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A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun
Traditionally, runaway stars are O- and B-type stars with large peculiarvelocities. We would like to extend this definition to young stars (upto ?50 Myr) of any spectral type and to identify those present in theHipparcos catalogue by applying different selection criteria, such aspeculiar space velocities or peculiar one-dimensional velocities.Runaway stars are important for studying the evolution of multiple starsystems or star clusters, as well as for identifying the origins ofneutron stars. We compile the distances, proper motions, spectral types,luminosity classes, V magnitudes and B-V colours, and we utilizeevolutionary models from different authors to obtain star ages. We studya sample of 7663 young Hipparcos stars within 3 kpc from the Sun. Theradial velocities are obtained from the literature. We investigate thedistributions of the peculiar spatial velocity and the peculiar radialvelocity as well as the peculiar tangential velocity and itsone-dimensional components and we obtain runaway star probabilities foreach star in the sample. In addition, we look for stars that aresituated outside any OB association or OB cluster and the Galactic planeas well as stars for which the velocity vector points away from themedian velocity vector of neighbouring stars or the surrounding local OBassociation/cluster (although the absolute velocity might be small). Wefind a total of 2547 runaway star candidates (with a contamination ofnormal Population I stars of 20 per cent at most). Thus, aftersubtracting these 20 per cent, the runaway frequency among young starsis about 27 per cent. We compile a catalogue of runaway stars, which isavailable via VizieR.
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Multicolor CCD Photometry and Stellar Evolutionary Analysis of NGC 1907, NGC 1912, NGC 2383, NGC 2384, and NGC 6709 Using Synthetic Color-Magnitude Diagrams
We present the first CCD photometric observations of NGC 2383 and NGC2384 in B, V, R, and I, NGC 1912, NGC 6709 in B, V, and I and NGC 1907in B and V passbands, reaching down to a limiting magnitude of V~20 magfor ~3300 stars put together. The results of the spectroscopicobservations of 43 bright stars in the field of NGC 1912, NGC 2383, NGC2384, and NGC 6709 are also presented. The color-magnitude diagrams(CMDs) of the clusters in V versus B-V, V versus V-R, and V versus V-Iare presented. The distances and reddening to these clusters aredetermined using the cluster CMDs. The distances to the clusters NGC1907, NGC 1912, NGC 2383, NGC 2384, and NGC 6709 are 1785+/-260,1820+/-265, 3340+/-490, 2925+/-430, and 1190+/-175 pc, respectively.Some gaps in the cluster main sequence have been identified. We havecompared the observed color-magnitude diagrams of these four openclusters with the synthetic ones derived from one classical and twoovershoot stellar evolutionary models. Overshoot models estimate olderages for clusters when compared to the classical models. The age of theclusters estimated using the isochrones of Bertelli et al. are 400, 250,400, 20, and 315 Myr for the clusters NGC 1907, NGC 1912, NGC 2383, NGC2384, and NGC 6709, respectively. A comparison of the syntheticcolor-magnitude diagrams with the observed ones indicates that theovershoot models should be preferred. The comparison of integratedluminosity functions do not clearly indicate as to which model is to bepreferred. The values of the mass function slopes estimated for theclusters are x=1.7+/-0.15 for NGC 1912 (mass range: 1.7-3.9 M_solar) andNGC 6709 (1.7-3.4 M_solar), x=1.3+/-0.15 for NGC 2383 (1.7-3.1 M_solar),and x=1.0+/-0.15 for NGC 2384 (2.0-14.0). The present age estimates showthat the closely located cluster pair NGC 1912 + NGC 1907 have similarages, indicating that they may have born together, making them a goodcandidate to be a binary open cluster.
| Distance Moduli of Open Clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1965ApJS...12..215H&db_key=AST
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