University of Groningen Photo-Ionization Studies Of

University of Groningen

Photo-ionization studies of nebulae Hoof, Peter Andreas Maria van

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Publication date: 1997

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Citation for published version (APA): Hoof, P. A. M. V. (1997). Photo-ionization studies of nebulae s.n.

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Download date: 10-02-2018 PHOTO-IONIZATION STUDIES OF NEBULAE Cover: The cover shows the planetary nebula NGC 6543 (the cat’s-eye nebula). The original image was taken with the Hubble Space Telescope and is distributed by STScI. This image and many others can be found on: http://oposite.stsci.edu/pubinfo/Subject.html The spectrum shown on the cover is a synthetic SWS spectrum, based on the CLOUDY model of NGC 6543 presented in Chapter 6. RIJKSUNIVERSITEIT GRONINGEN

Photo-Ionization Studies of Nebulae

Proefschrift ter verkrijging van het doctoraat in de Wiskunde en Natuurwetenschappen aan de Rijksuniversiteit Groningen op gezag van de Rector Magniﬁcus Dr. F. van der Woude in het openbaar te verdedigen op vrijdag 19 september 1997 des namiddags te 2.45 uur

door

Peter Andreas Maria van Hoof

geboren op 17 juli 1959 te Heer (Limburg) Promotor : Prof. Dr. S.R. Pottasch Copromotor : Dr. J.M. van der Hulst Referenten : Dr. L.B.F.M. Waters : Dr. M.W.M. de Graauw v

Contents

Nederlandse samenvatting 1 De evolutie van sterren ix 2 Openstaande vragen x 3 Waarnemingen en modellen van planetaire nevels x 4 Inhoud van dit proefschrift xi

1 Introduction 1.1 The late stages of stellar evolution 1 1.1.1 Nebular abundances 2 1.1.2 The Hertzsprung-Russell diagram 3 1.1.3 The shaping of planetary nebulae 3 1.1.4 Direct observation of central star evolution 4 1.2 The Infrared Space Observatory 4 1.2.1 The ISO spectrometers 5 1.3 Outline 5 1.4 References 6

2 Photo-ionization modeling of planetary nebulae 2.1 Introduction 7 2.2 The method 9 2.3 Testing the method 11 2.3.1 The artificial test model 11 2.4 The influence of measurement errors 12 2.4.1 The emission lines 12 2.4.2 The angular diameter, radio flux and the IRAS fluxes 16 2.5 Different model assumptions 19 2.5.1 The distance and the filling factor 19 2.5.2 Modeling more realistic nebulae 20 2.6 Modeling of some galactic bulge PN 23 2.6.1 Individual remarks 23 2.6.2 Discussion 25 vi CONTENTS

2.7 Conclusions and future research 29 2.8 Appendix: Symbols 29 2.9 References 30

3 Measuring angular diameters of nebulae 3.1 Introduction 33 3.2 Assumptions and computational methods 34 3.2.1 Method 1: gaussian fits 35 3.2.2 Method 2: second moments 35 3.3 The conversion factor for simple geometries 35 3.3.1 The constant surface brightness disk 36 3.3.2 The constant emissivity shell 36 3.4 Comparison of the results 36 3.4.1 Comparison with a different technique 36 3.4.2 Comparison with published results 37 3.5 Optical depth effects 39 3.6 Imaging in emission lines 40 3.7 Non-constant density geometries 40 3.8 Conclusions 42 3.9 References 42 3.10 Appendix: Determining diameters using gaussian fits 43 3.10.1 Fitting a gaussian to a surface brightness profile 43 3.10.2 An expression for the convolved surface brightness profile 45 3.10.3 The width of the convolved surface brightness profile 46 3.11 Appendix: Determining diameters using second moments 50 3.12 Appendix: Additional proofs 51 3.13 Appendix: Symbols 54

