THE FIRST CALTECH JODRELL-BANK VLBI SURVEY .1. LAMBDA=18 CENTIMETER OBSERVATIONS OF 87 SOURCES

We present the first results from the first Caltech-Jodrell Bank VLBI survey (the CJ1 survey). The CJ1 sample includes 135 radio sources wit h total flux density 1.3 Jy > S-6 cm greater than or equal to 0.7 Jy, declination delta(1950) greater than or equal to 35 degrees, and Galac tic latitude \b(II)\ > 10 degrees. It extends the nux density limit of the complete ''PR'' sample studied by Pearson and Readhead from 1.3 t o 0.7 Jy and increases the total number of sources from 65 to 200. The complete survey includes VLBI images at both lambda-18 and 6 cm of al l the objects in the extended sample that have cores strong enough to be mapped with the Mark II VLBI system. These images provide a large e nough sample to study, for example, the variety of morphologies exhibi ted by compact radio sources, cosmological evolution, superluminal mot ion, and misalignment between parsec-scale and kiloparsec-scale radio structures. In this paper we present lambda-18 cm VLBI observations of 56 CJ1 and 31 PR sources made in 1990-1991, including images of 82 so urces. The observations were made with a ''snapshot'' technique in whi ch each source was observed in three 20-30-minute scans using an array of 12-16 antennas. The images have resolution 3-10 mas and dynamic ra nge greater than 100:1. Later papers in the series will present the re maining lambda-18 cm observations, the lambda-6 cm observations, and t he analysis and interpretation ofthe results.