thesis - IRS, The Infrared Spectrograph

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50 CHAPTER 4: Abundances of Planetary Nebulae BD+30 3639 and NGC 65434.1 IntroductionBoth BD+30 3639 and NGC 6543 have a low temperature exciting star which translates intoa spectrum dominated by lines of ions with low ionization potential. Past abundance studiesof these two Planetary Nebulae (PNe) have been mostly focused on the optical and ultravioletspectra. Nevertheless, some lines from important stages of ionization (those which contributemost to the total abundance) of some elements lie in the infrared region of the spectrum andhad to be inferred in previous studies. The inclusion of the infrared data from the ISO satelliteallows us to accurately derive abundances of neon, argon, sulfur and chlorine. They alsoprovide complementary information of other important stages of ionization such as N ++ andO 3+ and have the advantage that they are not temperature dependent. The extinction plays aminor role in these lines. Other advantages of the infrared data have been briefly discussed byBeintema & Pottasch (1999) and Bernard Salas et al. (2001, chapter 2). All these advantageshave allowed us to derive accurate abundances for both PNe.4.1.1 BD+30 3639BD+30 3639 is a compact planetary nebula with a low extinction and a carbon Wolf–Rayetcentral star. It has been the object of many previous studies. Earlier observations with theInternational Ultraviolet Explorer (IUE) were reported by Torres-Peimbert & Peña (1981).Pwa et al. (1986) derived ionic abundances for several ions, and using ionization correctionsfactors (ICF), derived the total abundances for some elements. They found the dust-to-gasratio to be 1.8%, and determined an extinction for the interstellar component of E B−V =0.12.Using the P Cygni profile of the C III 2297 Å line they find a terminal velocity of 790 ± 50km/s. A recent X-ray study of this nebula by Kastner et al. (2000) using the ACIS instrumenton board the Chandra X-ray Observatory shows that the X-ray emission originates within theionized gas, and is concentrated to one side. They found T X = 3 × 10 6 K. The spectroscopicstudy reveals that the X-ray emitting region may be enriched as a result of nuclear burning.An optical and near-infrared study was made by Rudy et al. (1991), while Aller & Hyung(1995) used high resolution observations from the Hamilton echelle spectrograph at LickObservatory to study the physical conditions and abundances of the nebula. They foundan electron density (N e ) of 10 000 cm −3 and an electron temperature (T e ) of 8800 K, andabundances very similar to solar. In spite of all these studies BD+30 3639 still needs moreattention. The SWS infrared spectrum shows silicates, which are related to oxygen rich PNe,and Polycyclic Aromatic Hydrocarbon (PAHs) features, related to a carbon-rich nebula . Thisremains a puzzle.4.1.2 NGC 6543PN NGC 6543 shows a very interesting morphology with bubbles and an extended halo. Ithas a central star classified as Of/WR. The diameter of the nebula is 19.5 ′′ (Hyung et al.2000), and it has a halo with a radius of 165 ′′ (Middlemass et al. 1989). Castor et al. (1981)using IUE observations estimated the terminal velocity of the wind to be 2150 km/s anddeduced a mass-loss rate of 1.0 × 10 −7 M ⊙ /yr. Aller & Czyzak (1979) studied a sampleof 40 PNe, with emphasis on the weak lines, including NGC 6543. X-ray observations havebeen done by Guerrero et al. (2001) and they have detected a point source at the position ofthe central star of NGC 6543. They derived a X-ray temperature of a few times 10 6 K. A
