thesis - IRS, The Infrared Spectrograph

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Table 5.3–. PNe abundances ♮ w.r.t. hydrogen in number. The number between parenthesis (x) stands for 10 x . Abundancereference values for the Sun, Orion, and LMC are also included.Name Helium Carbon(-4) Nitrogen(-4) Oxygen(-4) Neon(-4) Sulfur(-5) Argon(-6)NGC 2440 0.119 7.2 4.4 3.8 1.1 0.5 3.2NGC 5315 0.124 4.4 4.6 5.2 1.6 1.2 4.6NGC 6302 0.170 0.6 2.9 2.3 2.2 0.8 6.0NGC 6445 0.140 6.0 2.4 7.4 2.0 0.8 3.8NGC 6537 0.149 1.8 4.5 1.8 1.7 1.1 4.1NGC 6543 0.118 2.5 2.3 5.5 1.9 1.3 4.2NGC 6741 0.111 6.4 2.8 6.6 1.8 1.1 4.9NGC 7027 0.106 5.2 1.5 4.1 1.0 0.9 2.3NGC 7662 0.088 3.6 0.7 4.2 0.6 0.7 2.1He 2-111 0.185 1.1 3.0 2.7 1.6 1.5 5.5Sun ∗ 0.100 3.55 0.93 4.9 1.2 1.86 3.6Orion † 0.098 2.5 0.60 4.3 0.78 1.5 6.3< LMC > ♯ 0.089 1.10 0.14 2.24 0.41 0.65 1.9♮ See Sect. 5.3.1 for references.∗ Grevesse & Noels (1993) and Anders & Grevesse (1989) except the oxygen abundance which was taken fromAllende Prieto et al. (2001).† Esteban et al. (1998).♯ From Dopita et al. (1997).76 CHAPTER 5: Probing AGB nucleosynthesis via accurate Planetary Nebula abundances
5.3. Accurate abundances of ISO-observed PNe 77The presence of the latter can affect the abundance composition which has been derivedassuming that the ionization is produced by the hot central star. For He 2-111 the velocity ofthe shocks have been estimated by Meaburn & Walsh (1989) to be ∼380 km/s. They show thatthese high velocity shocks are localized in the outermost parts of the bi-polar lobes (which areless dense). They conclude that photo-ionization by a hot star is the most plausible dominantprocess in the core and dense disk. Since these shocks affect the less dense regions the effectthat they might have on the abundance determination is very small and can be neglected.High velocity shocks in NGC 6302 were first presumed to be detected by Meaburn & Walsh(1980) from a study of the wings in the Ne V line at 3426 Å. However, this is not supportedin more recent work by Casassus et al. (2000) using echelle spectroscopy of IR coronal ions.Even if these shocks were present, a study of Lame & Ferland (1991), in which they fitphoto-ionization models to their spectrum, indicate that only very high stages of ionization,such as Si 6 + (IP 167 eV), are produced by shocks. These high stages of ionization havenegligible weight on the overall abundance which is therefore not affected by the presenceof the shocks. The speed of the shocks in NGC 6537 is ∼ 300 km/s (Corradi & Schwarz1993). Hyung (1999) studied this specific problem of the source of the nebular emissionarising either by the hot central star or by shock heating, with the help of photo-ionizationmodels. He concludes that the radiation of the hot central star is responsible for the emission.In summary, the high velocity shocks present in these PNe do not play a role in the abundancedetermination.It should be noticed as well, that the UV flux from the hot central stars (see Table 5.2) inthese three nebulae produces a high degree of ionization. In fact, Si 5+ and Si 6+ have beenmeasured in both NGC 6302 and NGC 6537 (Beintema & Pottasch 1999; Casassus et al.2000), and in NGC 6302 even Si 8+ and Mg 7+ that require very high ionization potentials.The oxygen abundance measured in these nebulae by Pottasch et al. (2000); Pottasch &Beintema (1999) account for oxygen up to O 3+ and it may be that the ICF adopted forthese nebulae (∼1.3) could be underestimating species such as O 4+ , O 5+ , O 6+ . The sameargument applies to the carbon abundance. Nonetheless, the ionic abundance of O 2+ isalways larger (approximately a factor 2) than the contribution of O 3+ . Thus, one wouldexpect that the ionic abundances of higher stages of ionization are smaller. In fact, the ionicdistribution of neon abundance in these nebulae, peaks at Ne ++ for NGC 6302 and He 2-111,and at Ne 3+ for NGC 6537, decreasing dramatically with higher stages of ionization (Ne 4+and Ne 5+ ). The IP of Ne 4+ and Ne 5+ are 97.1 and 126.2 eV respectively, and that of O 4+113.9 eV. We therefore do not think that the ICF used by Pottasch et al. (2000); Pottasch& Beintema (1999) for the determination of the oxygen abundance in these nebulae isunderestimated. However, the error on the ICF used to derive the carbon and oxygenabundance could be reduced with the aid of photo-ionization models or with the analysis ofrecombination lines from O 2+ to O 6+ (Barlow, private communication). This uncertaintydoes not apply to nitrogen and neon since high stages of ionization were measured, and thereforethe neon and nitrogen abundances are better determined than those of oxygen and carbon.The error in the abundances in Table 5.3 is about 20 to 30%. These errors only includethe uncertainty in the intensities of the lines used to derive the abundances. Other errors, e.g.using Ionization Correction Factor (ICF) to derive abundances or the effect of uncertaintiesin the atomic parameters (especially the collisional strengths) are difficult to quantify. Theabundances shown in Table 5.3 have been derived using an ICF near unity. Often all important
