There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy.
-- Hamlet, Act 1, Scene 5
I received my Sc.B. in Bio physics from Brown University in 1973, and my Ph.D. in Astrophysics from the University of Colorado in 1982, with a graduate assistantship at the High Altitude Observatory of the National Center for Atmospheric Research . My initial graduate studies began with a year in the Astronony Department at the Ohio State University
I'm a member of the American Astronomical Society (AAS), and the International Astronomical Union (IAU). I have served on IAU commisson #36 for Stellar Atmospheres, and since August 2000 on the "Organizing Committee" for the IAU "Working Group for Massive Stars". In September 2006, I was elected chair of this OC. From 2003-2006, I served as OC Chair for the IAU Working Group for Active B-Stars". For more information on these fields of study, check out the Massive-Star Newsletter and the Be Star Newsletter .
Inspired by the arrival of grandchildren, I've recently begun writing children's books with astronomy themes:
- Big Stars for a Little Star -- dedicated to my eldest grand-daughter, Eva Sue, this relates to my own work on massive stars.
- 26 Jellybeans to Ginormity -- dedicated to my second grand-daughter, Saloma Maryam, this was inspired by a graphic I made for my astronomy students to teach about size scales in the universe.
Preprints , of submitted but not-yet-published journal papers, and Reprints , of review articles & conference proceeding papers. Published papers , via links provided by ADS abstract service .
Instruction and Collaboration
From 1992 to1996, I supervised UDel. Ph.D. graduate student, Steven Cranmer . Find out about his thesis research on Hot-Star Winds , as well as various astronomy-related WWW links. I work closely with David Cohen , focusing on the origin of X-ray emission from early-type stars, under support of a 5-year grant from the NASA Long-Term-Space-Astrophysics (LTSA ) program. From 1998-2000, David was a Bartol Research Scientist, but in September 2000 he moved to an assistant professor position in the Department and Physics and Astronomy at nearby Swarthmore College . I also continue close collaboration with Ken Gayley , who worked with me as a Bartol Research Scientist from fall of 1993 till summer of 1997, when he moved to take a professor position in the Department of Physics and Astronomy at the University of Iowa . From 2003-2008 Bartol Research Scientist, Rich Townsend (also affiliated with University College London ) worked with me on various topics related to disk formation in Be and Bp stars. He is now an assistant professor at University of Wisconsin.
From 1999-2002, I supervised thesis research from University of Delaware Physics PhD. Asif ud-Doula. Check out his thesis on The Effect of Magnetic Fields and Field-Aligned Rotation on Line-Driven Hot-Star Winds (25MB) [Here is smaller version (0.5 MB) without figures]. From 2005-2008, Asif returned to work in our group as a post-doc. He is now an assistant professor at Penn State - Scranton.
I am currently supervising Ph. D. thesis research of two UDel Physics graduate students, Chris Russel & Mary Oksala.
I have ongoing collaborations with numerous other colleagues around the world, including: Joachim Puls of the Universitaet Sternwarte Muenchen Mark Runacres of the Royal Observatory of Belgium. Achim Feldmeier of University of Potsdam Luc Dessart, now in Marseilles
Nir Shaviv of the Rahcah Institute of Physics, Hebrew University, Jerusalem, Israel
Outreach and General Reviews
For the Encyclopedia of Astronomy and Astrophysics , I wrote a general-astronomy-level review article on Radiatively Driven Stellar Winds from Hot Stars , which can be accessed as either a PDF (290Kb), postscript (404Kb), or gzipped ps (125Kb) file. Several of our research projects on hot-star winds were featured in a general-level summary article, Winds that Sail on Starlight , that appeared in the Spring 1997 issue of the the San Diego Supercomputer Center (SDSC) magazine, Gather/Scatter The spring 1999 Centennial meeting of the American Physical Society included an invited poster session highlighting Great Discoveries in Astronomy . For this I prepared a poster featuring Solar and Stellar Winds . I've also created a slide-show version of this. Using Microsoft's free PowerPoint viewer , you can also browse either the poster source file (~1.3Mb) or the slide-show source file (~1.3Mb). For this APS poster there is now a version with the text translated into french by Dr. Roland Grappin of the Observatoire de Paris-Meudon , in Meudon, France. Every three years each IAU commission is asked to prepare a report on progress in its field. These are compiled with other commission contributions in the triennial IAU Reports on Astronomy . As a member of IAU Commission #36 for Stellar Atmospheres, my own contribution toward this includes a 2-page summary for the period 1996-9 of " Recent Advances in Studies of Stellar Mass Loss " , which is also available as a TeX , gzipped Postscript , or PDF document. You can also access copies of my 1993-6 periodic report in TeX , gzipped P ostscript , or PDF formats. I am a member of the IAU "Organizing Comittee" (OC) for the "Massive Star Working Group". Among other activities, this group publishes the Massive-Star Newsletter . I am also currently (until Aug. 2006) serving as chair of the OC for the IAU Working Group on Active B-Stars . For information of these stars, check out the Be Star Newsletter . Finally, here is an incomplete and rather outdated overview of our Hot Star Wind Astrophysics research program at Bartol. I still hope to update this, someday...
"Radiatively Driven Winds and Aspherical Mass Loss ", an invited paper presented at a conference on the "Fate of the Most Massive Stars" held in Jackson Hole, Wyoming in May 2004. ppt or pdf format.
