Colloquium
The nova outburst: a changing paradigm
Dr. Robert Williams
Abstract
Spectroscopic observations of novae date back a century, and the fundamental nature of the outburst has been understood for 50 years. Yet, recent observations suggest possible major modifications to the standard nova paradigm. A high-resolution spectroscopic survey of novae has revealed short-lived heavy element absorption systems near maximum light consisting of Fe-peak and s-process elements. The absorbing gas is circumbinary and it must pre-exist the outburst. Its origin appears to be mass ejection from the secondary star, implying large episodic mass transfer events from the secondary that initiate the nova outburst. The spectroscopic evolution of novae is interpreted in terms of two distinct interacting gas systems in which the bright continuum is produced by the outburst ejecta but absorption and emission lines originate in gas ejected by the secondary star in a way that may explain dust formation and X-ray emission from novae.About the talk
The nova outburst: a changing paradigm
iCalendar Google Calendar
Dr. Robert Williams
Space Telescope Science Institute, USA
Space Telescope Science Institute, USA
Friday November 20, 2009 - 0:00 GMT (Aula)
iCalendar Google Calendar
About the speaker
Dr. Robert Williams is currently Distinguished Research Scholar of the Space Telescope Science Institute (STScI) in Baltimore, USA, having served as Director of the Institute from 1993-98. The Institute, together with Goddard Space Flight Center, operates the Hubble Space Telescope for NASA. Before assuming his present position Williams spent 8 years in Chile as Director of the Cerro Tololo Inter-American Observatory, the national observatory of the U.S. in the southern hemisphere. Previous to that time he was Professor of Astronomy at the University of Arizona in Tucson for 18 years. Dr. Williams' research specialties are nebulae, novae, and emission-line spectroscopy and analysis.
He was a Senior Fulbright Professor at University College London from 1971-72, and received the Alexander von Humboldt Award from the German government in 1991. In 1998 he was awarded the Beatrice Tinsley Prize of the American Astronomical Society for his leadership of the Hubble Deep Field project, which revealed the early universe with Hubble Telescope. For this project he was awarded the NASA Distinguished Public Service Medal in 1999. He is currently President of the International Astronomical Union.