thesis - IRS, The Infrared Spectrograph

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158 English SummaryFigure 3–. The elliptical nebula (left) M 57 also called the Ring Nebula compared to the bipolar nebulaMz 3 (right). The causes of this differences in shape among Planetary Nebulae is still a matter of debateamong astronomers. Photo credits: M 57 → Hubble Heritage Team (AURA/STScI/NASA). Mz 3 →NASA, ESA and The Hubble Heritage Team (STScI/AURA).is hot enough to light up the ejected envelope; the planetary nebulae phase has started. Thisgas that is being light up by the central star is called Planetary Nebula. This phase of stellarevolution is very short in comparison to the whole life of a star, it lasts only about 10 000years. The nuclear reactions that have occurred in the interior of the star have resulted ina core of carbon and oxygen. The core of the star is not sufficiently hot to ignite nuclearreactions to transform carbon and oxygen into other elements and produce more energy. Atthis point the nuclear reactions stop. The star cools down and dies and the ejected envelopewill also fade away since it is no longer illuminated.Earlier, during the rapid (∼1000 years) transition from the giant branch to the planetarynebula phase, the central object may drive strong jets in its surroundings. Also, during theplanetary nebula phase, the hot central star develops a fast (∼1000 km/s) stellar wind. Thesejets and fast stellar winds sculpt the more or less spherical winds ejected during the giantbranch evolution, shaping the planetary nebula in all its beautiful forms (see Fig. 3). Theinteraction of these winds leads to strong shocks which heat and compress the gas. The gasis of course also heated through the interaction with stellar photons. The relative importanceof these two processes – dynamical heating and radiation heating – is not always obvious forlines originating in the neutral and molecular gas.Physical processesStarlight as a source of informationThe light received from a star can tell a lot to an astronomer. It can be used not only todeduce how bright the star is, but also can reveal temperature and composition. Elements(carbon, nitrogen, neon etc..) are composed of protons, neutrons and electrons. The electronsare bound to the nucleus by the electromagnetic force. For instance the element carbon isformed by six protons (positive charge) and six neutrons (neutral charge) that constitute itsnucleus and 6 electrons (negative charge) orbiting it. In this form the atom will be denoted asC 0 (6 positive charges - 6 negative charges =0). These electrons orbit the nucleus at a certain
English Summary 159PHOTOIONIZATIONRECOMBINATIONE5free electronCradiation from the starspectrometerphotonBEnergyE4E3E2E 1A400 nm 700 nmgamma raysX−raysultravioletvisibleinfrared0.01 nm 10 nmwavelengthmicrowavesradio1 mm 1 cmFigure 4–. On the left the permitted levels for an electron in an atom and various processes involvingthese levels are illustrated. See text for explanation of the different cases. On the right: The star is emittingradiation which after passing through a spectrometer is decomposed into its different components.distance which can vary depending on the energy of the electron. This distance cannot beany distance but only certain distances, in other words, the electrons can only have certainenergies and actually they will tend to orbit at the lowest energy levels (closer to the nucleus).We can relate the energy of an electron to the speed at which it is moving. The more energythey have, the faster they move.As an example the possible orbits of an electron in an atom are represented by theircorresponding energy levels in the left panel of Fig. 4; an explanation is given below:• Case A. When an electron goes from a higher to a lower energy level the excess inenergy is emitted as a photon. This photon is light!!The photon emitted will have an energy equal to the energy difference of the levels, inthis case E 3 -E 2 .• Case B. A photon hitting the atom or collisions among atoms can excite an orbitingelectron to a higher energy level. If the energy input from the photon or collision ishigh enough the electron will move very fast and can escape from the atom; this iscalled photo-ionization. The atom will have an electron less and for instance, in thecase of carbon, will be denoted as C + (6 protons with positive charge - 5 electrons ofnegative charge = +1). An element can lose as many electrons as it has (6 in the case ofcarbon), but every time one electron is pulled out, the others get more strongly attachedto the atom and therefore the energy of the radiation needed to pull another electron outincreases, in other words, the electron has to move faster to escape the atom. When anelement loses an electron, we say that this element is singly ionized. If it loses anotherelectron it will be doubly ionized (C 2+ ). In general, ionized atoms (C + , C 2+ etc...) arecalled ions.• Case C. Free electrons can get captured again by an atom; this is called recombination.These electrons recombine to a certain energy level, and from there they can graduallygo to the lowest energy state producing light as in Case A.There are many elements in a star and they all emit photons. Thus, the starlight that wesee is a combination of all the photons that escape from the star. This combination of photons
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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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5.7. Summary and conclusions 103Fig
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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
Page 145 and 146: 6.12. Summary and Conclusions 137su
Page 147 and 148: 7Conclusions and future workTHE res
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: English Summary 157Figure 2-. Two e
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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thesis - IRS, The Infrared Spectrograph

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