Henry Emil Kandrup died on 18 October 2003 at his home in Gainesville Florida. Henry was a theoretical astrophysicist specializing in the application of chaotic dynamics to stellar systems. At the time of his death, Henry was a Professor at the University of Florida where he had taught for 13 years.
Henry was born in Manhasset, New York on July 24, 1955 and spent most of his childhood in Great Neck. His parents, Jytte and Fred, were immigrants from Denmark where his father had worked as a silver smith. Henry was a precocious child, skipping both third and fifth grades. With the help of Sidney Spivack, a professor of sociology at Columbia University, his parents enrolled Henry in the Brooks Preparatory School in Andover, Massachusetts. After graduating at age 16, Henry enrolled at Cornell, transferring to Princeton the following year.
Henry's parents adored their only child and worked hard to provide him with intellectual opportunities. Henry became an accomplished musician (organ, piano, French horn) and linguist (English, Danish, German) and was a passionate devotee of opera and ballet.
Henry received his PhD in 1980 from the University of Chicago, where his thesis advisor was James Ipser. He taught at Oakland University in Michigan and Syracuse University in New York before coming to the University of Florida in 1990.
Henry was sui generis. He shunned conventionality in his personal appearance and in his public demeanor, and always chose forthrightness and candor over polite silence. But to those of us who knew Henry well, his bluntness was a reflection of his intellectual consistency. Henry always said exactly what he thought, both in his published work and his public presentations, and never compromised himself for the sake of appearances. Nothing that he said or wrote was less than fully thought out.
Henry's PhD thesis was entitled "Stochastic Problems in Stellar Dynamics," and most of his subsequent research was in this field. Motion in stellar systems can be stochastic for three reasons: deflection of trajectories by close encounters; non-integrability of the smoothed-out potential; and an oscillating mean field. Henry made important contributions to our understanding of all three sorts of chaos. In a series of papers from the early 1990's, Henry developed the idea of ``chaotic phase mixing," the process by which an ensemble of points evolves toward a uniform coarse-grained population of phase space. Prior to Henry's work, the evolution of stellar systems to a steady state was attributed loosely to "violent relaxation," defined as phase-space repopulation driven by changes in the smooth potential. Henry pointed out that changes in the gravitational potential do not by themselves constitute relaxation; at best, they can contribute to relaxation by inducing a degree of chaos in the stellar trajectories. But it is the chaos that is responsible for the mixing and hence for the approach to a steady state.
Among his other important contributions to stellar dynamics were a formal demonstration of the equivalence of Landau damping and phase mixing, and a proof (with J. F. Sygnet) of the linear stability of a broad class of stellar systems. Shortly before his death, Henry was working on the chaotic dynamics of charged particle beams and on the influence of binary super massive black holes on orbital motion in galaxies.
Henry was one of the principle organizers of more than a dozen workshops on non-linear dynamics in astronomy and astrophysics that were held at the University of Florida. At the time of his death, he was negotiating with Springer Verlag over publication of a monograph, Hamiltonian Galactic Dynamics.
Henry was famous for the energetic quality of his lectures. Like many other excellent teachers, he drew upon his research to enliven his undergraduate teaching. Under Research Interests, his web site lists "creative utilization of playdough, margaritas, and spirographs in graduate and undergraduate teaching." Henry received numerous teaching citations and awards; he was consistently voted the best teacher in the department by his University of Florida students, and his Introductory Astronomy courses at Syracuse were cited as "Recommended Courses" in Lisa Birnbach's New and Improved College Book for 1990.
Henry was also well known for his dedication to students and postdocs. He was an exceptionally patient and gentle advisor, never openly critical, and often gave more credit to his students than was strictly necessary. He also took a deep personal interest in his students' welfare; as he told one of them, "an advisor should spend half of his time as the student's analyst."
Henry was a model scientist in many ways. It is hard to imagine stellar dynamics without him.