Judith G. Cohen
California Institute of Technology
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Primary Section: 12, Astronomy Membership Type:
Member
(elected 2017)
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Biosketch
Judith Cohen is an astronomer recognized for her work on our Milky Way galaxy. She is known particularly for her work on the Galaxy's outer halo and its extremely metal-poor stars, as well as for her involvement in the design and construction of the Keck Telescope and its first light instruments. Cohen was born in New York City and grew up in Brooklyn. She attended public schools and also the Workmen's Circle schools there. With support from a National Merit Scholarship, she graduated from Radcliffe College in 1967 with a degree in astronomy. In 1971 she was awarded a PhD in astronomy from the California Institute of Technology (Caltech). She was a Miller Postdoctoral Fellow at the University of California, Berkeley from 1971 to 1974. She then became an assistant astronomer at the Kitt Peak National Observatory in Tucson, Arizona. In 1979 she joined the faculty of Caltech. In 2005 she became the Kate Van Nuys Page professor of astronomy there. She also serves as the Caltech co-chair of the Keck Science Steering Committee and is a member of the National Academy of Sciences.
Research Interests
Judith Cohen is interested in using the chemical abundances of stars to infer the history of our Milky Way galaxy, the formation of the Galactic halo, and the properties of other "local" galaxies as well as those of the high-redshift Universe. She modeled the integrated light of simple stellar systems to determine their age and metallicity. Subsequently, she and her team of postdoctoral fellows pursued detailed abundance analyses of globular cluster red giant stars, as well as the very rate extremely metal-poor stars in the Milky Way halo, looking for patterns that could be used to determine the nucleosynthetic origin of the elements. This helped to establish that the trends of abundance ratios with overall metallicity can be understood in most cases by the normal nucleosynthetic processes operating in massive stars at their deaths via core collapse supernova explosions combined with ejecta from thermonuclear explosions on white dwarfs. A careful study of the stable isotopes of magnesium in dwarf stars led to a better understanding of when various nuclear reaction chains within stars each began to make significant contributions to the interstellar gas in the Milky Way. With postdoctoral fellow Jorge Melendez, she carried out the first extremely high precision detailed abundance analysis of dwarf stars, looking for evidence of planets via very small changes in the ratios of refractory to volatile elements in the host star. Her current work focuses on using RR Lyr variables to study the outer halo of our galaxy. From roughly 1986 to 1995, she and the late J.B. Oke (professor of astronomy, Caltech) led the team that built the Low Resolution Imaging Spectrograph, one of the first light instruments at the Keck Telescopes, which is still very popular and in active use.
