Thesis Is Closely Related to This Question

UvA-DARE (Digital Academic Repository) The processing and evolution of dust in Herbig Ae/Be systems. Bouwman, J. Publication date 2001 Document Version Final published version Link to publication Citation for published version (APA): Bouwman, J. (2001). The processing and evolution of dust in Herbig Ae/Be systems. General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. UvA-DARE is a service provided by the library of the University of Amsterdam (https://dare.uva.nl) Download date:10 Oct 2021 Thee processing and evolution of dustt in Herbig Ae/Be systems Jeroenn Bouwman Thee processing and evolution of dust in Herbig Ae/Be systems s Thee processing and evolution of dust in Herbig Ae/Be systems s Dee evolutie van stof in Herbig Ae/Be systemen. Academischh Proefschrift terr verkrijging van de graad van doctor aann de Universiteit van Amsterdam, opp gezag van de Rector Magnificus prof. dr J.J.M. Franse, tenn overstaan van een door het college voor promoties ingestelde commissie, inn het openbaar te verdedigen in de Aula der Universiteit op p dinsdagg 25 september 2001, te 12:00 uur door r Jeroenn Bouwman geborenn te Zaandam PROMOTIF.CO.MMISSIH. PROMOTORFSS prof. dr L.B.F.M. Waters prof.. dr J.W. Hovenier CO-PROMOTORR dr A. de Koter OvF.RICHH LFDHX prof. dr E.P.J. van den Heuvel drr A. Natta prof.. dr T. de Jong prof.. dr P.M.A. Sloot prof.. dr A.G.G.M. Tielens prof.. dr C. Waelkens Sterrenkundigg Instituut "Anton Pannekoek' Faculteitt der Natuurwetenschappen Universiteitt van Amsterdam ISBNN 90-9015117-6 Cover/Omslag:: Scattering and absorption or light by silicate grains. TSJA, , ditt is r dan. Contents s 11 From dust to planets 1 1.11 Introduction 1 1.22 Pre-Main-Sequence evolution: T Tauri and Herbig Ac/Bc stars .... 3 1.33 Protoplanetary disks and dust processing 5 1.44 The geometry or the circumstellar disks 8 1.55 Conclusions & outlook 10 22 Dust physics, radiative transfer and spectral analysis 13 2.11 Radiative transfer 13 2.1.11 An optically thin medium 15 2.1.22 Radiative transfer in axisvmmetric geometry 16 2.22 Chemical composition and grain structure of circumstellar dust .... 18 2.2.11 Silicates 18 2.2.22 Other dust species 20 2.2.33 Dust chemistry 21 2.2.44 The grain structure 23 2.33 The optical properties of dust grains 24 2.3.11 The refractive index 24 2.3.22 Basic scattering theory 25 2.3.33 Extrapolation of the refractive index to short and long wavelengths 27 2.44 The spatial distribution of the dust 28 2.55 I he strategy of modeling 29 33 ISO spectroscopy of circumstellar dust in 14 Herbig Ae/Be systems: towards ann understanding of dust processing. 33 3.11 Introduction 34 3.22 Targets and Observations 36 3.2.11 Spectral Hnergy Distributions 38 3.2.22 Properties of the cold grains: mass and grain size 43 3.33 ISO-SWS spectra and their wealth of features 43 3.3.11 I he 2-7 micron wavelength region 45 3.3.22 The PAH bands .../../ 46 i i CONTENTS S 3.3.33 The silicates 47 3.3.44 The 23 micron feature 47 3.3.55 Notes on individual sources 47 3.44 Discussion 49 3.4.11 Geometry of the disc and its effects on the SED 50 3.4.22 Evidence for grain growth 53 3.4.33 Influence of the stellar age on dust properties 53 3.4.44 The amorphous silicate behaviour 54 3.55 Conclusion 55 44 Processing of silicate dust grains in Herbig Ae/Be systems 57 4.11 Introduction 58 4.22 Dust composition and spectral analysis 59 4.2.11 Adopted dust components and grain shapes 59 4.2.22 Spectral analysis 62 4.2.33 Detection of aliphatic hydrocarbons in HD 163296 64 4.33 Results 64 4.3.11 Correlations 68 4.3.22 Correlation to the overall Spectral Energy Distribution .... 