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Evolution of mass segregation in open clusters: some observational evidences
On the basis of the best available member list and duplicityinformation, we have studied the radial structure of Praesepe and of thevery young open cluster NGC 6231. We have found mass segregation amongthe cluster members and between binaries and single stars, which isexplained by the greater average mass of the multiple systems. However,the degree of mass segregation for stars between 1.5 and 2.3 M_sun isless pronounced in Praesepe than in the Pleiades. Furthermore, masssegregation is already present in the very young open cluster NGC 6231although this cluster is likely still not dynamically relaxed. Wediscuss the implications of these results and propose a qualitativescenario for the evolution of mass segregation in open clusters. InPraesepe the mass function of single stars and primaries appears to besignificantly different, like in the Pleiades. We observe an absence ofellipticity of the outer part of Praesepe. Tables 2 and 3 are availableonly in electronic form from the Strasbourg ftp server at 130.79.128.5
| Washington photometry of open cluster giants - Nine old disk clusters in the third Galactic quadrant
Washington photoelectric photometry for 136 stars in nine old openclusters is presented and used to determine the luminosity class, T(e),and metallicity. The virtually unstudied cluster NGC 2324 is found tohave a metallicity one tenth that of the sun, as is the cluster NGC 2660for which previous estimates have ranged from about +0.1 to -0.5. Athird cluster, NGC 3960, with a Galactocentric distance of only 8 kpc,is found to have a metallicity of -0.7, also substantially lower thanpublished values. Such clusters indicate that substantial scatteractually exists in the tight relation found by Friel and Janes (1992)between the metallicity of an open cluster and its currentGalactocentric distance. Outer disk clusters have a metallicity at agiven age that is much more like that of the LMC counterparts than thatof solar neighborhood disk field stars or clusters.
| The luminosity function of Praesepe. I - A proper motion and photometric search for candidate members
Proper motions have been measured for a color selected sample of starsin a square 4 x 4 deg region centered on the Praesepe open cluster. Themagnitude limit of the photometry is about 19 and of the proper motionsabout 18. A list is presented of 765 probable and possible members from9 to 18 based on the proper motions, magnitudes, and colors. The resultsare compared with other proper motion surveys, and a preliminaryluminosity function of M(v) = 11 is calculated.
| Investigation of the Praesepe cluster. I - Identification of halo members
Coravel radial velocities and UBVRI (Kron) photometry of 117 starsselected by their proper motion in the region surrounding Praesepe (NGC2632, C 0837 + 201) have permitted identification of 48 members of thecluster halo, up to a distance of 4 deg from the cluster center. The 43(F5-K0) new members represent 51 percent of the number of nucleusmembers known in this spectral interval. Ten spectroscopic binaries havebeen discovered among the F5-F0 members, resulting in a frequency of 23percent, which rises to 33 percent four probable binaries are taken intoaccount. Six orbits have been obtained, with periods ranging from 1.2 to143 d. Four additional binaries have been detected among the non-memberstars.
| Novye chleny korony skopleniia Iasli
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| Photometrie der Präsepe-Umgebung mit kurzbrennweitigen Schmidt-Spiegeln. Mit 7 Textabbildungen
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