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Quantitative spectroscopy of stellar atmospheres and clumped hot star winds [Elektronische Ressource] : new methods and first results for deriving mass-loss rates / submitted by Jon Sundqvist

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QUANTITATIVE SPECTROSCOPY OFSTELLAR ATMOSPHERES AND CLUMPEDHOT STAR WINDS- NEW METHODS AND FIRST RESULTS FORDERIVING MASS-LOSS RATES.Jon SundqvistQUANTITATIVE SPECTROSCOPY OFSTELLAR ATMOSPHERES AND CLUMPEDHOT STAR WINDS- NEW METHODS AND FIRST RESULTS FORDERIVING MASS-LOSS RATES.Dissertationan der Fakulta¨t fu¨r Physikder Ludwig–Maximilians–Universita¨t (LMU) Mu¨nchenPh.D. Thesisat the faculty of Physicsof the Ludwig–Maximilians–University (LMU) Munichsubmitted byJon Sundqvist¨from Ostersund, SwedenthMunich, September 29 2010st1 Evaluator: Priv. Doz. Dr. Joachim Pulsnd2 Evaluator: Prof. Dr. Andreas BurkertthDate of the oral Defense: 20 December 2010ContentsContents viiList of Figures xivList of Tables xvZusammenfassung xviiPreface xix1 Introduction 11.1 The role of mass loss from hot, massive stars in modern astrophysics . . . . . . . . 11.2 Stellar winds, mass loss, and evolution . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Radiation driven winds of hot, massive stars . . . . . . . . . . . . . . . . . . . . . . 31.4 A clumped hot star wind? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.4.1 Theoretical predictions of a small-scale inhomogeneous wind . . . . . . . . 41.4.2 Observational indications of an inhomogeneous wind . . . . . . . . . . . . . 41.4.3 Indirect indications of an inhomogeneous wind . . . . . . . . . . . . . . . . 51.4.4 Some implications of modified mass-loss rates due to wind clumping .

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QUANTITATIVE SPECTROSCOPY OF
STELLAR ATMOSPHERES AND CLUMPED
HOT STAR WINDS
- NEW METHODS AND FIRST RESULTS FOR
DERIVING MASS-LOSS RATES.
Jon SundqvistQUANTITATIVE SPECTROSCOPY OF
STELLAR ATMOSPHERES AND CLUMPED
HOT STAR WINDS
- NEW METHODS AND FIRST RESULTS FOR
DERIVING MASS-LOSS RATES.
Dissertation
an der Fakulta¨t fu¨r Physik
der Ludwig–Maximilians–Universita¨t (LMU) Mu¨nchen
Ph.D. Thesis
at the faculty of Physics
of the Ludwig–Maximilians–University (LMU) Munich
submitted by
Jon Sundqvist
¨from Ostersund, Sweden
thMunich, September 29 2010st1 Evaluator: Priv. Doz. Dr. Joachim Puls
nd2 Evaluator: Prof. Dr. Andreas Burkert
thDate of the oral Defense: 20 December 2010Contents
Contents vii
List of Figures xiv
List of Tables xv
Zusammenfassung xvii
Preface xix
1 Introduction 1
1.1 The role of mass loss from hot, massive stars in modern astrophysics . . . . . . . . 1
1.2 Stellar winds, mass loss, and evolution . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Radiation driven winds of hot, massive stars . . . . . . . . . . . . . . . . . . . . . . 3
1.4 A clumped hot star wind? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4.1 Theoretical predictions of a small-scale inhomogeneous wind . . . . . . . . 4
1.4.2 Observational indications of an inhomogeneous wind . . . . . . . . . . . . . 4
1.4.3 Indirect indications of an inhomogeneous wind . . . . . . . . . . . . . . . . 5
1.4.4 Some implications of modified mass-loss rates due to wind clumping . . . . 9
1.5 Spectroscopic analyses of stars using model atmospheres . . . . . . . . . . . . . . . 11
1.5.1 Model atmospheres and spectrum synthesis . . . . . . . . . . . . . . . . . . 11
1.5.2 Spectral line formation and the assumption of LTE . . . . . . . . . . . . . . 11
Particle velocities. . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Level population numbers and the Kirchoff-Planck relation. . . . . . 13
Spectral line formation. . . . . . . . . . . . . . . . . . . . . . . . . . 14
The equations of statistical equilibrium. . . . . . . . . . . . . . . . . 15
1.5.3 Comparisons of atmospheric codes - photospheric models . . . . . . . . . . 16
1.5.4 NLTE line formation in the infra red . . . . . . . . . . . . . . . . . . . . . . 18
1.5.5 Comparisons of atmospheric codes - unified models . . . . . . . . . . . . . 19
2 Mass loss from OB-stars 22
2.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.3 Line-driven winds from hot stars – theoretical predictions . . . . . . . . . . . . . . . 23
2.3.1 Scaling relations and WLR . . . . . . . . . . . . . . . . . . . . . . . . . . . 24viii CONTENTS
2.3.2 Theoretical 1-D models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Results and predictions from hydrodynamic modeling. . . . . . . . . 25
