Angular Diameters of Quasars of Unusual Colour

TWO neutral-coloured stellar objects, OH471 and OQ172, have been shown to be QSOs with redshifts of 3.40 and 3.53 respectively1,2. This has stimulated interest in other radio sources identified with stellar objects which lack the ultraviolet or blue colour excesses normally associated with quasars. Browne and McEwan3 have published a list of objects which, though blue, show no ultraviolet excess; I. W. A. B., J. H. Crowther and R. L. Adgie have prepared a list (unpublished) of sources identified with neutral coloured objects, which includes both OH471 and OQ172. Sources of both types have been put forward as possible high redshift QSOs. We have measured the radio angular diameter of the sources on both lists, and of four further objects which may possibly be similar. These objects4,5, OJ287, W Com, ON235 and BL Lac, show no spectral lines but resemble OH471 and OQ172 in colour.