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RIJKSUNIVERSITEIT GRONINGENPhysics
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To my parents
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Contents1 Introduction 11.1 Evoluti
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CONTENTSvii5 Probing AGB nucleosynt
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1IntroductionPLANETARY NEBULAE are
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1.1. Evolution of low and intermedi
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1.2. Planetary Nebulae 5Flash−Dri
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1.3. Physics in PNe 7their whole li
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1.3. Physics in PNe 95.35 eVO IIIλ
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1.4. Studying PNe in the infrared 1
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2The ISO-SWS Spectrum ofPlanetary N
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2.3. Data reduction 15Table 2.1-. C
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2.4. Line flux discussion 17Table 2
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2.5. The visual and the ultraviolet
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2.6. Analysis 21Table 2.5-. Electro
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24 CHAPTER 2: The ISO-SWS Spectrum
Page 34 and 35: 26 CHAPTER 2: The ISO-SWS Spectrum
Page 36 and 37: 28 CHAPTER 2: The ISO-SWS Spectrum
Page 39 and 40: 3An ISO and IUE study of PlanetaryN
Page 41 and 42: 3.3. Corrections to line fluxes 33[
Page 43 and 44: 3.4. Line fluxes 35Table 3.1-. Comp
Page 45 and 46: Table 3.3-. IUE intensities, fluxes
Page 47 and 48: 3.5. Physical parameters 393.4.3 Op
Page 49 and 50: 3.5. Physical parameters 41Table 3.
Page 51 and 52: 3.6. Chemical abundances 43Table 3.
Page 53 and 54: 3.6. Chemical abundances 45Table 3.
Page 55: 3.7. Conclusions 47Acknowledgements
Page 58 and 59: 50 CHAPTER 4: Abundances of Planeta
Page 77 and 78: 5Probing AGB nucleosynthesis viaacc
Page 79 and 80: 5.1. Introduction 71about the synth
Page 81 and 82: Table 5.2-. Radius, Zanstra tempera
Page 83: 5.3. Accurate abundances of ISO-obs
Page 87 and 88: 5.4. Nucleosynthesis in low- and in
Page 89 and 90: 5.5. Synthetic TP-AGB calculations
Page 91 and 92: 5.6. Comparison between models and
Page 111 and 112: 5.7. Summary and conclusions 103Fig
Page 113 and 114: 5.7. Summary and conclusions 105A s
Page 115 and 116: 6Physical Conditions in PDRs around
Page 117 and 118: 6.2. Observations 109are not promin
Page 119 and 120: 6.4. General parameters of the PNe
Page 121 and 122: 6.4. General parameters of the PNe
Page 123 and 124: Table 6.3-. Radius, Zanstra tempera
Page 125 and 126: 6.6. Lines fluxes 117Figure 6.2-. S
Page 127 and 128: 6.7. Physical conditions of the PDR
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6.8. PDRs versus Shocks 127Figure 6
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6.10. Atomic, ionized and molecular
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6.10. Atomic, ionized and molecular
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6.11. General discussion 133Table 6
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6.11. General discussion 135Figure
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6.12. Summary and Conclusions 137su
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7Conclusions and future workTHE res
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141• PNe with He/H > 0.14. The st
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143HERSCHEL The launch of this sate
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Nederlandse SamenvattingSTERREN wor
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Nederlandse Samenvatting 147Figuur
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Nederlandse Samenvatting 149PHOTOIO
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Nederlandse Samenvatting 151Figuur
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Nederlandse Samenvatting 153infraro
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English SummarySTARS are born, live
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English Summary 157Figure 2-. Two e
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English Summary 159PHOTOIONIZATIONR
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English Summary 161Figure 5-. Spect
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English Summary 163all) stages of i
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BibliographyAcker A., Marcout J., O
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BIBLIOGRAPHY 167Henry R.B.C., Kwitt
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BIBLIOGRAPHY 169Pottasch S.R., Bern
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List of PublicationsPublications in
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AcknowledgementsI could easily writ
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Acknowledgements 175sense of humor,
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