73 4.44 Discussion 75 4.4.11 Explanation for the change of the 10 ^m feature 75 4.4.22 The chemical composition of the silicate dust 76 4.4.33 Deviating objects 77 4.55 Conclusions 79 55 The composition of the circumstellar dust around the Herbig Ae stars ABB Aur and HD 163296 81 5.11 Introduction 81 5.1.11 Geometry of the circumstellar dust 82 5.1.22 The onset of near-IR emission 84 5.22 Method and assumptions 85 5.2.11 Model approach and assumptions 85 5.2.22 Adopted chemical composition of the dust 87 5.33 Results 91 5.3.11 The 2—8/jm spectral region 93 5.3.22 The 8-30 /urn region 94 5.3.33 The cold dust component 97 5.3.44 PAHs and crystalline silicates 100 5.44 Discussion 101 5.55 Summary 104 ii i CONTENTS S 66 The formation of crystalline silicate dust: From HD100546 to Hale-Bopp 105 6.11 Introduction 106 6.22 The deviating dust composition and spectral energy distribution of HDD 100546 107 6.33 Modelling 110 6.3.11 Size and shape properties of grains Ill 6.3.22 Chemical composition of grains 112 6.44 Results H2 6.4.11 HD 100546 113 6.4.22 Hale-Bopp 121 6.55 Discussion 124 6.5.11 The mass temperature distribution 124 6.5.22 The disk structure of HD 100546 and the origin of the crys- tallinee silicates 128 6.66 Summary 131 77 Constraints on HAEBE disk geometry from Spectral Energy Distributions 133 7.11 Introduction 133 7.22 The disk model 134 7.33 Discussion 13o Nederlandsee samenvatting 141 Bibliographyy 146 iii i CONTENTS S IV V CHAPTERR 1 Fromm dust to planets 1.11 Introduction nee of rhe most intriguing questions in astronomy was, and is, how our solar system,, the sun, planets, and objects like comets were formed. The work pre- O sentedd in this thesis is closely related to this question. In the following chapters severall studies of young stellar objects (YSOs) are presented, which are believed to be in thee process of forming a planetary system. Though the process of star formation is far fromm completely understood, the most generally accepted view on how stars form was putt forward by Shu et al. (1987). Star formation can be divided into five distinct phases. Thee first phase is the formation of dense molecular cores inside a giant molecular cloud,, such as for instance the Orion nebula. Typically these cores have masses in the orderr of a few solar masses and sizes of less than a parsec. (see for instance Evans 1999, forr an overview of the core properties). The cores are initially supported against gravity byy magnetic fields and turbulence, but eventually will collapse due to processes such ass ambipolar diffusion (i.e. the drift of the magnetic field relative to the neutral gas), reducingg the magnetic field. This marks the beginning of the second evolutionary phase. Ass the slowly rotating core collapses, a central protostar and surrounding disk will form, stilll deeply embedded within an infalling envelope of gas and dust. In the third phase, as thee central star accretes matter through the disk, a strong stellar wind can develop along thee rotational axis of the system, creating a bipolar outflow. In the fourth phase, this stellarr wind will disperse the surrounding gas and dust terminating the infall of matter, leavingg the protostar and circumstellar disk. Finally, the dust and gas in the circumstellar diskk will be dispersed or incorporated into a planetary system. Observationallyy the last four phases in the formation of a star as described above, can bee identified by the spectral energy distribution (SED) of the YSOs. Lada and Wilking (1984)) suggested a classification based on the properties of the SED into three classes, whichh were shown to correspond to different evolutionary stages of the protostar (Adams ett al. 1987). This classification was expanded with an additional class (Class 0), after the discoveryy of a new group of objects by Andre et al. (1993) representing an earlier evolu- tionaryy phase. Fig. 1.1 shows a schematic representation of this classification. 1 he panels onn the left show the tvpical SED of objects within a group, the panels on the right show thee corresponding geometry or spatial distribution of material in the system. Class 0 objectss represent second phase of star formation, and are only visible at far infrared (1R) andd millimetre wavelengths. Class I objects represent the third phase in which the star iss still embedded, resulting in deep absorption features. Class II objects represent the 1 1 CHAPTERR 1 \ \ \\t \\t M M CLASSS II >"7 7 %% -8 n n /^ ^ -9 9"" , / / , ; 122 13 14 15 5 Logg v (Hz) Figuree 1.1: Schematic overview of the various stages in the formation of a star evolving from aa Class 0 to a Class III object (after Nana 1999).

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