Space-age distribution of young open clusters and observational selectionстатья
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Дата последнего поиска статьи во внешних источниках: 18 декабря 2013 г.
Аннотация:Based on published photoelectric and CCD photometry and using the empirical ZAMS of Kholopov (1980) and the evolutionary-deviation curves obtained from the grid of isochrones computed by Maeder and Meynet (1991), we determine the distances, color excesses, and ages for 203 Galactic open clusters with log t < 8.2. The validity of the derived distance scale is corroborated by the Hipparcos trigonometric parallaxes of seven clusters. The age distribution of the clusters is distorted by observational selection, which is enhanced with increasing heliocentric distance and which is virtually independent of interstellar extinction. As a result, the youngest (log t < or = 7.5) clusters are represented almost exclusively at heliocentric distances > 2 kpc, and the mean age of the cataloged clusters with log t < or = 100 Myr decreases from 50 Myr in the solar neighborhood down to 15 Myr at heliocentric distances > 2.4 kpc.