thesis - IRS, The Infrared Spectrograph

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86 CHAPTER 5: Probing AGB nucleosynthesis via accurate Planetary Nebula abundancesThe “normal” helium group in the ISO sample (with He/H < 0.145; smaller filled squares)is within the range of abundances given by Henry et al. (2000) and Kingsburgh & Barlow(1994). However, both studies lack PNe with high He abundances. Actually, PN PB 6 (fromHenry et al. 2000 sample) has a helium abundance of 0.2 but that value is highly uncertain,and 0.146 is the highest helium abundance among those PNe that we have excluded from theKingsburgh & Barlow (1994) sample (those with no measured carbon).Conversely, the three ISO PNe with high helium abundances (with He/H > 0.145; largerfilled squares) agree well with the LMC PNe from Dopita et al. (1997), not only in the Heabundance but also in the N/O and C/N ratios. Besides supporting the division of the ISOsample into two subclasses, this also suggests that an initial sub-solar metallicity may be akey factor in the subsequent nucleosynthesis.For all these reasons, it seems advantageous to separate those PNe which exhibit highhelium content from the others having “normal” helium abundances, and to discuss the twogroups separately.5.6.3 PNe with “normal” He abundancesLet us examine the PN data with He/H 0.14 (Fig. 5.3). For the sake of clarity we summarisethe main features pointed out in Sect. 5.3.1.• Most of the data present a clear enhancement in He, C, N compared to the abundancesof these elements for the Sun. In particular, some of them should descend from carbonstars given their C/O ratio larger than one.• Oxygen abundances are underabundant when compared to the Solar determination byAnders & Grevesse (1989). On the other hand they are consistent with a constant, orslightly increasing trend with He/H, if compared to the recent oxygen estimation forthe Sun by Allende Prieto et al. (2001).• Neon seems to exhibit a constant, or perhaps moderately increasing trend with He/H.We first consider the elemental changes expected after the first and second dredge-upepisodes. The predicted envelope abundances are displayed in Figure 5.5 for two values ofthe initial metallicity, i.e. Z = 0.019 and Z = 0.008. Compared to their original valuesoxygen and neon are essentially unaffected, carbon is somewhat reduced, while nitrogenand helium may be significantly increased particularly after the second dredge-up in stars ofintermediate mass (M > 4 M ⊙ ).The comparison with the PN data indicates the necessity to invoke further chemicalchanges in addition to those caused by the first and second dredge-up, especially if oneconsiders the observed enhancement in carbon. The most natural explanation resides in thethird dredge-up process occurring during the TP-AGB phase. To this respect, as alreadymentioned in Sect. 5.6.1, the “old” models with fixed solar-scaled molecular opacities predicttoo large carbon enrichment (Fig. 5.3). This point and its possible solution are discussedbelow.
5.6. Comparison between models and observations 87Figure 5.5–. Observed PN abundances (squares with error bars) compared to expected surface abundances(taken from Girardi et al. 2000) just before the onset of the TP-AGB phase, as a function ofthe initial stellar mass, and for two values of the original metallicity, i.e. Z = 0.019 (upper curves)and Z = 0.008 (lower curves). The initial mass ranges from 0.6 to 5.0 M ⊙ at increasing He/H alongthe curves. Predicted abundances are those expected after the first dredge-up (solid line) for stars with0.6 ≤ M/M ⊙ ≤ 4.0; and after the second dredge-up (dashed line) for stars with 4.0 < M/M ⊙ ≤ 5.0.
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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
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3An ISO and IUE study of PlanetaryN
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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 and 84: 5.3. Accurate abundances of ISO-obs
Page 85 and 86: 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
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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
Page 135 and 136: 6.8. PDRs versus Shocks 127Figure 6
Page 137 and 138: 6.10. Atomic, ionized and molecular
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Page 141 and 142: 6.11. General discussion 133Table 6
Page 143 and 144: 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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