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Interferometric Radio Observations of the Interactive Winds of Massive Stars

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Interferometric Radio Observations of the Interactive Winds of Massive Stars Interferometric Radio Observations of the Interactive Winds of Massive Stars by DIANE PATRICIA BROOKES A thesis submitted to The University of Birmingham for the degree of DOCTOR OF PHILOSOPHY Astrophysics and Space Research Group School of Physics and Astronomy The University of Birmingham February 2016 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. Abstract Massive stars have very strong stellar winds which interact with their environment. This work has involved the study of these interactive winds at radio and other wavelengths. Radio obser- vations have been made of the massive runaway star BD+43◦ 3654 and its bow shock which is interacting with the inter-stellar medium. These observations, together with archive data at other wavelengths, have revealed stratified dust and turbulent gas in this interaction zone. Further radio studies have been undertaken of the interaction zones of the colliding winds of massive binary systems. Observations of the colliding wind binary WR 147 at 5GHz have revealed a curved collision zone, suggestive of simple interactive models. Measurements of the flux from the Wolf-Rayet component of this massive binary system has allowed a mass-loss rate to be derived and though the companion O-star is not detected, an upper flux limit has allowed upper limits on the mass-loss rate and limits on the terminal velocity to be inferred. Also revealed is a curious ’bridge’ feature previously observed in WR 147 which occurs between the two binary components. One mechanism is suggested to explain this anomalous feature, the ionising flux of one binary component, the O-star, may be ionising the wind of the other, the WR component. Modelling of the ionisation structure of the stellar winds has been undertaken to verify that this may be occurring. Radio observations of massive stars made at low-frequency have produced detections of WR 147 and the brighter colliding wind binary, WR 146. These detections have allowed modelling of the non-thermal emission in order to deduce where the non-thermal absorption turn-over occurs in these systems. The resultant modelling has illustrated that these colliding wind regions are complex, with multiple absorption regions best describing their nature. To Nye Acknowledgements I would like to thank my supervisor, Dr. Ian Stevens, for his guidance and support. I would also like to thank the University of Birmingham for their part-time research bursary. I am grateful for the staff at the GMRT and the e-MERLIN team at the University of Manchester who made these radio observations possible and I also thank them for their assistance with radio data reduction. I would like to thank my collaborators for their inciteful and enormously helpful comments and particularly Prof. C.H. Ishwara-Chandra for his assistance with the BD+43◦ 3654 data reduction together with Dr. Danielle Fenech and Dr. Sean Dougherty for sharing with me their knowledge of MERLIN/e-MERLIN data reduction and the WR 147 system. I am very grateful for the IT help and assistance from David Stops, who was always willing to assist with the vagaries of computer systems and software. I would like to thank Nye for all the love and encouragement he has given me during my research. And to Andrea for believing in my ability from the beginning. Thank you. Preface The work that is presented in this thesis has been undertaken by the author between 2010 and 2016 at the University of Birmingham under the supervision of Dr. Ian R. Stevens. The research which is presented in the main chapters of this thesis is the work of the author, however, the work has involved collaboration with a number of co-authors which are noted below. These chapters have been prepared as stand alone research papers for publication in peer reviewed journals; they are, therefore, identical to the published papers with minor alterations for clarity and will, by their individual nature, also contain some duplication of material. Chapter 3 New Observations of the Wolf-Rayet Colliding Wind Binary System WR 147 at 5 GHz with e-MERLIN - This chapter was written by the author in collaboration with Dr. Danielle Fenech, Dr. Sean Dougherty, Dr. Ian R. Stevens, Dr. Peredur Williams, Dr. Ronny Blomme, Dr. Julian M. Pittard, Prof. Raman Prinja and Dr. Debra Wallace. The paper is to be submitted to Monthly Notices of the Royal Astronomical Society (MNRAS). Chapter 4 Low-Frequency GMRT Observations of Massive Stars