Dave Jauncey

3C273: The Role of the Parkes Occultations in the Discovery of the First Quasars -- Dave Jauncey Colloquium

During 1962 a series of lunar occultations of the strong radio source 3C273 were observed by Hazard, Mackey and Shimmins (1963, Nature, 197, 1037) with the newly completed Parkes radio telescope. Analysis of these observations by Hazard gave the position of the two components, A and B, of 3C273 with sub-arcsecond precision. Most importantly the position was given in the optical reference frame, which allowed a unique identification of the optical counterpart. Such arc-second precision had not been achieved previously. It was soon found (Schmidt 1963, Nature, 197, 1040) that component B was coincident with a bright 13th magnitude stellar object, while component A coincided with a faint wisp or jet which ends 20" from B. Schmidt's spectrum of the bright 'star' with the 200" telescope found that the only explanation involved a redshift of 0.158 which allowed identification of the Balmer lines of Hydrogen, in addition to emission lines of MgII 2798 and [OIII] 5007. Now with two similar stellar-like objects, 3C48 and 3C273, the possibility of a chance-identification was vanishingly small. These new objects were called "quasars", and the remainder of 1963 saw a dramatic change in our understanding of the Universe. These changes and their origin are beautifully recorded in the First Texas Symposium on Relativistic Astrophysics.