Citation
Amiri, N. (2011, October 26). Developing asymmetries in AGB stars : occurrence, morphology and polarization of circumstellar Masers. Retrieved from
https://hdl.handle.net/1887/17981
Version: Corrected Publisher’s Version
License: Licence agreement concerning inclusion of doctoral thesis in the Institutional Repository of the University of Leiden
Downloaded from: https://hdl.handle.net/1887/17981
Note: To cite this publication please use the final published version (if applicable).
Developing Asymmetries in AGB Stars:
Occurrence, Morphology and
Polarization of Circumstellar Masers
Developing Asymmetries in AGB Stars:
Occurrence, Morphology and Polarization of Circumstellar Masers
PROEFSCHRIFT
ter verkrijging van
de graad van Doctor aan de Universiteit Leiden,
op gezag van de Rector Magnificus prof. mr. P. F. van der Heijden, volgens besluit van het College voor Promoties
te verdedigen op woensdag 26 oktober 2011 klokke 13.45 uur
door
Nikta Amiri
geboren te Mashhad, Iran in 1983
Prof. dr. V. Icke Prof. dr. K. Kuijken
Contents
1 Introduction 1
1.1 Outline . . . 2
1.2 Asymptotic Giant Branch Phase . . . 2
1.2.1 Planetary Nebulae . . . 4
1.3 Circumstellar Envelopes . . . 4
1.3.1 What is a Maser? . . . 4
1.4 Masers as Tools to Probe the Stellar Evolution . . . 9
1.4.1 Morphology of the CSEs . . . 9
1.4.2 Polarization of Masers . . . 10
1.4.3 Variability of the Masers . . . 13
1.5 This Thesis . . . 13
1.5.1 Outline of the Thesis & Main Results . . . 13
1.5.2 Conclusions and Outlook . . . 16
2 The magnetic field of the evolved star W43A 17 2.1 Introduction . . . 19
2.2 Observations and Data Analysis . . . 20
2.2.1 MERLIN Observations . . . 20
2.2.2 GBT Observations . . . 20
2.2.3 Determining Zeeman Splitting . . . 21
2.3 Results . . . 21
2.4 Discussion . . . 25
2.4.1 OH maser polarization . . . 25
2.4.2 H2O maser polarization . . . 28
2.4.3 The role of the magnetic field . . . 28
2.4.4 OH maser shell expansion of W43A . . . 30
2.5 Conclusions . . . 30
3 The kinematics and magnetic fields in water-fountain sources based on OH maser observations 33 3.1 Introduction . . . 35
3.2 MERLIN Observations . . . 36
3.3 Results . . . 37
3.3.1 OH maser observations of OH 12.8-0.9 . . . 37
3.3.2 OH maser observations of OH 37.1-0.8 . . . 39
3.4 Analysis . . . 42
3.4.1 Description of the kinematical reconstruction procedure . . . 42
3.4.2 Application to individual sources . . . 49 v
4.2 Observations . . . 66
4.3 Zeeman Splitting of H2O masers . . . 67
4.3.1 Non-Zeeman effects . . . 67
4.4 Results . . . 68
4.4.1 Individual sources . . . 68
4.4.2 RX Oph . . . 68
4.4.3 V1416 Aql . . . 71
4.4.4 IRAS 17230+0113 . . . 71
4.4.5 IRAS 19422+3506 . . . 71
4.4.6 IRAS 19579+3223 . . . 72
4.5 Discussion . . . 72
4.5.1 Magnetic field . . . 72
4.5.2 Variability . . . 73
4.6 Conclusion . . . 74
5 The evolution of H2O masers in the circumstellar environment of AGB stars in transition to Planetary Nebulae 75 5.1 Introduction . . . 77
5.2 Observations and Data Reduction . . . 78
5.3 Analysis . . . 81
5.3.1 New masers . . . 81
5.3.2 Variability of the H2O masers with respect to stellar pulsation cycle 83 5.3.3 Disappearing H2O masers . . . 83
5.3.4 Individual Sources with double peak profiles . . . 85
5.4 Discussion . . . 89
5.4.1 Water Fountain Candidates . . . 89
5.4.2 IRAS 18455+0448, Youngest proto-PNe candidate . . . 90
5.4.3 Variability . . . 90
5.5 Conclusions . . . 91
6 VLBA SiO maser observations of the OH/IR star OH 44.8-2.3: magnetic field and morphology 103 6.1 Introduction . . . 105
6.2 Observations . . . 106
6.2.1 VLBA observations and reduction . . . 106
6.2.2 EVLA observations and reductions . . . 107
6.2.3 VLA observations of the 1612 MHz OH masers of OH 44.8-2.3 . 108 6.3 SiO maser polarization theory . . . 108 vi
Contents
6.3.1 Linear polarization . . . 108
6.3.2 Potential non-Zeeman effects for circular polarization . . . 111
6.4 Results . . . 111
6.4.1 Total intensity . . . 111
6.4.2 Linear polarization . . . 112
6.4.3 Circular polarization . . . 112
6.4.4 OH maser observations of OH 44.8-2.3 . . . 117
6.5 Discussion . . . 117
6.5.1 Linear polarization . . . 117
6.5.2 Circular polarization . . . 119
6.5.3 CSE morphology and magnetic field . . . 119
6.5.4 SiO emission in OH 44.8-2.3 . . . 120
6.6 Conclusions . . . 121
Nederlandse Samenvatting 123
References 129
Publications 133
vii