I: The Wolf-Rayet Colliding Wind Binary System - WR 147 - This chapter was written by the author in collaboration with Dr. Ian R. Stevens and Dr. Julian M. Pittard. The paper is to be submitted to Monthly Notices of the Royal Astronomical Society (MNRAS). Chapter 5 Low-Frequency GMRT Observations of Massive Stars II: The Wolf-Rayet Colliding Wind Binary System - WR 146 - This chapter was written by the author in collaboration with Dr. Ian R. Stevens. The paper is to be submitted to Monthly Notices of the Royal Astronomical Society (MNRAS). Chapter 6 Anatomy of a Bow Shock: Multi–Wavelength Observations of the Bow Shock Around The O4 Supergiant star BD+43◦ 3654 - This chapter was written by the author in collabo- ration with Dr. Ian R. Stevens, Dr. Paula Benaglia, Prof. C. H. Ishwara–Chandra and Dr. Josep Mart´ı. The paper is to be submitted to Monthly Notices of the Royal Astronomical Society (MNRAS). Chapter 7 E-BOSS: an Extensive stellar BOw Shock Survey I - This chapter is a summary of work as a co-author in collaboration with Dr. Cintia Peri, Dr. Paula Benaglia, Dr. Ian R. Stevens and N. L. Isequilla. This paper was published on 10 February 2012 in Astronomy & Astrophysics, volume 538, page A108. Contents 1 Massive Stars - Drivers of Galactic Evolution 1 1.1 MassiveStars,MassiveEffects. ....... 1 1.1.1 Whatisamassivestar? ........................... 1 1.1.2 Thestructureofmassivestars . .... 5 1.2 Massive Star Formation in Stellar Clusters . ........... 8 1.2.1 Starbirth.................................... 8 1.2.2 MassiveStarsinStellarclusters. ....... 10 1.3 TheWindsofMassiveStars. 12 1.3.1 Radiativelydrivenstellarwinds. ....... 12 1.3.2 Mass-lossfrommassivestars . 13 1.3.3 A comparison of different methods of mass-loss determination. 18 1.4 Multi-Wavelength Properties of Massive Stars . ............ 21 1.4.1 Radioemission ................................. 21 1.4.2 Infra-redemission ............................. 28 1.4.3 Optical and Hα emission ........................... 29 1.4.4 Ultravioletemission . 29 1.4.5 High energy emission - X-rays and Gamma-rays . ...... 30 1.5 ShocksinStellarWinds ............................ 32 1.5.1 Windblownbubbles .............................. 32 1.5.2 Theanatomyofshocks ............................ 32 1.5.3 The Solar bow shock: in-situ measurements of a bow shock ........ 36 1.5.4 Runawaystarsandstellarbowshocks . ..... 37 1.5.5 Massive binary systems and colliding wind shocked regions ........ 39 1.6 Conclusion ...................................... 42 vi Contents vii 2 An Introduction to Radio Interferometry 43 2.1 Summary ........................................ 43 2.2 AnIntroductiontoRadioAstronomy. ....... 43 2.2.1 Thetransparencyofthesky. 43 2.2.2 Abriefhistoryofradiotelescopes. ....... 44 2.3 WhatisanInterferometer? . ..... 44 2.3.1 Interferometerdesign. 44 2.3.2 Whatisacorrelator? ............................ 46 2.3.3 Baselinesandu-vcoverage . 47 2.3.4 Telescopesensitivity . 49 2.4 CurrentRadioInterferometers . ....... 52 2.4.1 TheGiantMetrewaveRadioTelescope . ..... 53 2.4.2 The Multi-Element Radio Linked Interferometer Network,e-MERLIN . 55 2.5 RadioDataReduction .............................. 57 2.5.1 AHistoryofAIPS ............................... 57 2.5.2 Thesequenceofdatareduction . 58 2.6 Conclusion ...................................... 60 3 Observations Of WR 147 At 5 GHz With e-MERLIN 61 3.1 Introduction.................................... 61 3.2 e-MERLIN Observations and Data Reduction . ........ 64 3.3 Results......................................... 66 3.3.1 Newe-MERLINdata ............................. 66 3.3.2 Stellarfluxesandmass-lossrates . ...... 66 3.3.3 System orientation and location of the wind collision region ........ 72 3.3.4 ArchiveMERLINdata............................. 77 3.3.5 Thebridge ................................... 77 3.4 Conclusion ...................................... 81 4 Low-Frequency GMRT Observations Of WR 147 82 4.1 Introduction.................................... 83 Contents viii 4.2 TheWR147System.................................. 84 4.2.1 ThecomponentsofWR147. 84 4.2.2 Colliding wind binary considerations . ........ 86 4.2.3 Previousradioobservations . ..... 86 4.3 GMRTObservations ................................ 88 4.3.1 Observations .................................. 88 4.3.2 GMRTresults ................................. 90 4.4 WR147SpectralEnergyDistribution . ....... 90 4.4.1 TotalradioSEDandNTemission . 93 4.5 SpectralFitting................................. 93 4.5.1 Introduction - fitting the radio spectrum . ........ 93 4.5.2 Aonecomponentmodel...........................
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