2.4 Observations vs. Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.4.1 Central results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.4.2 The bi-stability jump: predictions and observations . . . . . . . . . . . . . . 26
2.4.3 The FLAMES survey of massive stars . . . . . . . . . . . . . . . . . . . . . . 26
2.5 Weak winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.6 Wind clumping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.7 Weak winds again – Br as a diagnostic tool . . . . . . . . . . . . . . . . . . . . . . 31
2.8 Addendum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3 Radiative transfer in stochastic media and hot star winds
- microclumping, vorosity, and porosity revisited 33
3.1 Transfer in stochastic media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.2 Microclumping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.3 Vorosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.4 Porosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.4.1 Isotropic clumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.4.2 Fragmented shells, radial streaming of photons. . . . . . . . . . . . . . . . . 40
3.4.3 Fragmented shells, including non-radial photons. . . . . . . . . . . . . . . . 40
23.4.4 A porosity formalism for -diagnostics. . . . . . . . . . . . . . . . . . . . 41
4 Mass loss from inhomogeneous hot star winds
I. Resonance line formation in 2D models 43
4.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Optically thin vs. optically thick clumps. . . . . . . . . . . . . . . . 45
4.3 Wind models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.3.1 Radiation-hydrodynamic wind models . . . . . . . . . . . . . . . . . . . . . 45
4.3.2 Stochastic wind models . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
A model clumped in density. . . . . . . . . . . . . . . . . . . . . . . 47
A model clumped in density and velocity. . . . . . . . . . . . . . . . 48
4.4 Radiative transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.5 First results from 2D inhomogeneous winds . . . . . . . . . . . . . . . . . . . . . . 49
4.5.1 Observer’s position and opening angles . . . . . . . . . . . . . . . . . . . . 50
4.5.2 Radiation-hydrodynamic models . . . . . . . . . . . . . . . . . . . . . . . . 51
4.5.3 Stochastic models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Strong lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Intermediate lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Weak lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.5.4 Comparison between stochastic and radiation-hydrodynamic models . . . . . 54
4.6 Parameter study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.6.1 The effective escape ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.6.2 Density parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.6.3 Velocity parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
arCONTENTS ix
4.7 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.7.1 The shapes of the intermediate lines . . . . . . . . . . . . . . . . . . . . . . 59
4.7.2 The onset of clumping and the blue edge absorption dip . . . . . . . . . . . 61
4.7.3 The velocity spans of the clumps . . . . . . . . . . . . . . . . . . . . . . . . 62
4.7.4 3D effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.7.5 Comparison to other studies . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.7.6 Comparison to observations . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.8 Summary and future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.8.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.8.2 Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.9 The Monte-Carlo transfer code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.9.1 The code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Geometry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Releasing photons. . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Absorption. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Re-emission. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.9.2 Radiative transfer code tests . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.10 The effective escape ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
5 Mass loss from inhomogeneous hot star winds
II. Constraints from a combined optical/UV study 75
5.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
5.3 Wind models and radiative transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
5.3.1 Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
5.3.2 Parameters describing a structured wind . . . . . . . . . . . . . . . . . . . . 80
