James R. Graham

James R. Graham is an Irish astrophysicist who works primarily in the fields of infrared astronomy instrumentation and adaptive optics.

Graham pursued physics as his undergraduate major at Imperial College London, graduated with a BSc in 1982. He went on at Imperial College London to receive his PhD in physics in 1985. After receiving his PhD, Graham first held a research position at Lawrence Berkeley Lab, followed by a position at the California Institute of Technology. Since 1992, he has been a professor of astronomy at University of California, Berkeley.

In 1994, Graham was a member of a team that made one of the first definitive identifications of a brown dwarf in the Pleiades open cluster, which was also one of the first important discoveries made using the Keck telescopes. In the preceding years, other claims of brown dwarf detections were made and then often retracted or disputed. Graham's team looked for the signature of lithium absorption lines in the spectrum of the object. Lithium is quickly depleted in low mass stars due to mixing that brings the lithium in to contact with the hydrogen fusing core. As brown dwarfs by definition lack hydrogen fusion, the presence of lithium in the atmosphere of a low mass object is either an indicator of extreme youth or the absence of fusion. As such, the abundance of lithium in the atmosphere of PPL 15, along with the estimated age of the stars in Pleaides, indicate that PPL 15 is a brown dwarf.

...
Wikipedia