust continuum
10
b-f continuum 1
0 0
1
10
100
Wavelength (m)
However, the chemical composition of the dust is not the same
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The dust continuum • Strong continuum emission from a few μm to mm wavelengths • Cold component (T~50-100 K): remnant of AGB dust envelope • Warm component (T~200 K): dust formed in post-AGB evolution
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When are the aromatic compounds synthesized? • Aromatic infrared bands (AIB) not seen in AGB stars • AIBs are strong in young planetary nebulae • Must have emerged during the evolution between AGB and PN phases
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Proto-planetary nebulae • Objects in transition between AGB and PN stages • ~30 PPN are known, most discovered as the result of follow up of the IRAS survey (Kwok 1993, Ann. Rev. Astr. Ap., 31, 63) No UV radiation, visible image due to scattered starlight
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3.4 μm aliphatic C-H stretch • • • • •
3.38 μm: asymmetric CH3 3.42 μm: asymmetric CH2 3.46 μm: lone C-H group 3.49 μm: symmetric CH3 3.51 μm: asymmetric CH2 The 3.4 µm feature just as strong as the 3.3 µm feature
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Aliphatic sidegroups in young PN 8.0 3.29
21282+5050
F (10-10erg cm-2 s -1)
7.0
Keck NIRSPEC 3.29: arom atic C-H stretch
6.0
3.40: as ym . CH 2, CH 3 3.46: lone C-H group
5.0
3.4
3.51: sym m etric CH 2 3.56: aldehydes C-H stretch
3.462
4.0
3.515 3.56
3.0 2.0 1.0 3.0
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
4.0
Wavelength (m)
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6.9 µm aliphatic C-H bending mode in PPN spectra 120 12.1
ISO SWS01
11.3
100
F(10-10erg cm-2 s-1)
13.3
12.4
80 broad 8
60
07134+1005
7.6 6.9 6.2
40
20 22574+6609
0
6
7
8
9
10
11
12
13
14
Wavelength (m)
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Sizes of the aromatic units • • • •
Solo: 11.1-11.6 μm Duo: 11.6-12.5 μm Trio:12.4-13.3 μm Quarto: 13-13.6 μm
Frequencies of out-of-plane bending modes depend on the number of exposed edges Hugdins and Allamandola 1999
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Broad emission plateaus ratioed spectrum
ratioed spectrum
3 2 1 0
0
2
1
0
2
4 6 8 10 12 14 16 wavelength (m)
6 4 2 0
2
20
IRAS 19500-1709
2
IRAS 16594-4656
8
0
4 6 8 10 12 14 16 wavelength (m)
ratioed spectrum
ratioed spectrum
3
0
10
IRAS Z02229+6208
4
4 6 8 10 12 14 16 wavelength (m)
IRAS 23304+6147
16 12 8 4 0
0
2
4 6 8 10 12 14 16 wavelength (m)
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8 and 12 µm plateau features 6 6.9
IRAS 22272+5435 6.2
5
ISO SWS01
ratioed spectrum
7.7
4 26 4.8
3
11.3
6.2: sp 2 C=C stretch 6.9: sp 3 C-H bend 7.7: sp 2 C-C stretch 11.3: sp 2 C-H out-of-plane bend 12.2: sp 2 C-H out-of-plane bend
12.2 20.3
2
1
0
0
10
20
30
40
50
Wavelength (m)
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Aliphatic bending modes 1.4
IRAS 22272+5435
11.4
1.2
6.9
normalized spectrum
12.1 6.2
1.0
7.3
0.8
7.7 13.4
0.6 14.2
0.4 0.2 0.0
2
4
6
8
10
12
Wavelength (m)
• •
14
16
18
Kwok et al. 2001
8m plateau: -CH3 (7.25 m), -C(CH3)3 (8.16 m, “e”), =(CH3)2 (8.6 m, “f”) 12 m plateau: C-H out-of-plane bending modes of alkene (“a”, “b”), cyclic alkanes (9.5-11.5 m, “c”), long chains of -CH2- groups (13.9 m, “d”).