4.2. Observations and data reduction 51recent study, in terms of physical conditions and abundances, has been carried out by Hyunget al. (2000). They combine Hamilton echelle observations in two positions (east and north ofthe central star), with IUE data. They found an T e = 8000∼8300 K and an N e = 5000 cm −3 .They predicted a progenitor mass star of ∼ 1 M ⊙ . Manchado & Pottasch (1989) presentedobservations of the central region and the halo of NGC 6543. For the central region theyderived N e =4000 cm −3 and T e =7000 K. For the halo they obtained a higher temperature andconcluded that the radiation from the halo is thermal and not due to dust reflection. A detailedstudy of different parts of the halo can be found in Middlemass et al. (1989) comparing theabundances of the halo with the central core of the nebula.4.1.3 Layout of this chapterIn the next section the observations and reduction analysis is briefly discussed. Sect. 4.3discusses the possibility for the need of aperture corrections. In Sect. 4.4 the infrared data ispresented and the extinction derived. The optical and IUE data used in this study is listed inSect. 4.5. The physical parameters are derived in Sect. 4.6 and the abundances in Sect. 4.7.Conclusions are given in the last section.4.2 Observations and data reduction4.2.1 ISO observationsSWS observationsThe Short Wavelength Spectrometer on board ISO (de Graauw et al. 1996) covers thespectral range from 2.38 to 45.2 µm. ISO-SWS uses different size apertures for four differentspectral regions. These apertures are 14 ′′ x20 ′′ , 14 ′′ x27 ′′ , 20 ′′ x27 ′′ and 20 ′′ x33 ′′ and coverrespectively the wavelength intervals: 2.38–12.0 µm, 12.0–27.5 µm, 27.5–29 µm and29.0–45.2 µm.The observations used for BD+30 3639 and NGC 6543 correspond to the SWS01observing template. The observation number for BD+30 3639 is TDT=86500540. It is aslow observation, Speed 3, which corresponds to an exposure time of 3453 seconds. Itwas centered at RA(2000) 19 h 34 m 45.2 s and Dec(2000) +30 ◦ 30 ′ 58.8 ′′ . For NGC 6543the observation used is TDT= 02400714. This is a Speed 4 (slow) observation of 6544seconds. It was centered at RA(2000) 17 h 58 m 33.4 s and Dec(2000) +66 ◦ 37 ′ 59.5 ′′ . Theobservations were pointed at the center of the nebulae. The pointing errors for ISO are ∼1.5 ′′ .A description of the tools used to reduce the data can be found in the interactive analysissoftware package which is distributed by the SWS consortium, IA3 (de Graauw et al. 1996).Each wavelength range is covered by both an up and a down scan. Each is sampled by twelvedetectors. Both scans were reduced separately and combined to produce the spectra seen inFig. 4.1. The reduction consists of several steps;• Dark current subtraction. Sometimes some detectors were affected by memory effectsand were not used when deriving the dark current.• De-fringing: Fringes were present in the BD+30 3639 spectrum. The patterns are severein bands 3A, 3C, 3D and 3E. These were removed using the IA tool fringes.
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RIJKSUNIVERSITEIT GRONINGENPhysics
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To my parents
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Contents1 Introduction 11.1 Evoluti
Page 7 and 8: CONTENTSvii5 Probing AGB nucleosynt
Page 9 and 10: 1IntroductionPLANETARY NEBULAE are
Page 11 and 12: 1.1. Evolution of low and intermedi
Page 13 and 14: 1.2. Planetary Nebulae 5Flash−Dri
Page 15 and 16: 1.3. Physics in PNe 7their whole li
Page 17 and 18: 1.3. Physics in PNe 95.35 eVO IIIλ
Page 19 and 20: 1.4. Studying PNe in the infrared 1
Page 21 and 22: 2The ISO-SWS Spectrum ofPlanetary N
Page 23 and 24: 2.3. Data reduction 15Table 2.1-. C
Page 25 and 26: 2.4. Line flux discussion 17Table 2
Page 27 and 28: 2.5. The visual and the ultraviolet
Page 29: 2.6. Analysis 21Table 2.5-. Electro
Page 32 and 33: 24 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 60 and 61: 52 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
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Page 87 and 88: 5.4. Nucleosynthesis in low- and in
Page 89 and 90: 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
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6Physical Conditions in PDRs around
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6.2. Observations 109are not promin
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6.4. General parameters of the PNe
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6.4. General parameters of the PNe
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Table 6.3-. Radius, Zanstra tempera
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6.6. Lines fluxes 117Figure 6.2-. S
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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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