John G. Mengel, a computer specialist who made significant contributions to the study of Population II stars and subsequently to terrestrial atmosphere models, died of cancer on 10 July 2007 at age 62. Born to Dr. John G. and Mary Bender Mengel in Lebanon, Pennsylvania, on 30 April 1945, he graduated from Lebanon High School, and went on to receive his bachelor’s degree in physics from Franklin and Marshall College in 1967 (where he received the Rawnsley Prize for Excellence in Science) and his masters degree in astronomy from Harvard University in 1969.
Mengel transferred to Yale University’s astronomy department after taking a summer course on stellar-evolution research while at the University of Arizona in 1968, where Yale astronomer Pierre Demarque delivered a series of lectures on the subject. In 1972, Mengel completed his Ph.D. thesis under Demarque titled “Evolution on the Asymptotic Branch of a Globular Cluster Star of Low Mass.” Of that period, Demarque explains that “the quest for understanding the evolution of stars in globular clusters was a central research focus in astronomy. With the advent of fast computers, stellar theorists had turned to the construction of stellar evolutionary sequences based for the first time on physically realistic stellar models. Most aspects of stellar evolution were only sketchily known at the time. In particular, the advanced phases, on the giant branch and beyond, still had to be elucidated.”
Mengel’s thesis and his subsequent research during his post-doctoral years at Yale led to the publication of a series of papers, variously co-authored with Demarque, fellow post-doc Allen V. Sweigart, and others, on the evolutionary stages of Population II stars in globular clusters. Computations to reveal the outcome of the red-giant helium core flash were so demanding that they outstripped the capacity of Yale’s computers at the time and had to be carried out on more powerful machines at the Goddard Space Flight Center in New York City.
Among Mengel’s notable papers are “Binary Hypothesis for the Subdwarf B Stars,” with John Norris and Peter Gross (1976, ApJ, 204, 488); and “Meridional Circulation and CNO Anomalies in Red Giant Stars,” with Allen V. Sweigart (1979, ApJ, 229, 624). According to Demarque, John Mengel “remained a mainstay of the Yale stellar evolution group well into the 1970's, during which time we collaborated very closely on many projects.”
Afterward, Mengel moved to the Washington, D. C., area, where he was employed at the NASA Goddard Space Flight Center, Laboratory for Atmospheric Sciences, Greenbelt, Maryland; Applied Research Corp., Landover, Maryland; and most recently Science Systems and Applications Inc., Lanham, Maryland. During this latter part of his career, which spanned more than 25 years, he developed sophisticated, computer-based models of Earth's atmosphere. He authored or co-authored nearly 100 papers in scientific journals and conference proceedings.
“John was a gifted scientist,” Pierre Demarque recalls, “very private and overly self-effacing. Those who knew him well remember his friendly intensity, his loyalty to the group, and his wry sense of humor.” Mengel’s frequent research collaborator and longtime friend, Allen V. Sweigart comments, “In all of his work, John was always creative in his scientific thinking, very concise in his writing and insistent on maintaining a high scientific standard, in addition to being personally very modest. I look back with fond memories on those days and still cherish the opportunity to work with John.”
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