The distribution of nearby stars in phase space mapped by Hipparcos - III.Clustering and streaming among A-F type stars

This paper presents the detailed results obtained in the search of density- velocity inhomogeneities in a volume limited and absolute magnitude Limited sample of A-F type dwarfs within 125 parsecs of the Sun. A 3-D wavelet ana lysis is used to extract inhomogeneities, both in the density and velocity distributions. Thus, a real picture of the phase space is produced. Not onl y are some clusters and streams detected, but the fraction of clumped stars can be measured. By estimating individual stellar ages one can relate the streams and clusters to the state of the interstellar medium (ISM) at star formation time and provide a quantitative view of cluster evaporation and s tream mixing. Having established this picture without assumption we come back to previous ly known observational facts regarding clusters and associations, moving gr oups or so-called superclusters. In the 3-D position space, well known open clusters (Hyades, Coma Berenices and Ursa Major), associations (parts of the Scorpio-Centaurus association) as well as the Hyades evaporation track are retrieved. Three new probably loose clusters are identified (Bootes: Pegasus 1 and 2). The sample is rela tively well mixed in the position space since less than 7 per cent of the s tars belong to structures with. coherent kinematics, most likely gravitatio nally bound. The wavelet analysis exhibits strong velocity structuring at typical scales of velocity dispersion <(sigma)over bar>(stream) similar to 6.3, 3.8 and 2 .4 km s(-1). The majority of large scale velocity structures (<(sigma)over bar>(stream) similar to 6.3 km s(-1)) are Eggen's superclusters (Pleiades S Cl, Hyades SCl and Sirius SCl) with the whole Centaurus association. A new supercluster-like structure is found with a mean velocity between the Sun a nd Sirius SCl velocities. These structures are all characterized by a large age range which reflects the overall sample age distribution. Moreover, a few old streams of similar to 2 Gyr are also extracted at this scale with h igh U components. We show that all these large velocity dispersion structur es represent 63% of the sample. This percentage drops to 46% if we remove t he velocity background created by a smooth velocity ellipsoid in each struc ture. Smaller scales (<(sigma)over bar>(stream) similar to 3.8 and 2.4 km s (-1)) reveal that superclusters are always substructured by 2 or more strea ms which generally exhibit a coherent age distribution. At these scales, ba ckground stars are negligible and percentages of stars in streams are 38% a nd 18% respectively.