GEORGE HERBIG and Early Stellar Evolution
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GEORGE HERBIG and Early Stellar Evolution Bo Reipurth Institute for Astronomy Special Publications No. 1 George Herbig in 1960 —————————————————————– GEORGE HERBIG and Early Stellar Evolution —————————————————————– Bo Reipurth Institute for Astronomy University of Hawaii at Manoa 640 North Aohoku Place Hilo, HI 96720 USA . Dedicated to Hannelore Herbig c 2016 by Bo Reipurth Version 1.0 – April 19, 2016 Cover Image: The HH 24 complex in the Lynds 1630 cloud in Orion was discov- ered by Herbig and Kuhi in 1963. This near-infrared HST image shows several collimated Herbig-Haro jets emanating from an embedded multiple system of T Tauri stars. Courtesy Space Telescope Science Institute. This book can be referenced as follows: Reipurth, B. 2016, http://ifa.hawaii.edu/SP1 i FOREWORD I first learned about George Herbig’s work when I was a teenager. I grew up in Denmark in the 1950s, a time when Europe was healing the wounds after the ravages of the Second World War. Already at the age of 7 I had fallen in love with astronomy, but information was very hard to come by in those days, so I scraped together what I could, mainly relying on the local library. At some point I was introduced to the magazine Sky and Telescope, and soon invested my pocket money in a subscription. Every month I would sit at our dining room table with a dictionary and work my way through the latest issue. In one issue I read about Herbig-Haro objects, and I was completely mesmerized that these objects could be signposts of the formation of stars, and I dreamt about some day being able to contribute to this field of study. As fate would have it, Herbig-Haro objects did become my main focus after I became a professional astronomer. But it was not until I was 40 that I got to meet and talk to George Herbig in person, when he attended a conference I was organizing at ESO in Germany. Afterwards we had occasional correspondence. After Herbig retired from the University of California in 1987, he moved to Honolulu and took up a professorship at the Institute for Astronomy at the University of Hawaii in order to focus exclusively on his research. Later, in 2001, I also moved to the University of Hawaii, and soon we developed strong scientific and personal ties, meeting frequently for lunch or dinner to talk about the latest results in star formation. During the last year of his life, when Herbig’s health started to decline, he asked me to act as his scientific executor and to take care of his voluminous writings, documents, notes, letters, and data. Herbig was a highly organized and disciplined person, and his archives are full of meticulous notes on his numerous projects, both completed and unfinished, from his entire career. Of special interest is his carefully kept collection of thousands of letters exchanged with essentially all of the leading astronomers of the 20th century. Herbig never wrote a full length memoir, but he left extensive notes and com- ments about his work and times. And sometime in his mid-seventies, he de- cided to put together a brief account of his scientific endeavours up to that time, notes meant only for his family. But shortly before his death, he gave me a copy of these autobiographical sketches. With the permission of his wife, Hannelore Herbig, I will throughout the present book cite from this mate- rial, as well as from many other documents, letters, and extensive notes found among Herbig’s archives. In doing so, I hope to give voice to Herbig on many of the epochal events and scientific results throughout his life. Written by hand on the cover of his autobiographical notes, Herbig added “... perhaps it may ii prove useful to that hapless soul who has to write my obituary.” Indeed I have found it very useful, and quotes from Herbig’s various writings will appear in italics throughout this book. The autobiographical notes are introduced thus: “For reasons not entirely clear, I have thought it worthwhile to try to put down a kind of inventory or outline of the various astronomical activities that I have pursued, and how my involvement in each of them came about – to the extent that I can remember or reconstruct reasons and motives at this late date (January 1993). The scornful phrase ‘jack of all trades, master of none’ has more than once come to my mind, for I recall old-timers speaking with contempt of colleagues who frittered away their energies on a host of activities, rather than spending their lives bearing down hard in a single area. Probably my uneasiness about the checkered nature of my own career arises from recollection of such scornful remarks by conservatives, Paul Merrill and Joseph Moore in particular, who I heard on such matters in my early days. Obviously, I did not hew