Biographical Memoirs Volume 66 (1995) / Chapter Skim
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Louis George Henyey
Louis George Henyey
Pages 168-189
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From page 169... ...
Major administrative posts included service as chairman of the Berkeley Astronomy Department, director of the Leuschner Observatory, director of the Berkeley computer center, and presiclent of the Astronomical Society of the Pacific. He was elected to the National Academy of Sciences in 1968.
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From page 170... ...
Henyey married Elizabeth Rose Belak, born in Budapest, on April 28, 1934; they h act three children: Thomas Louis, Francis Stephen, and Elizabeth Maryrose. He spent the years 1934-37 as a graduate student at Yerkes Observatory of the University of Chicago, where he served as an assistant astrophysicist and earner!
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From page 171... ...
As Greensteini remarks, "His perfectionism blencled with my somewhat coarser energy into confidence that we could finish everything we tried." The combination of observational and theoretical work involved both elaborate analytic radiative transfer calculations as well as observations of the spectra of emission and reflection nebulae, for example, those of the North America nebula and the Cygni nebula. During the war years, however, most of the effort of those staff members who remained at Yerkes (inclucling Henyey and Greenstein)
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From page 172... ...
learned about general numerical methods for solving nonlinear problems. He also c3 evelopect links with the Livermore Radiation Laboratory, which had probably the worId's most powerful computational facility during the 1950s.
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From page 173... ...
First, he developed a method for automatic solution of the equations of stellar evolution, suitable for electronic computers and applicable to a wide range of physical conditions and phases in the lifetime of a star. Second, he made a significant new calculation of the evolution of stars during their early history when gravitational contraction provides the main energy source, and during the transition phase when nuclear energy takes over from the gravitational source.
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From page 174... ...
If there are N zones in the star, and 4 dependent variables whose variations through the star are to be solved for, the method essentially involves solving 4N linear equations for the 4N unknown corrections to the basic variables. Once the model has convergent, the time is advanced en c!
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From page 175... ...
Once gravitational instability sets in, the protostar collapses in near freefall until internal temperatures and pressures become high enough so that the collapse is stopped and the star approaches hydrostatic equilibrium. At this point maximum
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From page 176... ...
The results showed that as a star contracts and heats in the interior, the luminosity gradually increases and the surface temperature increases until nuclear reactions become important. As the nuclear energy source gradually replaces the gravitational energy source the track changes direction and the star gradually declines in Juminosity and decreases slightly in surface temperature before settling onto the main sequence.
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From page 177... ...
With it the models made a transition from evolution at almost constant luminosity on the way over to the giant branch to rapidly increasing luminosity and slowly varying surface temperature in the giant branch itself; these theoretical models agreed with observations. It was demonstrated in 1961 by Professor Hayashi of Kyoto University9 that stars, in their evolution prior to the main sequence, exhibit roughly the inverse behavior.
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From page 178... ...
He wished to see a confirmation based on a full numerical solution. Before Hayashi made his discovery of the nature of pre-main-sequence evolution, Henyey had been in the process of developing an advanced stellar evolution computer code that took into account a wide variety of physical processes, including a detailed "mixing length" theory of the surface convection zones on coo]
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From page 179... ...
Although the interior radiative zone persisted for some time, its presence did not appreciably affect the evolution of the surface temperature and luminosity, which proceeded according to Hayashi's theory. By this time there was also convincing observational evidence supporting Hayashi's evolutionary tracks.
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From page 180... ...
The third paper considered the physical and mathematical approach to the calculation of the model atmosphere boundary condition that was combined with the stellar evolution program, identified several uncertain parameters in convection theory, and tested the influence of those parameters in the pre-main-sequence and post-mainsequence evolutionary phases of a star of five solar masses. These results helped to establish that the Hayashi phenomenon was insensitive to uncertainties in the treatment of stellar surface layers.
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From page 181... ...
On several occasions he invited groups of them to his home, which was beautifully located in the hills overlooking San Francisco Bay and was surrounded by a very fine garden to which he devoted much attention. The meetings were sometimes social affairs, but at other times they involved discussions of particularly difficult problems with the stellar evolution code.
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From page 182... ...
He discussed which version of the theory was most likely to be correct through a comparison with observed cluster stars. Three students jointly published a paperer in which they used the Berkeley stellar evolution program to produce solar models and to compare the theoretical neutrino fluxes observable at the Earth to the early experimental results.
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From page 183... ...
Henyey also devoted considerable energy to departmental and university affairs. When Otto Struve took a leave of absence in 1959 to become director of the National Radio Astronomy Observatory, Henyey took over his position as chair of the Astronomy Department and director of the Leuschner Observatory for the next five years.
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From page 184... ...
A radio astronomy laboratory had been established on the Berkeley campus during the late 1950s and an observing site had been set up at Hat Creek in northern California. He served on the advisory committee of the laboratory from 1961 to 1965.
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From page 185... ...
Mary Brunn, for providing the photograph and other historical information from the faculty files. Although this article is based primarily on my personal experience as a graduate student in the Berkeley department from 1960 to 1965, I have also benefited from Professor Greenstein's vivid review, from comments by Professor Martin Schwarzschild and from an article by Berkeley professors John G
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From page 186... ...
Stellar evolution in early phases of gravitational contraction. Publications of the Astronomical Society of Japan 13:450-52 (1961~.
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From page 187... ...
The spectra of the North American nebula and of the gamma Cygni nebula. Astrophys..~.
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From page 188... ...
93:327-32. 1945 Office of Scientific Research and Development reports on tank telescope; assorted chest X-ray optics f/1.4; wide angle lens mirror for pilot training; binocular scanner; and miscellaneous designs.
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From page 189... ...
VIII. The time scale for the diffusion of energy in the stellar interior.
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