Synthesis of Organic Compounds in Triple- reaction the Late Stages - PDF document

11/24/2011 Evolution of intermediate mass (1-8 M ⊙ ) stars Synthesis of Organic Compounds in • Triple-  reaction the Late Stages of Stellar Evolution (He  C) • Slow neutron Sun Kwok capture (s-process) (Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, etc) International conference on interstellar dust, molecules, and chemistry • Thermal pulse and Pune, November 22, 2011 dredge up 3 M ⊙ track Remnant AGB dust envelope in PN 21318+5631 SWS 100 10000 BD +30  3639  F  (10 -10 erg cm -2 s -1 ) In young PN, 1000 2500 BB LWS ~1/3 of flux Flux (10 -10 erg s -1 cm -2 ) emitted in IR 10 100 (Zhang & Kwok 1991) 10 Dust continuum 1 b-f continuum 1 Model 0 0 0 1 10 100 0.1 1.0 10.0 100.0 Wavelength (  m) Wavelength (  m) Amorphous Silicates & silicon carbide Unidentified infrared emission bands IRAS LRS 1500 6000 • 11.3 µm: Gillett et al.  F  (10 -10 erg cm -2 s -1 ) 5000 V CrB 1500 1973 4000 [SiIV] [NeIII] TX Cam [NeV]  F  (10 -10 erg cm -2 s -1 ) NGC 7027 1000 3000 • 3.3 µm: Merrill et al. 11.3 2000 12.7  F  (10 -10 erg cm -2 s -1 ) 1975 1000 AFGL 5357 SiC 1000 13.5 500 0 12.0 • 6.2, 7.7, 8.6 µm: 6 8 10 12 14 16 18 20 22 24 Wavelength (  m) 7.7 Russell et al. 1978 2000 0 (from KAO) 5 10 15 20 8.6 1800 [MgV] Wavelength (  m) 500 6.2  F  (10 -10 erg cm -2 s -1 ) 1600 AFGL 2591 3.3: sp 2 C-H stretch 6.2: sp 2 C=C stretch 1400 7.7: sp 2 C-C stretch • 4000 stars detected to have 1200 3.3 8.6: sp 2 =C-H in-plane bend 11.3: sp 2 =C-H out-of-plane bend 1000 amorphous silicates by IRAS LRS 800 600 0 400 AFGL 230 0 2 4 6 8 10 12 14 16 18 20 • 700 stars detected in SiC Wavelength (  m) 200 0 6 8 10 12 14 16 18 20 22 24 Wavelength (  m) 1

11/24/2011 Aromatic ( sp 2 ) hydrocarbon bands 200 11.3 2400 IRAS 21282+5050 • Aromatic 180 Aromatic Bands in the Red Rectangle 12.4 ISO SWS01 2200 grains: ISO SWS06 160 2000 (Knacke  F  (10 -10 erg cm -2 s -1 ) C-C stretch 140 7.7  F  (10 -10 erg cm -2 s -1 ) C=C stretch 1800 1977, Duley 120 8.6 & Williams 1600 C-H out-of-plane bend 100 6.2 C-H in-plane bend 1979, 1981; 1400 80 C-H stretch Puetter et al. 1200 60 1979) 1000 40 6.2: sp 2 C=C stretch 3.3 8.6: sp 2 C-H in-plane bend 800 20 7.7: sp 2 C-C stretch 11.3: sp 2 C-H out-of-plane bend 12.4: sp 2 C-H out-of-plane bend 600 0 400 -20 2 4 6 8 10 12 14 16 2 4 6 8 10 12 14 16 18 20 Wavelength (  m) Wavelength (  m) When are the aromatic compounds Proto-planetary nebulae synthesized? • AIB features not seen in AGB stars • Objects in transition between AGB and PN stages • AIB features are strong in young planetary nebulae • ~30 PPN are known, most discovered as the result of • Have to study the missing link between follow up of the IRAS AGB and PN phases survey (Kwok 1993, Ann. AFGL 2688, the Rev. Astr. Ap ., 31, 63) Egg Nebula PPN as imaged by the HST 3.4 μ m aliphatic C-H stretch • 3.38 μ m: asymmetric CH 3 The The Cotton Silkworm Candy • 3.42 μ m: asymmetric CH 2 Nebula Nebula • 3.46 μ m: lone C-H group • 3.49 μ m: symmetric CH 3 • 3.51 μ m: asymmetric CH 2 Reflected starlight, not emission! The Walnut Nebula The Water The Spindle Nebula Lily Nebula 2

