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

5. 12C/13C 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 chemistry1. 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: Tk, n (total), and radiation field (or AV )

3. Chemical Models - Simulation in astrochemistry (gas-phase)

Elemental Abundances

C/H N/H O/HSolar 4.6 (-4) 1.0 (-4) 8.3 (-4)Orion 3.4 (-4) 0.7 (-4) 4.0 (-4)HII region average 2.9 (-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)

C3H2, OH, CH, CH+, CO+, N2H+ 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)

IRAS21282 HCO+, HCN, CN, [C2H] Likkel et al. (1988)

BV 5-1 HCO+, HCN, CN Josselin&Bachiller (2003)

K 3-94 HCO+, HCN, HNC, CN

M 1-13 HCO+, HCN, HNC, CN

M 1-17 HCO+, HCN, HNC, CN

K 3-34 HCO+, HCN, CN

IC 5117 HCO+, HCN, HNC, CN

KjPn 8 CN Huggins et al. (1997)

CPD-56 HCO+ Sahai et al. (1992)

Molecular Detections in Planetary Nebulae – continued

NGC 7027JCMTHasegawa & Kwok 2001 ApJ, 562, 824

NGC 7027JCMTHasegawa & Kwok 2001 ApJ, 562, 824

NGC 6302JCMTHasegawa & Kwok

NGC 6302JCMTHasegawa & Kwok

Molecular Abundances and Densities from (sub-)mm lines

NGC 7027 NGC 6302Element abundance C > O > N N > O > CTk (assumed) (K) 800 800

nH

(cm-3) [obs] 1.3 - 5.0 (+5) 1.3 - 4.1 (+6)

X(HCO+) 1.5 (-9) 2.2 (-10)X(H13CO+) 4.0 (-11) 9.3 (-11)X(HCN) 1.2 (-9) 4.1 (-10)X(H13CN) 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.

• IUV(inner boundary) = 3.4 x 104 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 – 12C/13C measurements in the (sub-)mm band

RGB stars – 12C/13C = 5 – 20 in 10 – 50 % of samples. Optical-IR obs stimulated theoretical work. [Mid 1970s ~]

AGB stars – 12C/13C = 3 – 10 in 5 – 20 % of ~ 60 carbon stars. Optical-IR obs + elaborate atmosphere-models. [Mid 1980s ~](Sub-)mm 13CO & CO obs + advanced radiative transfer models.(Sub-)mm obs of various 13C-molecular species.=> Modelers are responding with replications and predictions.

PNe – 12C/13C = 10 – 30 ( 2-3 in a few PNe. > 60 in a few PNe).(Sub-)mm 13CO (& 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 13CO.3. Confirmation obs in H13CO+, H13CN, 13CN lines are needed.

12C/13C estimates in PNe – examples

NGC7027 NGC6302 IRAS21282I (CO) / I (13CO) 24 1.5 87I (HCO+) / I (H13CO+) 38 9.I (HCN) / I (H13CN) 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 (12C/13C) in 40 PNe can be estimated through molecular line observations in the (sub-)mm band at modest costs.

• Your supports will be appreciated.