Cover Page
The handle
http://hdl.handle.net/1887/79194
holds various files of this Leiden University
dissertation.
Author: Bosman, A.D.
Uncovering the ingredients
for planet formation
Proefschrift
ter verkrijging van
de graad van Doctor aan de Universiteit Leiden, op gezag van Rector Magnificus prof. mr. C.J.J.M. Stolker,
volgens besluit van het College voor Promoties te verdedigen op woensdag 8 oktober 2019
klokke 16:15 uur door
Arthur Daniel Bosman
Promotiecommissie
Promotores: Prof. dr. E. F. van Dishoeck Prof. dr. A. G. G. M. Tielens
Overige leden: Prof. dr. H. J. A. Röttgering Prof. dr. B. R. Brandl
Prof. dr. E. A. Bergin University of Michigan
Dr. J. R. Najita National Optical Astronomy Observatory Dr. K. M. Pontoppidan Space Telescope Science Institute
ISBN: 978-94-028-1688-4 Front cover:
Contents
1 Introduction 1
1.1 Star and planet formation . . . 1
1.1.1 The initial stages of star formation . . . 3
1.1.2 Disk formation and evolution . . . 4
1.1.3 Disk structure . . . 5
1.1.4 Dust evolution . . . 8
1.1.5 Planet formation . . . 10
1.2 Astrochemistry . . . 11
1.2.1 Gas-phase chemistry . . . 11
1.2.2 Grain surface chemistry . . . 12
1.2.3 Chemistry in disks . . . 12
1.3 Infrared spectroscopy . . . 13
1.3.1 Energy levels and transitions . . . 14
1.3.2 Line formation . . . 14
1.3.3 Observational challenges . . . 17
1.4 Disk modelling . . . 19
1.5 This thesis . . . 19
1.5.1 Future outlook . . . 21
2 CO destruction in protoplanetary disk midplanes: inside versus out-side the CO snow surface 23 2.1 Introduction . . . 25 2.2 Methods . . . 27 2.2.1 Parameter space . . . 27 2.2.2 Chemical network . . . 28 2.2.3 CO destruction routes . . . 31 2.3 Results . . . 34
2.3.1 Physical parameter space . . . 34
2.3.2 Chemical parameter space . . . 40
2.4 Discussion . . . 42
2.4.1 When, where and how is CO destroyed within 3 Myr . . . 43
2.4.2 Implications for observations . . . 45
2.4.3 Observing chemical destruction of CO . . . 46
2.4.4 Interactions with disk dynamics . . . 47
2.5 Conclusions . . . 47
Appendix . . . 49
2.A Dali protoplanetary disk models . . . 49
ii CONTENTS
2.B.1 Initial abundances . . . 52
2.B.2 H2 formation rate . . . 53
2.B.3 Calculation of grain-surface rates . . . 53
2.B.4 Implications of modelling assumptions . . . 54
3 CO2 infrared emission as a diagnostic of planet-forming regions of disks 57 3.1 Introduction . . . 59
3.2 Modelling CO2 emission . . . 62
3.2.1 Vibrational states . . . 62
3.2.2 Rotational ladders . . . 62
3.2.3 Transitions between states . . . 64
3.2.4 CO2 spectra . . . 65
3.2.5 Dependence on kinetic temperature, density and radiation field 68 3.3 CO2 emission from a protoplanetary disk . . . 68
3.3.1 Model setup . . . 70
3.3.2 Model results . . . 71
3.3.3 Line-to-continuum ratio . . . 83
3.3.4 CO2 from the ground . . . 84
3.3.5 CO2 model uncertainties . . . 86
3.4 Discussion . . . 87
3.4.1 Observed 15 µm profiles and inferred abundances . . . 87
3.4.2 Tracing the CO2 iceline . . . 91
3.4.3 Comparison of CO2 with other inner disk molecules . . . 94
3.5 Conclusion . . . 94
Appendix . . . 95
3.A Collisional rate coefficients . . . 95
3.B Fast line ray tracer . . . 97
3.C Model temperature and radiation structure . . . 97
3.D Model fluxes g/ddust . . . 98
3.E LTE vs non-LTE . . . 98
3.F Line blending by H2O and OH . . . 102
3.G Spitzer -IRS spectra . . . 104
4 Efficiency of radial transport of ices in protoplanetary disks probed with infrared observations: the case of CO2 107 4.1 Introduction . . . 109
4.2 Physical model . . . 111
4.2.1 Gas dynamics . . . 111
4.2.2 Dust growth and dynamics . . . 112
4.2.3 Model parameters . . . 115
4.2.4 Boundary conditions . . . 116
4.3 Chemical processes . . . 116
4.3.1 Freeze-out and sublimation . . . 116
4.3.2 Midplane formation and destruction processes . . . 118
4.3.3 Simulating spectra . . . 123
4.4 Results . . . 123
4.4.1 Pure viscous evolution . . . 123
CONTENTS iii
4.4.3 Viscous evolution and CO2destruction . . . 127
4.4.4 Viscous evolution, grain growth and CO2 destruction . . . 129
4.4.5 Model spectra . . . 129
4.5 Discussion . . . 134
4.5.1 Chemical processes . . . 134
4.5.2 Physical processes . . . 136
4.6 Summary and conclusions . . . 142
Appendix . . . 144
4.A UV dust cross sections . . . 144
4.B Chemical modelling . . . 144
4.B.1 Gas-phase only models . . . 144
4.B.2 Grain surface chemistry between the H2O and CO2 icelines . . 146
4.C Viscous evolution and grain growth . . . 147
5 Probing planet formation and disk substructures in the inner disk of Herbig Ae stars with CO rovibrational emission 153 5.1 Introduction . . . 155
5.2 Data overview . . . 159
5.3 Slab modelling of the vibrational ratio . . . 160
5.3.1 Analytical line ratios . . . 161
5.3.2 RADEX models . . . 164
5.3.3 LTE vs non-LTE . . . 165
5.3.4 Absolute fluxes . . . 165
5.3.5 Physical conditions in the CO emitting region . . . 169
5.4 DALI modelling . . . 169
5.4.1 Model setup . . . 169
5.4.2 Model results . . . 173
5.4.3 Disk surface emission . . . 176
5.4.4 Tgas≈ Tdust . . . 179
5.5 Discussion . . . 180
5.5.1 Implications for sources with low v2/v1 at small radii . . . 184
5.5.2 Implications for high v2/v1 at large radii . . . 188
5.5.3 Comparison to T-Tauri disks: distribution of UV flux matters . 189 5.5.4 Predictions for future observations . . . 191
5.6 Conclusions . . . 192
Appendix . . . 193
5.A CO molecule model . . . 193
5.A.1 Rovibrational . . . 193
5.A.2 Electronic . . . 193
5.B Excitation tests . . . 194
5.C Line profiles . . . 196
5.D Near-infrared excess . . . 196
5.D.1 CO as tracer of the inner disk radius . . . 196
5.E Lowering the flux of the outer disk . . . 201
iv CONTENTS
6 The dry and carbon poor inner disk of TW Hya: evidence for a
gigantic icy dust trap 205
6.1 Introduction . . . 207
6.2 Methods . . . 208
6.3 Results . . . 209
6.4 Discussion . . . 212
6.4.1 Constraining the inner disk chemical structure . . . 212
6.4.2 Hiding C and O carriers? . . . 212
6.4.3 Implications of uniform depletion . . . 213
Appendix . . . 214
6.A DALI model . . . 214
Bibliography 214
Nederlandse samenvatting 231
List of Publications 237
Curriculum Vitae 239
