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Table of contents
1 Introduction
1.1 Hot stars
1.2 Magnetic fields in hot stars
1.3 Origin of the magnetic field in hot stars
1.3.1 The dynamo hypothesis
1.3.2 The mergers hypothesis
1.3.3 The fossil field origin
1.4 The dichotomy between strong and weak fields
1.4.1 Bifurcation between stable and unstable configurations
1.4.2 Failed fossil field
1.5 Goal of the thesis
2 Detecting magnetic fields
2.1 Polarization
2.2 Zeeman effect
2.3 Measuring polarization
2.4 The spectropolarimeter Narval
2.5 Data analysis
2.5.1 Data reduction with Libre-Esprit
2.5.2 Least Square Deconvolution technique
2.5.3 Detection probability
2.5.4 Longitudinal magnetic field
2.5.5 Oblique rotator model
I Strong magnetic fields
3 The supergiant ζ Ori A
3.1 Introduction
3.2 Observations
3.2.1 Narval spectropolarimetric observations
3.2.2 Archival spectroscopic observations
3.3 Checking for the presence of a magnetic field
3.4 Separating the two components
3.4.1 Identifying the lines of each component
3.4.2 Spectral disentangling of Narval data
3.4.3 Disentangling using the archival spectroscopic data
3.5 Measuring the longitudinal magnetic field of ζ Ori Aa
3.5.1 Using the Narval data and correcting for the companion
3.5.2 Using synthetic intensity profiles
3.5.3 Using disentangled spectroscopic data
3.6 No magnetic field in ζ Ori Ab
3.6.1 Longitudinal magnetic field values for ζ Ori Ab
3.6.2 Upper limit on the non-detected field in ζ Ori Ab
3.7 Magnetic field configuration
3.7.1 Rotational modulation
3.7.2 Field strength and geometrical configuration
3.7.3 Stokes V modeling
3.8 Magnetospheres
3.8.1 Magnetospheric parameters
3.8.2 Hα variations
3.9 Discussion and conclusions
4 The upper limit of the magnetic desert
4.1 Introduction
4.1.1 Choice of targets
4.2 Data Analysis and longitudinal field measurements
4.2.1 HD12447
4.2.2 HD19832
4.2.3 HD22470
4.2.4 HD28843
4.2.5 HD32650
4.2.6 HD96707
4.3 Dipolar magnetic field
4.3.1 HD19832
4.3.2 HD32650
4.3.3 HD96707
4.3.4 HD22470
4.3.5 HD28843
4.4 Conclusion
II Ultra-weak magnetic fields
5 The magnetic field of normal stars
5.1 Vega
5.1.1 Introduction
5.1.2 Observations
5.1.3 Data Analysis
5.1.4 Conclusion
5.2 UZ Lyn
5.2.1 Introduction
5.2.2 Observations
5.2.3 Data Analysis
5.2.4 Conclusions
5.3 B stars
5.3.1 Introduction
5.3.2 Choice of targets
5.3.3 Observations
5.3.4 ι Her
5.3.5 γ Peg
5.3.6 Conclusion for B stars
5.4 Conclusion
6 Weak magnetic fields in chemically peculiar stars
6.1 The Am stars: β UMa and θ Leo
6.1.1 Introduction
6.1.2 Selected targets
6.1.3 Data analysis
6.1.4 Results
6.1.4.1 LSD profiles with complete line mask
6.1.4.2 Possible instrumental artifacts at high SNR
6.1.4.3 Establishing the Zeeman origin of Stokes V signatures
6.1.5 Discussion
6.1.5.1 Peculiar Stokes V signatures in Am stars
6.1.5.2 Origin of the magnetism of Am stars
6.1.5.3 Towards a systematic exploration of weak magnetic fields in Am stars
6.2 The Am star of Alhena
6.2.1 Introduction
6.2.2 Observations
6.2.3 Magnetic analysis
6.2.4 Discussion and conclusion
6.3 The HgMn star: α And
6.3.1 Introduction
6.3.1.1 The target: α And
6.3.2 Observations and data analysis
6.3.3 Data Analysis
6.3.4 The secondary: α And B
6.3.5 Conclusion
6.4 Conclusion
7 Conclusions and perspectives