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17 µm plateau • Aromatic C-C-C inand out-of-plane distortion? (Van Kerckhoven et al. 2000)
Zhang et al. 2010
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Unidentified 21 m Feature 230
SWS01 KAO LRS
-2 -1 F(10-10erg cm s )
07134+1005 180
130
80
30
-20 0
10
20
30
40
50
Wavelength (m)
First detected by IRAS LRS in C-rich post-AGB stars (Kwok, Volk & Hrivnak 1989)
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Asymmetric profiles 1.2
1.0
07134+1005 22272+5435 23304+6147
ISO SWS06
0.8 normalized profile
• ISO SWS06 (λ/Δλ~2000) • Uniform asymmetric shape after removal of cool continuum • Consistent peak wavelength of 20.1 μm • No sign of substructuresolid state
0.6
0.4
0.2
-0.0
-0.2 16
17
18
19
20
21
22
23
24
25
wavelength (m )
Volk et al. 1999
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Consistent profiles
λ0=20.1±0.1 µm
Spitzer IRS
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Carrier of the 21 m Feature • Solid SiS2: Goebel (1993), Begemann et al. (1996) • Maghemite (Fe2O3) or magnetite (Fe3O4): Cox (1991) • Amides (urea or thiourea): Courisseau et al. (1992), Papoular (2011) • Hydrogenated amorphous carbon: Buss et al. (1990) • Hydrogenated fullerenes (C60Hm, m=1, 2…60) and their ions: Webster (1995) • nanodiamonds (Hill et al. 1998) • TiC nanoclusters (von Helden et al. 2000) • O-substituted 5-member carbon rings (Papoular 2000) • 3-1Σ transition of C2 (Gruen 2001) • SiC (Speck & Hofmeister 2004)
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Features at 15.8 and 16.4 µm 22
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15.8 µm feature • Δλ~1.3 µm • Strong in 21 µm sources 21 µm
15.8 µm
Hrivnak et al. 2009, Zhang et al. 2010
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Unidentified 21 and 30 µm features 26
F(10-10erg cm-2 s-1)
500
IRAS 22272+5435 20.3
400 12.2 11.3
ISO SWS01
16.0
300 7.8 6.9
200
6.2 6.2: sp2 C=C stretch 6.9: sp3 C-H bend 7.8: sp2 C-C stretch 11.3: sp2 C-H out-of-plane bend 12.2: sp2 C-H out-of-plane bend
100
0 0
10
20
30
40
50
Wavelength (m)
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30 Micron Feature First detected in IRC+10216, AFGL 3068, IC 418, and NGC 6572 (Forrest
250 27 m
30 m
19500-1709
F(10-10erg cm-2 s-1)
200
et al. 1981)
21 m
150
Now observed in a number of PPNs
100
dust continuum
50
0
0
Stellar continuum
10
20
30
40
50
Wavelength (m)
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AIB, 21, and 30 µm features in C-rich PPN 120
23304+6147
30 m 27 m
F(10-10erg cm-2 s-1)
100 21 m
80
60
40
AIB
dust continuum
20
0 0
Stellar continuum
10
20
30
40
50
Wavelength (m)
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The roles of O, S, and N
Red: O Green: C Grey: H
Aliphatic chains of CH2 groups, oxygen bridges, and OH groups Papoular 2011
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30 μm feature first appear in carbon stars 600
21318+6531 20.1 m
F(10-10erg cm-2 s-1 )
500
ISO SWS01 25.5 m 27.5 m
400 C2 H2
300
5 fundamental at 13.7m.
200
100
0
0
10
20
30
40
50
Wavelength (m)
Extreme carbon stars with optically thick envelopes
Volk et al. 2000
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From acetylene to benzene
IRC+10216: bending modes of C2H2 (Cernicharo et al. 1999)
AFGL 618: C4H2, C6H2, C6H6 (Cernicharo et al. 2001)
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Polymerization of C2H2 in Post-AGB evolution 2000 ISO SWS06
-2 -1 F(10-10erg cm s )
AFGL 618
1500 HC5N HC3N C6H2
1000 C4H2
HCN
C2H2
500 13
14
15
16
17
Wavelength (m)
30
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Chemical evolution from AGB to PN • Extreme carbon stars (t~104 yr): C2H2C6H6 • PPN (t~103 yr): clusters of aromatic rings with peripheral aliphatic bonds • PN (t~104 yr): loss of H and a progressive formation of clusters of rings into more structured units
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Photochemistry • The 8 and 12 m plateau features are due to a variety of alkane and alkene groups attached to hydrogenated aromatic rings. • When exposed to UV light, the aliphatic side groups are modified, leading to larger aromatic rings. • Isomerization, bond migrations, cyclization reactions. • Ring closure and cycloaddition transform alkenes into ring systems. • H loss leads to fully aromatic rings
Net result: UV transforms aliphatic to aromatic groups
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Advantages of circumstellar chemistry • Single energy source • Simple geometry • Well-determined physical environment (density (r), temperature T(r), radiation background I(r)) • Chemical time scale defined by dynamical time scale (AGB: 104 yr, PPN:103 yr, PN: 104 yr)
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Spectroscopic properties • A strong continuum from 3-200 µm • Aromatic features at 3.3, 6.2, 7.7, 8.6, and 11.3 µm • Aliphatic features at 3.4, 6.9 µm • Other features at 15.8., 16.4, 17.4, 17.8, and 18.9 µm • Plateau features at 8, 12, 17 µm
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Spectral fitting
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Proto-planetary nebulae
