Planetary Nebulae as a Testground of Interstellar Molecular Chemistry Tatsuhiko Hasegawa

1.Chemical Models – Interstellar Clouds 2.Elemental Abundances 3.Molecules in Planetary Nebulae 4.Chemical Models – Planetary Nebulae C/ 13 C from molecular line observation 6.Summary

- Studies of molecules in space (Astrochemistry). 1. What (and how much) molecules are present in space ? 2. How are these molecules created and destroyed ? What are the expected molecular abundances ? 3. Better understanding of chemical reactions rates and molecular constants – collaborations with chemists and molecular spectroscopists, or looking into chemistry journals. A chemical model = a simulation of chemistry with a chemical code Types of chemistry 1. Gas-phase reactions (gas-phase model) 2. Grain chemistry – reactions between adsorbed molecules – reactions between molecules and grain

1. How many (and what) elements to consider ? H, C, N, O, S, Si,,,, [then, Elemental Abundances ] 2. How many (and what) molecular species to consider ? => 50 to 350 species. 3. Building a data base of chemical reactions between the molecules under consideration. => 500 to 3500 reactions. 4. Generating and coding chemical rate equations for the set of molecules under consideration. dn(i)/dt = -n(i)  n(j) R(i+j->k+l) – n(i)  R(i+hv->k+l) +  n(l) n(k) R(l+k->i+j) +  n(k) R(k+hv->i+j) 5. Application to your astronomical project/object. => Steady state or time dependent ? Cloud structure or only one point ? => Input: T k, n (total), and radiation field (or A V ) 3. Chemical Models - Simulation in astrochemistry (gas-phase)

Elemental Abundances C/HN/HO/H Solar4.6 (-4)1.0 (-4)8.3 (-4) Orion3.4 (-4)0.7 (-4)4.0 (-4) HII region average2.9 (-4)0.4 (-4)5.0 (-4)  -Oph [HI cloud]0.7 (-4)0.2 (-4)1.8 (-4) NGC 7027[C-rich PN]13. (-4)1.9 (-4)5.5 (-4) NGC 6302 [Type I PN]1.0 (-4)8.3 (-4)5.0 (-4) - Chemistry simulations have been done with O > C > N [the solar abundance set;  -Oph set; scaled variants]. - Chemistry simulations are possible with N > O > C or C > O > N. => No way to test the models in galactic molecular clouds. - Molecular regions in PNe are suitable for observational tests of a chemical code.

NGC 7027 HCO +, HCN, HNC, CN, [CCH], Bachiller et al. (1997) C 3 H 2, OH, CH, CH +, CO +, N 2 H + Josselin&Bachiller (2003) NGC 6720 HCO +, HCN, HNC, CN Bachiller et al. (1997) NGC 7293 HCO +, HCN, HNC, CN NGC 6781 HCO +, HCN, HNC, CN M 4-9 HCO +, HCN, HNC, CN NGC 2346 HCO +, HCN, HNC, [CCH] Bachiller et al. (1989) NGC 6072 HCO +, HCN, HNC, CN Cox et al. (1992) IC 4406 HCO +, HCN, HNC, CN NGC 6302 HCO +, HCN, [SO, CCH, CN] Sahai et al. (1992) Molecular Detections in Planetary Nebulae (in addition to CO detections in 50 planetary nebulae)

IRAS21282HCO+, HCN, CN, [C2H]Likkel et al. (1988) BV 5-1HCO +, HCN, CN Josselin&Bachiller (2003) K 3-94HCO +, HCN, HNC, CN M 1-13HCO +, HCN, HNC, CN M 1-17HCO +, HCN, HNC, CN K 3-34HCO +, HCN, CN IC 5117HCO +, HCN, HNC, CN KjPn 8CN Huggins et al. (1997) CPD-56HCO + Sahai et al. (1992) Molecular Detections in Planetary Nebulae – continued

NGC 7027 JCMT Hasegawa & Kwok 2001 ApJ, 562, 824

NGC 7027 JCMT Hasegawa & Kwok 2001 ApJ, 562, 824

NGC 6302 JCMT Hasegawa & Kwok

NGC 6302 JCMT Hasegawa & Kwok

Molecular Abundances and Densities from (sub-)mm lines NGC 7027NGC 6302 Element abundanceC > O > NN > O > C Tk (assumed)(K) n H (cm -3 ) [obs] (+5) (+6) X(HCO + )1.5 (-9)2.2 (-10) X(H 13 CO + )4.0 (-11)9.3 (-11) X(HCN)1.2 (-9)4.1 (-10) X(H 13 CN)1.1 (-10) X(CN)1.7 (-8)5.5 (-9) X(CCH)1.1 (-8) X(CO + )4.3 (-10)

Chemical Model of NGC 7027 and Elemental Abundance Effects Steady state, gas-phase chemistry 9 elements, 106 species, 1500 reactions Radiative transfer for UV–optical photons  with dust opacity. I UV (inner boundary) = 3.4 x 10 4 x DISRF (determined with CLOUDY ionization code). Density and temperature are given. No dynamics. 1-D spherical geometry (91 grid points) 3 models with different sets of elemental abundances : 1. NGC7027 (C-rich elemental abundances). 2. NGC6302 (extreme Type I elemental abundances). 3. Solar elemental abundances.

Model molecular abundances. Heavy elements are mostly atomic or ionized.

Model molecular abundances. Notice high abundances of OH, CH, HCO +.

PNe – 12 C/ 13 C measurements in the (sub-)mm band RGB stars – 12 C/ 13 C = 5 – 20 in 10 – 50 % of samples. Optical-IR obs stimulated theoretical work. [Mid 1970s ~] AGB stars – 12 C/ 13 C = 3 – 10 in 5 – 20 % of ~ 60 carbon stars. Optical-IR obs + elaborate atmosphere-models. [Mid 1980s ~] (Sub-)mm 13 CO & CO obs + advanced radiative transfer models. (Sub-)mm obs of various 13 C-molecular species. => Modelers are responding with replications and predictions. PNe – 12 C/ 13 C = 10 – 30 ( 2-3 in a few PNe. > 60 in a few PNe). (Sub-)mm 13 CO (& CO) line obs. ~20 detections. [Late 1980s ~] Palla, Bachiller, Stanghellini, Tosi, Galli (2000) [Italy] Balser, McMullin, Wilson (2002) [NRAO] Bachiller, Forveille, Huggins, Cox (1997)[France] 1. Better S/N (re-observing) are needed. 2. More PNe should be observed in 13 CO. 3. Confirmation obs in H 13 CO +, H 13 CN, 13 CN lines are needed.

12 C/ 13 C estimates in PNe – examples NGC7027NGC6302IRAS21282 I (CO) / I ( 13 CO) I (HCO + ) / I (H 13 CO + )389. I (HCN) / I (H 13 CN)4.7 testing

Summary Diversity in elemental abundance makes PNe a suitable testground of astrochemistry. Molecular abundance studies in 12 PNe in the (sub-)mm band are possible at modest costs. Isotopic ratios ( 12 C/ 13 C) in 40 PNe can be estimated through molecular line observations in the (sub-)mm band at modest costs. Your supports will be appreciated.