4 The spectral evolution of post-AGB stars 4.1 Introduction 55 4.2 The central star evolution 56 4.2.1 Determination of the evolutionary timescales 57 4.2.2 The inﬂuence of mass loss on the evolutionary timescales 58 4.2.3 Distribution over spectral type 59 4.3 The model 60 4.3.1 Density proﬁles of the circumstellar shell 61 4.3.2 The AGB circumstellar shell 62 4.3.3 Expansion velocities 62 4.4 The model runs 62 4.4.1 Silicate dust 64 4.4.2 Carbon-rich dust 67 4.4.3 Constant mass loss 69 4.4.4 Different end of the AGB 69 4.4.5 A near-IR color-color diagram 70 4.5 Discussion and conclusions 71 4.6 References 72 CONTENTS vii

5 Radio and infrared emission from a [WC] type planetary nebula in the LMC 5.1 Introduction 73 5.2 Observations 74

5.3 The radio–H discrepancy 74 5.4 IRAS detections of LMC planetary nebulae 75 5.5 A model for the optical, IRAS and radio data of SMP 58 76 5.6 Comparison with galactic [WC] stars 78 5.7 Other possible causes for blue IRAS colors 78 5.8 Conclusions and future prospects 79 5.9 References 79

6 The central stars of the planetary nebulae NGC 7027 and NGC 6543 6.1 Introduction 81 6.2 The ISO SWS observations 81 6.3 The photo-ionization models 82 6.4 Discussion of the NGC 7027 results 83 6.5 Discussion of the NGC 6543 results 84 6.6 Conclusions 84 6.7 References 85

7 Conclusions and outlook 7.1 Conclusions 87 7.2 Outlook 89

APPENDIX

8 Changes to cloudy Implementation 8.1 New and changed cloudy commands 93 8.2 Changes to the output 98 8.2.1 Compilation identiﬁer 98 8.2.2 Output units 98 8.2.3 Output frequency 98 8.2.4 Additional model output 98 8.2.5 Additional optimizer output 100 8.3 Additional emission lines 100 8.4 References 100 xiii

Acknowledgments

First of all I would like to thank my supervisors Stuart Pottasch, Thijs van der Hulst, Rens Waters and Thijs de Graauw for making this promotion possible, for all their support in the past five years and for giving me all the freedom I could ever wish for. I would like to thank Griet Van de Steene for her very friendly and stimulating collaboration, which I hope will continue for many years to come. Griet, your work and ideas were very important in finding my way in astronomy and I have little doubt that they will remain to do so in the future. Yourintuition,which enabled you to detect any weak spot in my reasoning immediately, never ceased to amaze me. I also wish to thank Rene Oudmaijer for his friendship and support. Rene, I always admired your thorough knowledge of the literature, something I could only wish to equal. I must mention that I have learned much from our collaboration. All of this makes it very regrettable that you switched to another line of research; nevertheless I wish you lots of success. Furthermore I would like to thank my other co-authors Bert Zijlstra, Cecile Loup, Douwe Beintema and Fred Lahuis for their pleasant collaboration. I would like to thank Gary Ferland for making his photo-ionization code CLOUDY available and for his help in modifying and debugging this code. Without all of this, this thesis would not have been possible. I would liketo thank the computer group for all of their support and for creating a superb computer system here in Groningen. More in particular I would like to thank Wim Zwitser and Kor Begeman which have helped me on many occasions. Their support can only be characterized as above and beyond the call of duty. Also I would like to thank Nanne Zuidema for the fact that he always had a friendly word for me. Furthermore I would like to thank our secretaries Jantina Hoving, Gineke Alberts en Jacky Zwegers-Morris for all of their help and patience with my clumsy way of dealing with bureaucracy. I would liketo thank ASTRON, the Leids Kerkhoven Bosscha Fonds, the Kapteyn Institute, SRON Groningen,the European Union and ESO for the financial support I received in the past five years. I thank the rest of the Kapteyn institutefor the pleasant atmosphere they created and which made my work always enjoyable. Last but not least, I would like to thank all those people which I inadvertently forgot to mention, but whose help nevertheless was very much appreciated.