Herman Lawrence (Larry) Helfer, a respected professor emeritus of astronomy at the University of Rochester, died in Marlton, New Jersey, on 11 April 2021. He carried out fundamental, groundbreaking studies of the elemental abundances in stars during the 1950s and 1960s, when astronomers were just beginning to understand the role of stellar nucleosynthesis in determining the elemental abundances in the cosmos. His scientific interests were far broader than this, however, extending from highly theoretical work in fluid dynamics, plasma physics and general relativity, to observational investigations in radio, infrared, and optical astronomy, and his research subjects bridged broad scales, from planetary to cosmological.
Larry was born on November 11, 1929, in the Bronx, New York. He developed his lifelong interest in astronomy as a young boy, and he met his future wife, Joanne Salomon, in the first grade. As a teenager he and his friends rode public transportation all over Manhattan to take advantage of the cultural and intellectual opportunities—such as the Hayden Planetarium—available within the metropolitan area, and he was an officer of New York City’s student-run Junior Astronomy Club , sponsored by New York University.
He graduated from the Bronx High School of Science in February 1947 and earned his Bachelor of Philosophy from the University of Chicago in June 1948. He continued graduate studies in astronomy at the University of Chicago, where he had physics courses under Enrico Fermi, Edward Teller, and Gregor Wentzel. He completed his doctoral research under the direction of the late Nobel Laureate Subrahmanyan Chandrasekhar (1910–1995). He was a National Science Foundation Predoctoral Fellow from 1952 to 1953 and earned his Ph.D. in astronomy in 1953 . His doctoral research may have been the first work to demonstrate that magnetic disturbances in interstellar (atomic) clouds can steepen and amplify—but resist the strong compression of a purely hydrodynamic shock—forming what are now called “magnetic precursors.” This phenomenon was rediscovered by others decades later, long after Larry had moved on to other interests.
Upon receiving his degree, Larry served in the U.S. Army for two years. He then became a Fellow of the Carnegie Institution of Washington, working in radio astronomy at the Department of Terrestrial Magnetism from 1956 to 1957, where he participated in 21-centimeter radio surveys of hydrogen gas in the Milky Way Galaxy . He married Joanne Salomon on December 22, 1956, and the newly married couple was toasted at the December 1956 meeting of the American Astronomical Society in New York City.
Following his Carnegie Institute fellowship, Larry held a postdoctoral appointment at the California Institute of Technology, where he worked at the Mount Wilson and Palomar Observatories. There he carried out some of his most often-cited work on the abundances of elements in the stars, in collaboration with George Wallerstein (1930–2021), then another young astronomer about his own age, and the late Jesse L. Greenstein (1909–2002). This work , which demonstrated that globular cluster giants are deficient in metals when compared to stars in the Galactic disk, was cited as a landmark paper in the Centennial Issue of the Astrophysical Journal “for helping to establish the foundation of the modern understanding of the link between Galactic structure and Galactic nucleosynthesis” .
Larry joined the faculty of the Department of Physics and Astronomy at the University of Rochester as an Assistant Professor in 1958. In addition to his new teaching and committee responsibilities, he continued his astronomical research, both individually and in collaboration with colleagues old and new. His most-frequently cited paper—done in collaboration with Wallerstein, Greenstein, and others in 1963—concerned red giant stars with extreme deficiencies of heavy elements, by factors ranging up to 800 . That same year Larry was promoted to Associate Professor of Astronomy. He was awarded a Guggenheim Fellowship in 1965, which supported a sabbatical year at Leiden Observatory (Leiden University). Larry was also one of the founders of the University of Rochester’s C.E.K. Mees Observatory in 1965. In 1970, he was promoted to Professor of Astronomy.
During the late 1970s, when University of Rochester infrared (IR) astronomer Judith L. Pipher undertook high-altitude (up to 45,000 feet) observations on the Kuiper Airborne Observatory (KAO, a modified Lockheed C-141A Starlifter jet aircraft), Larry enthusiastically joined Judy and her colleagues. The high-altitude flights required the on-board astronomers to undergo flight training in advance and to wear oxygen masks during the observing flights. Larry participated in several of the IR observing runs, joining in interactions with the graduate students in the IR program, and co-authoring several of the papers that resulted from these and other IR and multiwavelength observations .
Larry’s observational work did not prevent him from continuing with theoretical work, however. He was the single author or a co-author of several papers from 1970 on . In 1986, he was appointed a Senior Scientist in the University’s Laboratory for Laser Energetics (LLE), where he engaged actively with the LLE scientists, regularly attended the weekly presentations on the status of various LLE projects and other topics, and published papers in plasma physics .
In 1990, he published a paper on the likelihood that several billion years ago, the northern plains of Mars may have been the sites of ancient oceans, which may have left fossil evidence of primitive lifeforms . The Mars Odyssey spacecraft, which has been orbiting the Red Planet since 2001, has confirmed that large bodies of water may once indeed have existed on Mars.
Larry supervised PhD students John Perry, Jim McMullin, and Peter Jennens, and he served as co-advisor for several more. He was a mentor who offered encouragement and advice to many undergraduates, graduate students and postdoctoral scholars; he and Jo welcomed students and postdocs to their home for many barbeques and meals over the years. He was an avid participant in department colloquia and was known for his probing questions on a variety of topics in astronomy and physics.
He retired as an active member of the Rochester faculty in November, 1999, becoming a Professor Emeritus and a Senior Faculty Associate, but he continued to be active in research. His final, single-author paper, “The Motions of Dark Matter,” was published shortly before he turned 90 in 2019 . He posted another paper on dark matter in 2020  and was working on a theoretical manuscript at the time of his death.
Larry’s interests extended well beyond science; he read history, political and social theory, and literature. He and Jo were passionate about travel and the performing and fine arts. She predeceased him in 2010, after nearly 54 years of marriage.
Larry lived in the Rochester, New York, area for most of his adult life, but in 2020 he moved to Marlton, NJ, to be closer to family. All four of his children—Adam, Elizabeth, Martha, and Tamara—were with him during his final week. Larry will be greatly missed, not only by his family—including his children, their spouses and his grandchildren—but also by his many friends and colleagues around the world. He was a passionate scientist whose curiosity about the universe in which we live never waned.