The Velocity Dispersion And Dispersion Profile Of Abell 963

Abell 963 (z = 0.206) is still the best candidate for a true arc-counterarc lens configuration (Lavery & Henry 1988). A simple model explains the positions, lengths and patchy light distribution of the two arcs. Photometry indicates the arcs also have the same B-R color (Lavery & Henry 1988; Ellis et al. 1991). However, spectroscopic observations have not confirmed that these arcs originate from the same background galaxy. Ellis et al. (1991) detected a single emission line in the spectrum of the smaller northern arc, identifying it as [O II] λ3727 at a redshift of 0.77. Neither Lavery (1989) or Ellis et al. (1991) detected this emission line in the larger southern arc.