5.3.3 Code verifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
The He II blend in H . . . . . . . . . . . . . . . . . . . . . . . . . . 81
5.4 Theoretical considerations of resonance and recombination line formation in clumpy
winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
5.4.1 Analytic treatment of resonance lines in clumpy winds . . . . . . . . . . . . 82
5.4.2 Recombination lines in clumpy winds . . . . . . . . . . . . . . . . . . . . . 84
Analytic treatment of recombination lines. . . . . . . . . . . . . . . . 86
5.5 A multi-diagnostic study of Cep . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
5.5.1 Clump optical depths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
5.5.2 Constraints from inhomogeneous radiation-hydrodynamic models . . . . . . 87
Comparison with the microclumping technique. . . . . . . . . . . . . 88
5.5.3 Constraints from empirical stochastic models . . . . . . . . . . . . . . . . . 90
Comparison with the microclumping technique. . . . . . . . . . . . . 92
5.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
5.6.1 Are O star mass-loss rates reliable? . . . . . . . . . . . . . . . . . . . . . . 92
Theoretical rates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Empirical rates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
5.6.2 Structure properties of the clumped wind . . . . . . . . . . . . . . . . . . . 93
5.7 Additional considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
lax CONTENTS
5.7.1 Weak wind stars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
5.7.2 Resonance line doublets . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
5.8 Summary and future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
5.9 Analytic treatment of line formation in clumped hot star winds . . . . . . . . . . . . 98
Resonance lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Recombination lines. . . . . . . . . . . . . . . . . . . . . . . . . . . 100
6 Mg I emission lines at 12 & 18 m in K giants 102
6.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
6.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
6.3 Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
6.4 Departure coefficient ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
6.5 Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
6.5.1 Model atmospheres and stellar parameters . . . . . . . . . . . . . . . . . . . 106
6.5.2 The model atom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Enlargement of the model atom . . . . . . . . . . . . . . . . . . . . . . . . 107
Collisional data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
Collisions with neutral hydrogen . . . . . . . . . . . . . . . . . . . . . . . . 108
Collisional excitation from electrons . . . . . . . . . . . . . . . . . . . . . . 110
l-changing collisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
6.6 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
6.6.1 Emission lines at 12 m . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
6.6.2 Mg I emission lines at 18 m . . . . . . . . . . . . . . . . . . . . . . . . . 114
6.7 Discussion and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
6.7.1 The model atom extension . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
6.7.2 Effects from extra collisions . . . . . . . . . . . . . . . . . . . . . . . . . . 116
6.7.3 Observations of Rydberg emission lines around 12 m . . . . . . . . . . . . 117
6.7.4 Comparison with other studies . . . . . . . . . . . . . . . . . . . . . . . . . 117
7 Summary and outlook 119
7.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
7.2 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
7.2.1 Quantitative spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
7.2.2 Theoretical wind models of hot stars . . . . . . . . . . . . . . . . . . . . . . 122
7.2.3 Further applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
A More on the radiative transfer codes 124
A.0.4 Geometry - the Monte-Carlo resonance line code . . . . . . . . . . . . . . . 124
Updating the radiation coordinates. . . . . . . . . . . . . . . . . . . 126
The path length l. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
Crossing wind-slice borders in . . . . . . . . . . . . . . . . . . . . 126
Collecting escaping photons. . . . . . . . . . . . . . . . . . . . . . . 128
A.0.5 Geometry - the recombination line code . . . . . . . . . . . . . . . . . . . . 129
A.0.6 Geometry - the patch wind model . . . . . . . . . . . . . . . . . . . . . . . 129
Modifying the patch geometry. . . . . . . . . . . . . . . . . . . . . . 130
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