Abstract i
Contents iii
1 Introduction 1
1.1 Evolution of low- and intermediate-mass single stars . . . 2
1.1.1 The Main Sequence phase . . . 4
1.1.2 The Red Giant Branch phase . . . 7
1.1.3 Helium ignition and the core-helium burning phase . . . 8
1.1.4 The Asymptotic Giant Branch phase . . . 9
1.1.5 The Post-AGB phase and beyond . . . 12
1.2 Giant stars in binary systems . . . 15
1.2.1 The Roche model . . . 15
1.2.2 Orbital evolution . . . 17
1.2.3 Binary interaction mechanisms . . . 18
1.2.4 The eccentricity-period diagram . . . 24
1.3 Barium stars . . . 25
1.3.1 The discovery of Ba stars and their binarity . . . 25
1.3.2 Formation and evolution . . . 27
iii
1.3.3 Observational properties . . . 28
1.3.4 The other progeny of AGB binaries . . . 33
1.3.5 Open questions . . . 34
1.4 Motivation and thesis outline . . . 36
2 Analysis methodology 39 2.1 Spectroscopic binaries and Keplerian orbits . . . 39
2.1.1 Radial-velocity data . . . 41
2.1.2 Fitting Keplerian orbits . . . 43
2.1.3 The mass function . . . 46
2.2 Ba stars in the HR diagram . . . 46
2.2.1 Spectral Energy Distributionfitting . . . 46
2.2.2 Luminosity determination in theGaiaera . . . 51
2.3 STAREVOL models and Ba star masses . . . 54
2.4 Companion masses . . . 57
2.5 BINSTAR evolutionary models . . . 57
3 Hertzsprung-Russell diagram and mass distribution of barium stars 61 3.1 Introduction . . . 62
3.2 The sample . . . 64
3.3 Hertzsprung-Russell diagram . . . 68
3.3.1 Atmospheric parameters . . . 68
3.3.2 Input physics for the stellar grid calculations . . . 70
3.3.3 Discussion . . . 72
3.4 Mass distribution . . . 76
3.4.1 Comparison with M- and K-type giants . . . 78
3.4.2 Discussion . . . 80
3.5 Location in the HRD and orbital period . . . 82
3.6 Conclusions . . . 89
4 Barium and related stars, and their white-dwarf companions: Main- sequence and subgiant stars 91 4.1 Introduction . . . 93
4.2 Sample overview and data description . . . 94
4.2.1 Radial-velocity measurements with CORAVEL and CORALIE . . . 95
4.2.2 Radial-velocity monitoring with the HERMES spectrograph . . . 96
4.2.3 Radial velocities with SALT-HRS . . . 97
4.2.4 Stellar sample . . . 98
4.3 Orbital analysis . . . 99
4.4 Results . . . 100
4.4.1 Single-lined spectroscopic binaries . . . 101
4.4.2 HD 48565 . . . 101
4.4.3 HD 114520 . . . 103
4.4.4 HD 26455 and HD 177996 . . . 107
4.4.5 Binaries with incomplete orbital phase coverage and uncon- firmed binaries . . . 107
4.5 Hertzsprung–Russell diagram . . . 109
4.6 Discussion . . . 114
4.6.1 Eccentricity-period diagram . . . 114
4.6.2 dBa vs. sgCH . . . 116
4.6.3 Mass distribution . . . 116
4.6.4 Mass function and companion masses . . . 117
4.6.5 Comparison with evolutionary models . . . 120
4.7 Summary and conclusions . . . 123
5 Binary evolution along the Red Giant Branch with BINSTAR: The
barium star perspective 125
5.1 Introduction . . . 126
5.2 Observational constraints . . . 128
5.3 Modeling methodology . . . 129
5.3.1 Input stellar and binary physics . . . 130
5.3.2 Tidally-enhanced wind mass loss . . . 132
5.3.3 Reduced circularisation efficiency . . . 133
5.3.4 Model grid set-up . . . 133
5.4 Results of the simulations . . . 134
5.4.1 Standard binary evolution . . . 134
5.4.2 Tidally-enhanced wind mass loss . . . 137
5.4.3 Reduced circularisation efficiency . . . 140
5.4.4 The combined effect . . . 140
5.4.5 Validity of the assumptions . . . 140
5.5 Comparison with observations . . . 144
5.6 Summary and conclusions . . . 149
6 Summary and future plans 151 6.1 Conclusion summary . . . 151
6.2 Future plans . . . 153
6.2.1 The search for main-sequence Ba stars at higher masses . . . 153
6.2.2 The masses of the white dwarf companions . . . 157
6.2.3 The formation of Ba stars . . . 158 A Sample of barium and related stars with accurate parallaxes 161 B Ba dwarf candidates: classification and radial-velocity data 163
C Orbital solutions of the Ba dwarfs 167
Bibliography 177
Acknowledgements 193
List of publications 197
