Planetary Nebulae as a Testground of Interstellar Molecular Chemistry

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Planetary Nebulae as a Testground of Interstellar
Molecular Chemistry

• Tatsuhiko Hasegawa

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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

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- 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
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3. Chemical Models - Simulation in
astrochemistry (gas-phase)
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 ? gt 50 to 350 species.
3. Building a data base of chemical reactions
between the molecules under consideration.
gt 500 to 3500 reactions. 4. Generating and
coding chemical rate equations for the set of
molecules under consideration. dn(i)/dt
-n(i) S n(j) R(ij-gtkl) n(i) S R(ihv-gtkl)
S n(l) n(k) R(lk-gtij) S n(k)
R(khv-gtij) 5. Application to your astronomical
project/object. gt Steady state or time
dependent ? Cloud structure or only
one point ? gt Input Tk, n (total), and
radiation field (or AV )
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Elemental Abundances
C/H N/H O/H Solar 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) z-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 gt C
gt N the solar abundance set z-Oph
set scaled variants. - Chemistry simulations
are possible with N gt O gt C or C gt O gt N.
gt No way to test the models in galactic
molecular clouds. - Molecular regions in PNe
are suitable for observational tests of a
chemical code.
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Molecular Detections in Planetary Nebulae (in
addition to CO detections in 50 planetary
nebulae)
NGC 7027 HCO, HCN, HNC, CN, CCH, Bachiller
et al. (1997) C3H2, OH, CH,
CH, CO, N2H JosselinBachiller (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)
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Molecular Detections in Planetary Nebulae
continued
IRAS21282 HCO, HCN, CN, C2H Likkel et al.
(1988) BV 5-1 HCO, HCN, CN
JosselinBachiller (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)
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NGC 7027 JCMT Hasegawa Kwok 2001 ApJ, 562, 824
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NGC 7027 JCMT Hasegawa Kwok 2001 ApJ, 562, 824
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NGC 6302 JCMT Hasegawa Kwok
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NGC 6302 JCMT Hasegawa Kwok
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Molecular Abundances and Densities from (sub-)mm
lines
NGC 7027 NGC 6302 Element abundance C gt
O gt N N gt O gt C Tk (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)
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Chemical Model of NGC 7027 and Elemental
Abundance Effects

• Steady state, gas-phase chemistry
• 9 elements, 106 species, 1500 reactions
• Radiative transfer for UVoptical 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.

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Model molecular abundances. Heavy elements are
mostly atomic or ionized.
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Model molecular abundances. Notice high
abundances of OH, CH, HCO.
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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. gt Modelers are
responding with replications and predictions.
PNe 12C/13C 10 30 ( 2-3 in a few PNe. gt
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.
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12C/13C estimates in PNe examples
NGC7027 NGC6302 IRAS21282 I (CO) / I
(13CO) 24 1.5 87 I (HCO) / I
(H13CO) 38 9. I (HCN) / I (H13CN) 4.7
testing
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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.