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Martin Cohen (1948–2020)

Cohen was a pioneer in the field of infrared astronomy, in particular through studies of star formation, evolved stars and infrared calibration.

Published onFeb 02, 2021
Martin Cohen (1948–2020)

Credit: UC Berkeley Department of Astronomy.

Martin Cohen died on Saturday the 7th of March, 2020.

A pioneer in the field of infrared astronomy, in particular through studies of star formation, evolved stars and infrared calibration, Martin Cohen was born on July 27, 1948 in Manchester, England. He was educated at Manchester Grammar School and then read for a Natural Sciences degree at Clare College, Cambridge, England. Upon graduating in 1969 he embarked on a PhD at the Cambridge Observatories under the supervision of David Dewhirst. A large portion of Martin’s PhD studies were spent at the University of Minnesota, supported by a UK Science Research Council scheme to provide training in the rapidly growing new field of infrared (IR) astronomy. At Minnesota, where he worked with Nick Woolf and Ed Ney, the very cold winters and the consequently low atmospheric water vapor content provided excellent conditions for thermal infrared astronomy. While based at Minnesota, he helped commission a new 1.5m telescope at Mount Lemmon Observatory in the Catalina mountains outside Tucson, Arizona, where he obtained 2 to 20 micron bolometer observations of a wide range of T Tauri and Herbig Ae/Be stars. These observations were published in a series of four MNRAS papers along with an analysis of the stellar optical to mid-IR spectral energy distributions, from which he concluded that the majority of the sources were on pre-main sequence radiative cooling tracks.

Upon completion of his PhD, Martin took up a research position at the University of California, Berkeley, where he worked with Len Kuhi and others. In addition to gaining access to Lick Observatory telescopes, he continued to carry out extensive mid-IR observations using the Mt. Lemmon 1.5m telescope, averaging nearly a week per month of observing time for several years and carrying out mid-IR surveys of pre-main-sequence stars, Wolf-Rayet and OB stars, and planetary nebulae. During this period, he began a collaboration with Russell Walker and Stephan Price of the US Air Force’s Cambridge Research Laboratories who were conducting a low angular resolution rocket-borne all-sky survey at 4, 11 and 18 microns. Using ground-based optical and mid-IR observations Martin identified a large number of sources from the AFCRL survey, the most famous of which was probably the Red Rectangle nebula associated with the post-main-sequence star HD 44179 and found to be the emitter of an archetypal unidentified infrared band (UIB) spectrum, now usually associated with polycyclic aromatic hydrocarbons (PAHs).

In 1979 he published with Kuhi a 100-page paper in the Astrophysical Journal Supplement Series [1] in which they presented optical and IR spectrophotometry for 500 young stellar objects in six star-forming clusters and associations, enabling their placement in H-R diagrams. This paper has received over 1300 citations. In 1980 Martin moved from Berkeley to the NASA Ames Research Center on the other side of the Bay (later returning to Berkeley). At Ames, he collaborated on programs that used the Kuiper Airborne Observatory to obtain mid- and far-IR observations of post-AGB PAH sources, Wolf-Rayet stars, Herbig-Haro objects and SN 1987A. In 1983 he proposed that the T Tauri star HL Tau had a circumstellar disk — much later, the disk was directly imaged by ALMA.

With the importance of accurate infrared calibration ever clearer, he also embarked on a series of papers that set out infrared spectral calibration methods and defined calibration sources for both ground-based and spaceborne observations. Infrared space projects to which he provided key calibration expertise included ESA’s ISO and Herschel observatories, the US’s MSX, Spitzer and WISE missions and the Japanese AKARI mission. He was heavily involved in the scientific exploitation of these facilities, for example leading a series of papers on planetary nebulae and post-AGB objects that showed dual dust chemistries, e.g., both O-rich silicate bands and C-rich PAH bands.

In 2012 Martin decided to retire from astronomy research due to having been diagnosed with a rare neurodegenerative condition. During his career he published more than 300 refereed papers, 124 of them as first author and was a highly cited researcher, with a Hirsch h-factor of 88. He also published two popular-level books. “In Quest of Telescopes,” about his experiences using different telescopes around the world, was published in 1980 [2] while “In Darkness Born: The Story of Star Formation” was published in 1988 [3]. Martin died on March 7, 2020 in Oakland, California and is survived by his wife Barbara and his two children, Daniel and Nicola.

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