Matthias Ammler

Characterisation of young, nearby stars - The Ursa-Major group

Dissertation, 188 Seiten
8 Farbseiten

30. 01. 2007 ISBN: 978-3-00-019738-3   VVPN 00001005  

	Buchhandel-Info
	Kritikforum
Autor-Info:
	Dr. Matthias Ammler-von Eiff Göttingen matthias.ammlervoneiff@gmx.de
	Zusammenfassung
	Leseprobe

ZUM INHALT

Überblick
Die Ursa-Major-Gruppe setzt sich aus Sternen des Ursa-Major-Haufens im Sternbild Großer Wagen und vielen weiteren Sternen zusammen, die sich in die gleiche Richtung wie der Haufen bewegen und über den gesamten Himmel verteilt sind. Die Sterne der Ursa-Major-Gruppe haben ein relativ junges Alter von 200-600 Millionen Jahren. Zieht man ihre Nähe und ihre gemeinsame Bewegung in Betracht, macht die Jugend dieser Sterne sie zu interessanten Objekten verschiedenster astrophysikalischer Untersuchungen.
Jedoch ist die Liste der zugehörigen Sterne nicht vollständig. Wenige Dutzend von gesicherten Mitgliedern stehen Hunderten von zusätzlichen Kandidaten gegenüber. Daher stellt der Autor die spektroskopischen Eigenschaften der Ursa-Major-Gruppe auf die Grundlage einer detaillierten Untersuchung und kann tatsächlich bestätigen, dass die Mitglieder neben der ähnlichen Bewegung noch weitere Gemeinsamkeiten aufweisen.

abstract
The Ursa Major group is composed of the Ursa Major open star cluster in the Big Dipper constellation and of many co-moving stars spread over the whole sky. The stars of the Ursa Major group have a relatively young age of 200-600 million years. Taking into account their proximity and their common motion, the youth makes these stars interesting targets for various astrophysical studies.
However the list of members is not complete. A few dozens of assured members face hundreds of additional candidates. Therefore the author considers the spectroscopic properties of the Ursa Major group on grounds of a precise analysis and indeed confirms that the stars have more features in common than just the motion.

LESEPROBE

Contents

List of Figures xi

List of Tables xiii

Abstract xv

Zusammenfassung xix

Remarks and Acknowledgements xxiii

 

1 Introduction 25

1.1 What is the Ursa Major group? 25

1.1.1 Co-moving stars in the Big Dipper constellation 25

1.1.2 Stellar motion and moving groups 26

1.1.3 Formation and evolution of open clusters and associations 29

1.1.4 The nature of the UMa group – cluster or association, or something else? 33

1.2 Why is the UMa group interesting? 34

1.2.1 A snapshot in stellar evolution 34

1.2.2 A laboratory in front of the door 34

1.2.3 The census of the solar neighbourhood 36

1.3 Constraining the UMa group – previous approaches 37

1.3.1 Spatial clustering 38

1.3.2 Kinematic criteria – derived from a "canonical" member list 38

1.3.3 Kinematic parameters – derived from kinematic clustering 44

1.3.4 Stellar parameters and abundances 45

1.3.5 The age of the UMa group – photometric criteria 47

1.3.6 Spectroscopic indicators for age and activity 48

1.3.7 Combining kinematic, spectroscopic, and photometric criteria 50

1.4 A new homogeneous spectroscopic study 51

1.4.1 Defining the sample 51

1.4.2 How to obtain precise stellar parameters? 56

 

2 Observations, reduction and calibration 57

2.1 Required data 57

2.2 Instruments 58

2.3 Observations 61

2.4 Reduction and calibrations 67

 

3 Deriving the stellar parameters – Methods 73

3.1 Differential analysis 73

3.2 Model atmospheres and synthetic line formation 74

3.2.1 Radiative transfer 75

3.2.2 Radiative transfer in solar-like stars – defining the geometry 76

3.2.3 Thermodynamic equilibrium 77

3.2.4 Local thermodynamic equilibrium (LTE) 78

3.2.5 Contributions to absorption and emission 79

3.2.6 Line profiles 81

3.2.7 Hydrostatic equilibrium 89

3.2.8 Convection 89

3.2.9 Three-dimensional hydrodynamics versus one-dimensional hydrostatics 89

3.3 The stellar parameters 90

3.3.1 Effective temperature 90

3.3.2 Surface gravity 93

3.3.3 Abundances and microturbulence 100

3.3.4 Instrumental profile, rotation, and macroturbulence 101

3.3.5 Estimating the stellar mass 101

 

4 Results and implications for the UMa group 103

4.1 How accurate are the resulting stellar parameters? 103

4.1.1 The Moon spectra and the solar parameters 106

4.1.2 Consistency with Fuhrmann (2004) 106

4.1.3 Comparison of spectroscopic distance with Hipparcos distance 108

4.1.4 Notes on individual stars 111

4.1.5 Comparison of single star parameters with previous determinations 113

4.2 The properties of the UMa group 119

4.2.1 Kiel diagram 119

4.2.2 Abundances of iron and magnesium 121

4.2.3 Rotation 123

4.2.4 Equivalent width of the Li I λ 6707.8Å absorption line 124

4.2.5 Filling-in of the H α line core 128

4.3 Conclusions on the age 130

4.4 Concluding remarks on membership criteria 130

 

5 Summary and outlook 133

 

Bibliography 137

A. The kinematic membership criteria of Eggen (1958, 1995) 149

A.1. Preliminaries 149

A.2. Moving cluster method 150

A.3. Peculiar velocity criterion 151

A.4. Radial velocity criterion 151

A.5. Adaption by Montes et al. (2001a) 152

B. Details on the used spectra 153

C. Line data 155

D. Solution of the model atmosphere problem with MAFAGS 161

D.1. Flux conservation 161

D.2. Solution of the model atmosphere 161

E. Individual spectra near H α and Li I 6707.8Å 165

F. Residuals of LTE fits to the observed H α profile. 173

Index 175

 

Persönliche Danksagung 179

Ehrenwörtliche Erklärung 183

Lebenslauf 185