11/24/2011 Aliphatic sidegroups 26 500 IRAS 22272+5435  F  (10 -10 erg cm -2 s -1 ) 400 20.3 12.2 8.0 11.3 ISO SWS01 3.29 21282+5050 16.0 7.0 Keck NIRSPEC 300  F  (10 -10 erg cm -2 s -1 ) 3.29: aromatic C-H stretch 6.0 3.40: asym. CH 2 , CH 3 7.8 3.46: lone C-H group 6.9 5.0 200 3.4 3.51: symmetric CH 2 6.2 3.56: aldehydes C-H stretch 3.462 4.0 3.515 6.2: sp 2 C=C stretch 3.56 6.9: sp 3 C-H bend 100 3.0 7.8: 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 2.0 0 1.0 0 10 20 30 40 50 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 Wavelength (  m) Wavelength (  m) Number of CH groups in aromatic 120 13.3 molecules 12.4 12.1 ISO SWS01 11.3 100 • Solo: 11.1-11.6 μ m ) s -1 • Duo: 11.6-12.5 μ m 80 m -2 • Trio:12.4-13.3 μ m c broad 8 07134+1005 g r 60 e 7.6 • Quarto: 13-13.6 μ m 0 -10 6.9 6.2 1 ( 40 F   20 22574+6609 0 6 7 8 9 10 11 12 13 14 Wavelength (  m) Hugdins and Allamandola 1999 Broad emission plateaus 6 6.9 IRAS 22272+5435 6.2 5 10 ISO SWS01 4 IRAS Z02229+6208 IRAS 16594-4656 7.7 ratioed spectrum ratioed spectrum 8 3 ratioed spectrum 6.2: sp 2 C=C stretch 6 6.9: sp 3 C-H bend 4 2 7.7: sp 2 C-C stretch 4 11.3: sp 2 C-H out-of-plane bend 1 26 2 12.2: sp 2 C-H out-of-plane bend 11.3 4.8 0 0 3 12.2 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 wavelength (  m) wavelength (  m) 20.3 2 3 20 IRAS 19500-1709 IRAS 23304+6147 ratioed spectrum ratioed spectrum 16 2 12 1 8 1 4 0 0 0 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 0 10 20 30 40 50 wavelength (  m) wavelength (  m) Wavelength (  m) 3

11/24/2011 Aliphatic bending modes 120 23304+6147 30  m 100 27  m 1.4 21  m  F  (10 -10 erg cm -2 s -1 ) IRAS 22272+5435 11.4 1.2 6.9 12.1 80 normalized spectrum 6.2 1.0 7.3 0.8 7.7 13.4 60 0.6 14.2 0.4 40 0.2 0.0 2 4 6 8 10 12 14 16 18 Wavelength (  m) 20 Kwok et al. 2001 • 8  m plateau: -CH 3 (7.25  m), -C(CH 3 ) 3 (8.16  m, “e”), =(CH 3 ) 2 (8.6  m, “f”) • 12  m plateau: C-H out-of-plane bending modes of alkene (“a”, “b”), cyclic 0 alkanes (9.5-11.5  m, “c”), long chains of -CH 2 - groups (13.9  m, “d”). 0 10 20 30 40 50 Wavelength (  m) Acetylene: first step to organic synthesis Polymerization of C 2 H 2 in Post-AGB evolution  5 fundamental at 13.7  m. 2000 ISO SWS06 AFGL 618 600 21318+6531  F  (10 -10 erg cm -2 s -1 ) ISO SWS01 20.1  m 25.5  m 1500 500 27.5  m  F  (10 -10 erg cm -2 s -1 ) 400 HC 5 N C 2 H 2 HC 3 N 300 1000 C 6 H 2 200 C 4 H 2 HCN 100 C 2 H 2 500 0 0 10 20 30 40 50 13 14 15 16 17 Wavelength (  m) Wavelength (  m) Chemical evolution from AGB to PN Advantages of circumstellar chemistry • Extreme carbon stars (t~10 4 yr): • Single energy source C 2 H 2  C 6 H 6 • Simple geometry • PPN (t~10 3 yr): clusters of aromatic rings • Well-determined physical environment (density  (r), temperature T(r), radiation with peripheral aliphatic bonds background I(r)) • PN (t~10 4 yr): loss of H and a progressive • Chemical time scale defined by dynamical formation of clusters of rings into more time scale (AGB: 10 4 yr, PPN:10 3 yr, PN: structured units 10 4 yr) 4

11/24/2011 Polycyclic aromatic What is the carrier of the UIR hydrocarbons (PAH) features? • Aromatic features: 3.3, 6.2, 7.7, 8.6, and 11.3 µm • Fused ring molecules made up of pure C • Aliphatic features: 3.4 and 6.9 µm and H • Features at 15.8, 16.4, 17.4, 17.8, and 18.9 µm • Broad plateau features at 8, 12, and 17 µm. The PAH hypothesis Problems with the PAH model (Allamandola et al. 1989, Puget & Léger 1989) • PAH molecules have well-defined sharp features but the UIR features are broad • the UIE features are the result of infrared • PAHs primarily excited by UV, with little absorption in the visible fluorescence from small (~50 C atoms) gas-phase • UIR features seen in PPN and reflection nebulae with no UV PAH molecules being pumped by far-ultraviolet radiation photons ( Tielens 2008 ) • Shapes and peak wavelengths independent of stellar temperature • The strong and narrow predicted gas phase features in the UV are • The central argument for the PAH hypothesis is not seen in interstellar extinction curves that single-photon excitation of PAH molecules • No PAH molecules have been detected in spite of the fact that can account for the 12 µm excess emission the vibrational and rotational frequencies are well known • In order to fit the astronomical observations, the PAH model has observed in cirrus clouds in the diffuse interstellar to appeal to a mixture of PAH of different sizes, structures medium by IRAS ( Sellgren 1984, 2001 ) . (compact, linear, branched) and ionization states, as well as broad intrinsic line profiles. Reflection nebulae Excitation problem • The 3.3 and 7.7 µm radiate at too short a • The UIR features have wavelength for the grains to be in thermal consistent profiles and peak wavelengths in equilibrium spite of the fact that • Stochastic heating by single photon the nebulae are heated by central stars of • Alternate explanation: sudden release of 11000, 19000 and chemical energy as a source of transient 6800 K heating ( Duley and Williams 2011 ). • No UV background Uchida et al. (2000) 5