CRITICAL TESTS OF STELLAR EVOLUTION IN OPEN CLUSTERS .1. NEW PHOTOMETRY AND RADIAL-VELOCITIES FOR NGC-3680

We present new CCD photometry in the b and y colours of the Stromgren uvby system for 310 stars in a 13' x 13' field centered on the interme diate-age open cluster NGC 3680. Careful cross-checks indicate that pr eviously published BV photometry of NGC 3680 is affected by random and /or systematic errors precluding its use in critical comparison with t heoretical isochrone computations. Detailed notes on several individua l stars are given. In addition, we present approximate to 400 new phot oelectric radial-velocity observations of 109 stars obtained with the CORAVEL scanner during the period 1988-1994. These data allow substant ially complete identification of member and non-member stars in the fi eld, and of spectroscopic binaries in both groups. Rotational velociti es have also been derived for the programme stars, and our velocity va riability criteria for stars of all rotations are described. The furth er astrophysical discussion of the data, including the definition of r adial-velocity membership criteria, theoretical isochrone fitting, and the dynamical state of the cluster and the origin of its ''bimodal tu rnoff'', will appear in a separate paper (Nordstrom et al. 1996).