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Extremely Extended Dust Shells Around Evolved Intermediate Mass Stars: Probing Mass Loss Histories,Thermal Pulses and Stellar Evolution

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Extremely Extended Dust Shells Around Evolved Intermediate Mass Stars: Probing Mass Loss Histories,Thermal Pulses and Stellar Evolution EXTREMELY EXTENDED DUST SHELLS AROUND EVOLVED INTERMEDIATE MASS STARS: PROBING MASS LOSS HISTORIES,THERMAL PULSES AND STELLAR EVOLUTION A Thesis presented to the Faculty of the Graduate School at the University of Missouri In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy by BASIL MENZI MCHUNU Dr. Angela K. Speck December 2011 The undersigned, appointed by the Dean of the Graduate School, have examined the dissertation entitled: EXTREMELY EXTENDED DUST SHELLS AROUND EVOLVED INTERMEDIATE MASS STARS PROBING MASS LOSS HISTORIES, THERMAL PULSES AND STELLAR EVOLUTION USING FAR-INFRARED IMAGING PHOTOMETRY presented by Basil Menzi Mchunu, a candidate for the degree of Doctor of Philosophy and hereby certify that, in their opinion, it is worthy of acceptance. Dr. Angela K. Speck Dr. Sergei Kopeikin Dr. Adam Helfer Dr. Bahram Mashhoon Dr. Haskell Taub DEDICATION This thesis is dedicated to my family, who raised me to be the man I am today under challenging conditions: my grandfather Baba (Samuel Mpala Mchunu), my grandmother (Ma Magasa, Nonhlekiso Mchunu), my aunt Thembeni, and my mother, Nombso Betty Mchunu. I would especially like to thank my mother for all the courage she gave me, bringing me chocolate during my undergraduate days to show her love when she had little else to give, and giving her unending support when I was so far away from home in graduate school. She passed away, when I was so close to graduation. To her, I say, ′′Ulale kahle Macingwane.′′ I have done it with the help from your spirit and courage. I would also like to thank my wife, Heather Shawver, and our beautiful children, Rosemary and Brianna , for making me see life with a new meaning of hope and prosperity. I also thank my long - term child-hood friend, Tholinhlanhla Henry Ngcobo for helping me during trying times and furthermore for his encouragement repeat grade 11 that I already passed in order to do physical science at Mqhakama high school in South Africa. These early periods marked the beginning of my science career that has led to this position I am in today. During heavy moments while writing this thesis, I got encouraged by looking back in time when my friend and I used stones and the sticks arguing about space geometry from our mathematics class, while taking our long walks back from school. This has been / still is a long journey worth taking as I am begining to realize that there is still a lot to learn concerning the physics of the stars and their recycling of their material in space, all of which is connected to the science of our well being. ACKNOWLEDGMENTS I would like to thank Dr. Peter. Abrahams at Kolonky observatory / Max– Planck Insitute for Physics for helping me with ISO data analysis, and also his useful comments about the PHT32 data; especially, the reduction and analysis of Omi Cet - Mira observations. I am also thankful to the Spitzer help desk for assistance on MIPS data especially with PSF subtraction. I recieved very useful comments from Dr Tuan Do, Professor Mark Morris at UCLA on Mips data. I would not have done this thesis without my adviser Dr. Angela Speck for making this research the whole success. ii TABLE OF CONTENTS ACKNOWLEDGMENTS .......................... ii LISTOFTABLES .............................. viii LISTOFFIGURES ............................. x ABSTRACT ................................. xxv CHAPTER .................................. 1 Introduction ................................ 1 2 Intermediate Mass Stars and their Evolution . 22 2.1 Intermediate Mass Stars and the Hertzsprung-Russell Diagram. 22 3 Asymptotic Giant Branch Stars . 34 3.1 EarlyAsymptoticGiantBranch . 34 3.2 StructureofanAGBStar ........................ 35 3.3 AtmospheresofAGBstars . 38 3.4 ThermallypulsingAGB ......................... 42 3.4.1 The effect of Core Mass on Thermal Pulses . 45 12 3.5 Production of Carbon (6 C) during thermal pulsing AGB phase . 47 3.6 Nucleosynthesis at AGB phase . 49 3.6.1 Hydrogen - shell burning site . 50 3.6.2 Helium shell burning site . 52 3.6.3 Helium shell producing s-process elements . .. 53 3.6.4 HotBottomBurning-HBB . 59 4 Mass loss and dust formation . 62 iii 4.1 Introduction................................ 62 4.2 HistoricalreviewofMassloss . 64 4.3 TheEffectofDustFormationonMassLoss . 69 4.4 DynamicsofGasandDustmotion . 70 4.4.1 Momentumtransferbyphotons . 70 4.4.2 Motionofgasanddustparticles. 72 4.5 AGB Mass loss and Stellar Evolution Models . .. 80 4.6 Spectroscopic Observations of Mass loss . .... 87 4.6.1 PCygniinhotstars ....................... 87 4.6.2 AtomicEmissionlines . 88 4.6.3 Molecular Emission lines . 