A pioneer in studies of low-mass stellar evolution, globular clusters, deep mixing in stellar interiors, and the origin of UV-bright stars, Allen died of non-Hodgkin’s lymphoma in Silver Spring, Md., Feb. 1, 2022.
Born in Ephrata, Pa., Feb. 5, 1944, Allen graduated from Franklin & Marshall with an A.B. in mathematics. In 1970, he earned a Ph.D. in astrophysical sciences from Princeton. His dissertation was “A Method for Suppression of the Thermal Instability in Helium Shell Burning Stars.” Prior to receiving his Ph.D., Allen co-authored an influential study of the dynamical collapse of an isothermal gas cloud. He took a postdoctoral appointment at Yale.
In 1977, Allen became an NRC senior research associate at NASA’s Goddard Space Flight Center, retiring in 2012. He published improved model grids and made efforts to refine and update the numerical methods (along with the input physics) adopted in his stellar evolution code, and to automate it, so that long sequences of models covering the different evolutionary phases of low-mass stars could be covered in a single run. He participated in observing proposals with the Hubble Space Telescope and other ground- and space-based facilities.
Allen is survived by his wife, Tamsen; children Christine and Erik; and two grandchildren.
Graduate alumni memorials are prepared by the APGA.