Quantitative Studies of W Olf-Rayet Stars in Group
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Quantitative studies of Wolf-Rayet stars in Group Galaxies A Thesis submitted for the Degree of Doctor of Philosophy of the University of London by Luc Dessart UCL Department of Physics & Astronomy University College London University of London November 1999 ProQuest Number: 10630784 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 10630784 Published by ProQuest LLC(2017). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 2 a Dieu 4 Acknowledgement This thesis represents not only the research I have been carrying out for the last three years, but also overlaps with a great many happenings, personal changes, encounters... I must first thank very much Mike Barlow and David Williams, my interviewers, for allowing me to carry out this PhD research in the first place, as well as letting me benefit from the Perren fund. My work thanks go nearly all to Paul, who helped and supported me all the way through this Ph.D thesis. He permitted my first observing trip on a major size telescope, an unforgettable memory. I am greatly indebted to John Hiller for letting me use ”his piece of art”. I thank Allan for his help in finding funding for the realisation of the projects I undertook. Not directly related to my PhD work, I nevertheless greatly benefited from discussions with Daniel and Nick. From the stables of Hackney to the castles of Highgate, from a frosty bed and cold shower to a welcoming and warm home. I wish to thank Rose and Bernard for all these days shared under the same roof. What a pleasant introduction to ’’Englishness”. Pockets of Frenchness were however resilient, luckily since they were needed: Daniel and the metaphysics, Peter and Dounia for the remembrance of things lost, Daniel and the ever-lasting chats (yes, we have time...), Francois me bro for the call of the mountains, mum and dad for their unconditional love. My strongest English connection goes back to the Berkeley years, to Dickon, and Isabel, with whom I discovered that discussions could not only be enjoyable but also constructive. And, Dorthe, the embodiment of happiness, Cath, the literary leaf. But these years would not have been nearly as enjoyable without any artistic support from the dead and alive. The literary: Simone De Beauvoir, J.P. Sartre, Feodor Dosto evsky, Michel Del Castillo, Franz Kafka, Emily Bronte; The musical: Daniel Rego, Paco De Lucia, Vicente Amigo, Baden Powel, Carlos Jobim, without forgetting... Mozart. The pictorial: Giacometti, Modigliani, Van Gogh, Monet, Picasso. 5 6 Abstract Fundamental properties of Wolf-Rayet (WR) stars in Local Group galaxies have been obtained using high quality UV, optical and IR spectroscopy coupled with a sophisticated model atmosphere code including line-blanketing and clumping. Quantitative analyses of WR stars in the cores of two giant HII regions, HD97950 in NGC3603 and R136a in 30 Doradus - is presented, based on archive HST spectroscopy. We find very large luminosities ( 1O 6L0) for these H - rich objects (H/He ~ 3-6). In the two core regions, WNL stars provide about 20% of the total ionizing flux and about 60% of the total kinetic energy injected into the ISM, despite representing <10% of the massive star population. HD97950 and R136a overall show similar global properties, although Rl36a. is embedded in a denser (and older) region than its Galactic counterpart. I studied the recently discovered He I emission line stars in the Galactic Centre region using K and L band observations obtained at UKIRT, making use of Hell 3.09/um to derive reliable surface temperatures. That line was observed in three objects, for which stellar parameters were determined, revealing properties typical of LMC or Galactic WN8-9 stars. I present an analysis of Galactic WC5 —8 stars, including ISO—SWS datasets. For all stars studied (WR146, WR90, WR135, and WR 11), the derived neon abundance shows a strong enrichment, though up to 50% lower than evolutionary expectations. Earlier discrepancies arose from unrealistic distances and/or mass loss rates. Analyses of seven LMC WC4 and one WO stars were carried out. LMC WC4 stars reveal an overlap in surface composition and temperature with Galactic WC4-8 stars, dif fering from these principaly by their lower surface mass flux and/or higher wind expansion velocity. While no trend in C/He is found between Galactic WCE and LMC WC4 stars, the WO star studied, Br93, possesses the greatest C/He and O/He values in the present W R sample. Finally, multifibre observations of 47 WR stars in M33 are presented, with new classi fications and line information obtained. I confirm the absence of WO stars, and provide a precise determination of most WC subtypes. 8 Contents Title Page 1 Acknowledgements 5 A b stract 7 Table of Contents 9 List of Tables 15 List of Figures 25 1 Introduction 41 1.1 Star formation in galaxies .............................................................................................. 44 1.2 W R s t a r s ............................................................................................................................ 46 1.2.1 The evolutionary view .........................................................................................46 1.2.2 The spectroscopic view ..................................................................................... 49 1.2 .2.1 Classification Schemes ........................................................................50 1.2 .2.2 Modelling tools ..................................................................................... 50 1.3 The physics of W R w i n d s ...............................................................................................55 1.3.1 Bizarre patterns?: wind variability and asymm etries ................................. 58 2 Tools for quantitative spectroscopic analysis 61 2.1 Model atmospheres: a tool for the determination of stellar parameters . 61 9 2 .1.1 Presentation of the model atmosphere ....................................................... 62 2 .1.2 Presentation of the physics of the m odel ................................................... 62 2.1.2.1 Radiative transfer in an expanding wind ................................. 62 2.1.2.2 Statistical equilibrium equations ................................................. 64 2.1.2.3 Treatment of full and super lev els ............................................. 65 2.1.3 Physical inputs .................................................................................................. 65 2.1.3.1 Wind density structure: smooth or clumped? ........................ 65 2.1.3.2 Wind velocity structure ................................................................ 68 2.1.3.3 Stellar luminosity, radius and temperature ............................. 70 2.1.3.4 Chemical enrichments..................................................................... 70 2.1.4 Atomic processes and data sources .............................................................. 71 2.1.5 Atomic data inputs ............................................................................................ 73 2.1.5.1 Model atom s ...................................................................................... 73 2.1.6 Practicalities about the model .................................................................... 79 2.2 Extinction law s ................................................................................................................ 79 3 WNL stars in HD 97950 and R136a 83 3.1 Observations .................................................................................................................... 89 3.1.1 Stellar spectroscopy ......................................................................................... 89 3.1.2 Optical spectral classification ........................................................................ 90 3.1.2.1 Previous classifications .................................................................. 90 3.1.2.2 New classifications ............................................................................ 91 3.1.3 Ultraviolet spectroscopy .................................................................................. 95 3.2 Distance and interstellar reddening towards NGC3603 ......................................... 95 3.2.1 Updated My-compilation for early 0 s ta rs ............................................. 97 3.2.2 Distance modulus and interstellar reddening to NGC3603 .................. 97 3.3 Observed properties of individual WN s ta rs ..............................................................101 3.3.1 Absolute visual magnitudes ............................................................................. 101 10 3.3.2 Terminal wind velocities .....................................................................................104 3.4 Spectroscopic analysis of WN stars in HD 97950 and R 136a .................106 3.4.1 Analysis technique ...............................................................................................106 3.4.2 Model results .........................................................................................................109