88 5 Thermal Emission from Dust . 90 5.1 Introduction................................ 90 5.2 DustGrainOpacities ........................... 91 5.3 Equilibrium temperature of the dust in circumstellar shells ...... 99 5.4 Determination of the mass of the dust contained in the circumstellar shell .................................... 102 5.5 Mass of the Circumstelar Dust Shell . 104 5.5.1 MassofgastoDust.. .. .. 105 5.5.2 Spectral index (β)fromFIRemission . 106 5.6 DustMassLossRatesbyFIRemission . 109 5.7 Other methods of getting the flux density . 113 5.8 RadiativeTransfer ............................ 114 6 Observations ............................... 115 6.1 Introduction................................ 115 iv 6.1.1 ISO-Imaging photo-polarimeter: ISOPHOT . 116 6.1.2 Photometry ............................ 123 6.1.3 ISOPHOTbackgrounds . 127 6.1.4 DataReduction.......................... 129 6.2 MappingAlgorithms . .. .. .. 131 6.3 ExtendedEmission ............................ 132 7 Probing Dust Around Oxygen-rich Stars . 137 7.1 Introduction................................ 137 7.2 ISOPHOT PHT C 32 Observations of six O-rich AGB stars . 138 7.3 Analysisofradialprofiles. 142 7.3.1 1–DPSFSubtraction. 151 7.4 Circumstellar dust shell size determination . ...... 154 7.4.1 ObservationSimulations . 158 7.4.2 Gaussians fitted in oxygen – rich radial profiles . 159 7.5 Circumstellar dust flux in the extended emission . .... 168 7.5.1 Emisivity and Dust temperature . 169 7.6 Mass of circumstellar dust shell and the mass of the core . ...... 169 7.7 TimeScales ................................ 171 7.8 Disscusion ................................. 172 7.8.1 Oxygen rich results comparison with Initial mass relations . 174 8 Probing Dust around C-rich stars . 175 8.1 Introduction................................ 175 8.2 CarbonRichstarsObservations . 176 8.3 Imagesandradialprofilesresults . 178 8.3.1 PHT32ImagesofCarbon–richstars . 178 v 8.3.2 Linear Scan results: Radial profiles . 185 8.4 Analysis of radial profiles for Carbon rich stars . ...... 187 8.4.1 Carbonrichstars: 1–DPSFSubtraction . 187 8.4.2 Gaussians fitted on carbon – rich stars radial profiles . .... 194 8.5 Flux measured in the extended emission . 203 8.6 Mass of circumstellar dust shell and the mass of the core . ...... 204 8.7 Timescalesderived ............................ 205 8.8 Discussion on the results on carbon rich stars . .... 206 8.8.1 Carbon rich result′s comparison with Initial - final mass relations208 9 Summary and concluding remarks . 209 BIBLIOGRAPHY .............................. 213 APPENDIX .................................. 234 A Primer on stellar properties and related physics . 234 A.1 Main-sequence: Nucleosynthesis at the Hydrogen burningCore. 240 A.1.1 Evolution on the main sequence of intermediate mass stars . 256 A.1.2 Sh¨onberg - Chandrasekhar limit . 259 A.1.3 Convective Envelope of Intermediate mass stars at main sequence260 A.1.4 Electron degeneracy of CO core of an intermediate mass star . 262 A.2 Evolutionoffmainsequence . 264 A.2.1 Subgiantphase .......................... 266 A.2.2 RedGiantphase ......................... 267 A.2.3 Horizontal Branch Stars and Helium burning . 270 A.3 Nucleosynthesis at AGB phase . 273 12 A.3.1 Production of Carbon (6 C) during thermal pulse . 273 A.3.2 Lithium production during Hot bottom burning . 274 vi A.4 The interplay of Luminosity and Pulsation of AGB stars . ..... 277 A.4.1 Period - Luminosity relations . 277 A.5 PostAGBEvolution ........................... 284 A.5.1 The formation of Planetary Nebula and White Dwarfs . 284 A.6 ProtoPlanetaryNebula . 288 A.6.1 Theplanetarynebulastage . 290 A.7 Initial Masses and Luminosity Variations . .... 292 A.7.1 Initialmassrelations(IMF) . 292 B Initial Mass Function Relations . 296 B.1 Theoretical framework of IMF in AGB populations . 296 C General Radiative Transfer Equation . 298 C.1 Spectroscopic Observations of Mass loss . .... 299 C.1.1 PCygniinhotstars . .. .. 300 C.1.2 AtomicEmissionlines . 300 C.1.3 Molecular Emission lines . 301 D Programs developed for data analysis . 302 D.0.4 FittingGaussianprofiles . 302 D.0.5 Calculation of emissivity and dust temperature . 307 VITA ...................................... 312 vii LIST OF TABLES Table Page 6.1 Photometricparameters . 125 7.1 Selected target evolved oxygen-rich intermediate-mass stars imaged by Infrared Space Observatory (ISO) using far-infrared PHT32-C camera. 139 7.2 Basic observed parameters of target O-rich evolved stars. ....... 139 7.3 ISO PHT C32 observational information for six target evolved oxygen- rich. .................................... 140 1 7.4 Flux brightnesses from Figures 7.1 – 7.6 in MJy sr− . ......... 140 7.5 Simulations ................................ 158 7.6 Full width half maximum values derived from the fitted gaussian pro- filestoobservedradialprofiles . 161 7.7 Observed fluxes used to calculate dust masses . 168 7.8 Dust temperature
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