21 µm C-H out-of-plane bending modes
C-H in-plane bending modes
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How do they form? • Surface temperature of red giants: 3000 degrees • Solid grains condensed from gas in the stellar wind under near vacuum conditions • Theoretically impossible, especially during the PPN phase • Observationally we see aliphatics and aromatics form in PPN on time scales as short as hundreds of years • In novae, they form on a time scale of days
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Organics in novae
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What is the chemical structure of the carrier? • Natural substances: coal (Papoular et al. 1989), kerogen, petroleum fractions (Cataldo et al. 2002), soot • Artificial substances: hydrogenated amorphous carbon (HAC, Jones et al. 1990), quenched carbonaceous composites (QCC, Sakata et al. 1987), carbon nanoparticles (Duley & Hu 2009, Jäger et al. 2009), tholins, HCN polymer
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Infrared Spectrum of Coal
Emission plateaus Guillois et al. 1996
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Kerogen • random arrays of aromatic carbon sites, aliphatic chains (-CH2-)n), and linear chains of benzenic rings with functional groups made up of H, O, N, and S attached • a solid sedimentary, insoluble, organic material found in the upper crust of the Earth
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Petroleum fractions Anthracite coal
Modified fraccion 2
Distillate aromatic extract
PPN 22272+5435 Cataldo et al. 2004
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Laboratory Simulations of Cosmic Dust • Quenching of plasma of 4-torr methane (Sakata et al. 1987) • Hydrocarbon flame or arc-discharge in a neutral of hydrogenated atmosphere (Colangeli et al. 1995) • HAC films prepared by laser ablation of graphite in a hydrogen atmosphere (Scott and Duley 1996) • Infrared laser pyrolysis of gas phase molecules (C2H4, C4H6)C-based nanoparticles (Herlin et al. 1998)
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Pure C & H or with N? • QCC: hydrocarbon plasma deposition • Tholins: refractory organic materials formed by UV photolysis of reduced gas mixtures (N2, NH3, CH4, etc.) • HCN polymers: amorphous hydrogenated carbon nitride, formed spontaneously from HCN
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Organics in the Solar System • Planets and their satellites, asteroids, comets, minor bodies in the outer Solar System • Traditional picture: made up of minerals, metals, and ices • Organics represent a major component of meteorites, comets, asteroids, and IDPs (talk by Alexander)
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Carbonaceous Chondrite Meteorites • Over 70% of the organic matter in meteorites is in the form of insoluble macromolecular material similar to kerogen (Kerridge 1999) • possibly of interstellar origin due to excess of D, 13C, 15N, etc.
Functional groups identified in Murchison IOM (Cody et al. 2011)
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Interplanetary Dust • Few microns to tens of microns in size (Brownlee 1978) • Silicates (olivine & pyroxene) • 10-12% carbon content • 3.4 µm aliphatic feature and sometimes C=O group (Flynn et al. 2003, Keller et al. 2004)
O-XANES spectrum of IDP
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Comparison between 3.4 µm features in Titan haze, comets, and PPNs
Kim et al. 2011 Kim et al. 2011
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A model • the organic matter in PN and PPN show a lot of similarities to IOM in meteorites and organic solids in comets and IDPs. • An amorphous solid with mixed aromatic/aliphatic structure • Contains impurities (O, N, S, ) beyond C and H • Small aromatic islands linked by aliphatic bridges • Nanometer to micrometer in size
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• R: organic moiety • Aromatic rings and aliphatic chains • O, N, S impurities
Derenne & Robert 2010
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Summary • Organic compounds are everywhere in the Universe (from solar system to ISM to galaxies) • Hydrocarbons with linear, aromatic and aliphatic structures are detected in the circumstellar envelopes of evolved stars • These carbonaceous materials undergo a change from aliphatic to aromatic structures during the transition from PPN to PN • Chemical evolution leading to complex organic compounds can take place over only a few thousand years in the circumstellar environment
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Summary (cont.) • The detection of pre-solar grains suggests that grains from AGB stars can survive the journal through the ISM and reach the Solar System • Macromolecular organics in meteorites, IDP, comets, and planetary satellites show similarities with organics produced by planetary nebulae • To what extent was the Early Earth chemically enriched by the early bombardment?
A star-Earth connection
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