The very long north–south baseline between Medicina (Italy) and Hartebeesthoek (South Africa) has been used to search for very compact structure in a sample of 16 strong 1665-MHz OH masers, distributed in galactic longitude from 355° to 50°. Three sources were detected and their OH spot sizes are estimated. The spot sizes are consistent with previous determinations of the galactic distribution of interstellar scattering.
Kemball, A. J., Diamond, P. J., & Mantovani, F. (1988). A search for very compact structure in 16 OH masers. Monthly Notices of the Royal Astronomical Society, 234(3), 713-718. https://doi.org/10.1093/mnras/234.3.713