Philip C. Keenan (1908–2000)

Philip Keenan was Professor of Astronomy Emeritus at Ohio State University when he died at age 92 on 20 April 2000 at Riverside Hospital in Columbus. Keenan was one of the most distinguished researchers of the 20th century in the field of stellar spectroscopy. The Morgan, Keenan, and Kellman classification system, which was published in 1943, became the standard system in the field and remains so today, over half a century later. The system provided the fundamental observational framework for developing our understanding of the nature and evolution of the stars, an understanding that is one of the intellectual triumphs of the 20th century.

Professor Keenan had a remarkably long and productive career in astronomy, with a publication record covering 71 years. His first research paper in a professional journal was written while he was an undergraduate at the University of Arizona and appeared in 1929. He continued to be active in research until shortly before his death, and his most recent paper in the Astrophysical Journal was published in 1999.

Philip Keenan was born in Bellevue, Pennsylvania on 31 March 1908. He received his BS and MS degrees from the University of Arizona in 1929 and 1930. Then he went on to earn his PhD in 1932 at the University of Chicago, where he was an instructor from 1936 until 1942. He was a physicist with the Navy Bureau of Ordnance from 1942 to 1946. In 1946 he became assistant professor at the Ohio State University and a staff member of the Perkins Observatory of Ohio State and Ohio Wesleyan University. He was on the Ohio State faculty until 1976, when he retired as professor and became Professor Emeritus. He continued his research at Ohio State for another 24 years.

Keenan was particularly interested in stars cooler than the sun, whose spectra are complex and contain a large number of atomic and molecular features. The intrinsically luminous cool stars are in advanced stages of evolution. Their spectra indicate both the products of nuclear processing that has occurred in their cores and the processes of mixing of the outer layers of the star. These stars eject their outer envelopes into space as they complete their life cycles and are important contributors to the evolution of galaxies like our Milky Way.

Philip's dedication to astronomy, his long career, and his extensive knowledge of the field were an inspiration to all the members of the Ohio State Astronomy Department, and especially to the students who knew him. At the Perkins Observatory he also found time to maintain a lovely wild flower garden by a small stream near the observatory building.