A USAGE OF THE VLBA: GRAVITATIONAL LENSING AND COMPACT/MEDIUM SYMMETRIC OBJECTS Pedro Augusto 1 (et al. 2 ) 1 Departamento de Matemática e Centro de Ciências Matemáticas, Universidade da Madeira, Caminho da Penteada, 9050 Funchal, Portugal 2 Too many institutions (see acknowledgments for names of collaborators) 0. Summary of the VLBA Observations 1.The VLBA as the “Last Word”: A ” gravitational multiple imaging search 3. The Ongoing Study of ~1 kpc CSO/MSO Candidates Confirmed 3.2 Uncertain3.3 Ruled out 3.4 Still reduction awaiting sources Next month, after (lots of and prolonged) technical problems at Univ. Madeira, data on 21 sources will be reduced. Results to be published on Augusto et al (2003b). Two confirmed CSOs observed with the MERLIN+VLBA (Augusto et al. 1999). One confirmed MSO observed with the MERLIN+VLBA (Augusto et al. 2003a). Are these two sources, imaged by MERLIN+VLBA, a nuclear core plus one sided jet or are they double-hotspots (hence CSO/MSOs)? This MERLIN+VLBA image shows one example of a source that consists of a core plus one-sided jet. Useless? Not at all.These are excellent narrow- -line region probes via their jets, which often show strong features. 2. The First Unambiguous Double-Screen multiply imaged system: B Although B was suspected as a lens system since its 1991 VLA serendipitous discovery (MERLIN+HST image on top), the VLBA was the breakthrough (adapted from Augusto 1996 and Augusto et al. 2001). The A & D components are believed to be the same multiple image, while B & C are probably physically related to the closest of the two lenses seen with the HST (G1 at z = ; G2 is at z = ). For the model see Chae et al. (2001) and Augusto et al. (2001) for other details. References: Ackowledgments: The final clarification on two lens candidates, with the vital help of the VLBA. Adapted from Augusto et al. (1996). VLA (1991) MERLIN (1995) VLBA (1995-6) Thirteen lens candidates have been ruled out with the vital help of the VLBA (Augusto et al. 1998). In the end of the project, no gravitational multiple images were found and the cosmological implications of this result are presented in Augusto & Wilkinson (2001) and the continued study of this sample of sources is described below in a new emerging project. I thank Fundação Calouste Gulbenkian (Portugal) for the grant that allowed me to come to this conference. I also acknowledge the Fundação para a Ciência e a Tecnologia for the several PhD/PostDoc/Project grants that have allowed almost all of the work presented here to get done. Finally, I would like to warmly acknowledge the following collaborators (in alphabetical order) without whom most of the work presented would not have happened: Aparício, N., Blandford, R.D., Browne, I.W.A., Caires, N.B., Chae, K.-H., Chandler, C. J., de Bruyn, A.G., Edge, A.C., Fassnacht, C.D., Garrett, M.A., Gizani, N.A.B., Gonçalves, A.L., Gonzalez-Serrano, J.I., Henstock, D.R., Hjorth, J., Jackson, N., Jaunsen, A. O., Koopmans, L., Leahy, J.P., Mao, S., Marlow, D.R., Muxlow, T.W.B., Myers, S.T., Nair, S., Patnaik, A.R., Pearson, T.J., Perez-Fournon, I., Polatidis, A.G., Readhead, A.C.S., Taylor, G.B. Vermeulen, R.C, Wilkinson, P.N., Womble, D., Xu, W. Augusto, P. (1996): “A search for intermediate scale gravitational lenses”; Ph.D. Thesis; University of Manchester (UK). Augusto, P.,Wilkinson, P.N., Browne, I.W.A. & Henstock, D.R. (1996); “The dark matter problem cannot be solved by Mo black holes” in ‘Sources and Detection of Dark Matter in the Universe’; Nuclear Physics B (Proc. Supp.); 51B, 118; ed. Cline, D.B.; Elsevier Science. Augusto, P., Wilkinson, P.N., Browne, I.W.A. (1998): “Flat-spectrum radio sources with kpc-scale structure”; MNRAS, 299, Augusto, P., Wilkinson, P.N., Browne, I.W.A. (1999): “The population of kpc-scale flat-spectrum radio sources” in ‘The non-Sleeping Universe’; Astroph. & Spa. Sc., vol. 261, p ; eds: Lago, M.T.V.T., Blanchard, A.; Kluwer Academic Pub. Augusto, P., Wilkinson, P.N. (2001): “An observational constraint on gravitational lensing by objects of mass – M 0 ”; MNRAS, 320, L40-L44. Augusto, P. et al. (2001): “B : a distant radio source gravitationally lensed by a starburst galaxy”; MNRAS, 326, Augusto, P., Edge, A.C., Wilkinson, P.N., Chandler, C. J. (2003a): “The radio properties of the cD galaxy of Abell 2390”, MNRAS, in prep. Augusto, P., Gonzalez-Serrano, J.I., Edge, A.C., Perez-Fournon, I., Gonçalves, A. L. (2003b): “Compact- medium symmetric objects with ~1 kpc sizes II. Radio high resolution imaging of 30 candidates”, MNRAS, in prep. Chae, K.-H., Mao, S., Augusto, P. (2001): “Modelling the first probable two plane lens system B : reproducing two compact radio cores A, D”; MNRAS, 326,