1. Greenberg, J. M. and Hong, S. S.: 1974a, in F. S. Kerr and S. C. Simonson (eds.), ?Galactic Radio Astronomy?,IAU Symp. 60, 155.
2. Greenberg, J. M. and Hong, S. S.: 1974b, in A. F. M. Moorewood (ed.), ?Hii Regions and the Galactic Centre?,Proc. of the 8th ESLAB Symp., p. 153.
3. Greenberg, J. M. and Stoeckly, R.: 1971,Nature 230, 15.
4. Herbig, G. M.: 1967, in H. van Woerden (ed.), ?Radio Astronomy and the Galactic System?,IAU Symp. 31, 85.
5. Herbig, G. M.: 1975,Astrophys. J. 196, 129.