Gray was a high-resolution spectroscopist, best known for his widely used textbook on the analysis of stellar spectra.
David F. Gray passed away peacefully in Stratford, Ontario on August 15, 2022, at the age of 83.
Gray was born in Chicago, Illinois, graduating with a B.S. in Physics from the University of Wisconsin in 1960, and an M.Sc. (1962) and Ph.D. (1966) in Astronomy from the University of Michigan. His Ph.D. thesis, titled “Photometric Determination of Stellar Radii,” was supervised by Allen C. Cogley and Louis Kauffman. He joined the newly-formed Department of Astronomy at the University of Western Ontario (informally known as Western University) in London, Canada in 1966, and retired from Western’s combined Department of Physics & Astronomy in 2004.
As Professor Emeritus, Gray was active in research until his death, including the 2022 publication of the fourth edition of his well-known textbook “The Observation and Analysis of Stellar Photospheres.” His contributions to astronomy included being president of the International Astronomical Union Commission 36 on the Theory of Stellar Atmospheres (1988–1991) and serving on the observing-time allocation panels for the Hubble Space Telescope and the Canada-France-Hawaii Telescope. He was an active member of the Canadian Astronomical Society and the American Astronomical Society. He was invited to lecture world-wide at many institutions, including the Canary Islands Winter School of Astrophysics, the Catania Observatory and the Beijing Observatory. The asteroid 236616 Gray is named in his honor.
Gray was a high-resolution spectroscopist, using the technique to investigate many properties of stars including photospheric granulation, rotation, magnetic activity, temperatures, radial velocities and radii. He was instrumental in the 1969 establishment of Western’s Elginfield Observatory near London, which featured a 1.2-meter Ritchey-Chrétien telescope built by Boller and Chivens. Gray was the builder and principal user of the Observatory’s coudé spectrograph; its data provided the basis for a majority of his 146 refereed papers. Familiar names such as Antares, Betelgeuse, and Arcturus were among the individual bright stars which received his thorough attention. Gray’s departmental webpage asserted his view that “observing stars and analyzing starlight has got to be the best profession around.”
His dedication to analyzing starlight, agnostic to any particular model, led many colleagues to describe Gray as a “pure observer”, someone who believed that the real truth was in the data. Gray’s expertise in stellar spectroscopy led to his brief involvement in the early studies of exoplanets via radial velocity observations. With two papers in 1997 (one co-authored with A.P. Hatzes) he challenged Mayor and Queloz’s 1995 claim that radial velocity variations in the spectrum of 51 Peg were due to a planetary companion. In 1998 he followed up with a paper that retracted his earlier results and concluded that “a planet may indeed be the best explanation for the radial-velocity results.” D. Cenadellia and A. Bernagozzi recount the history in their 2015 paper, “Youth plus experience: the discovery of 51 Pegasi b” .
One of Gray’s best-known contributions to astronomy is his textbook, first published by Cambridge University Press in 1976, with a fourth edition completed in 2021. The more than 2300 citations to the various editions indicate that he taught generations of astronomers how to derive stellar parameters from spectra; more than a few have remarked that the book’s explanation of Fourier transforms cemented their understanding. His self-published text “Lectures on Spectral-Line Analysis: F, G, and K Stars” appeared in 1988, featuring hand-drawn diagrams and the occasional cartoon! His webpage description of the book commented that its “ideas and concepts remain valuable for scientific investigation.” It is fitting that the last paper Gray published before his death, authored in 2019 with graduate student T. Kaur, is titled, “A recipe for finding stellar radii, temperatures, surface gravities, metallicities, and masses using spectral lines,” completing his legacy in teaching others how to understand and interpret the spectra of stars.
For additional information see Gray’s AstroGen entry.