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Description
The Cosmic Lens All-Sky Survey (CLASS) is an international collaborative program aimed at obtaining high-resolution radio images of over 10000 flat-spectrum radio sources in order to create the largest and best studied statistical sample of radio-loud gravitationally lensed systems. CLASS is aimed at identifying lenses where multiple images are formed from compact flat-spectrum radio sources, which should be easily identifiable in the radio maps (Browne et al., 2003MNRAS.341...13B). In four observing ``seasons'' from 1994-1999, CLASS has observed 13832 radio sources. When combined with the JVAS survey, the CLASS sample contains over 16,000 images. Using the GB6 and NVSS surveys, a complete statistical subset of 11685 sources has been constructed. These were selected from the NVSS 20-cm (Condon et al., 1998, Cat. <VIII/65>) and GB6 6-cm (Gregory et al., 1996, Cat. <VIII/40>) catalogues by the selection criteria: declination >0deg, |b|<10deg, S(6cm)>=30mJy, and spectral index between 6 and 20cm flatter than -0.5 (S proportional to frequency^+alpha^). The remaining sources were selected using earlier versions of these catalogues or with slightly relaxed versions of these criteria.
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