closely to their examples or their admonitions.” From this brief quote, two of Herbig’s characteristics are evident: his complete lack of awe over his many and major contributions to science, and his unique mastery of the written word. This book attempts to give an overview of the scientific life of George Herbig. Little will be said about Herbig’s personal life, mainly because scientists gen- erally live dynamic lives in their minds, while living unremarkable daily lives. Herbig was no exception, he enjoyed a quiet life, was happily married to his wife Hannelore, and spent all of his time doing great intellectual voyages. In the course of these journeys, he nearly singlehandedly built the foundation for the observational study of infant stars. Almost all papers published today on young stars rest in some way on the results established by Herbig. The Danish philosopher Søren Kirkeg˚ard said “We live life forwards, but un- derstand it backwards”. When new ideas are developed and refined over time, what in hindsight appears as a gradual but ordered evolution of a subject towards a correct answer in reality was often a chaotic process, with much groping in darkness for answers, and with many explorations of blind alleys. While Herbig ultimately succeeded in establishing the foundations for the mod- ern view of early stellar evolution, also he from time to time embraced ideas that he later realized were inconsistent with observations, his own or others. This self-correcting process is at the heart of scientific progress. To the extent that such forks in the road are reflected in the literature, I have attempted to describe the wrong turns. It should be emphasized that this book is not a general history of how star formation studies have unfolded over time, and no attempt has been made to iii mention all important papers in the history of the field. The focus here is on Herbig’s pioneering work, and other studies are discussed only as context for the development of his ideas, or to show how a subject has later evolved. Herbig tended to open up a new field, work on it only long enough to establish the foundation and the key facts, and then move on to new ideas and endeavors, often leaving it to others to polish the details. While efforts have been made to write this book so it is also understandable for a more general readership, the audience that the book targets is drawn from researchers and advanced students, who know the terminology of the field of star formation, and who understand the underlying scientific issues. Other readers who may wish to first get an overview of the field of star formation can read the popular-level book by Bally & Reipurth ‘The Birth of Stars and Planets’ from Cambridge University Press. Many people have contributed to the present book, for a full list see the Ac- knowledgements, and I am grateful to all. First and foremost I wish to thank Hannelore Herbig, who has been indefatigable in answering my many questions, in finding photos, and in facilitating my work with Herbig’s major collections of documents. Bo Reipurth iv CONTENTS 1 The Budding Astronomer .............................. ... 1 1.1 Early Years ........................................ ................ 1 1.2 UCLA and Griffith Observatory .......................... .......... 5 1.3 Assistantship at Lick Observatory ...................... ............ 8 1.4 Alfred Joy ......................................... ............... 11 1.5 PhD at Berkeley ..................................... ............. 12 1.6 Pasadena, Yerkes, McDonald Observatory . .......... 15 1.7 Lick Observatory ................................... ............... 19 2 The T Tauri Stars .................................... .... 20 2.1 Joy’s 1945 paper .................................... .............. 20 2.2 RWAur and V380 Ori .................................. .......... 21 2.3 Thesis ............................................ ................ 23 2.4 Are T Tauri Stars Young? ............................. ........... 25 2.5 Objective-prism and Grism Surveys ...................... ......... 30 2.6 The Herbig-Rao and Herbig-Bell Catalogs . ....... 35 2.7 Spectral Properties of T Tauri Stars ................... ............ 37 2.8 Lithium ............................................ ............... 43 2.9 Rotation of Young Stars .............................. ............. 48 2.10 Radial Velocities and Proper Motions of T Tauri Stars . .... 49 2.11 Variability of T Tauri Stars and Flare Stars. ........ 51 2.12 Binarity of T Tauri Stars ............................. ............ 54 2.13 The Post-T Tauri Problem ............................ ............ 56 2.14 The Early Solar System ............................... ............ 61 2.15 Peculiar Young Stars ................................ .............. 63 2.16 Putting it All