thesis - IRS, The Infrared Spectrograph

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138 CHAPTER 6: Physical Conditions in PDRs around Planetary Nebulaemass grows at the expenses of the atomic and molecular mass. While the uncertainties arelarge, there is a good relationship between the total gas mass and the core mass of the PNe,supporting the notion that higher mass progenitors produce more massive envelopes and leavemore massive stellar cores.AcknowledgementsJ. Bernard-Salas is grateful to N.L. Martín-Hernández for reducing some of the LWS spectra. J.Bernard-Salas wants also to thank M. Kaufman, W. Latter and D. Fong for providing respectively theO-rich and C-rich PDR models. F. Molster, D. Fong, J. Cami and S. Hony are thanked for useful discussions.We thank M.J. Barlow, L.B.F.M. Waters, J.M. van der Hulst, S.R. Pottasch, P.R. Wesselius andM. Spaans for carefully reading of the manuscript whose comments have improved this chapter. IA3is a joint development of the SWS consortium. Contributing institutes are SRON, MPE, KUL and theESA Astrophysics Division. This research has made use of the SIMBAD database, operated at CDS,Strasbourg, France.
7Conclusions and future workTHE research carried out in this thesis tries to attain a better understanding of the planetarynebula phase of stellar evolution. Since planetary nebulae (PNe) enrich the interstellarmedium by the ejection of their envelope, special emphasis has been put on deriving elementalabundances for a sample of PNe. In particular the questions that we have tried to answerare: 1) What are the abundances and physical conditions in PNe? 2) What are the nuclearprocesses taking place in the interior of the central stars? 3) Which physical processes areinvolved in transporting freshly synthesized elements to the stellar surface? 4) What is thecontribution of low mass stars to the chemical enrichment of the galaxy? 5) How does thestar interact with the previously ejected material during the planetary nebula phase?In this chapter the main conclusions of this thesis are summarized followed by suggestionson how to extend this work using the current and future generations of telescopes.Accurate abundance determinationThe main objective of this thesis has been to derive reliable abundances for a sample ofnearby PNe. This provides information on the amount of material returned to the interstellarmedium by these objects. The objects presented in this thesis are: NGC 7027 (chapter 2),NGC 2440 (chapter 3), BD+30 3639 and NGC 6543 (chapter 4), and NGC 5315, NGC 6741,and NGC 7662 (chapter 5).Previous estimates of PNe abundances using only optical and/or ultraviolet data have toresort to using large ionization correction factors to correct for unseen stages of ionization.Predicting unseen stages of ionization is tricky and may lead to large errors in the derivedabundances. We have used spectroscopic data from the Infrared Space Observatory (ISO),that has flown in the period 1995-1998. In addition, ultraviolet spectral observations fromthe International Ultraviolet Explorer (IUE) and optical data have been included in theanalysis. The use of infrared data has particularly improved the abundance determinations.The reasons for this are three fold. First, many unseen ions emit in the infrared stronglyreducing the need for ionization correction factors. Second, the infrared line intensities arenot sensitive to the adopted temperature or temperature fluctuations in the nebula. Third,
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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[
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3.4. Line fluxes 35Table 3.1-. Comp
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Table 3.3-. IUE intensities, fluxes
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3.5. Physical parameters 393.4.3 Op
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3.5. Physical parameters 41Table 3.
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3.6. Chemical abundances 43Table 3.
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3.6. Chemical abundances 45Table 3.
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3.7. Conclusions 47Acknowledgements
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50 CHAPTER 4: Abundances of Planeta
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5Probing AGB nucleosynthesis viaacc
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5.1. Introduction 71about the synth
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Table 5.2-. Radius, Zanstra tempera
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5.3. Accurate abundances of ISO-obs
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5.3. Accurate abundances of ISO-obs
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5.4. Nucleosynthesis in low- and in
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5.5. Synthetic TP-AGB calculations
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5.6. Comparison between models and
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5.6. Comparison between models and
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Page 117 and 118: 6.2. Observations 109are not promin
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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
Page 145: 6.12. Summary and Conclusions 137su
Page 149 and 150: 141• PNe with He/H > 0.14. The st
Page 151 and 152: 143HERSCHEL The launch of this sate
Page 153 and 154: Nederlandse SamenvattingSTERREN wor
Page 155 and 156: Nederlandse Samenvatting 147Figuur
Page 157 and 158: Nederlandse Samenvatting 149PHOTOIO
Page 159 and 160: Nederlandse Samenvatting 151Figuur
Page 161 and 162: Nederlandse Samenvatting 153infraro
Page 163 and 164: English SummarySTARS are born, live
Page 165 and 166: English Summary 157Figure 2-. Two e
Page 167 and 168: English Summary 159PHOTOIONIZATIONR
Page 169 and 170: English Summary 161Figure 5-. Spect
Page 171 and 172: English Summary 163all) stages of i
Page 173 and 174: BibliographyAcker A., Marcout J., O
Page 175 and 176: BIBLIOGRAPHY 167Henry R.B.C., Kwitt
Page 177 and 178: BIBLIOGRAPHY 169Pottasch S.R., Bern
Page 179 and 180: List of PublicationsPublications in
Page 181 and 182: AcknowledgementsI could easily writ
Page 183: Acknowledgements 175sense of humor,
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