Photographic History and Suggested Nature of the Radio Source 3C-48.
HARLAN J. SMITH, Dorrit Hoffleit · The Astronomical Journal · 1961
In what has been suggested as the first identification of a star with a radio source, Mt. Wilson astronomers noted (Sandage 1960, New York A.A.S. Meeting, December 31, unpublished; but see Sky and Tel. 21,148,1961) that the Cambridge object 3C-48 seems to coincide with a peculiar 16th magnitude star. With kind permission of Harvard Observatory and extensive help from C. Brooks, E. Dirkswager, S. Gross, B. Marsden, and J. Rodman, we have examined the location of 3C-48 on all plates in the Harvard collection which contain the region. Of some 2500 plates, most penetrated below 11th magnitude, 600 reached 13th, less than 100 reached 15th, and only 75 showed an image of the 3C-48 object. Between 1895 and 1952, no year had fewer than nine plates, the average being around 40. A full nova or supernova explosion at any time in that interval could scarcely have escaped detection. Careful magnitude estimates on all the plates showing the image indicate no variation greater than +0.2 mag. since 1898. The plate material is ill-suited for proper motion work, but no conspicuous motion has appeared in first rough measurements. Despite the negative results reported above, the size and Doppler-broadening of a faint nebulous shell around the star suggest that 3C-48 is nevertheless an exploded object. In fact, a consistent interpretation of the available data can be found with a picture in which 3C-48 is the remnant of a type I supernova similar to the Crab nebula, but intrinsically several times weaker, only 15 the age, and about six times farther away.