Biographical Memoirs Volume 67 (1995) / Chapter Skim
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Harold Lester Johnson
Harold Lester Johnson
Pages 242-261
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From page 243... ...
Here he met Albert Whitford, an astronomer then applying electronic techniques to photoelectric measurements of the light of stars. Toward the end of the war years Johnson moved to the Naval Ordnance Test Station, Inyokern, California, where he worked with Gerald Kron, also an astronomer engaged in the photoelectric photometry of stars.
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From page 244... ...
His first two papers, published in 194849 in The Astrophysical Journal and the Publications of the Astronomical Society of the Pacific, dealt with electronic circuitry and with the ultimate sensitivity limit set by quantum noise. These marked the beginning of a lifetime of dedication to high-precision astronomical photometry, a field of which he was to become the leading practitioner.
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From page 245... ...
Slipher, that a second try at using his talents would be in the best interest of the observatory. This was agreed and in August 1952 Harold Johnson returned as staff astronomer to Lowell Observatory, where free of teaching (luties and under a favorable sky, he could devote full time to his efforts to push stellar photoelectric photometry to its ultimate limits.
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From page 246... ...
The charge sensitivity fell far short of reaching the quantum noise limit. The thermionic amplifier introduced by Whitford in 1930 considerably increased the sensitivity of photoelectric observations.
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From page 247... ...
Attempts to match the international photographic magnitudes were complicates! by the wide spectral range covered by blue-sensitive photographic emulsions, a difficulty that had led to poor agreement between magnitudes measurect with different telescopes; the ultraviolet cutoff was dependent on absorption by the flint glass component in refractors or on the falling reflectivity of the silvered mirrors in reflectors.
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From page 248... ...
Johnson, alone or in collaboration with AlIan Sand age, Richard Mitchell, Braulio Iriarte, and others, made massive applications of this system to galactic clusters, producing well-defined, precise color-magnitude and color-color cliagrams, that is, plots of apparent V magnitude versus B-V color inclices (resembling the Hertzsprung-Russell diagram of luminosity versus effective temperature) and of U-B color versus B-V.
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From page 249... ...
Meine} in the site survey for the future National Optical Astronomical Observatory (NOAO) , which was eventually built on Kitt Peak near Tucson.i In 1956 he actually spent six months in Phoenix, where the initial NOAO office was located at the time.
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From page 250... ...
It is during this period in Texas that Johnson first came In contact with Frank I~ow, who was then a physicist with Texas Instruments in Dallas, where some very sensitive infrared detectors were being developed. Johnson immediately seized on this opportunity to build a photometer extending the U
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From page 251... ...
It was also during his stay in Austin that Harold Johnson became aware of the remarkable work of Larry Mertz, at Harvard Observatory, where he had built the first experimental Fourier-transform interference spectrometer (195859~. This author, who was there at the time, remembers vividly how the Harvard faculty failed to appreciate the significance of what Mertz was doing and dismissed him as a mere "tinkerer." Made aware of Mertz's work, Johnson immediately grasped the enormous potential of interference spectrometry, particularly for the infrared, and before leaving Texas proceeded to build the first successful Fouriertransform stellar interferometer working in the near infrared.
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From page 252... ...
During the same period Johnson utilized the accumulated observational data on the spectral energy distributions of stars of all types to derive a new set of bolometric corrections to their visual magnitudes and then to establish a revised temperature scale more directly based on observed
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From page 253... ...
The infrared excess at the longest wavelengths in certain clusters over the normal absorption was, in the end, identified as radiation from warm circumstelIar crust shells, rather than abnormal properties of the interstellar dust particles. The fundamental contributions were summarizer!
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From page 254... ...
Haro, identifying a peak in the Sierra de San Pedro Martir, Baja California, at an altitucle of 2,800 meters (9,200 feet) among the pine trees of a protected national forest, as suitable for the proposed observatory, was crucial—according to Mendoza, 'without his help, no SPM observatory, most likely." Of special importance and of interest to Johnson was the low water vapor content of the atmosphere, making it very suitable for work in the infra
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From page 255... ...
In grateful recognition of his role in this project and in the development of Mexican astronomy in general, the National University of Mexico conferred him the degree of doctor honoris cause in 1979 and, after his untimely death the next year, the Universities of Mexico en cl Arizona named after him the I.5-meter aluminum-mirror infrared telescope Johnson had brought from Arizona to Mexico. Symposium 96 of the International Astronomical Union on Infrared Astronomy held in 1980 was dedicated to Harold ~ohnson's memory.
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From page 256... ...
After HaroIcl's untimely death in 1980 in Mexico City, Mary returned to Tucson, where she lives in retirement. To those who clid not know him well, Harold Johnson may have seemed to be often blunt, brusque, and lacking in the suave polish necessary to become a successful academic.
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From page 257... ...
With his colleagues he measured thousands of stars that became reference standards. Johnson applied these measurements to calibrate spectral energy distributions of stars and thus provide an improved observational basis for the stellar temperature scale en c!
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From page 258... ...
NOTES 1. The writer remembers that iohnson's own preference for the site of the new observatory was an isolated peak, Slate Mountain, in the desert northwest of Flagstaff as a better, darker, and dryer site than Kitt Peak and likely to remain free of light pollution for many years, but practical considerations of accessibility, development costs, and living convenience for the staff prevailed in the end.
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From page 259... ...
Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas. Astrophys.
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From page 260... ...
The colors, bolometric corrections and effective temperatures of the bright stars.
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From page 261... ...
Thirteen-color photometry of 1380 bright stars over the entire sky.
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