Strömberg, Gustaf Benjamin
STRöMBERG, GUSTAF BENJAMIN
(b. Göteborg, Sweden, 16 December 1882; d. Pasadena, California, 30 January 1962)
Strömberg spent thirty years, the greater part of his working life, at the Mount Wilson observatory. His main contributions to astronomy were statistical analyses of stellar motions, made at a time when both the size and the manner of rotation of our galaxy were still uncertain quantities.
The son of Bengt Johan Gustaf Lorentz Strömberg and Johanna Elisabeth Noehrman, Strömberg prepared in Göteborg for study at the universities of Kiel and Stockholm. He was an assistant in the Stockholm. He was an assistant in the Stockholm observatory for eight years, ending in 1914, the year he married Helga Sofia Henning. In 1916, at age thirty-three, he obtained a Ph.D. from the University of Lund; his dissertation was written under the direction of Carl Vilhelm Ludwig Charlier.
In June 1916 Strömberg arrived at Mount Wilson. He served one year as a volunteer assistant in stellar spectroscopy and then was appointed to the staff as astronomer, a position he held until his retirement in 1946. The director in 1916 was Walter S. Adams, who had just developed a technique for estimating a star’s distance from its spectrum–referred to as a spectroscopic parallax–thus providing for the first time a way to convert large numbers of stellar brightnesses as observed into intrinsic luminosities, that is, absolute magnitudes. Strömberg’s first assignment was to help Adams analyze data on some 1,300 stars, looking for a statistically valid relation between motions through space and absolute magnitudes. They found that faint dwarf stars seemed to move faster than bright giant stars of the same spectral class.
Strömberg continued to analyze the wealth of observational material being obtained at Mount Wilson, and also took his turn at the telescope acquiring it. He was looking for large-scale preferential motions of stars. Having obtained a statistical estimate of how the sun moves through space, he used this to calculate the peculiar motions of stars (across the line of sight), and also the so-called K-term in radial velocities, which for any selected group of stars refers to a net speed either toward or away from us. His discovery of what was referred to at the time as“Strömberg’s asymmetry”confirmed tentative conclusions reached earlier by Boss, by Adams, and by Joy; he found that stars in the plane of the Milky Way had a marked preferential motion, directed around a galactic center approximately coincident with the one proposed by Shapley in 1918. Strömberg thus provided an early confirmation of Shapley’s theory, and also supplied the basic data to be used by Lindblad and by Oort in developing the presently accepted picture of galactic rotation.
Strömberg’s publications include“The Relationship of Stellar Motions to Absolute Magnitude,”in Astrophysical Journal, 45 (1917), 293–305, written with Walter S. Adams;“A Determination of the Solar Motion and the Stream-Motion From Radial Velocities and Absolute Magnitudes of Stars of Late Spectral Types,”ibid., 47 (1918), 7–37; “Space Velocities of Long-Period Variable Stars of Classes Me and Se,”ibid., 59 (1924), 148–154, written with Paul W. Merrill;“The Asymmetry in Stellar Motions and the Existence of a Velocity-Restriction in Space,”ibid ., 59 (1924), 228–251;“Analysis of Radial Velocities of Globular Clusters and Non-Galactic Nebulae,”ibid., 61 (1925), 353–362; and“The Asymmetry in Stellar Motions as Determined From Radial Velocities,”ibid., 61 (1925), 363–388.
Eighty-seven publications by Strömberg are listed in the Yearbook of the Carnegie Institution of Washington, 15 (1916)–46 (1946–1947). In addition Strömberg wrote“Angenäherte allgemeine Störungen des Planeten 471 Papagena und 123 Brunhild,”in Astronomische Nachrichten, 195 (1913), cols. 129–140, written with Vilhelm Hernlund; Strömberg’s dissertation,“On a Method for Studying a Certain Class of Regularities in a Series of Observations, With Application to the Temperature Curve of Uppsala”(Lund, 1915); and the two books mentioned above.
Sally H. Dieke