In October 2003, at a school on "Stellar Winds and Mass Loss" held in Oleron, France, I was invited to give a series of 4 x 1.5 hour lectures on "Stellar Wind Mechanisms and Instabilities". A brief description of the lectures, with links to PDF files of the lecture slides is as follows: lec1-sw.pdf (6.9 MB) "Overview + Solar Wind": A general overview of wind equations and formalism, with then a summary of the gas-pressure driven outflow of the solar wind that results from solar coronal heating. lec2-hswcak.pdf (5 MB) "CAK Line-DrivenWinds from Hot-Stars": A simplified review of the basic Castor, Abbott, and Klein (1975; CAK) theory for line-driven mass loss in hot-stars, but emphasizing the physically more transparent `Qbar' notation.first introduced by Ken Gayley (1996, ApJ). lec3-hswrot.pdf (8 MB) "Rotation and other Multi-D Effects in Hot-Star Winds":Extension of line-driven wind theory for hot-stars to account for the vector nature of the line-force, with particular application to cases with rapid rotation. This lecture emphasis the peculiar properties of the vector line-force, and summarizes many of the points made in the general colloquium I give on 'Winds that Sail on Starlight'. It also concludes with a brief summary of my ideas for rotational mass ejection to make Be-star disks, a topic also covered elsewhere in my collouquium on 'The Launching of Be Star Disks'. lec4a-csw.pdf (1.9 MB) "Wave-Pressure Models of Cool-Star Winds": Summarizes the little I know about cool-star mass loss, briefly reviewing attempts to explain this through Alfven-wave-pressure driven winds, and also emphasizing the general `Fine-tuning problem' of obtaining a large mass loss rate with a terminal speed that is significantly smaller than the surface escape speed. lec4b-sedd.pdf (0.8 MB) "Continuum-Driven Winds from Super-Eddington Stars": Summarizes recent ideas about continuum-driven winds based on instabilities that could occur when a star approaches and exceeds the Eddingoton limit. lec4c-ldi.pdf (5.9 MB) "Line-Deshadowing Instability": Reviews the basis of the strong, intrinsic instabilites that can lead to extensive small-scale structure in line-driven stellar winds.
"MHD Simulations of Line-Driven Winds from Hot Stars ", a poster paper presented with my graduate student, Asif ud-Doula, at the AAS meeting in Washington DC Jan. 2002. Also available in PDF format , as a PowerPoint show , and as aJPEG file. There is also a reprint of this work in gzipped postscript or pdf format. "Winds that Sail on Starlight ", a general colloquium presented at Space Telescope Science Institute (STScI) on 11/07/01; available in PDF format , as a PowerPoint show , and even as RealPlayer video of the actual talk. This is latest version of a similar talk I've given at several institutions, including at Penn State University (2/01.), Harvard-Smithsonian Center for Astrophysics (6/01), and Univ. de Montreal (9/01). " The Rocket Science of Launching Stellar Disks " a general colloquium presented at several institutions, including U. of Del (4/00), Johns Hopkins U. (5/ 00), and Swarthmore College (9/01). Here is PDF version of the talk , and here is html slide show of talk. " (Possible) Links Between Pulsation and Line-Driven Mass Loss in Massive Stars ", an invited introductory review presented at the IAU Colloquium #185 on Radial and Nonradial Pulsations as Probes of Stellar Physics , held in Leuven, Belgium from July 26-31, 2001. Here is a PDF version of the talk . Here is a digital picture gallery of photos taken during the conference. Here is link to proceedings write-up for the talk, in PDF or gzipped PostScript
" Interacting Stellar Winds: Theoretical Overview ", an invited introductory review presented at the workshop on ` held July 2000 on Isle-de-la-Magdelene, Quebec, Canada. Here is a PDF version of the talk. There is also a reprint of the proceedings write-up of this talk, in PDF or gzipped PostScript . Finally, here is a digital picture gallery of photos taken during the conference and its associated bike-trips. " The Outer Evolution of Wind Structure ", contributed talk at the Tartu (Estonia) workshop on " Thermal and Ionization Apects of Flows from Hot Stars ", August 1999. (There is also a reprint of the proceedings write-up of this talk, in PDF or gzipped-postscript .) " Effect of Clumping on Wind-Compressed-Disk Inhibition ", contributed talk presented at IAU Colloquium #175 on " The Be Phenonemon in Early-Type stars ", July 1999. (There is also a reprint of the proceedings write-up of this talk, in PDF or gzipped-postscript .) " Radiatively Driven Winds and Disks ", a summary overview of my research program presented to our instiute's annual `visiting committee'. " The Peculiar Physics of Line-Driving ", seminar presented at the University of Pittsburgh, March 1999. "Solar and Stellar Winds ", a 36"x36" single page, Powerpoint source file of Invited Poster presented at the " Great Discoveries in Astronomy " session of the Centennial meeting of the American Physical Society , April 1999. This is also available as a multi-page slide-show in Powerpoint , or its HTML export. As noted above, there is now a version with the text translated into french by Dr. Roland Grappin of the Observatoire de Paris-Meudon .
Effect of inner disk radius on Be star emission profile A Radiatively Driven Orbital Mass Ejection ( RDOME ) scenario for production of Be star disks. The basic ideas for this are contained the above-noted Powerpoint presentation on "The Rocket Science of Launching Stellar Disks ", for which I've also exported an html version .
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